" TR a® o £Fa cm.n B M T e & - A . S Y i 2 vy Fomm " - f - & [ oy & 2 : Do o s T, 3 f— O3 7T e 3 V. . W L. 1. J. ER‘JI! .Vnr e ki, SRS vf..(.@ o i el Y X > a% M.,.vfl A S ,fi,?tw S S T 2 i Lol o i :,‘\*1}. 9 o v L.;,f Wy 3 ol T AR S R T R owey 0 i 2 2 VT e S 5 G WM%WM = oy e D SEOy AT Y eaiEl i nn am e mmr e e rrr———— ORNL/TM~6474 Dist. Categories UC-79b,-c Contract No. W-7405-eng-26 METALS AND CERAMICS DIVISION CHEMICAL TECHNOLOGY DIVISION HEALTH AND ENVIRONMENTAL SAFETY DIVISION ENVIRONMENTAL ASSESSMENT OF ALTERNATE FBR FUELS: RADIOLOGICAL ASSESSMENT OF AIRBORNE RELEASES FROM THORIUM MINING AND MILLING V. J. Tennery ™ H. R. Meyer »% E. S. Bomar \ J. E. Till #¢ W. D. Bond ~7 M. G. Yalcintas ¢ L. E. Morse ¢ * Date Published: October 1978 NOTICE This document contains information of a preliminary nature. 1t is subject to revision or correction and therefore does not represent a final report. OAK RIDGE HATTONAL LABORATORY Dak Ridge, Tennessee 37830 cperated by UNION CARBIDE CORFORATION for the DEPARTMENT OF ENERGY CONTENTS LIST OF FIGURES . . & ¢ v ¢ o o 4 o o o s s o « s = LIST OF TABLES » - - - * . * - - . . - - > . - ABSTRACT & v v v ¢ o & o o « o o & o « o o o = 1. 2. INTRODUCTION + & ¢ o & @ o o o o o o 2 o o o o FACILITY SITING, METEOROLOGY, AND POPULATION CHARACTERISTICS PERTAINING TO THORIUM ORE DEPOSITS 2.1 U.S. Thorium Deposits . . « . « ¢« « « + & 2.2 GSites Selected for Analysis . . . . . . . 2.3 Characteristics of Deposits in the Lemhi Pass District o o« o « ¢ & ¢ o o o o « « Population Distribution . . . . . . . . . Meteorological Data . . . . . « . . « . . References . ¢« ¢ o o o « o o o &+ o o« o & - NN Ch U b~ DESCRIPTION OF MODEL MINE AND MILL . . . . 3.1 Facility Description . . . « ¢« « ¢« ¢ + & 3.2 Thorium Mining . . +« + & o ¢ ¢ o « o 4 & 3.3 Thorium Milling and Refining . . . . . 3.3.1 Introduction . . . . « . . . . . The ore storage pile . . . . . . Ore preparation « . « « +« + « . Sulfuric acid leaching . . . . . Countercurrent decantation . . . Amine solvent extraction . . . . Stripping « « ¢« o o 4o ¢ 6o e 4 s Steam distillation . . . . . . . Filtrationm . . . . . . . . . . . 0 Thorium refining . . . . . . . . 3.3.11 The tailings pond . . . . . . . 3.4 References .« o« o« o o 2 o o o o 4 o o o » . . - - £ - . . » w L wwiwiwwww * W W wwWwiwwww H WO~V P WD GENERATION OF SOURCE TERMS . . . .« + « & + .« . 4.1 Mining .« ¢ o« o ¢« ¢ 4 s e e s e a4 e e . 4,1.1 Radon-220 . . + . &« ¢« v s 4+ & o 4.1.2 Fugitive dust . . . . + + . . . . 4.2 MI1lIng . & ¢ 4 4 v e e e e e e e e e e s 4.2.1 Introduction . « + ¢ v 4 4 ¢ v 4 . . . 4.2.2 The ore stockpile . . . . . . . . . . 4.2.3 Dry crushing and sizing . . . . . . . . 4.2.4 Acid leaching of ore . . . . . . . . 4,2.5 Other mill operations . . . . . . . . . 4.2.6 Thorium refining . . . . . ¢« « + « . . 4.2.7 Source terms for the tailings impoundment 4,3 References .« v v 4 ¢ v v 4 e v 4w e 4 . iii * Page vi oo~ 10 11 11 16 20 20 23 23 23 26 26 26 27 27 27 28 28 28 29 31 32 32 32 32 34 34 36 38 38 39 39 40 47 5. RADIOLOGTCAL ASSESSMENT METHODOLOGY . . + « o« o « o & & « 5.1 5.2 Additional Assumplbions . + ¢« + + o ¢ « o 4 ¢ 4 0 0 References « v o« o o o o o o o o o s s « s s o o & o 6. ANALYSIS OF RADIOLOGICAL IMPACT . . . « +« + « « + & & 6.1 oo 0N 6. 6. oy i Maximum Individual Doses . . .« .« « « ¢ « ¢« ¢ « o & + & Population DosSes .+ « + ¢« ¢ o ¢ ¢ o « o o o o+ 0 s e . Dose Commitments Following Plant Shutdown . . . . . . Impact of Mine~and Mill-Generated 220Rp on Populations Outside the 50-mile Radius . . . . . . . . DiSCUSSiOD - - - - . . - - . * - . - . . » - . . - . - RefeTenCes v o o » o o o o o s o o s o o o o o &« RECOMMENDATIONS FOR FUTURE WORK . . . . .+ « ¢ « « ¢« & o« « « & ACKNOWLEDGMENTS . & v 4 ¢« o o o o o o &+ o s s o o o « o s s o & Appendix 1. SUMMARIES OF METEOROLOGICAL DATA . . . . . . . . Appendix 2. DIFFUSION EQUATION USED FOR THE ESTIMATION OF Appendix Appendix Appendix Appendix Appendix Appendix Appendix RADON"'Z 20 EMISSIONS . . . . . . . . . . . . . . . 3. RADON-220 RELEASE FROM THE OPEN-PIT THORIUM MINE . & ¢ & o o « o o o o o o o o o o s o o« o o 4, RADIOACTIVITY CONTAINED IN DUST GENERATED BY MINING OPERATIONS . . . . « « o ¢« o v « o 4 . 5. ORIGIN CODE CALCULATIONS OF RADIONUCLIDES iIN EQUILIBRIUM WITH THORIUM IN THE ORE AND IN THE MILL TAILINGS . . .+ &« o ¢« ¢ o &+ o o o o+ & 6. MODEL TAILINGS IMPOUNDMENT . . . . + « +« « o« « + & 7. CALCULATION OF AREAS FOR DRY TATILINGS BEACH AND POND DURING THE 20-YEAR OPERATION OF THE MILL . 8., EVAPORATION OF THE TAILING POND AFTER MILL CLOSING AND EXPOSURE OF DRY TATILINGS SURFACE . . . . . . . 9. RADON-220 FLUX FROM THE DRY TAILINGS AND FROM THE POND SURFACE . . v & ¢ v 4« 6 v & o 4 o o o o « o & iv 53 54 56 56 58 60 64 66 68 69 70 Al-1 A2-1 A3-1 Ab4-1 A5-1 Ab-1 A7-1 Figure 2.1 2.2 3.1 3.3 3.4 3.5 5.1 6.1 A.6.1 LIST OF FIGURES Thorium resources in the United States . . Topographical map of Lemhi Pass district of Idaho and Montana . . . o « + « o o o & + & Identified vein deposits of thorium ore in the vicinity of the Lemhi Pass . . . . . . . . . Typical features of open-pit mine . . . . . Artist's rendition of ore-treatment mill . . Conceptual thorium milling. Flow diagram Conceptual thorium milling. Flow diagram Exposure pathways toman . . . . +« . . . . . Thorium—232 decay chain . . . « . « + « .« . Cross section of the natural wedge-shaped basin 22 22 23 24 25 50 63 A6-3 Table 2.1(a) 2.1(b) 2.2 2.3 3.1 4.1 b,2 4.3 b.b 4.5 4.6 4.7 4.8 4.9 LIST OF TABLES Page Vein thorium deposits — United States . . . . . « + « « . 6 Other thorium deposits -~ United States . . . . . « . . . 7 Population data for Lemhi Pass thorium resource site region — 1970 census informatiomn . . . « . . . « .+ o . . 12 Population data for Wet Mountains thorium resource site region — 1970 census information . . . . . . . . . . 12 Characteristics of the open-pit thorium mine and the model thorium mill and refinery . . . . « « « ¢ « « + + & 21 Mass and volume flow rates for principal process streams of the model mill and refinery . « ¢« ¢ o ¢ + « o« & « o . 25 Radioactivity contained in dust generated by wmining OpPerations .+ « ¢ 4 ¢ ¢ e e 0 4 e e 4 e s e e e e e e e e 33 Estimated source terms for operation and closing of the model nlill - . . . . - . - . - * - * . - * * - . - . 35 Values of concentrations of radionuclides in thorite ore and in dry mill tailings that were employed in calculation for 20-year mill operation . . . . . . . . . 35 Estimation of areas of the dry tailings beach and pond during mill operation for the hypothetical Montana and Colorado 1locations « « v v o o ¢ o « o« o o o & 0 e . e s 41 Estimation of areas of dry beach and pond as a function of time after closing down mill operations at the hypothetical Montana and Colorado locations . . . . . . . 42 Source terms for 220gg during will operating life and during final evaporation of the pond and covering of the dry tailings after the mill is closed . . . . . . . . 43 Wind velocities and particle size distribution used in saltation model calculation . « . « « « ¢« o ¢ « + « « . 45 Calculated suspension rates as a function of wind velocity, using the saltation model . . . . . . . . . . . 45 Suspension rates weighted for wind velocity distribution - . . - . - . - * - . - . . - . - - - - . - 46 vi Table Page 5.1 Dose conversion factors for total body, bone, and lungs for radionuclides in the 232Th decay chain . . . . 52 6.1 Maximum individual 50-year dose commitment to total body and various organs from radiocactivity released to the atmosphere during one year of facility operatiom . 4 v 4 i e h i s s e e e e e e e e e e e e 56 6.2 Radionuclide contributors to the dose commitment to various organs for maximally exposed individual . . . . 57 6.3 Contribution of exposure pathways to dose commitment to total body, bone, and lungs for maximally exposed individual . . ¢ v L e e e s e s e e e e e s e e e e e s 58 6.4 Population dose commitment to total body and various organs from radioactivity released to the atmosphere during one year of facility operation . . . . . . . . . 39 6.5 Radionuclide contributions to the population dose commitment to VATious OYELANS + « o ¢ » o o o s o s o s+ 59 6.6 Contribution of exposure pathways to population dose commitment to total body, bone, and lungs . . . . . . . 60 6.7 Maximum individual 50-vyear dose commitments to total body and various organs from radioactivity released to the atmosphere during the first vear after facility Shutdowll L ] » . - . ® o & - 3 o * > . . - » - a * . - a » 61 6.8 Radionuclide contributors to the dose commitments to various organs for individuals exposed during the first year after facility shutdown . . . . « « ¢« ¢« + « . 61 6.9 Contribution of exposure pathways to the dose commitment to total body, bone, and lungs for individuals exposed during the first year after facility shutdown - . . * » * - - . » - - . . L - . . - 62 6.10 Population dose commitments to total body and wvarious organs from radicactivity released to the atmosphere during the first year after facility shutdown . . . . . 62 6.11 Radionuclide contributors to the population dose commitment to various organs for exposures during the first year after facility shutdown . . . . . . . . . 63 A.5.1 Calculated values of radionuclide activities and masses in equilibrium with 1 g of thorium (by ORIGEN COAE) v « v v o v v v v o o 4 & o v e e v v v o . A5-3 vii Table Page A.5.1 Calculated values of radionuclide activities and masses in equilibrium with 1 g of thorium (by ORIGEN code) v v ¢« o o o o « o o o o o o o o o o o o « = AS5-3 A.5.2 Activity of tailings left from the extraction of 1 g of thorium: 917% extraction {(from ORIGEN code calculations) -+ « « + « s e o 4 4 e e e e 4 e s e e AS5-4 A.6.1 Relationship of triangular areas and sides to the dam height (d.h) . . . . . . . . . . . . . . . . * . . . A6""4 A.6.2 Characteristics of model tailings pile . . + + + « + .+ . Ab~5 A.7.1 Constants used in Bond-Godbee equation and the calculated steady-state volume cf the tailings pOfld - . . . . . - . . . - . . . . . . . . . . » . . - . A7—5 A.7.2 Calculated values of the minimum water addition rate required to keep tailings under water over the 20-year life of mill . . .« « ¢ &« v & & ¢ ¢« ¢ o 4 o . . A7-5 A.7.3 Change in volume of pond (V_) with time as a result of evaporation . . . . . . . A7-6 A.7.4 Evaporation surface area of tailings pond (A.) and values of AC used to calculate area of tailings underneath the pond . ¢« ¢ v ¢ v « ¢ ¢ e« t e s e 0 . A7-6 A.7.5 Calculated values for the area of tailings covered by water and of the dry tailings beach . . . . . . . . . A7-7 A.8.1 Volume of liquid in the tailings pond (V.) as a function of elapsed time after closing the thorium mill - . . . . . . . . - . . - . . - . . - . . - . . . . A8—3 viii ENVIRONMENTAL ASSESSMENT OF ALTERNATE FBR FUELS: RADIOCLOGICAL ASSESSMENT OF AIRBORNE RELEASES FROM THORIUM MINING AND MILLING* V. J. Tennery't H., R. Meyer® E. S. Bomar® J. E. Ti118/ W. D. Bond¥ , M. G. Yalcintas? L. E. Morse ABSTRACT A radiological environmental assessment was performed for airborne releases from a thorium mining and milling facility based on site-specific analyses for known vein-type U.S. thorium ore deposits, using proximate meterological data for the geo- graphical region where these deposits are located. The assess- ment was done for a conceptual open-pit thorium mine plus a mill having a throughput rate of 1.5 Gg (1600 metric tons/day). The thorium ore was assumed to have an average ThO, equivalent content of 0.5%4. The mill facility consisted of a mill and refinery whose product was reactor—-grade thorium nitrate tetrahydrate. Several assumptions were necessary in order to conduct this analysis due to scarcity of data specific to erosion and dusting of thorium ore storage piles and a thorium mill-derived tailings beach. Radiological dose commitments were calculated for airborne effluents from the mine and mill facility, using the AIRDOS-II code. The 50-year dose commitment to the maximally exposed individual and to the population, as shown by the 1970 census, living within 50 miles of the operation site was estimated for both Lemhi Pass, Idaho, and Wet Mountains, Colorado, sites. Principal airborne radionuclides which contribute to the popu- lation dose commitment for either site are 228Ra and 220Rrn plus the daughters of 2ZPRrp. Total-body dose commitments to the maximally exposed individual for one year of facility operation for the Lemhi Pass and Wet Mountains sites are V2.4 and 3.5 millirems respectively. Population dose commitments to total body for the Lemhi Pasz and Wet Mountains sites are 0.05 and 0.3 man-rem respectively. Tor both sites and both types of dose commitment, inhalation and ingestion are the largest pathway con- tributors to the dose. Several operations for thorium ore mining and milling were identified during this assessment for which the data base required for radionuclide source term generation was % Work performed under DOE/RRT 189a OH107/1488, "Environmental Assessment of Advanced FBR Fuels." +Metals and Ceramics Division. & Chemical Technology Division. §Health and Safety Research Division. Consultant. either small or nonexistent. For operations where the data base was judged insufficient for generation of at least a first-approximation source term, data appropriate to the similar operation for uranium mining or milling were used as the basis for the source term. Areas where data needs are greatest include (1) quantitative wvalues of emanation factors and diffusion coefficients for %20Rn for thorium ore materials, (2) fugitive dust generation rates from mine activities and thorium ore piles, (3) release rates of 220Rpn from thorium ores under various storage conditions, (4) release rates of 220Rn from thorium ores for various milling process treat- ments, (5) properties of soils in mountainous locations of vein-type thorium deposits to determine their suitability for construction of tailings ponds and retention of radioactive species contained in the mill tailings, and (6) site-specific meteorvlogy appropriate to prime candidate sites for thorium mines and mills. 1. INTRODUCTION The thorium-—uranium nuclear fuel cycle is being studied in several programs in the United States in order to better identify the nuclear weapons proliferation resistance of this cycle compared with that of the uranium-plutonium cycle. Another important feature of any fuel cycle considered for commercialization is the radiological impact of the cycle on the population. The impact derives from several sources, including contributions from ore mining and milling, fuel fabricatioua, reactor operation, transportation, fuel reprocessing, and fuel refabri- cation, This report describes the results of a radiological analysis of the impact of thorium ore mining and milling from vein deposits at two specific sites, one in the Lemhi Pass district of Idaho and Montana and the other in the Wet Mouantains of Colorado. Mining of vein-type deposits was analyzed because they are of the highest grade, and it is estimated that as much as 407 of United States thorium reserves reside in such deposits. Compositional data for the known vein-type thorium ore deposits plus the local topography of the region were employed in establishing details of a model mine capable of providing 1.6 Gg (1600 metric tons) of ore per day plus a mill of equivalent throughput capacity. This plant is considered to be of reasonable size for such a mining endeavor. This analysis differs in certain respects from a related and recently published study of thorium mining and milling reported in ERDA 1541 con~ cerning the Light-~Water Breeder Reactor Program. In the current work, recently improved assessment codes were employed and two site-specific cases were analyzed. The entire mining operation was considered to be open-pit type based on the geology of the known ore deposits at the sites. Source terms are included based on dust from the mining, movement of ore at the mine and mill, and ore crushing, plus the release of 220y from the mine, ore pile, mill, and tailings pond. The appropriate source terms‘were used along with population density and meteorological data for the sites to estimate the population dose commitment associated with the extraction and processing of the thorium ore. 2, FACTLITY SITING, METEOROLOGY, AND POPULATION CHARACTERISTICS PERTAINING TO THORIUM ORE DEPOSITS 2,1 U.S. Thorium Deposits For the purposes of this report, it is assumed that the sources of thorium to be considered are within the continental United States. Thorium is found in several types of deposits in this country, including (1) veins, (2) stream and beach placer deposits or placer deposits incorporated in sedimentary rock, and (3) concentrations in igneous or metamorphic rocks. The largest recoverable thorium reserves are in the form of vein or placer deposits. Thorium dioxide resources in the United States available at a cost of $11 to $22 per kg ($4 to $10 per pound, 1969 dollars) are placed at approximately 600 Gg (600,000 metric tons).?! Monazite sands, which are primarily phosphates of the rare-earth elements, are formed as a result of the weathering of rocks such as granites. Running water carries the sands to locations remote from the original rock formations to places where conditions permit the heavier minerals to settle; this may occur in a river, or the sands may be carried to the ocean and coastal locations. Wave action has resulted in placer deposits of heavy minerals, such as ilmenite and wmonazite, along some beaches on the Atlantic Coast of the United States. A few of these deposits have been worked commercially to recover titanium-bearing minerals with monazite as a secondary product. Large-scale working of beach deposits in the future is unlikely, however, because of the high populdtion density of the coastal region. Figure 2.1 and Tables 2.1(a) and 2.1(b) present available information concerning significant thorium resource sites in the contiguous United States., Table 2.1(a) gives the locations, extent of sampling and observed thorium content, physical dimension, and nearby populations for vein- type deposits of thorium in the United States.' 1?2 Table 2.1(b) identifies deposits of other types but which are predominately monazite ores.13717,31-3% Ttrems A and B give the locations of placer deposits of monazite sands: the thorium content of these deposits at Jacksonville, ORNL-DWG 78-19R KILOMETERS ; 0 500 } i / i i { 0 200 400 T~ MILES +—_ ! i I Fig. 2.1. Thorium resources in the United States. Table 2.1{a}. Vein thorium deposits — United States Max Max vein Thorium Population Location County, state Latitude Longitude Num?er of vein length thickness content within 80 km Ref (see map) (°N) (°W) samples (m) {m) (%) {1979) i. Lemhi Pass Lemhi, iID 44,93 113.5 200+ 1.2 x 103 9 0.001-16.3 14,242 2-5 Beaver, MT 2. Diamond Lemhi, ID 45 114 9 1.7 x 102 7.5 0.02-1.71 7,364 3 Creek 3. Hall Mt. Boundary, 1D 48.99 116. 38 14 1 x 102 0.01-21 15,359 6 4, Powderhorn Gunnison, CO 38.25 107 200+ 1.1 x 103 5.5 0.01-4.3 32,192 7 5. Wet Mts. Custer, CO 38.25 105.35 400+ 1.5 x 163 i5 0.02-12.5 252,144 8,9 6. Laughlin Colfax, NM 36.75 104.25 16 2.4 x 102 5.1 0.05-0.82 27,615 2 Pk, 7. Capitan Lincoln, NM 33.5 105.78 12 46 2.4 0.01-1.12 47,668 10 Mts. 8. Gold Hill Grant, NM 33 109 2 12 0.05-0.72 39,900 2 9. Quartzite Yuma, AZ 33.75 114.25 2 15 2.4 0.027-0.27 22,613 2 10. Cotronwood Yavapai, AZ 34,75 112 1 30 i8 0.013-0.91 64,769 2 11. Monroe Seiver, UT 38. 58 112 1 7.6 15 0.18-0.29 19,868 2 Canyon 12. Mountain San Bernardino 35. 4% 115.5 18 4.9 x 102 3 0.02-4.9 30,321 11 Pass CA 13. Wausau Marathon, WI 45 89.5 20 4.6 x 102 0.5 338,408 12 Table 2.1(b). Other thorium deposits — United States Population Location County, state Latitude Longitude Thorium content within 80 km Ref. (see map) (°N) (°W) {ppm) (1970) 14. Conway Conway, NH 44,00 71.16 b4 29 15, Mineville Essex, NY 44,16 73.58 100-3800 30 16. Palmer Marquette, MI 46,5 87.5 50,000 31 17. Owl Creek Hot Spring, WY 43.48 165.50 134 30,292 13,14 18. Rowlins uplift Carbon, WY 41,78 107.13 146 13,201 13,14 19. Wind River Fremont, WY 43.5 109.5 366 31,648 13,14 20, Wind River Fremont, WY 43,5 109.6 66 31,648 13,14 21. Seminoe Natrona, WY 42,47 106.75 194-273 51,995 13,14 22, Deer Creek MT 45.2 112.5 30 23. Blue Mt. Greenlee, AZ 32.55 109.20 40 30,481 13,15 24, Dos Cabesas Cochise, AZ 32.2 109.42 19 30,098 13,15 25. Mineral Hill Lemhi, IB 45.6 114.9 13,15 26. Diamond Rim Gila, AZ 34,25 111.08 24 10,416 13,15 27. Little Big Horn Big Horn, WY 44,66 106.95 28. Bear Lodge Crook, WY 44,5 104.33 4002500 30 29. Idaho Idaho, ID 46 115 200 32 30. McCullough Mt. Clark, NV 36 116 55-283 145,059 13,15 31. Black Mts, Mohave, AZ 35.5 114.5 180-253 137,958 13,15 32. S. Peacock Mts. Mohave, AZ 35 114 37-153 137,958 13,15 33. Big Maria Mts. Riverside, CA 33.5 116 29-146 136,470 13,15 34, Marble Mts. San Bernardino, CA 35 116 75-148 136,470 13,15 35. 8t. Ffrancois Mts. St. Francois, MO 37.5 90 47 320,378 13,17 36, Idaho Batholith Boise, ID 44.0 115.90 100 32 37. Gallinas Lincoln, NM 34.15 105.63 33 3B. HWorcester Worcester, MA 42,25 71.75 300 30 A, Georgla Charlton, GA 32 81.6 <1000 34 . Florida Nassau, FL 30.2 81.3 <1000 34 C. California San Bernardino, CA 36 117 200-5000 30 D. Piedmont District VA, NC, SC, AL 32-38 78-87 [5.67%] 30 Florida; Folkston, Georgia; and on Hilton Head Island, South Carolina;3° was estimated at 14 Gg (15,600 tons). The Folkston deposit has been reported more recently, however, to have been exhausted.3® Basnaesite deposits are being mined at Mountain Pass, California (item C). Two extensive deposits are identified as item D, The western belt extends for 1 Mu (600 miles) from eastern Virginia southwest to Alabama. It ranges from 0.02 to 0.8 Mm (10 to 50 miles) wide with an average width of about 0.03 Mm (20 miles). The eastern belt originates near Fredericks- burg, Virginia, and continues for about 200 miles into North Carolina with an average width of about 0.01 Mm (5 miles). 2.2 Sites Selected for Analysis The most promising thorium deposits for large—scale exploitation are thorite-bearing veins such as those located in Colorado, Idaho, and Montana. As much as 407 of U.S. thorium reserves occur as vein deposits.18 Reserves equal to about 100 Gg (100,000 metric tons) of ThO, at $22 per kg ($10 per pound) or less (1969 dollars) are estimated to be available in the Lemhi Pass district of Idaho and Montana,1 which lies astride the Continental Divide about 16 km (10 miles) east of Tendoy, Idaho. The Lemhi Pass is shown on the relief map19 in Fig. 2.2 between the vertical coordinates UEO~-UEl and the horizontal coordinates 8-9. The thorium resources of the Lemhi Pass district could supply the requirements of a very large number of FBRs fueled with (Th, U)C and ThC, since calculations by Caspersson et al.?0 show a core blanket requirement of 83 to 117 Mg (83 to 117 metric tons) of thorium carbide equivalent per 1200-MW(e) core, depending on the core and blanket configuration. Additional vein deposits have been found in the Powder- horn and Wet Mountains districts of Colorado. The winters in the Lemhi Pass district are described as moderate, and some of the deposits at the lower elevations can be worked vyear round. In severe winters, operations may, however, be shut down for several months. ——— = -DWG 78-15182 : T T . ORNL “a B! ‘flllifl;" T ’ A Y 'k / Fig. 2.2. Topographical map of Lemhi Pass district of Idaho and Montana. (Photograph of selected portions of relief maps titled Dillonm, Montana, NL12-7, and Dubois, Idaho, NL12-10; Hubbard Co., Northbrook, Illinois 60062.) 10 2.3 Characteristics of Deposits in the Lemhi Pass District Information on the topography, general geology, and the nature of the thorium-bearing deposits in the Lemhi Pass area is given in Atomic Energy Commission reports by Sharp and Hetland and by Austin issued in 1968,21,22 Over 200 samples were taken from about 100 pros- pects along a 110-km (70-mile) trend paralleling the Idaho-Montana border from Leadore, Idaho, to North Fork, Idaho. Elevations in this region range from 1.5 km (5000 feet) above sea level along the Lemhi River up to 2.7 km (9000 feet) at the Continental Divide. The ore minerals include phosphatic thorite, monazite, and rare—earth concen- trations. Rare-earth phosphates such as xenotime (YPO,) form an isomor- phous series with thorite (ThSiO,) to yield the mineral aueralite. The ratio of rare earth to thorium in these deposits varies from 10:1 to 23 on 1:5. Additional information was reported by Ross and George metallurgical amenability tests and compositions of Idaho-Montana thorium ores. Spectrographic analyses show that these ores contain undetectable amounts of uranium (<0.0001 to 0.001%). The thorium-bearing veins are, in general, not exposed but are covered by a thick layer of soil. The presence of the veins can often be detected by surveying the soil cover for radiocactivity with sensitive instruments., Detection is possible due to a degree of mixing of minerals from the veins with the soil. Bulldozing is necessary to expose the veins. The vein deposits show a northwesterly trend paralleling the Continental Divide from the vicinity of Leadore, Idaho, at the southern end, and all are found in an area about 110 km (70 miles) long and 13 km (8 miles) wide. The inclination of the veins varies, particularly near major faults. It is estimated that 60% of the veins dip at angles of 45 to 60° and 40% dip at >60°. The flatter-dipping veins are from 0.9 to 4,6 m (3 to 15 ft) wide, while the steeper veins measure 0.15 to 1.5 m (0.5 to 5 ft) wide. Flat-dipping veins paralleling canyon walls can be mined by open-cut methods, possibly to 91 to 122 m (300 to 400 ft) below the outcrop. Underground methods would eventually have to be used to recover a major portion of the thorium. This study does not, however, consider the radiological hazards of underground thorium mines. 11 Borrowman and Rosenbaum?" demonstrated the recovery of the thorium content of thorite samples by acid dissolution. These samples were taken from vein deposits in the Lemhi Pass district of Tdaho~Montana and the Powderhorn and Wet Mountains districts of Colorado. The samples ranged in content from 0.2 to 3.9 wt % thorium dioxide equivalent. 2.4 Population Distribution Population data specific to the thorium resource sites under study in this report were obtained via the "Reactor Site Population Analysis" computer code available at ORNL. Output from this code is based on U.S. 1970 census information. Approximation of future population data was not deemed necessary for the purposes of this report, since thorium mining and milling population doses were found to be low, and population centers with the potential for significant growth are located at dis- tances in excess of 32 km (20 miles) from either the Lemhi Pass or Wet Mountains sites, a condition which renders the dose estimation procedure relatively insensitive to moderate vpopulation increases., Tables 2.2 and 2.3 present population data breakdowns as input to the AIRDOS-~II dose estimation code. 2.5 Meteorological Data Since variations in meteorology have the potential for significantly modifying both individual and population doses calculated via methodologies using wind and stability category-dependent radionuclide dispersal models, use of local rather than generic meteorological data was deemed necessary in this study. Best available meteorological data for both the Lemhi Pass and the Wet Mountains resource sites were obtalned from first-order weather stations located near each site. Two sets of data were obtained for each resource site, since no first-order weather station is located in the immediate wvicinity of either Lemhi Pass or Wet Mountains. These data were obtained through the courtesy of the National Oceanic and Atmospheric Administration offices located at the National Climatic Center (NCC) in Asheville, North Carolina, and were provided in the form 12 Table 2.2, Population data for Lemhi Pass thorium resource site region — 1970 census Information Population distribution? Compass direction 0-8.0Y 8.0-16 16~32 12-48 48~64 64-80 N 0 0 /8 211 0 NNE 0 0 0 0 0 NE 0 0 0 557 0 ENE 0 0 245 0 0 5,897 E 0 0 0 129 0 ESE 0 0 0 0 589 SE 0 0 0 0 0 SSE 0 0 111 0 70 s 0 0 0 0 0 SSW 0 412 0 0 4 SW 0 0 0 0 277 784 WSW 0 0 0 181 0 0 W 0 0 0 0 0 0 WNW 0 0 0 825 0 0 NW 0 0 337 2,910 534 168 NNW 0 0 0 0 0 0 0 412 693 3,916 1,782 7,438 aTotal population = 14,241, Distance x 10~3 m {(applicable to each heading). Tahle 2.3. Population data for Wet Mountains thorium resource site region — 1970 census information Population distribution? Compass direction 0-8.0F 8,0-16 16-32 32-48 48-64 64—80 N 0 0 0 0 0 835 NNE 0 264 12,264 70 791 18,910 NE 0 6,662 1,246 0 93,790 ENE 0 713 0 753 0 E 0 0 884 65,014 46,808 ESE 0 0 0 0 106 SE 0 318 0 0 1,563 404 SSE 0 0 0 0 170 0 S 0 0 164 0 363 0 SSW 0 126 0 0 20 741 SW 0 0 512 34 0 859 WSW 0 0 0 0 98 642 W 0 0 0 350 0 10 WNW 0 0 377 0 2,164 3,567 NW 0 0 0 0 0 0 NNW 0 0 0 346 24 182 0 708 20,692 2,930 70,960 166,854 aTotal population = 262,144, bDistance x 10=3 m (applicable to each heading) . 13 of monthly or seasonal summaries of wind speed and Pasquill stability category data based on extended observation periods. The data were condensed into AIRDOS-II format via ORNL IBM-360/91 computer manipulation and are presented in this condensed format in Appendix 1 of this report. As noted in Sect. 2.2, it is anticipated that severe weather in the Lemhi Pass region may shut down mining (but not milling) operations for the winter months, since temperature, wind, and snowfall hinder outdoor operations. This report therefore assumes the establishment of an ore pile adjacent to the mill of a size sufficient to continue milling operations uninterrupted during the period December through February. It is concurrently assumed that mine-generated source terms are reduced to near zero during the winter season at the Lemhi Pass site. For this reason the appended AIRDOS-II meteorological summaries (Butte and Mullan Pass meteorologies) utilized in thorium mining AIRDOS-IT dose estimations were composed from data excluding the winter season., Dose calculations for the Lemhi mill, ore pile, and tailings beach utilize four—season meteorological summaries, as do all calculations for the Wet Mountains site, where the winter climate is less severe, The original STAR program meteorological summaries are on file at ORNL. and at NCC-Asheville and are accessible under NCC I1.D. as follows: Thorium resource site Best available meteorology Station No. STAR run Wet Mountains Alamosa, Colorado 23061 12/13/77 Wet Mountains Pueblo, Colorado 93058 1/23/75 Lemhi Pass Mullan Pass, Idaho 24154 11/21/77 Lemhi Pass Butte, Montana 24135 3/22/72 Because no reliable method is available to determine which of the substitute meteorologies best represents exact conditions at the thorium resource site under consideration, dose estimates in this study were calculated for all four sets of meteorological data, and discussion emphasizes those meteorologies found to maximize radiological dose, a conservative procedure. 14 Detailed long-term study of wind speed and stability class wvaria- tions at representative thorium resource sites is necessary before less conservative radiological studies can be performed for these sites, To assist the reader in visualization of climatological conditions at the two resource sites, narrative climatological summaries have been abstracted from the STAR program data as obtained from NCC, and from 25-27 other sources and are presented in the following pages. NARRATIVE CLIMATOLOGICAIL SUMMARY Lemhi Pass Area The thorium deposits in the Lemhi Pass area are centered approxi- mately 16 km (10 miles) east of Tendoy, Idaho, over an area of about 260 km? (100 square miles), astride the Continental Divide, which forms the Idaho-Montana border. The area 1s mountainous but not rugged and is characterized by rounded ridges rising steeply from the valley floors, providing sharp relief of as much as 0.91 km (3000 ft). The altitiude ranges from 1.5 km (4800 ft) above mean sea level in the Temhi Valley to 2.4 km (9000 ft) at the Pass. North~facing slopes in the higher elevations are well timbered with pine, fir, and hemlock. Nontimbered areas are covered primarily with bunchgrass and sagebrush. Predominant wind direction in the area is from the west with little seasonal variation in direction. Wind velocities average between 3.1 and 4.0 m/sec (7 to 9 mph) throughout the year.Z5,26 January is the coldest month, with an average temperature of -12°C (10°F). July and August both record approximately 16°C (60°F) mean temperatures as the warmest months of the year. Mean temperatures in spring through fall progress in an orderly fashion from cool to warm to cool, without secondary maxima or minima. The period between the last freeze of spring (late June) and the first freeze of fall (late August) averages about 60 days. The mean annual number of days for which the daily wminimum tewmperature is below freezing is 240, An average of two days each year exceed a temperature of 32°C (90°F). The average daily temperature range is 18 C° (32.5 F°), with the greatest range (22 C°, 40 ¥°) occurring in July, August, and September. 15 Total annual precipitation for the Lemhi area averages 0.6 m (24 in.), evenly distributed throughout the year. The mean annual number of days with measurable precipitation is 120. Mean annual snow-~ fall is 2.5 m (100 in.).28 NARRATIVE CLIMATOLOGICAL SUMMARY Wet Mountains Area The Wet Mountains are located about 80 km (50 miles) southwest of Colorado Springs and about 60 km (35 miles) west-southwest of Pueblo on the east side of the Sangre de Cristo Mountains and the San Isabel National TForest. These mountains are oriented northwest-southeast with peak altitudes of about 4 km (13,000 ft), and the terrain slopes down- ward to the east and northeast along the valley of the Arkansas River. The vegetation around Pueblo is sparse, and the region is largely tree- less. Along the skirts of the Sangre de Cristo Mountains the San Luis Valley lies from northwest to southeast, with the Great Sand Dunes National Monument located at the southwest extremity of the Sangre de Cristos. The town of Alamosa is located about 40 km (25 miles) south- west of the Great Sand Dunes National Monument within the San Luis Valley. The wind directions in Alamosa are usually from south-~southwest, southwest, and west-southwest with 8.5 te 11 m/sec (19 to 24 mph) maximum and 5.4 to 5.8 m/sec (12 to 13 wph) mean velocities. 1In Pueblo the wind is usually from the northwest or west, except in May and June, when it blows from the west or southwest. Seasonal mean wind velocities range from 3.1 to 5.4 m/sec (7 to 12 mph). Maximum wind velocities during December through July occur during the afternoon hours and reach 8.5 to 11 m/sec (19 to 24 mph). Between August and November, maximum velocities reach 5.8 to 8.0 m/sec (13 to 18'mph).29’30 The coldest month is normally December (-7°C, 20°F mean temperature), but differences between the mean temperatures of December, January, and February are small. August 1Is usually the warmest month, but differences between the mean temperature of June, July, and August are also relatively small. Mean temperatures of the spring and fall months progress in an orderly fashion from cool to warm to cool without secondary maxima or 16 minima. The average period between the last freeze of spring (May 30) and the first freeze of fall (August 15 to August 30) is 82 days. Annual occurrence of daily minimum temperature 0°C (32°F) or below is 210 days. Temperatures of 32°C (90°F) or above occur an average of 11 days annually. The average daily temperature range is about 18 C° (32.5 F°). Normal annual total precipitation is between 0.4 and 0.6 m (16 and 24 in.). Summer is the season of heaviest precipitation, with the monthly maximum normally occurring in July (0.08 m, 3 in.) or August (0.05 to 0.10 m, 2 to 4 in.). A mean of 92 days annually receives measurable (0.25 mm, 0.01 in. or more) precipitation. Annual snowfall is 1.5 to 2.5 m (60 to 100 in.).?%7 2.6 References 1. U.S. Bureau of Mines, 1970 Edition Mineral Facts and Problems, U.S. Department of the Interior, Bureau of the Mines Bulletin 650, 2. H. H. Staatz, "Thorium Veins in the United States," Feon. Geol. 69: 494 (1974). 3. S. R. Austin, Thoriwn, Yttrium and Rare Farth Analyses, Lemhi Pass — Idaho and Montana, USAEC Technical Memorandum AEC-RID-2, p. 12 (1968). 4, W, N, Sharp and W. S. Cavender, Geology and Thorium-Bearing Deposits of the Lewmhi Pass Area, Lemhi County, Tdaho and Beaverhead County, Montana, U,S. Geol. Survey Bulletin 1126, 76 (1962). 5. A. F. Triters and E. W. Tooker, Uranium and Thorium Deposits in East—-Central Idaho and Southwestern Montana, U.S. Geol. Survey Bulletin 933-H, 157 (1953). 6. M. H. Staatz, "Thorium Rich Veins of Hall Mountain in Northern-Most Idaho," Eeon. Geol. 67: 240 (1972). 7. J. C. Olson and S. R. Wallace, Thorium and Rare Farth Minerals in Powderhorn District, Gunnison County, Colorado, U.S. Geol. Survey Bulletin 1027-0, 693 (1956). 8. R. A, Christman et al., Geology and Thorium Deposits of the Wet Mountains, Colorado, U.S. Geol. Survey Bulletin 1072-H, 491 (1960). 10. 11. 12, 13. 14. 15. 16. 17. 18. 19. 17 M. R. Brock and Q. D. Singewald, Geologic Map of the Mount Tyndal Quadrangle, Custer County, Colorado, U.S. Geol. Survey Geol. Quad. Map GQ-596. G. B. Griswold, Mineral Deposits of Lincoln County, New Mexico, N. M. Bur. Mines Minerals Res. Bulletin 67, 117 (1959). J. C. Olson et al., Rare-Earth Mineral Deposits of the Mountain Pass District, San Bernardino, California, U.S. Geo. Survey Prof. Paper 261, 75 (1954). S. R. Vickers, Airborn and Ground Reconnaissance of Part of the Syenite Complex Near Wausau, Wisconsin, U.S. Geol. Survey Prof. Paper 300, 587 (1956). R. C. Malan, Swmmary Report — Distribution of Uranium and Thoriwn in the Precambrian of the Westerwn United States, USAEC AEC-RID-12 (1972). C. R. Anhaeusser et al., "A Reappraisal of Some Aspects of Precambrian Shield Geology,'" Geol. Soe. Am. Bull. 80: 2175 (1969). R, C. Malan and D. A. Sterling, An Introduction to the Distribution of Uranium and Thoriwnm in Precambrian Rocks Including the Results of Preliminary Studies in the Southwesterm United States, USAEC AEC-RID-9.54 (1969). R. C. Malan and D. A. Sterling, Distribution of Uranium and Thorium in Precambrian Rocks of the Western Great Lakes Region, USAEC AEC~-RID-10 (1969). R. C. Malan and D. A. Sterling, Distribution of Uranium and Thorium in the Precambrian of the West-Central and Northwest, USAEC AEC- RID-11 (1970). Fugene N. Cameron, Ed., The Mineral Position of the United States, 1975-2000, Society of Economic Geologists Foundation, Inc., Univer- sity of Wisconsin Press, 1973. Hubbard Co., Northbrook, Illinois 60062, Relief Maps Titled Dillion, Montana, NL 12-7 and Dubois, Idaho, NL 12~10. 20. 21. 22. 23. 24. 25. 26. 28. 29. 31. 18 J. A. Caspersson et al., CE~-FBR-77-370 (C00-2426-108), Initial Assessment of (Th,U) Alternate Fuels Performance in LMFBRs (August 1977). Byron J. Sharp and Domnald L. Hetland, Thorium and Rare Earth Resources of the Lemhi Pass Area, Idaho and Mowntana, USAEC AEC-RID-3 (July 1968). S. R. Austin, Thorium, Yttrium, and Rare Earth Analyses, Lemhi Pass — Idaho and Montana, USAEC Technical Memorandum AEC-RID-2 (August 1968). J. Richard Ross and D'Arcy R. George, Metallurgical Amenability Tests on Idaho/Montana Thorium Ores, Research Report 62.1, U.S. Department of Interior, Bureau of Mines, Salt Lake City Metallurgy Research Center (November 1966). S. R. Borrowman and J. B. Rosenbaum, Recovery of Thorium from Ores in Colorado, Idaho, and Montana, U.S. Bureau of Mines Report of Investigations RI-5916 (1962). Seasonal and Annual Wind Distribution for Butte, Montana, 1956-60, U.S. Department of Commerce, National Oceanic and Atmospheric Administration, Environmental Data Service, Asheville, N.C., 1972, Monthly and Annual Wind Distribution for Mullah Pass, Idaho, 1950-54, U.S. Department of Commerce, National Oceanic and Atmospheric Administration, Environmental Data Service, Asheville, N.C., 1977, Climatic Atlas of the United States, U.S. Department of Commerce, Environmental Data Service, Asheville, N.C., 1974, Revised Uniform Summary of Surface Water Hourly Observations for Alamosa, Colorado, from 1948 to 1972, Data Processing Braach USAFETAC, Air Weather Service, 1973. Summary of Hourly Observations for Pueblo, Colorado, from 1950 to 1955, U.S. Department of Commerce, Weather Bureau, 1956. J. A. Adams, "The Conway Granite of NH as a Major Low Grade Thorium Resource," Natl., Acad. Sei. Proc. 48: 1898 (1962). W. S. Twenhofel and K. L. Buck, "The Geology of Thorium Deposits in the U.S.," Peaceful Use of Atomic Energy, p. 562, Geneva, 1955. 32. 33. 34. 35. 36. 19 R. A. Vickers, '"'Geology and Monazite Content of the Gandrich Quart- zite, Palmer Area, Marquette County, Michigan," Peaceful Use of Atomie Energy, p. 597, Geneva, 1955. J. H. Mackin apnd D. L. Schmidt, "Uranium and Thorium-Bearing Minerals in Placer Deposits, Idaho," Peaceful Use of Atomic Energy, p. 587, Geneva, 1955, J. J. Glass, '"Basnaesite," Am. Mineral. 30: 601 (1945). C. K. McCauley, "Exploration for Heavy Minerals on Hilton Head Island, South Carolina," South Carolima Board Div., Geo. Bulletin, Vol. 26, p. 13, 1960. R. V. Sondermayor, "Thorium,'" Mineral Yearbook 1974, Dept. of Interior, U.S. Bureau of Mines, Vol. 1, p. 1269, 1974, 20 3. DESCRIPTION OF MODEL MINE AND MILL 3.1 Facility Description The characteristics of the mine and mill considered here are similar to those described in the environmental statement for the Light-Water 1 Mine and mill characteristics are listed in Breeder Reactor Program. Table 3.1. Actually, the ore may originate from concurrent mining of several veins at different locations. In a study of possible mining methods and costs applicable to the Lemhi Pass area, Peck and Birch reported2 selection of a mill site where power, water, and an area suitable for a tailings pond can be provided. This site wcould locate the mill at an average distance of 7 miles from the majority of the deposits. The distribution of Chese deposits in the viecinity of the Lemhi Pass and the towns of Tendoy and Lemhi, Idaho, is shown in Fig. 3.1. Location of the veins was identified from a reconnaissance map obtained from the Grand Junction Office of the Department of Energy,3 Locations of the veins are indicated on the relief map copy, Fig. 2.2, Flat or mildly dipping veins near the surface would be mined first using open—cut methods since this is least costly. The radiological effects on the environment of open pit vs underground mining should be similar. Figure 3.2 shows the principal features of an open-pit mine, which include overburden storage, surface-drainage diversion, and haul- road access. The actual appearance of the mine would depend on the local terrain and the characteristics of the particular vein being mined. The location of some veins will allow natural drainage rather than pumping from a sump. Not shown but required is a holding pond for mine drainage water to provide for removal of suspended solids by settling. 1If close enocugh to the mill, this water can be used as part of the mill-process requirements. Otherwise, it will be disposed of by evaporation or natural seepage to groundwater. The mill complex will be composed of an ore storage area, a tailings pond, and buildings to enclose ore processing and thorium nitrate tetra- hydrate (ThNT) product refining equipment. While it is possible that 21 Table 3.1. Characteristics of the open-pit thorium mine and the model thorium mill and refinery Mine Approximate total area (m?) Exposed thorium-bearing vein(s) (m?) Ore production (Mg/day) Average thorium content (% ThO, equivalent) Water drainage (m3 /day) Average depth (m) MLl and Refinery Ore capacity (Mg/day) Days of operation annually Thorium recovery efficiency (%) Mill Refinery Th(NOg),+4H,0 production (Gg/year) Water required (m3/day) Ore pile (m) (Gg) Tailings impoundment Montana Average area during 20-vear mill life (m®) Dry beach 4E3 Pond 57E4 Average area exposed durlng post-mill life (m?) Dry beach ' 4E3 Pond 38E4 Air discharge from complex (m3/sec) Filter losses (%) Crusher dust Th(NO3)y*4Ho0 product line (bags plus HEPA) 4,944 1.2E4 1600 0.5 6.8E2 23 1600 300 917% 99.5% 4.5 2.4E3 100 x 32 x 15 96 Colorado 36E3 49E4 4E3 27E4 11.3 0.7 4,984 = 4.9 x 10“. a thorium refinery may be located elsewhere, perhaps central to several thorium mine and mill operations in several states, the purposes of this study are best served by analyzing the impact of a local refinery, as well as mine and mill impacts. The thorium ore pile will contain a 60~-day reserve to allow operation of the mill during periods when winter 22 Fig. 3.1. Identified vein deposits of thorium ore in the vicinity of the Lemhi Pass. (Photograph of selected portion of relief map titled Dubois, Idaho, NL12-10, Hubbard Co., Northbrook, Illinois 60062.) Deposit locations identified by (e-e-e). 23 ORNL-DWG 78-15184 s OVERBURDEN SPOIL PILE TGP OF ORE BOLY BOTTOM OF QRE BOOY =ZE S L i _x\\ Fig. 3.2. Typical features of open-pit mine. (Taken from Tennessee Valley Authority Final Environmental Statement, Morton Ranch Uranium Mine.) 24 weather stops mining activities at the higher elevations. An artist's rendition of a typical mill complex is shown in Fig. 3.3. The ore will probably be stored in two or more piles based on thorium content. Selective blending will provide a more consistent thorium content of feed to the acid leaching step in the mill process. ORNL-DWG 78-12804 S = -» Fig. 3.3. Artist's rendition of ore-treatment mill. (Taken from U.S. Nuclear Regulatory Commission, Final Environmental Statement Bear Creek Project, NUREG-0129, Docket No. 40-8452, June 1977.) 3.2 Thorium Mining The overburden is first removed by bulldozers or other earth-moving equipment and transferred to a storage pile. The exposed vein(s) of thorium-bearing ore is broken up by bulldozers, dozer-rippers, or selective blasting as required. Spot analyses are made of the thorium content of the ore, and the results are used to classify the ore for subsequent blending. Front-end loaders of about 5.4 Mg (5.4 metric tons) capacity transfer the ore to 35-Mg-capacity (35-metric ton) trucks to haul the ore to the mill. Generation of dust at the mine will be mini- mized by frequent sprinkling of the surface with water. 3.3 Thorium Milling and Refining 3.3.1 Introduction The model plant chosen for identification of airborne effluents produces reactor-grade ThNT. The ore processing rate was 1.6 Gg of 25 thorite ore per day containing 0.5% ThO; and 300-day annual operations. A 91% recovery of thorium was assumed. This is the same processing rate as reported in a previous study.1 The nitrate salt was chosen as the end product since it is a convenient starting point for the denitration, sol-gel, or coprecipitation routes to preparation of metal oxides. Because there is at present no industry in the United States which produces thorium as a primary product, the model plant for the milling and refining of thorium ore was patterned after those reported for uranium ore.” The model plant selected for thorium ore consists of a milling and a refining operation (Figs. 3.4 and 3.5). The conceptual flowsheet for the mill was derived from chemical flowsheets reported by the U.S. Bureau of Mines,”»® whereas the conceptual flowsheet for the refinery was derived from a flowsheet developed for the reprocessing of irradiated Th02.7 Mass and the volumetric flow rates are given for key process streams in the conceptual flowsheets in Table 3.2. QRNL~-DWG TB-196 TO ATMOSPHERE {Taj}—@——-»m STACK 3 WATER ORE DRY GROUND WET SROM___ ol sTOCK (D sizE ORE - SIZE MINE PILE REDUCTION ST%fAGE REDUCTION IN H2504 WATER AMINE, KEROSENE (NH4)2C03 SCRUBBER e STACK [ FLOCCULANT ALCOHOL SOL'N. 1 1 y ACID COUNTER AMINE LEAGHERS »| CURRENT » SOLVENT STRIPPING DECANTATION EXTRACTION AQUEQUS RAFFINATE ORGANIC SANDS, SLIME, TO RECYCLE RAFFINATE LIQUID WASTES TO RECYCLE TO TAILINGS POND NM3£0, | RECYCLE ;"“*Hao STEAM OISTILLATION > FILTRATION »--w(:)-—--»Tn(co.s)z-tzo ~———=TO REFINERY l—*AQ. (NH4)2 S04 FOR NHM3 RECOVERY Fig. 3.4. Conceptual thorium milling. Flow diagram. 26 ORNL-DWG 78-195 TO RECYCLE ORGANIC ORGANIC EXTRACT CLEAN UP | AQUEOQUS WASHES M0 Q DILUTE HNOsx 3 " WASH RAFFINATES 2 ~ TO STORAGE o D O 3 o FEED °2 z AQ. Tnmc@p z o TO STORAGE HNOs SOL'N, zz o DILUTE HNO4 O [l 2 c 2 z ORGANIC @ 30% TBP IN NPH DILUENT AQ. RAFFINATE TO ACID RECOVERY AND WASTE CONC'N. Fig. 3.5. Table 3.2, Conceptual thorium refining. CONCEN- TRATOR CONC. Th(NQO3l4 HNO, SOU'N DILUTE AQ. PRODUCT Th(NQ:;)q . 4H20 RYSTALLIZER f=- PRODUCT 4 CRYSTALLIZE MOTHER LIQUOR TO RECYCLE &+ Flow diagram. Mass and volume flow rates for principal process streams of the model mill and refinery Mill Refinery Feed? Product Tailings Feed ThNT Aqueous product wastes Thorium kg/sec 8.14E-20 7.41E-2 7.33E-3 7.41E-2 7.37E-2 3.70E-3 (kg/day) (7.03E+3) {6.40E4+3) (6.33E+2) (6.40E4+3) (6.37E+3) (3.20E+2) Volume® m3/sec 3,47E-2 d 3.47E-2 4.06E~4 d 3.11E-3 (ft3/day) (1.06E+5) d (1.06E+5) (1.24E+3) d (9.50E+3) %Feed rate of ore is 18.5 kg/sec (1.6 Gg/day). bread as 8.14 x 10-2. “Includes both process liquids and solids. dNot determined. The mill employs sulfuric acid leaching of the ground ore to solu- bilize the thorium, which is then purified and concentrated by an amine extraction process to produce a crude thorium product. The crude product is subsequently refined by TBP (tributyl phosphate) solvent extraction to yield reactor-grade ThNT. It should be emphasized here that the chemical flowsheets utilized are conceptual in nature and have not been demonstrated on a pilot scale with all of the process steps operating in tandem. We assumed that the mill and refinery would be colocated for the purposes of this study. It is realized that the refinery could be geographically separated from the mill if overall economics, availability of skilled labor, or material resources dictate it. It was not the aim of this study to determine the best overall process and equipment configurations. 3.3.2 The ore storage pile An outdoor storage pile containing a 60-day supply (96 Gg) of ore is assumed to be located about 60 m from the mill (Fig. IX.G.3-2, ref. 1). The stockpile will have the form of a rectangular parallelepiped with a base 100 x 32 m and a height of 15 m. The ore will be transported from the stockpile to the ore crusher by front-end loaders. Due to thorium decay, 220Rn will escape from the stockpile. Ore dusts will be generated by the transportation associated with the stockpile. 3.3.3 Ore preparation Ore conditioning consists of a series of dry crushing and wet grinding operations preparatory to acid leaching. A gaseous radioactive effluent (stream 3, Fig. 3.4) results from the release of all the 220Rp inventory v and in the ore, which is assumed to occur in the dry crushing operation during its residence in the ore bins. Air from the dry crushing and the ore storage bins is assumed to contain entrained radioactive particulate matter which is removed by bag filters (stream 4, Fig. 3.4) before being released to the stack.l»" 3.3.4 Sulfuric acid leaching The wet ground ore is leached with sulfuric acid in order to solu- bilize the thorium values.”»® Radon-220 is released from the leachers 28 as a consequence of the decay chain ??"Ra (3.14 x 10° sec) ~ 220gp (55.6 sec). The leacher off-gases are scrubbed before being released to the stack. Mechanical stirring rather than air sparging is assumed to be employed in the leachers to minimize entrainment of liquid droplets which contain soluble radionuclides. 3.3.5 Countercurrent decantation The slurry from the leachers is passed through a liquid-solid separation to recover the solubilized thorium values. The solubilized thorium is transferred to the solvent extraction unit. The washed residual solids are pumped to a tailings pond for storage. The tailings pond, which contains 2327h daughters from the residual solids as well as a small amount of unrecovered thorium, is a source of radicactive effluents and is discussed in Sect. 3.3.11. 3.3.6 Amine solvent extraction The leached thorium values are purified and concentrated by solvent extraction, This is done utilizing a primary amine in a hydrocarbon diluent with an alcohol additive to obtain desirable physical properties for the extractant.%»2»6 Recycling the aqueous raffinate is employed to reduce the process requirements for water and mitigate the problem of disposing of a radioactive liquid effluent from the mill. About 5.7 x 1072 m3/sec (1.7 x 10° ft3/day) of aqueous raffinate is produced by the amine extraction (Fig. 3.4). In our conceptual flowsheet, about 95% of the flow of this stream is assumed to be recycled to the counter- current leaching and washing operations. Assumption of 95% recycle of this stream may be optimistic and requires experimental verification. There is not enough information available to determine whether recycle is severely hampered by buildup of deleterious impurities. 3.3.7 Stripping Thorium is stripped from the loaded organic extractant by an aqueous (NHy )2 COg solution.® Other aqueous salt solutions may be used for stripping;S’8 however, the potential advantages of (NH,),CO03 will become 29 apparent in the discussion of subsequent operations. The stripped organic is recycled after washing. 3.3.8 Steam distillation The aqueous strip solution is decomposed by steam distillation to yield a crude thorium solid product, and NH3 and CO, are recovered and recycled.® Experimental work is needed to determine the percentages of the NH; and CO, that may be recycled and to demonstrate feasibility. 3.3.9 Filtration The crude Th(CO3)> product of the milling operation is filtered and washed to remove the (NHL)»S0y, which is treated with Ca(OH), and steam- distilled to recover the NH3.6 Thorium carbonate undergoes further purification in the refinery to produce reactor-grade Th(NOj3),*4H,0. Over- all recovery of thorium through the milling process is estimated at 91%.°3 3.3.10 Thorium refining The Th(CO3)2 mill product (stream 7, Fig. 3.4) is dissolved in HNOjg and subjected to a solvent extraction cycle using 30%Z TBP in normal paraf- fin hydrocarbon diluent as the extractant (Fig. 3.5). Thorium is obtained from a stripping column as a dilute HNO3 solution which is concentrated and crystallized to obtain reactor-grade Th(NO3),;*4H,0. The organic extractant phase will be recycled in this operation. Packaging of the ThNT would generate airborne radioactive particulate matter. Before air from this operation is released to the stack, it 1s passed through a bag filter and then through an HEPA filter. Thorium recovery for the refining cycle is estimated to be 99.5%.7 Aqueous solutions of nitrate wastes (streams 2 and 3, Fig. 3.5) are produced in the refinery and are impounded separately from the mill tailings. The best method for impoundment has not yet been determined; but an example ;f an acceptable method? may be a neutralization of the combined waste streams to immobilize any soluble radionuclides and sub- sequent impoundment of the wastes in a barrier-lined evaporation pond. Although the present study does not deal with liquid wastes, those future 30 investigations which do should take cognizance that experimental infor- mation is needed in regard to (1) the radionuclide and chemical composi- tion of the aqueous nitrate wastes and (2) the possible process options for recycle of nitric acid and water, and the percentages of recycle of these waste components that are likely to be attained using these options. In the conceptual flowsheet for the refinery (Fig. 3.4), it was assumed that significant amounts of the nitric acid and water could be evaporated or distilled and recycled. However, it is not known whether deleterious impurities might be introduced into process streams by this recycle method. 3.3.11 The tailings pond Large quantities of liquid and solid wastes are produced in the milling of thorium ores. About 1 kg of solids and 1.5 kg of liquids will be produced per 1 kg of thorium ore processed. This waste is impounded in a tailings pond within the restricted mill area where the solids separate out and are eventually allowed to dry. The residual dry solids are per- manently impounded on this site. Since approximately 1.6 Gg/day of solids contains about 0.23 TBq (6.3 Ci) of radicactivity from the decay of 232Th, at the time of discharge the amount of activity available over the assumed 20-year life of the mill operation is appreciable. The tailings pond is a potential source of airborne radiocactive effluents due to (1) the release of 220Rn and (2) wind-generated radiocactive dusts from the dry solids. There is also a possibility of other types of radio- nuclide source terms because of the potential for seepage of liquids containing soluble radionuclides from the tailings pond into the sur- rounding terrain. Soluble radionuclides may also be present in the liquid phase of the mill wastes. If the solubilities of 2327h, 226Ra, and 210pp in liquid wastes from uranium mills" are assumed to be repre-- sentative of the solubilities of the corresponding radionuclides in the thorium mill waste liquids, the appropriate values for this case are: 4.11 MBq/m3 for ?32Th, 41 Bq/m? for 2?28Th, 70 MBq/m® for 22"%Ra, 5.14 MBq/m3 for 228Ra, and 290 MBq/m3 for 212Pb. Experimental data are needed to determine whether the analogy with the pond liquor for uranium mills is correct. The absence of certain elements such as barium in thorium ores could apptreciably increase the solubility of radium. Recommended practices 31 in the siting, construction, and management of tailings ponds to minimize release of radiocactive effleunts have been described previously,1=”’9’10 and these have been utilized in designing the pond described here. It was outside the scope of this study to determine radionuclide source terms resulting from seepage of liquids. The impoundment is formed by constructing a dam on terrain with favorable topographical and geological features to minimize the potential for seepage. At normal liquid discharge rates of mills in the early stages of the operation, the tailings solids will be covered by liquid. The combined effect of increasing tailings volume and water evaporation will eventually expose the tailings solids. During mill life, measures are taken to prevent the solids from completely drying and becoming subject to wind erosion. During the time liquid waste is present in the tailings pond, a potential exists for the seepage of soluble radionuclides into the surrounding terrain. 1If this seepage reaches the local aquifers, it becomes a radiocactive liquid effluent., Careful siting and construction of the tailings pond will minimize seepage. Monitoring for radiocactive seepage with provision for its collection and return to the tailings pond is employed in the design and is used as a control measure. Again it is emphasized that this study does not deal with the potential for liquid waste releases and its site-specific aspects, particularly the potential for seepage through the bottom of the tailings pile and for horizontal movements that might reach surface streams. At the end of the mill operation, the tailings pond is permitted to dry in a controlled manner so that only a relatively small area of dry tailings is exposed to the atmosphere at any time and is thus subject to wind erosion. After drying is completed, the active residue is covered with a layer of protective material sufficient to substantially reduce the escape of 229Rn to the atmosphere and to immobilize the dry tailings with respect to wind erosion. Because of the relatively short half-1life of 220Rn (55.6 sec), only about 0.30 m (v1 ft) of earth cover is required to reduce its emission by a factor of ~OE/. The stability of the dry tailings pile and its covering with respect to geological and climatological factors is beyond the scope of this study. 4 10, 32 3.4 References Energy Research and Development Administration, Final Environmental Statement, Light-Water Breeder Reactor Program, ERDA-1541, Vol. 4, Appendix 1X-G, June 1976. G. B. Peck and L. B. Birch, Mining Methods and Production Costs, USAEC AEC-RA-12, Grand Junction, Colorado (1968). Reconnaissance Geologic Map Showing Distribution of Thorium Veins, Lemhi County, Idaho, and Beaverhead County, Montana (south half). Provided by Eugene W. Grutt, Jr., Manager, Grand Junction Office, Department of Energy. M. B. Sears, R. E. Blanco, R. G. Dahlman, G. S. Hill, A. D. Ryon, and J, P. Witherspoon, Correlation of Radiocactive Waste Treatment Costs and the Envirommental Impact of Waste Effluents in the Nuclear Fuel Cycle for Use in Establishing "as Low as FPracticable" Guides — Milling of Uranium Ores, ORNL/TM-4903, Vol. 1 (May 1975). S. R. Borrowman and J. B. Rosenbaum, Recovery of Thorium from Ores in Colorado, Idaho, and Montana, Bureau of Mines Report of Investi- gation RI 5916 (1962). J. R. Ross and D. R. George, Metallurgical Amenability Tests on Idaho-Montana Thorium Ores, Bureau of Mines Research Report 62.1 (November 1966). G. F. Smith, Purex Plant Chemical Flowsheet for the 1970 Thorium Campaign, ARH-1748 (July 10, 1970). D. J. Crouse, Jr., and K. B. Brown, '"The Amex Process for Extracting Thorium Ores with Alkyl Amines," Ind. Eng. Chem. 51: 1461-64 (1959). U.S. Envirommental Protection Agency, Office of Radiation Programs, Envivonmental Analysis of the Uranium Fuel Cycle, Part I — Fuel Supply, EPA-520/9~73-003-B (October 1973). U.S. Environmental Protection Agency, Office of Radiation Programs, Environmental Analysis of the Uranium Fuel Cycle, Part IV -~ Supple~- mentary Analysis 1976, EPA 520/4-76-~017 (July 1978). 33 4, GENERATION OF SOURCE TERMS 4.1 Mining 4,1.1 Radon-220 Release of 220Rn from a thorium mine will depend on several physical and chemical characteristics of the ore plus the amount of exposed ore in the mine. It is assumed here, as in ERDA~1541,1 that 3 acres of thorium-bearing ore containing the equivalent of 0.5% ThO;, are exposed in one or more pits being worked to supply 1.6 Gg/day (1600 metric tons/day) of ore to the mill. There appears to be no information in the technical literature relating to the measurement of 220Rn release from vein-type ore deposits. Radon-220 release as reported in ERDA-1541 was calculated by assuming that the characteristics which control the release from thorium ore are the same as those of a sandstone uranium ore from Ambrose Lake, New Mexico.! Radon-222 release from this sand- stone was reported at 2.16 mBq/cm?+sec (0.0583 pCi/cm?+sec) by Schroeder and Evans. Using an expression developed by Culot and Schaigerl’2 and correcting for differences of 2%22Rn and 229Rn half-lives and of the concentration of their radium parents in the ores, a flux rate was cal- culated for 220Rn of 1.32 kBq/m%-sec (3.56 x 10" pCi/m?-sec), or a total of 16 MBg/sec (4.32 x 108 pCi/sec) from 3 acres of exposed ore in the open-pit mine. Additional details of the calculation of 220pn flux from the mine are shown in Appendixes 2 and 3. 4.1.2 Fugitive dust A number of activities at the mine site will contribute to entrain-~ ment of dust in the air. In most envirommental statements, dust formation and control is treated only in a qualitative manner by stating that appropriate measures will be taken to meet federal and state air quality standards with the expectation that the off-site effects will be negli- gible. Information upon which to make a quantitative determination of the amount of fugitive dust which will be generated is limited, and at best a number of assumptions must be employed. However, in spite of the required assumptions, a source term for fugitive dust generation at 34 the mine site is calculated as part of this analysis. Movement of heavy equipment, drilling, and blasting will contribute to generation of fugitive dust at the mine. A major portion of dust from vehicles will come from movement of front—-end loaders and ore haulers. Front-end loaders of 3 m® (4 yd3) capacity would make 296 "trips" per day, amounting to about 18 km (11 miles) to move 1.6 Gg (1600 metric tons) of ore. Concurrently, 35 Mg-capacity (35-metric ton) ore trucks would make 46 trips amounting to 27 km (17 miles). As shown in Appendix 4, the amount of dust raised by vehicular traffic can be estimated from the speed and distance traveled.® At an estimated average speed of 8.9 m/sec (20 mph), about 450 g (1 1b) of dust will be injected into the air for each mile traveled if the surface is dry, resulting in generation of about 13 kg (29 1b) of dust per day. Other activities at the mine will double this to about 26 kg/day (58 1lb/day). The expected dampness of the ore plus routine sprinkling of the mine area with water should reduce the rate of dust generation by about 50%.3 The concentration of thorium in the air- borne dust will be further reduced to about half that of the ore by dilution with rock containing no thorium. An estimate of the contribution of the mine dust to airborne activity is given in Table 4.1. For lack of the necessary information, no attempt was made to estimate wind-blown loss of ore dust from trucks in tramsit to the mill. Table 4.1. Radioactivity contained in dust generated by mining operations Radicactivity, Bg (pCi) Isotope 00— Per g of ore Per 13 kg (29 1b) dusta/day 2320, 1 (s.eEnt 1.2E5 (3.2E6) 128p, 18 (4.8E2) 1.2E5 (3.2E8) 228, 18 (4.8E2) 1,2E5 (3.2E6) 2287y, 18 (4.8E2) 1.2E5 (3.2E6) 224pa 18 (4.8E2) 1.2E5 (3.2E6) 220, 18 (4.8E2) 1.2E5 (3.2E6) 2l6pg 18 (4.8E2) 1.2E5 (3.2E6) 212py, 18 (4.8E2) 1.2E5 (3.2E6) 2124 18 (4.8E2) 1.2E5 (3.2E6) 212p, 11 (3.1E2) 7.5E4 (2.0E6) 2087q 6 (1.7E2) 4. 2E4 (1.1E6) a . . s Concentration of Th in fugitive dust is diluted by dust containing no Th to about half that of the ore. Dy 8E2 = 4.8 x 102, 35 4,2 Milling 4.2.1 Introduction Methods of calculations and calculated values of the airborne radio- active source terms from the model mill and refinery are presented in this section. Because there were no experimental data available for making source term calculations on thorium milling and refining, we made the assumption that the distribution of radionuclides throughout the liquid or solid process streams was essentially identical with that of a uranium wmill and refinery.L+ In the case of the gaseous radionuclide 22%Rn, we assumed it had the same escape potential from the ore and tailings as does 22ZRn (after correcting for half-1life difference) in the processing of sandstone ores of uranium. This assump- tion regarding 220Rn emission may lead to an overly conservative estima- tion of the source term, since the escape factors from different types of minerals vary greatly.?> Clearly, experimental data are needed for many of the operations in the thorium milling and refining flowsheet. Areas requiring experimental data will be pointed out in the subsequent discussions. Even with the uncertainties of the assumptions used in estimating source terms for thorium milling and mining, we believe our study shows that the airborne radionuclide releases for a thorium mill and refinery are comparable to that of a uranium mill and refinery of equivalent ore capacity and design. In order to determine the values of source terms with a reasonable degree of confidence, experimental data are needed regarding the escape of 220Rn and the distribution of all members of the thorium decay chain throughout the process streams. Source terms estimated for the ore storage pile, the mill and refinery, the tailings beach and pond during 20-year operation of the mill, and the covering of the dry tailings at the end of mill life are shown in Table 4.2. Concentration of the radionuclides in the ore and tailings as used in source term estimations were calculated by the ORIGEN code® and are given in Appendix 4. A summary of these concentrations is given in Table 4. 3. 36 Table 4.2, Estimated source terms for operation and closing of the model mill Source term” (Bq/sec) Tailings beach Covering dry and pond tallings Mill Ore + Nuclide handling refinery Montana Colorado Montana Colorado 2321y 0.52 0.18 0.037 0.33 0.37 0.37 228, 0.52 0.18 0.33 3.0 3.3 3.3 228p0 0.52 0.18 0.33 3.0 3.3 3.3 228t1p 0.52 0.18 0.26 2,2 2.4 2.4 224Ra 0.52 0.18 0.26 2.2 2.4 2.4 216pg 0.52 0.18 0.26 2.2 2.4 2.4 212p5 0.52 0.18 0.26 2.2 2.4 2.4 212py, 0.52 0.18 0.26 2.2 2.4 2.4 20873 0.18 0.07 0.09 0.8 0.8 0.8 212p 0.33 0.11 0.18 1.4 1.6 1.6 220g, 1.57° 3. 6E7 1.2E7 1.6E7 1.1E7 9.3E6 2} Bg/sec = 27 pCi/sec. b 587 = 1.5 x 107, Table 4.3. Values of concentrations of radionuclides in thorite ore and in dry mill tailings that were employed in calculation for 20-year mill operation Concentration (kBq/kg) Nuclide ore Bulk Tailings (<80 um tailings particle size)? 232yp 17.7 1.6 4.0 2281y 17.7 10,57 26. 87 2285, 17.7 17.7 45.1 228pg 17.7 17.7 45.1 224ga 17.7 17.7 45.1 220pq 17.7 17.7 45.1 216pg 17.7 17.7 45.1 212p, 17.7 17.7 45.1 21l2pj 17.7 17.7 45.1 212p, 11. 4 11.4 29.0 20871 6.3 6.3 16.1 %pssumes nuclides are of a concentration that is 2.55 times greater than the average in the bulk tailings (ref. 4). P raximum 228Th concentration in aged tailings (10.5 kBq/k%) occurs approximately three years after discharge because of 232Th decay. In calculating source terms, a correction factor allowing for the age of the tailings was utilized. Maximum concentration of other nuclides 1s at discharge. 37 4.,2.2 The ore stockpile The ore stockpile is assumed to contain 96 Gg of ore, which is equivalent to a 60-day supply for the model mill and is assumed to be in the form of a rectangular parallelepiped with a base 100 x 32 m and a height of 15 m. Its surface area is 7160 m?. The ore stockpile is a source of airborne effluents due to radioactive ore dusts and the emission of 22%Rn. WNo model was available for calculation of a source term resulting from the action of winds on the ore pile. The only source terms calculated were those of 2?0Rn emission and particulates resulting from the movement of ore to and from the site. 4,2.2.1 Radon-220 emission. The 220Rn emission from the ore stockpile was calculated in the following manner, using Eq. (5) developed in Appendix 2. The 220Rn flux from the surface of the ore stockpile is given by 3, = 4550 (kp~ 1y 1/2 | (1) where (xp~ 1) = 5E-6 m?/sec (a term related to the diffusion of 42%Rn in the porous medium; we assumed the wvalue for coarse sand“), 0 = bulk density of the ore stockpile, 2E3 kg/m?> . Substitution of these values into Eq. (1) gives Jo = 2.04 kBq/m?%ssec . The emission of 229Rn from the 7160-m? surface is 220pn = 7160 x 2.04 = 14.6 MBq/sec (3.94E8 pCi/sec) . 38 4,2,2.2 Ore movements at the mill site. Ore is transported from the stockpile to the mill by front-end loaders, and it is reasonable to assume that some spillage will occur. The spilled ore will be further pulverized by the road traffic and impacted into the unpaved road. Dust subsequently raised by traffic on this road will constitute a source of airborne radioactivity. The calculation of this source term is made in a similar manner to that for movement of ore at the mine site. A front-end loader transporting 5.4 Mg of ore per load will require 296 "trips" to move 1.6 Gg of ore per day from the stockpile to the mill, an assumed distance of 60 m one way or a round trip of 120 m. This is equivalent to an average speed of 0.41 m/sec. The road speed of the transporter is assumed to be 8.9 m/sec. The dust generated by this traffic3 as a function of vehicle speed is given by expression (2): 76(1.158)° (2) =2 I where vehicle speed in m/sec w it Substitution for s gives E = 280 mg/m of traffic, and the mass of dust W generated per day is given by E> I E(d) , (3) where o I total distance traveled per day. Substitution into (3) gives 115 mg/sec (22 1b/day) for a dry surface. Wetting the unpaved road is assumed to reduce dusting by 50%, that is, to 58 mg/sec. The rvoad dust generated in this manner is assumed to have a thorium content approximately 507% of that of the ore. The source term 39 for 232Th is calculated to be 520 mBq/sec. Source terms for the release of the other radionuclides from ore movements are shown in Table 4.2. 4.2.3 Dry crushing and sizing All of the 22%Rn inventory is assumed to be released during the crushing operation.l Ore particulate releases were calculated assuming that 0.008% of the ore was released as a dust! to bag filters which operate at 99.3% efficiency.1 This assumption implies that 0.77% of the dust entering the filters was released to the atmosphere; thus the fraction of ore that is airborme is 5.6 x 10~7., The source term was calculated to be 220g, 17.7 kBq/kg ore x 18.5 kg/sec 328 kBq/sec (8.9E6 pCi/sec) . An example calculation of the particulate source terms is as follows: 232TH = 328 kBq/sec x 5.6E~7 = 0.18 Bq/sec (5.0 pCi/sec) . The filter burden of ore dust for this operation is about 1.5 g/sec. 4.2.4 Acid leaching of ore Radon~220 produced by the decay of 22%Ra during the 12~hr leaching period is considered to be the only radiocactive emission from this opera- tion. It requires only about 10 min for the %2%Rn (t1/2 = 55.6 sec) to reattain secular equilibrium after it is released. Therefore, it was assumed that process holdup in bin storage allowed sufficient time for 220Rn to reattain secular equilibrium. For purposes of contrast, <22Rn present in uranium ore requires about 40 days to reattain secular equilibrium. The source term for 220Rn was calculated by the following equation: 220 = . . . . Rn = Cp = Agpg = E = w - £, (4) 40 where CRn = gecular equilibrium concentration of 220Rn, 17.7 kBq/kg ore, Aosg = decay constant for 229Rm, 0.0125/sec, t = leaching time, 4.32 x 10" sec, w = mass of ore processed per day, 1.6 Gg, (18.5 kg/sec), f =0.2. The factor f corrects for the decay of 220Rn in the time period between its generation and release.! Using Eq. (4), the calculated value of the 220Rn source term is 35.3 MBq/sec. Technology is available for increasing the holdup (factor f) so that the 2?ORn release is negligible, provided detailed cost~benefit analyses justify it. However, it was outside the scope of the present study to make this assessment. 4.2.5 Other mill operations The remaining mill operations, including amine solvent extraction, stripping, steam distillation, and filtration are not regarded as sources of airborne radioactive emissions. 4,2.6 Thorium refining The fraction of Th(NO3),+4H,0 dispersed as dust is assumed to be the same as the fraction of yellow cake dispersed as dust in a uranium milling operation. This quantity, 1.25% of the product, becomes airborne to the filters.'' The bag filters operate at 99.3% efficiency, which is equivalent to a product loss of 0.7%Z. An efficiency of 99.95% was assumed for the HEPA filter located downstream of the bag filter. Thorium recovery through refining but not including packaging is assumed to be 99.5%. The source term for 232Th was calculated using Eq. (5): 232Th = (W) (R) (D) (L) (?32Th) (w) , (5) where weight of Th in refinery feed, 7.4 x 1072 kg/sec, =] I = i Th recovery in refining, 99.57%, 41 D = suspended fraction of Th~bearing dusts, which is 1.257% of the refined product, L, = Th loss through bag filters, 0.77%, H = fraction of particulates passing through the HEPA filter, 5 x 107", (232Th) = thorium activity = 4.03 MBq/kg. The resulting source term for 232Th or 228Th 1g 13.0 mBq (35.0E~2 pCi/sec). Due to lack of data on dusting characteristics of Th(NOj3),*4H,0, it was assumed that they are similar to those of uranium yvellow cake powder. If this assumption is not supported by later experimental data, the calculation of a more realistic source term can be made easily. 4,2.7 Source terms for the tailings impoundment 4,2.7.1 Introduction. The tailings impoundment is a source of 220Rn and airborne particulates during both mill operation and final covering of the dry tailings after the mill operations have ceased. A 220Rn source term results from a flux generated at the surface of both the exposed dry tailings and the pond. Soluble 22%Ra in the pond liquor is responsible for the flux at the surface of the pond. We assumed there would be a negligible 220Rn flux resulting from wet tailings underneath the pond. The relaxation length for diffusion of 220Rp (tl/z = 55.6 sec) in water is about 300 ym. The flux resulting from this source would be negligible in comparison to those from the dry tailings beach and from the pond surface due to the “2%“Ra dissolved in the pond liquid. The particulate source terms resulted from a flux term generated by the prevailing winds at the specific site. The flux term for 220Rn was calculated by the diffusion model previously described (Sect. 4.1 and Appendix 2), wherecas the particulate flux term was cal- culated from the saltation model.’ Since the source terms are a product of a flux term and an area term, it was necessary to develop a model for determination of the average surface area of the dry tailings beach and of the pond during mill operations and during final covering of the tailings pile. 42 The general features of the tailings impoundment basin were previously described in Sect. 3.3.11. Details of the development of the calculational models for the estimation of the average surface area of dry tailings beach and the pond are given in Appendixes 6, 7, and 8. The rate of exposure of dry tailings and the growth of the surface area of the pond are a function of the evaporation rate and the geometric configuration 8 at the Montana and of the tailings impoundment. Evaporation rates Colorado sites were estimated to be 19 and 29 nm/sec respectively. The combined effects of increasing tailings volume and water evaporation eventually expose the tailings (Table 4.4) during mill operations. After mill operations have ceased, natural evaporation is utilized to dry up the pond so that covering of the residual tailings can be accomplished (Table 4.5). Covering may begin before the end of mill life or after mill operations have ceased. Note that the model tailings pond employed in this study never reaches a ''steady-state' surface area during mill operations.9 Table 4.4. Estimation of areas of the dry tailings beach and pond during mill operation for the hypothetical Montana and Colorado locations Dry beach area (w2 x E3) Pond area (m? x E4) Time (years) Montana Colaorado Montana Colorado 1 0 0 23% 22 2 0 0 31 29 3 0 0 37 34 4 0 0 42 38 5 o ¢ 46 41 6 0 0 49 44 7 0 Sb 52 46 8 Q 7 55 48 9 o 18 57 50 10 0 25 59 51 11 ¢ 32 62 53 12 0 39 64 54 13 0 47 65 55 14 0 54 67 56 15 4 61 68 57 16 8 68 70 57 17 12 76 71 58 18 16 83 72 59 19 21 91 73 59 20 26 98 74 60 Average 4 36 57 49 %Read as 230,000 m2. bRead as 5000 m?. 43 Table 4.5, Estimation of areas of dry beach and pond as a function of time after closing down mill coperaticns at the hypothetical Montana and Colorado locations Dry beach area (m? x E&4) Pond area (w2 x E4) Time (years) Montana Colorado Montana Colorado 1 9@ 24 62 31 2 16 33 50 13 3 23 40 38 0 4 30 40 25 Q 5 36 40 i3 Q 6 40 40 0 0 Read as 90,000 m2. During mill operating life, it was assumed that chemical sprays and/or wetting were utilized to reduce the amount of airborne particulates and that covering would commence near the end of mill life. This procedure was assumed to reduce the average effective dry tailings area by about 90%. For the Montana and Colorado sites the reduced areas were 4.0E2 and 36E2 m? respectively. After the end of mill life, it was assumed that, on the average, about 4.0E3 m? of dry beach surface was exposed per year during the tailings covering process at each site. We assumed that whenever 4.0E3 m? of dry beach (9 x 440 m) was exposed by evaporation, covering of the tailings pile commenced and was carried out at a rate commensurate with the rate of generation of an additional 4.0 x 103 m? of fresh tailings surface. 4.2.7.2 Source terms for the emmission of 220Rn. The flux terms for 220Rn for the surface of the dry tailings and the pond were calculated using the diffusion equation previously described. The calculated flux terms were Jo (tailings) = 1.67 kBq/mz-sec . J, (pond) = 19.3 Bq/mZ-sec . Details of the flux calculations are given in Appendix 9. The calculated source terms for the 20~year mill operation and covering of the tailings pile at the end of mill life for the hypothetical Montana and Colorado mills are given in Table 4.6, b Table 4.6. Source terms for 2%0Rn during mill operating life and during final evaporation of the pond and covering of the dry tailings after the mill 1s closed Area of Area of Source term (Bq/sec x E5) Hypothetical location dry tailings pond (m?2 x E2) (m? x E4) Dry tailings Pond Total Montana Mill operating life 44 57 7 110 117 Evaporation of pond and 40 38 40b 73 113 covering of tailings Colorado Mill operating life 36 49 60 95 155 Evaporation of pond and 40 27 40b 52 92 covering of tailings aRead as 4 x 102 n?, A factor of 0.6 was used to correct for decay of 22%Ra parent. It is possible to contour the surface of the tailings pile near the end of mill 1life, so that the time required to dry out the pond is decreased. However, this would not decrease the source terms significantly. The equivalent area of dry tailings would have to be exposed during mill life to accomplish it. There may be economic advantages to shortening the on—-site activities as quickly as possible after mill operatiomns cease. Again, it is pointed out that it was not the object of this study to determine the optimum operational methods, processes, and equipment for the thorium mill and vefinery. 4.2.7.3 Source terms for airborne particulate emissions. The source terms for radiocactive emissions from the milling waste solids are due to wind-borme dusts from the dry tailings beach. During mill operations the tailings deposit is either kept wet or treated chemically to prevent dusting. These procedures may not be completely effective, and it may be expected that a small dry beach will be subject to wind erosion. At the close of mill operations, the taillings impoundment is permitted to dry in a controlled fashion and at this time wmay be subject to wind erosion. It was assumed that the principal mechanism for the generation of dusts is saltation, a process whereby the larger wind-drivem particles with diameters >80 um impact on the smaller particles and cause their suspension in the air. The application of saltation theory permits the calculation of the amount of wind-borne dust generated and consequently 45 the amount of wind-borne radioactivity.7 The working equations for galtation calculations are d_ = 36.22V2 (6) v, = 0.166(ds)0-5 , (7) q = 9.318 x 10“3(ds)0-5 (V’-V£)3; v>v), (8) Q, = Kqg , (9) where dt = threshold diameter of the largest particle moved by the wind, um, V = wind velocity at 1 m above ground, m/sec, dS = gverage diameter for saltation for wind velocity V, um, Vt = threshold wind velocity for ds’ m/sec, q = saltation rate (q = 0 for V < Vt)’ kg/m-sec, QS = particulate suspension rate, kg/mz-sec, K = 1 x 10>, m ', The numerical values used in these equations result from various experimental values and estimates. The calculations are based on knowledge of the applicable wind velocities and the particle size dis- tribution for the tailings (Table 4.7). Saltation cannot be caused by particles <80 um in diameter, and since the tailings have a negligible concentration of particles >600 um in diameter, the particle size range leading to saltation of the tailings is established. First, the threshold diameter, dt, for each wind velocity is determined [Eq. (6)], and then the saltation diameter, dg, is calculated from the weighted average of particle diameters between 80 um and d¢ (Table 4.8). The threshold wind velocity, Vi, for each dg is then calculated by use of Eq. (7). These values along with corresponding wind velocities are used 46 Table 4.7, Wind velocities and particle size distribution used in saltation model calculation Wind velocities Wind velocities 1.85 3.14 4.98 7.02 9.23 11.08 12.93 {m/zec) Frequency 22 36 18 5 1.4 0.51 0.18 (%) Tailings particle size distribution (ref. 4, p. 230) Diameter 44 61 125 250 500 840 <10 10-80% (um) % less than stated size 26.6 27.6 38.1 65.4 96.8 99.5 10. 23.2 aCalculated from d = particle diameter linear regression equation for particle size distribution. (ym); ¥ = wt. % less than d. Table 4.8. Calculated suspension rates as a function of wind velocity, using the saltation model d = 0.1711x1-753; Threshold Wind Threshold Saltation wind Saltation Suspension veloclty (v) diam (dt) diam (ds) velocity (Vt) rate {q) rate (Qs) (m/sec) (um) (pm) {m/sec) (kg/m°sec) (kg/m-~=ec) 1.85 124 102 1.68 4.62E~7% 4.628-12 3.14 357 197 2.33 6.95E-5 6.95E~-10 4,98 898 270 2.73 1.74E-3 1.74E-8 7.02 1784 270 2.73 1.21E-2 1.21E-7 9.23 3086 270 2.73 4.20E~-2 4 ,20E-7 11.08 4447 270 2.73 8.91E-2 8.91E-7 12.93 6055 270 2.73 1.62E-1 1.62E-6 %Read as 4.62 x 1077, to calculate the saltation rate, q, with Eq. (8). Finally, the suspen- sion rate, Qg, is obtained according to wind velocity to obtain an average (Qgy) (9). frequencies appropriate to the specific site using Eq. These Qg values are weighted used in the source term calculations (Table 4.9). was 22.8 ug/m®-sec. The average value of Qg weighted for wind velocity distribution Source terms are calculated by multiplying the value of Quw by the radionuclide concentration times the area available for saltation, according to the following equation: source term = {(2,28E-8) Cr'AS , (10) 47 Table 4.9. Suspension rates weighted for wind velocity distribution Wind Wind Suspension Weighted velocity (v) frequency rate (QS) suspension (m/sec) (%) (kg/mZ-sec) rate (Q ) (kg/m2°se§y b i.85 22 4.52E-12 1,02E~12 3.14 36 6.95E~-10 2.50E~10 4,98 18 1.74E-8 3.13E-9 7.02 5 1.21E-7 6.05E~09 9.23 1.4 4. 20E-7 5.88E~9 11.908 0.51 8.91E~7 4 .54E-9 12,93 0.18 1.62E-6 2.92E-9 The average of the values in this column is 22.8 ug/m?-sec. bRead as 4.52 x 10712, 2 it radionuclide concentration, Bq/kg, > 0 H area available for saltation, m?. Source terms estimated from this equation are shown in Table 4.2. Values of C, listed in Table 4.3 for the <80 um particle size fraction were used in calculating the source terms during the 20-year operation of the mill. All of the particulate radionuclide concentrations except 232Th were reduced because of radioactive decay. The reduction factors utilized to correct the concentration for decay were as follows: Nuclides Factor 228pa, 22Bpc 0.8 Remaining nuclides 0.6 (except 432Th, 228Th) The reduction factors and the Cy values for 228Th were estimated from graphical plots of the data in Table A.5.2, Appendix 5. Values of Ag utilized in the calculations were the following: Montana Colorado 20-year mill life 4.0E2 m? 3.6E3 m? Post-mill life 4.0E3 m? 4.0E3 m? 48 4.2.7.4 Long-term stabilization of the dry tailings pile. A source term for the covered dry tailings pile after the mill operations have ceased and the residual pond liquid has been evaporated was not calculated. As pointed out in Sect. 3.3.11, in principle the 220Ryp (172 = 55.6 sec) source term can be reduced by a factor of about 5E7 with the use of about 0.3 m (1 ft) of earth cover. Also, the covering would reduce the airborne particulate source term to near zero. Such source terms would be negligible in relation to those calculated for our model plant during mill operation and final impoundment operations. The stabilized thorium mill tailings would not present the potential long-term radionuclide source terms as do the uranium mill tailings, which contain 22°Ra (t1/p = 1622 years) and its secular equilibrium daughter 222Rn (t1/2 = 3,82 days). The longest—-lived daughter in the 232y decay chain is 228Rg (t1/2 = 5.75 years). After a decay period of about ten half-lives, the tailings pile will be equivalent to a thorium ore body containing about 0.057% thorium oxide. 4.3 References 1. Energy Research and Development Administration, Final Environmental Statement, Light-Water Breeder Reactor Program, ERDA-1541, Vol. 4, Appendix IX-G, June 1976. 2. M, V. J. Culot and K. J, Schaiger, "Radon Progeny Control in Buildings,'" Colorado State University, Fort Collins, C00-2273-1 (May 1973). 3. PEDCO-Environmental Specialists, Inc., "Investigation of Fugitive Dust — Sources, Emissions, and Control," PB 226 693, Cincinnati, Ohio, May 1973. 4., M., B. Sears, R. E. Blanco, R. G. Dahlwan, G. S. Hill, A. D. Ryon, and J. P. Witherspoon, Correlation of Radiocactive Waste Treatment Costs and the Fnvirommental Impact of Waste Effluents in the Nuclear Fuel Cycle for Use in Establishing "as Low as Practicable” Guides — Mi1lling of Uraniwn Ores, ORNL/TM-4903, Vol. 1 (May 1975). 5. P. M, C. Barretto, R. B, Clark, and J. A, S. Adams, Physical Characteristics of Radon-282 Emanation from Rocks, Soils, and 49 Minerals: Its Relation to Temperature ond Alpha Dose, the Natural Radiation Envirowment II, Proceedings of the Second International Symposium on the Natural Radiation Environment, August 7-11, 1972, Houston, Texas, CONF~720805~-Ps, ed. J. A. S. Adams, W. M. Lowdeo, and T. F. Gesell. M. J. Bell, ORIGEN — The ORNL Isotope Generation and Depletion Code, ORNL-4628 (May 1973). M. T. Mills, R. C. Dahlmann, and J. S. Olson, Ground Level Air Concentrations of Dust Particles from a Tailings Area During a Typieal Windstorm, ORNL/TM-4375 (September 1974). Climatic Atlas of the United States, U.S. Department of Commerce (C. R. Smith, Secretary), Environmental Science Services Division, (Robert M. White, Administrator), Environmental Data Service, (Woodrow C. Jacobs, Director), June 1968, reprinted by the National Oceanic and Atmospheric Administration, p. 63, 1974. Humble 0il and Refining Company, Minerals Dept., Applicant's Environmental Report, Highland Uranium Mill, Converse County, Wyoming, Docket 40-8102 (July 1971). 50 5. RADIOLOGICAL ASSESSMENT METHODOLOGY The radiological impact to man resulting from the operation of the model thorium mining and milling complex is assessed by calculating the dose to the maximally exposed individual and the total dose to the population living within a 50-mile radius. There are several potential pathways of exposure to man from radioactive effluents released to the environment. These are illustrated schematically in Fig. 5.1. Radio~ nuclides enter the environment from a facility via either liquid or atmospheric transport modes. They reach man through one or more col- lectors (air, soil, or water) with possible reconcentration by animals, crops, or aquatic biota. Pathways of human exposure include inhalation, ingestion, immersion, land surface contamination, and submersion. Ulti- mately, energy is deposited in human tissue by the radionuclides via internal or external exposure. Radiological impact is calculated as the 50-~year dose commitment, to individuals or populations, in units of millirems or man-rems per year of facility operation. The dose commitment is calculated for a specific intake of radionuclide and is defined as the total dose to a reference organ, resulting from a one-year exposure, which will accrue during the remaining lifetime of an individual. For radionuclides that have short biological or physical half-lives, the 50-year dose commitment would be approximately the same as the annual dose rate. For example, all of the dose commitment for %29Rn exposure (including radon daughters) is received during the first year. On the other hand, 232Th is eliminated from the body very slowly and has a long half~life (1.4 x 10!0 years), so that an individual will continue to receive a dose from the ingested material for many years after exposure., Under these conditions, the approximate dose received in the year that the radionuclide enters the body is obtained by dividing the dose commitment by 50. Thus the average annual dose rate is only 1/50 of the dose commitment. Tf an individual is exposed to mill effluents for the 20-year operating life of the plant, his annual dose rate during the twentieth vear 1s about 20 times the annual dose rate for one year of exposure, and his total dose commitment is the ATMOSPHERIC RELEASE 51 NUCLEAR FACILITY IRRIGATION FiSH ORNL-DWG 78-15181 AGUATIC RELEASE 1 INTERNAL LAND SURFACE CONTAMINATION (Y - SUBMERSION v EXTERNAL SOURCE mMoo£ COLLESTORS ACCUMULATORS PATHWAYS TYPE OF EXPOSURE T ) Fig. 5.1. Exposure pathways to man. summation of the 50-year dose commitments for each of the 20 years. These generalized dose estimates are approximately correct for the con- ditions cited. However, a4 detailed calculation must be made to determine a more precise value for the actual dose received in a given year.l 52 The exposed person is assumed to be an adult, 20 years of age, having physiological parameters defined by the Intermational Commission on Radiological Protection (ICRP).? In our report the terms "dose commitment" and "dose'" are used interchangeably; each implies a 50-year dose commitment. Doses to specific organs can vary comnsiderably for internal exposure from ingested or inhaled radionuclides concentrated in certain organs of the body. Estimates of radiation dose to the total body and to major organs are, therefore, considered for all pathways of internal exposure and are based on parameters applicable to the average adult. Radiation dose to the intermal organs of children in the population may vary from those received by an adult because of differences in radionuclide metabolism, organ size, and diet.3 Population total~body dose estimates are the sums of the total-body doses to individuals within 50 miles of the mine-mill complex. It is assumed for the purposes of this report that radiation dose to the total body is relatively independent of age;"“ therefore, man-rem estimates are based on the total-body doses calculated for adults. Similarly, the population dose estimates for the various organs are the sum of specific adult organ doses for the individuals within 50 miles of the plant. The man-organ—-rem estimates are also based on adult organ doses. The AIRDOS-II computer code® was used to estimate 50-year dose commitments from effluents released to the atmosphere. The AIRDOS-II code is a FORTRAN-IV computer code that calculates the dose commitment to individuals and populations for up to 36 radionuclides released from one to six stacks. Site-specific annual average meteorological, popula- tion, beef cattle, milk cattle, and crop data are supplied as input to the computer code. OQutput data include ground-level radionuclide concentrations in air and rate of deposition on ground and water surfaces for each radionuclide at specified distances and directions from the release point. From these values, doses to man at each distance and direction specified are estimated for total body, GI tract, bone, thyroid, lungs, muscle, kidneys, liver, spleen, testes, and ovaries, via each of the five significant pathways illustrated in Fig. 5.1. Dose calculations are made with the use of dose conversion factors supplied as input data for each radionuclide and exposure mode. Dose 53 conversion factors for submersion in the gas-borne effluent, exposure to contaminated ground surface, and intake of radionuclides through inhalation and ingestion are calculated by the use of dosimetric criteria of the TICRP and other recognized authorities. These factors are computed and summarized in twe computer codes, one for external exposure, EXREM~III,® and one for intermal exposure, INREM-II.’ Because recent revisions have been made in the INREM-II data base, a number of dose conversion factors used in this study are listed in Table 5.1 and supercede those listed in ref. 7. Radiocactive particulates are removed from the atmosphere and deposited on the ground through mechanisms of dry deposition and scavenging. Dry deposition, as used in this analyvsis, represents an integrated deposition of radicactive materials by processes of gravi- tational settling, adsorption, particle interception, diffusion, chemical, and electrostatic effects. Deposition velocity values for particulates range from 0.1 to 6.0 cm/sec.® Based on an analysis of the effect of deposition velocities on estimates of radiological impact, a value of 1 cm/sec is used for calculation of ground concentrations of radioactive particles for this facility. Scavenging of radionuclides in a plume is a process through which rain or snow washes out particles or dissolves gases and deposits them on the ground or water surfaces. Methods for estimating the scavenging coefficient can be found in Meteorology and Atomic @nergz.B Table 5.1. Dose conversion factors for total body, bone, and lungs for radionuclides in the 2327h decay chain Conversion factors (rems/uCi) Total body Bone Lungs Radionuclide Inhalation Ingestion Inhalation Ingestion Inhalation Ingestion 2321y 7.9 x 10! 1.4 8.7 x 10% 1.8 x 10! 2.3 x 102 1.1 x 107% 228pa 5.0 3.8 1.3 x 1pl 9.8 2.6 2.4 x 1073 228p¢ 5.1 x 10-% 2.7 x 2,6 x 1077 1.2 x 107% 1.3 x 1071 2.6 x 1073 2287y 1.4 x 10! 2.8 x 1071 6.9 x 101 3.3 3.7 x 102 1.0 x 107" 224pa 1.4 x 107! 1.0 x 107} 1.2 x 107} 1.6 x 107! 4.5 1.3 x 107 220pn 1.6 x 1077 0 0 0 1.1 x 1073 0 212py, 1.2 x 1072 4.2 x 103 6.5 x 1077 4.6 x 102 9.2 x 10~1 5.3 x 107% 2124 2.2 x 1077 9.0 » 107° 8.0 x 107 1.3 x 10™% 1.4 x 1071 1.3 x 1075 2081 2.3 x 1076 3.2 x 1076 1.0 x 1076 1.0 x 1076 7.2 x 1075 2.6 x 107 54 5.1 Additional Assumptions Many of the basic incremental parameters used in AIRDOS-II indi- vidual and population dose estimates atre conservative; that is, values are chosen to maximize hypothesized intake by man. Many factors that would reduce the radiation dose, such as shielding provided by dwellings and time spent away from the reference location, are not considered. It is assumed that persons remain unghielded at the reference location 100% of the time. Moreover, in estimating the doses to maximally exposed individuals via the ingestion of vegetables, beef, and milk, all the food consumed by this individual is assumed Lo be produced at the reference location specified. Thus the dose estimated for the maximally exposed individual in this and other studies using AIRDOS-II is likely to be higher than doses that would occur in a real-world situation. A special case exists in the methodology for the calculation of dose from 22%Rn which deserves further elaboration. For purposes of this report, 220gn gas is released from four locations within the mine-mil]l complex: the mine proper, the ore storage pile, the mill- refinery, and the tailings beach. It was further assumed that the nearest residence is located no closer than 1 wile from these facilities, in the direction of the prevailing wind. Given the short half-life of 220gn (55.6 sec), we conservatively assumed in this study that all 220gp decays to airborne 212py particulates prior to crossing the l-mile facility boundary. Doses listed in the results as due to "220pn + D" (?20Rn + daughters) are therefore actually the result of ingestion and inhalation of 212pp, for both the maximally exposed individuals and the general populations. As confirmation of the accu- racy of this approximation, doses were independently calculated both for 220Rn gas alone and for 2!2pp suspended as dust (rather than created by decay of airborne 220Rn) from the four site operations. Doses calcu- lated for these cases were insignificant in comparison to %1%PL doses generated from airborne 220Rn and were excluded from the tabulated results. Additionally, dose commitment to the lung, as computed for this report via the INREM-II code7, is calculated as dose to the entire 55 lung, commonly identified as the "smeared lung' dose. Dose to the bronchial epithelium region of the lung from ?2ORn daughters may be higher than that to the entire lung. A discussion of this relationship is available in Dunning et al., Vol. II.? 5.2 References M. F. Sears, R. E. Blanco, R. G. Dahlman, G. S. Hill, A. D. Ryan, and J. P. Witherspoon, Correlation of Radicactive Waste Treatment Costa and the Environmmental Impact of Waste Effleunts in the Nuclear Fuel Cycle for Use in Establishing "As Low As Practicable' Guides — Milling of Uranium Ores, ORNL/TM-4903, Vol. 1 (May 1975). International Commission on Radiological Protection, Report of the Task Group on Reference Man, ICRP 23, Pergamon, New York, 1975. G. R. Hoenes and J. K. Soldat, Age~Specific Radiation Dose Commit- ment Factors for a One-Year Chronic Intake, NUREG-0172 (Novem- ber 1977). Federal Radiation Council, Fstimates and Evaluation of Fallout in the United States from Nuclear Weapons Testing Conducted through 1968, Report No. 4, Government Printing Office, Washington, D.C. (1963). R. E. Moore, The AIRDOS-II Computer Code for Estimating Radiation Dose to Man from Airborme Radionuclides in Areas Surrounding Nuclear Facilities, ORNL-5245 (April 1977). D. K. Truby and S. V. Kaye, The EXREM-III Computer Code for Esti- mating External Radiation Doses to FPopulations from Envivonmental Releases, ORNL/TM=-4322 (December 1973). G. G. Killough, D. E. Dunning, Jr., and J. C. Pleasant, INREM-IT: A Computer Implementation of Recent Models for Estimating the Dose Equivalent to Organs of Man from an Inmhaled or Ingested Radionuclide, ORNL/NUREG/TM-84 (in press). D. H. Slade, Meteorology and Atomic Energy, Atomic Energy Commission, TID~24190, Oak Ridge, Tennessee, 1968. 56 G. G. Killough et al., Fstimates of Internal Dose Equivalent to 22 Target Organs for Radionuclides Occurring in Routine Releases From Nuclear Fuel-Cycle Facilities, wol. 2, ORNL/NUREG/TM-190, in press (1978). 57 6. ANALYSIS OF RADIOLOGICAL IMPACT 6.1 Maximum Individual Doses The maximum individual doses at 1 one mile from the point of release of radionuclides are shown in Table 6.1. Data are listed for both the Lemhi Pass site and the Wet Mountains site; meteorologies for each site are also indicated. Table 6.1. Maximum individual 50-year dose commitment to total body and various organs from radiocactivity released to the atmosphere during one year of facility operation Dose commitment (millirems) 1 Meteorology Total body Gl tract Bone Thyreid Lungs Kidneys Liver Lemhi Pase site Butte 2.4 4.1 9.5 2.4 35.3 4.3 2.9 Mullan Pass 2.4 3.7 9.4 2.4 32.0 3.9 2.7 Wet Mountaine site Pueblo 3.7 3.8 13.1 3.7 33.4 4.2 3.3 Alamosa 3.2 3.3 11.2 3.2 28.7 3.7 2.8 For lemhi Pass, the Butte, Montana, meteorology gives doses that are slightly higher than those for the Mullan Pass meteorology. Therefore, the Butte meteorology will be considered in greater depth in this analysis. Lung is the critical organ, receiving a dose commitment of 35.3 millirems, while 9.5 and 2.4 millirems are delivered to bone and total body respectively. At the Colorado site, the Pueblo meteorology gives the highest doses. Again, lungs and bone are the organs receiving the highest doses, 33.4 and 13.1 millirems respectively, while dose to total body is 3.7 millirems. A breakdown of the dose by radionuclides to various organs is shown in Table 6.2. For the Lemhi Pass site, 229Rn and daughters are the primary contributors to all organs. The second most important radio- nuclide is 22BRa, delivering 367 of the dose to total body and thyroid. The relative distribution of the dose from radionuclides at the Wet Mountains site is similar to that for Lemhi Pass, with the exception that 22B8Ra is the major contributor to total body (59%) and thyroid (59%). 58 Table 6.2. Radionuclide contributors to the dose commitment to various organs for maximally exposed individual Contribution to dose commitment (%) Radionuclide Total body GI tract Bone Thyroid Lungs Kidneys Liver Lelmi Pass site (Butte meteorclogy) 2327h 3 <1 10 4 <1 1 13 228ga 36 2 23 36 <1 4 6 2285, <1 <1 <1 <1 <1 <1l <1l 2287y 1 <1 2 2 <1 g Th/g crust. Using an average soil density of 2 g/cm® and a decay rate A for 229Rn of 0.693/55.6 sec = 1.27 x 107%/sec, an exhalation rate from soil for 2?ORn of 0.336 pCi/cm?-sec has been calculated.? Multiplying this rate times the area of the contiguous U.S., 8 X 1016 cmz, gives the total 220Rp exhalation rate for the contiguous U.S., 2.69 x 10'® pCi/sec. Eichholz" has estimated that the human lung receives an annual alpha dose of 0.6 millirad from daughters of naturally emanating 220Rn; other organs receive lesser doses. The 229Rn activity leaving the 50-mile~radius circle surrounding the hypothetical mine and mill site may be calculated as follows: The average sum of the estimated 220Rn activities generated at the mine and mill site (from Sect. 4.1) is 2.2 x 10° pCi/sec. Allow a l-sec increment of 220rp gas (2.2 x 10° pCi) to travel downwind to the 50-mile radiums boundary at 15 mph (an arbitrarily chosen wind speed). During the 3.33 hr required for transit to the boundary, the 220Rn activity (A) At is reduced to A = A e , where A = 2.2 x 109 pCi, A = 1.27 x 107?%/sec 66 and t = 1.2 x 10" sec. Therefore, the 220Rp activity per second leaving the 50-mile diameter under these assumptions is 2.2 X 109 pCi x (7.6 x 10787y = 1.7 x 107°7 pCi, an insignificant activity when compared with the 2?9Rn exhalation rate calculated in the preceding paragraph. To complete the analysis, it is necessary to consider the impact of 212ph, daughter of 220Rn. Since one atom of ?12Ph is created per decay of an atom of 220Rn, 212py activity is calculated by multiplying the activity of 220pn released by the ratio of the radionuclide half-lives (see Fig. 6.1). Thus, release of 2.2 x 107 pCi/sec of 220Rn at the facility results in the effective release of - :212 g pCi _ 55 sec 1 hr _ g pCi“ " “Pb . 2.2 x 10 ec © 10.6 hr ~ 3.6 X 10° sec 3.2 x 10 sec The AIRDOS~II computer code was used to estimate air concentrations of this 212Pb particulate both at the l-mile facility boundary (locatiom of the hypothetical maximally exposed individual) and at the 50-mile study area boundary. Meteorology specific to Butte, Montana, was used (see Appendix 1), and parameters including radionuclide decay, dilution in the atmosphere, dry deposition, and scavenging (see Sect. 5) were incorporated. Under these conditions, maximum air concentrations occur in the northeasterly direction from the facility. The concentration in air for “12Pb particulates at 50 miles vs 1 mile is reduced by a factor of about 3 x 103. Table 6.1 lists doses to the maximally exposed individual at 1 mile under these conditions, and Table 6.2 lists the percent contribution of 220Rn + D (essentially 212pp) to these doses. Doses from 2'?Pb to a maximally exposed individual at 50 miles from the facility would be roughly proportional to the 212ph air concentration (above) and would therefore be reduced with respect to the tabulated doses by approxi- mately 2.9 x 103, Under the conservative conditions used for maximal exposure {(see Sect. 5), doses due to 220Rn + D (212pb) release would approximate 5 x 107" millirem to total body, 2 x 1073 millirem to bone, and 1 x 1072 millirem to lungs at 50 miles from the facility. Doses to individuals residing outside this boundary, and not subject to maxi~ mal exposure conditions, would be further reduced and are judged insignif- icant when compared with natural background 220gn + D exposures. o7 6.5 Discussion Effect on estimated doses of variation in population size One of the goals of this study was the radiological assessment of a range of thorium resource sites to estimate a range for the radiological hazards associated with the mining and milling of thorium. Analysis of available literature indicated the likelihood that, in the event of wide-spread implementation of a thorium~uranium~233 fuel cycle, extraction of large quantities of thorium would occur primarily in the vein deposits of the western United States. Ifispection of data estimating thorium reserves at the various western resource sites led to identification of the Lemhi Pass and the Wet Mountains areas as likely to be worked. These sites were chosen for further analysis based on data indicating nearly 20 times the population residing within a 50-mile radius of the Wet Mountains site as compared with the Lemhi Pass site. This size range in potentially impacted populations provides the primary basis for the study's range of a factor of 4 to 5 (Tables 6.4 and 6.10} in estimated radiological doses for the two populations. Effect on estimated doses of substitution of meteorological data sets As noted in Sect. 2.5, choices of meteorological assumptions have the potential for significantly modifying doses calculated for fuel cycle facilities. Table 6.1 indicates that, for the meteorological data sets used in this study (and described in Sect. 2 and Appendix 1), lung doses to maximally exposed individuals may vary by as much as 10% in the case of the Lemhi Pass site and 16%Z in the Wet Mountains case, depending upon choice of meteorological data. Presumably, choice of less site-specific meteorological data, including generic or average U.S. meteorological summaries, could lead to further uncertainty in maximum individual dose estimates. Population dose estimates (Table 6.4) are also found to be sensitive to choice of meteorological data, with lung doses to the general popula- tion varying by 147 in the Lemhi cases and by 32% in the Wet Mountains results. _ In general, given the likelihood of complex local ajr flow patterns over mountainous terrains such as are encountered at these study sites, 68 actual doses to individuals residing near operating facilities may be greatly affected by local topography, orientation, and specific diurnal wind regimes. Doses in this report are necessarily calculated without access to such information and should be recalculated when data become available. Conclusions This analysis of radiological impact suggests that maximum individual dose commitmeats at 1 mile from the point of release should be similar to those encountered in uranium operaiions. It was not possible to make a direct comparison of this assessment of thorium mining and milling with previous published assessments dealing with uranium ore. The primary reason for this difficulty is that this analysis incorporated different sets of meteorological data, site-specific population data, and assumed a l-mile (vs 0.5 mile) distance to the facility boundary. Also, no operational experience existed on which to base the development of source terms. Therefore, use of conservative assumptions was required. Doses to the maximally exposed individual at both sites were similar, between 2 and 4 millirems to the total body, 9 to 13 millirems to bomne, and 29 to 35 millirems to lungs. General population doses were estimated to be highest for the Wet Mountains site, at 0.3 man-rem (total body), 0.9 man-rem (bone), and 3.7 man-rems (lungs). Doses calculated were largely the result of ingestion and inhalation of 220Rn daughters for both the maximum individual and general population cases. Significant contributions to dose were also found for 228Ra, 232Th, and 228Th in order of decreasing importance. Radon-220 and daughter doses to individuals outside the 50-mile-radius study area were determined to be insignificant when compared with natural background. A distinct advantage of thorium mining and milling compared with uranium mining and milling may be that the radiological hazard encountered following plant shutdown is significantly lower and decreases rapidly after shutdown. Because radioactivity residual in the thorium tailings pile will be controlled primarily by the half-life of 2?8Ra (5.75 years), the need for extensive maintenance (compared to uranium facilities) of mill tailings for long periods after shutdown will be greatly reduced. In the 69 ALARA uranium mining and milling study,l it was concliuded that at the New Mexico site, maximum doses to bone and total body at 0.5 mile from an interim-treated (via chemical dust-reducing spray) tailings area could be as high as 933 and 92 millirems respectively, using conservative assumptions. The magnitude of these doses suggests that extensive final treatment and long~term maintenance of a uranium tailings area might be necessary. In comparison, in this study of thorium mining and milling, the tailings pile (assumed treated by chemical spray) results in maximum individual doses estimated at 6.8 millirems to lungs and 2.1 millirems to total body for the Lemhi Pass site immediately after shutdown. Doses are also estimated to be reduced with time fdllowing shutdown. Therefore, it is concluded that postoperational handling of a thorium mine and mill facility may be significantly less complex than for a uranium facility, and that the radiological doses associated with the post-operational thorium facility might be significantly less for a given level of tailings pile treatment. It should be emphasized, however, that no difficulties in meeting current or proposed radiological standards are anticipated | for either type of facility, given application of appropriate, available technologies. 6.6 References 1. M. F. Sears, R. E. Blanco, R. G. Dahlman, G. S. Hill, A. D. Ryan, and J. P. Witherspoon, Correlation of Radiocactive Waste Treatment Costs and the Envirommental Impact of Waste Effluente in the Nuclear Fuel Cycle for Use in Establishing "As Low As Practicable” Guides — Milling of Uranium Ores, ORNL/TM-4903, Vol. 1 (May 1975). 2. R. C. Malan, Summary Report — Distribution of Uranium and Thorium in the Precambrian of the Western United States, AEC-RID-12 (1975). 3. C. E. Junge, Air Chemistry and Radiocactivity, A.P., 1963. 4. G. G. Eichholz, "Environmental Aspects of Nuclear Power,'" Ann Arbor Science Publishers, Ann Arbor, Michigan, 1976. 70 RECOMMENDATIONS FOR FUTURE WORK During the conduct of this analysis, it became apparent that some of the technical data required for detailed radiological environmental assessments of thorium wmining and milling were not available. In these cases, appropriate data pertinent to uranium mining and milling were often substituted and used in this work. 1In order for more refined assessments of thorium mining and milling to be performed in the future, data pertaining to the following areas are needed: 1. Quantitative measurement of emanation factors and diffusion coefficients for 220Rn in thorium ore materials such as those found in vein deposits. 2. Determination of fugitive dust generation rates and the dust properties characteristic of mine activities and from exposed thorium ore deposits and ore piles. The latter should include studies of wind~ blown dust from ore piles and involve quantitative descriptions of the saltation behavior of the thorium ores, when appropriate. 3. Rates of release of 2?0Rn from thorium ore under various storage conditions are required. Effects of water sprays and/or other treatments in reducing dust and 220Rn releases from thorium ore storage piles should also be determined. 4. Determination of the release rate of 220Rn from thorium ores is required for such typical mill treatments as crushing, grinding, and dissolution. 5. The concentrations and compositions of thorium decay products in thorium mill waste liquors are required. 6. Specific properties of soils from the mountainous locations where vein-type thorium ore deposits are located should be determined to assess the soils' suitability for construction of tailings ponds, controlling leakage of waste liquor from the pond, and reduction of migration of radionuclides from the tailings waste liquor. 71 ACKNOWLEDGMENTS The authors wish to extend their thanks and acknowledge the contri- butions which several individuals made in the preparation of this report. K. H. Vogel and S. K. Beal* provided supplemental information on the assessment of thorium mining and milling as presented in the Light- Water Breeder Reactor Program envirommental statement. Eugene W. Grutt, Jr., and Donald L. Hetland™ provided copies of several reports containing information about thorium deposits in the Lemhi Pass region. R. E. Moore* performed AIRDOS-II radiological dose calculations, and Don E. Dunning and George G. Killougfi1C provided current dose conversion factors for the radionuclides of concern in this report. Mildred B. Searsi provided many helpful suggestions and discussions throughout the course of this study. Hershel W. Godsbee* contributed to the determination of the applicability of various diffusion models for estimation of ?20Rn releases and assisted in the development of the equations for estimating the change in area of the tailings pond during the operation and closing down of the mill. The support and encourage- ment of George L. Sherwood, RRT/DOE, during the conduct of this work were also appreciated. Typing assistance was given by Susan Masingo, Beverly Varnadore, and Rebecca Hamley. * Bettis Atomic Power Laboratory. +Grand Junction Office, DOE. % Oak Ridge National Laboratory. Appendix 1 SUMMARIES OF METEOROLOGICAL DATA OF ATMOSPHERIC STABILITY CLASSES FOR FACH DIRECTION FREAUENCY Pueblo, Colorado FRACYION OF TIME IN EACH STABILITY CLASS SECTOR a Al-3 DM D ar O 0N DY e PO M IO P = A D OO - DM et O S o P DO vt o] e el DO Ot DN OY MY (MY (DY * % 8 & 5 & & & & g % s 8 00 QODOOOOOOODOO OO PmINEFIO MO R e Dt e OO0 D d ATV MDD M DN S D D Voot g NN DAY O Y DO ok pod wot ik vd (Lo iyt wod i [ * » & & 5 8 4% & " g e B s s g COOOOOOOOOOORDOO0O IO Med 29O 2 0 P PN 2 OO MO e DM NN AN N Y ey e e A0S Y O O D I O ANNMM g NN . 2 & & B B & g o BB e e P DO2OOOOOCODOOLOD0 RO R U e S 20 P e 1Y o PG O N DM oUheoomm e Ny — g Y R OGO A D T QT e NGO st et QLTI O D i e * 4 % g o ® P o @ B 4" a2 g OOOOOOOOOOOOOLOD MO D) el GO P0G et e PR D Wit o PP (N2 vt ot P NN Moo NN S O WO M N U e OO DS ) " 3 5 2 & P B 9 B 9 e B & bHm DO OOOOOOOOO o ML o F NN O T e MY S G O A P O MY R S e YOG O e O e D Y e (D O O et £y CHEBEn OO QIDOAOCD G * .8 5 & P A 8 s B 5 g * K 8 oA OO OOLEC OO OQOM OO w OIS D O N S OO wof gk o o ok e Pueblo, Colorado - fFurguenNCTIFS 0OF #IND DIRECTIONS AND TRUCE=-AVERAGE WIND SPEEDS #IND TOWA®D FREQUENCY WIND SPEEDS FOR FACH STABILITY CLASS {METERSZSECH A £ C D F F 1 C.086 1470 2.22 381 4496 3,48 1e38 < CeaDBE 178 2.73 Ao 3D Sel2 1.75 1leh4 3 CeU8A8 1674 2.54 4,18 5,02 3.72 1.41 4 CeDT7E 1.81 2+54 4,25 5+28 372 1«55 5 CQGGQ 155 2elbd 1. 656 4,85 3,77 1«60 o Coelaf 123 2e04 3.648 5. 45 3.92 1.568 7 D.0548 155 1,70 3,656 £e20 3.956 153 8 0032 1415 1.85 4.1% 7«45 4,02 162 3 Ce64 1203 1,990 3,449 8,00 3493 1.63 1e D047 158 195 3.13 681 3.88 1476 11 Nel 86 107 1.84 3. 37 Hs29 3.75 1.54 1(2 3.5’}3 1053 1;9# 3-68 7.&1 3.71 1-71 13 0e107 1432 1.58 3,52 6451 3.84 1.62 14 DeU67 1e81 1.98 370 6. 34 3e.81 1,68 15 DeD489 1467 1.74% 1,67 6.18 3.57 a4 i 04029 1.756 2.08 3,65 6.01 3 .49 133 HIND DIRFCTYTIONS ARE NUMIBFRFD COUNTERCLOCK®WISE STARTINS AT 1 FOR DUE NORTH y=1Y FREQUENCY OF ATMOSPHERIC STABILITY CLASSES FOR EACH DIRECTION Alamosa, Colorado FRACTION OF TIME IN EACH STABILETY CLASS SECYOR Al-5 M DIONO QO DMNO OO DO OMNANOM NN S DN Nt AWM O D vl wt i MY i MOV N wd 0 e d O SN OO O ol O # VY O el v . h B 9 b & F 4 & H 2 s e COOAOOOOOROQLOOO =HOMNIONDZ O SNONONIOM MY P 10 A LY v o e Y MY O e SO YO MmN MNMNMsEMOIN M S * % % 0 & 0 A 0 "t 0P g COOOOOOOQOoOOQOODOO Th e sl 2150 O 0 V0 O o} 0 ¢ 0 0 G G 0 0 0 0 0 De BT el I el PIED O e 23000 @ O e D PO MNF "N OO U COOQ=IIRNCO A o0 L2 vt el ek g (0 O e L0 e O D €O KD D O 8 % » a8 8 s e 0 g e s AN N AN T e W DeAMNG I e NI O AL OO D *a B & A 5 & ® » ® 9 2 ¥ s p QOO MO0 OO0 vt DU N0 M DT D vl (PR O Alamosa, Colorado - ¥FwYGUFACIES OF WIND DIRFCTIONS AND TRUE-AVERAGE WIND SPEEDS HITND THwARD FREQUENCY WIND SPEFDS FNOR FALH STABILITY CLASS { METERSZSECH A 5 C D £ F 1 0e135 1664 2418 3,68 6e56 3.87 1480 2 NDe(HE 1.68 205 3+ 56 Sel 3 3.79 190 3 Ne053 152 2.13 3.33 S.11 3.86 1491 & 0,058 1.59 2450 3,11 5453 3,85 1e77 5 0073 1.46 2.05 1,02 624 3.569 170 5 O+ a2 1.74 2.06 2.76 4495 3,38 1.84 7 CeD 34 152 1,96 3.01 4,82 3,30 1e71%1 3 Ce033 1452 2.18 3,07 5.06 3,70 1.80 9 3005% 1058 2.‘43 3-21 6-@'3 3076 1085 14 Le0tbH 1.35 2441 3.77 H+13 3.70 1.89 11 T e(54 1 59 2.13 3,94 65615 3.66 175 12 7,051 ledl 197 2457 5 o0 3653 1.91 £3 CeN 72 1e¢ 35 2,21 3.30C Se 85 3.55 1.89 in CeD74 137 1.91 3.80 He7l 3.85 194 E De0 79 L1e37 2410 3,23 7e26 3.82 1-.82 lfi 603?1 1053 2.24 4.84 5.7; 3.93 108‘ ATND DINTCTINNS ARD MNUMRBRFRID CUOUNTERCLOCKWISE STARTING AT 1 FOR DUE NORTH 9~1V OF ATHMDSPHERIC STABILITY CLASSES FUR EACH DIRECTION FREGUENCY Mullan Pass, Idaho CLASS 0F TIME IN FACH STABILTITY FRACYION SECTOR 0 Al~7 C ot g g TR0 T T e O e P 2 o wed 7120V AT SOV 0 O OO I T N N DI SN e D MO D O et ot 0w 10 et ) et () ot 233w () vk *® % 4 @ ® R R P R e e IOl OOCo OO oo A E A O T Y S e 0 PO N MO N SN O DD e S NTIOO LMD - D ore et el ek gt T 0 O el et 0 (T 0 . 0 " 2 " 8 & P a2 s PR AN DOQOCOCOCTOoOOOmC . 63 De 0206 Qe OHBH 008 ™~ A P DN e P 00N 0 T O ST S e e T 0 A O O e B TN e U e LD DT 2 e O PN O N WD e O G A Y e T ® ® B % & & w 2 s & B 8 e * B QOQoOLOQOQOOQOLOOD MO O ONNO- DTN M NNNeORNC M2 Oy A D e e OO e LD D e M O Y ol ool e kg ot £ S LTS OO Y el et S 8 R & 0 O k& & & 5 s 28 COOOoOOC Qo OCODO00 e M e O T Nk N M AT L RNV OO PN SRR MO I O At OO OOCOOCOTOTO m * & % & » & O 4 & . p s 6 r 8 COQQUCODOTOoROOCCO NP OO T h MR A F e e D TR YNNI IO D O D et MDD OO OO w O owd O O CoOGOOOOOoOC OO 4 R ¥ P & 0 & & P BT B R B OO OOCOQ OOl OO e O P RS L e GO CR LD ek (N F D ol el et gl o ot g Mulian Pass, Idah0o -~ FREQUINMCIFS OF WIND DIRFCTIONS AND TRUF—-AVTRAGE #IND SPLYDS WIND T0OnRARD FRFEGUENCY #IND SPEEDRS FOH FACH STASILIYY CELASS v TURSASEL A & i i3 r & A De020 1e12 1.7% Ta04 Lef5 403 1«85 5 G026 1. 05 157 .12 e 2H LR 1268 5 0.030 D77 167 o &3 e 39 12 175 7 De5H1 103 1aD4 307 5«19 3.9%8 1.H68 8 0059 Oe498 2a0% 3228 L ah3 4402 1e5HB ¥ Gal24 1.10 1773 el G5« 85 Je71 153 10 Oe007 125 Ze18 Te 873 Hald 383 1,756 11 Cel59 102 2alt JeT01 SRR 377 Lo 88 12 Q.Ufif» io’afl ?'12 3-?3 %350 ‘g.fi? 1'?5 3 Ca 0813 101 {78 2 e B 49 36 383 1656 14 De376 1a0}4 2ali 350 S e23 4 e(8 172 15 D.,106 1.4 185 1420 5414 F 90 1553 15h CeTit 7 120 2623 Te 2% 4415 3287 1e0:4 HIND DIRCCYLIONS ART WNUMBERQUD COUNTERCLIOK @IS STARYING AT 1 508 UUT NIRRT 81V DIRECTION EACH OF ATMOSPHERIC STASILITY CLASSES FOR FREQUENCY Mullan Pass, Idaho - March through November average SECTOR L b ~ As CLASS STASTLIYY FACH N gF TIME FRACT N 2 X Al-9 ;JH.\}!; VAT NN e TN wfin)«ficll.:))_a‘.?.i.«\) A:.n?:r P U7 O A e S0 ek 7 d et (7 ek e e e T e (O ® & 8 % 3 8 5 &% ¢ 8 2 OO OoCOOOOGCDO0 D.1382 U« 1358 D.11190 0.0868 2D A I P 2 T e TN eed e e A e e e PO SE R P TR DD D e O O e NP T O e AT D T et 5T e TR T vl el ol ot v oo I LT el O D el g e (T * & & @ 2 2 ¢ F 2 b a2 % 2 *P» CoRUOoCCODTQoLQUooQo WD A ALy P Y b TN N e e T CRITO D A R G T YA P T T ed LT Y e T i g o Wit o NI Oy 2 % & & % g ¢ * » & 4 ® n CoOOOOOOOO0LOon + P = = . o 0."3(‘4 MRS et O O O D P DD e YOG D TN O N D P et e it g ] 0 OO N D W wed ok ot ol gl gt wod md o 3 (YD ® R 2 8 & 5 8 R 2R R S 2P o OO OoOOOCOoOoOoC WM OIS G e OO O e _H\,_nvnfivl.flqifflnbg.fln,i?r)nu) Rl s 0D T D e W S GO LD I Y e QOCAQQOQO SO OO0 0O D 4 " 2 8% 2 B 8 8 F e s 8 89 OCOOOOCOoOCOCOCooOC AL AL O D e 0 e MY 0 D SR LQ U O e NOT MO D SO COOoOToooool o e ® 2 & ® 2 F ® & 8 4 P A a® DPOCCOoOOLOODOOQOC vl AP D P DT Y el A e iy it rd et el pad et gt Mullan Pass, Idaho - FRUQUINCIFS March through November average AIND Tiw ARD 1 D085 ? O.i)qfw 4 NaD33 3 031 £3 Ceae024 7 D,011 B 0013 3 G018 i0 e85 11 I B 12 0 a7 i3 D079 14 010806 15 Galsh 15 DeORBY #IND DIRECTINONS AGF NUMKERYD FRUODITNCY OF WIND DIRFCTEONS AND TRUL -BYERAGE YIND SRR 4 - C L1 2 137 a7 e i3h 1,594 Te 28 e 38 1475 T.131 Gae?7 1RG0 Te 56 1.06 14873 1«07 DeBe 2e U4 tenn? faléd 1«28 1401 1,901 1491 2s98 1e 34 ] ettt ER 1.19 192 e it 14313 1232 3e 1) 1.{}) v“}-’)g 1. 2h 105 1.8 I.13 a8 2720 T 52 14086 2a2 0 3674 1.1% 14704 .72 COUNTENCLOCK®1SE STARTING Al r i = 24 4or A 3 e - b WAl S h o % B 5 & % Bt & b 8 8 e UTLY b e N O e B e D e W B ke g O Lt a Fun Wl CH g LA a0 P s DL D OSPEIDS STARTLEYTY LLASS {MoTeRRSIS5ECH Soed B ol ket ol G B B P Wl &L St o B de & LI B E 6 e RS 5N s s e ~ WD ONE Or N LD o} bbb LN N2 T F ie51 171 177 170 155 1«50 ieb64 1e 48 1«56 163 ie5e 157 1«74 1e 556 1.55 1268 OT-1IV EACH DIRECTION CLASSES FUR FREPGUEMCY OF ATMIOSOHERLIC STABILITY Butte, Montana STABILETY CLASS aF TIME IN £ACH FRACT LN SECT xR L Al-11 e BTN UL el B MO O e o O D O0 30 e (7 A |72 0 O A M et MO AT e P OO T e O P e A 4 9 2 8 & 8 B W 28" s a0 CCoOoOOoOOoOCooooOC o P ALY e N DU R O B MY ot Y OF T et (M O O e o L) e Y P WM SO OO AR Re® R e E RN R LN COOoOOoOCOoCCOOOQOo0 R A D N AN O S e TP e P D I N RN D A T el O N A e T YA PT e O et i T Aok O D M e m P A P D 00 ) ®* n s " 5 @& % 2 ¥y e P p e gpn DOOCCOODOODoOODooC WD M T O N O N D Ty G Pt i e o e Y0 OO MG W TN e SN AN O o w] el {0 et i C3 DO YD -t PR s & # v oBR AR e e . COOoOUOOoOQOoToooood 3 U O e R0 e B U MY P B MY et 10 G0 T O me WM O B YN et PO TN e e OO D . 2 ® & B T s ® a = O OoOQOODOOO 746 13 10 - 24 0400 3 Dal G»0501 0. 0769 FaY [ Co e Ot ) =T WO M DY 0 e OO v E DU PTG DU T N e U0 P D DD NN O et e KO DD QO QT OGO Ooe ® R ®* % # & 9 ¢ F & 3 ¥ B &P~ OO oo Om v O AT P S0 O e O3 o Butte, Montana - ¢erauirvC1sy 0% aInD {1070 10D T ARD FREIENTY A i fio%){;fi 1+05 2 D081 Tal5 : Dal 24 Na?7 h NaN14 1215 6 fl.fiiR 1-13 % G329 Qw35 7 Q0R7 lal5 £ 0118 DeT7 4 e 108 D477 in e 081 30 11 Ne D57 1.02 12 Ne 171 I«15 i e N4y 1) Yoi7 146 Qe y D e 46 i5 G100 1«15 15 0.089 1al1% ATHD DIHCCTINNS AVFE NUMETFD COUNTE PCLOCK 0] SE MSOAND TRUT-&VEIRPAGT VIR Te 35 1373 t 238 1o 2 fe31 o1 1437 14210 1a21 a2l 154 1.87% 174 {57 165 149 STARTING TLENS [ Dad el i kb R e e PN T TN s N O R RO D & & & a ¥ ® 0 8 @ B B B W s G DWW WO S Do NS N }.." S B TN e N AN -~ T b 030 ifed NI SPLINS D e FACH Mo T-RSISECH U P TN N e e e B a " 8 & & P 4 & & 8 g T @ ¥ £ W » WO e O L mow b (0D =y (5 30D WA G De e QD P O e s N D W 1 4e 3) DL NIRRT 3 & 9 3 8 & & ¥ & & 5 8B = D VNN O B N Wl DN Y e WD O o DN Lid G (o L LA L L) Sl Rl g L G IO G L o 48] Jett7 STABILITY CLASS & % 8 5§ 6 % 56 s s e W i L L e N L B NS R e D i BHEerAND AN ® e ek o ok ik b gk Pl pak Pt o Bk et ek o b ¢1-1V Butte, Montana - FREGUENCY 3F OATHMOSPHERIC STARILITY CLASSES March through November average SECTQO? A 00021 G.0019 Da00332 D«0139 et 393 D.0154 D+0719 D055 J0.0327 D052 C=0343 D.013%1 00055 00078 Je0128 DaN24813 FRACIION ® & & ¥ @ & & ¥ rJ Wk Lk B e 3O O N LD E D O R e DN b N LT L R P to U DB OODDODSO . n = 0. 1069 0. 0870 C.0523 0. 3893 Gae{)4RY 008428 N+0494 C 004859 0.0603 01225 J.0895 0N,1908 0«+1513 018732 Os 1565 0s-1313 01000 0208986 0.0877 00015 00366 J:0565 OF TIME 0 COoARDLI2ODToDOOQ 0 % 5 ¥ &N g b ®s w6 now NP IOME BN WL T e O W D e (OO NS B O N WO R &0 &0 5 U0 5 SO0 ON RN BRGNE AN DD IN FACH STABILITY CLASS FIOIR EACH DIRECTION rt PO ODOLOCODDOODDTOo0 & % % & 0N u o0 @ U B 5 e g D e e o S DO N WMy kT g e e B ek T L e LS b OB D B D N G P om0 ot o pomt pot e vk o ek (U O 1M ¢ET-TV Butte, Montana - ¢fRe@ITHCIFS OF ®IND DIRFCTIANS AND TRUF-AVERAGE AIND SPLEODS March through November average A IND TawAxD FROQJQUENCY W IND SPEEDS £ FACH STARILITY CLASS [METERS/ZSECH A i C 2 € ¥ 1 0.108 D277 Yo aH 207 72 .73 155 2 0ai19 D77 {712 Tad 2 541 22060 1. 36 3 {} o 3 A7 1450 14457 3427 5oae 5 3447 1.356 4 D032 1i.13 1,39 1.9 Se 37 3.05 1435 5 e 1H 150 14373 F2072 433 3222 1.44% % Qe 14 150 tall g Te 27 hel? 3. 29 1.17 7 3024 Da77 167 2¢e57 2ebB2 289 130 4 0080 150 iae882 2s 41 3. 50 3.438 1,15 9 DeDB3 1.01 1446 de 60 4 47 3. 39 1.33 () TaBG 170 f1aH28 1a 32 4 .83 3.H3 le22 i1 G104 150 T1e33 Ta ) 5:H0 3276 1+433 12 0100 Oa.R2 1.80 3, 8% 5895 3.82 130 13 a4 1.50 1835 1.127 Hal7 3.60 lal17 i3 P?-.G‘:)f! 1-:-'{) 1.’_311 4;21‘1‘:! f}tifi 3-59 1.21 10 De}&2 is6 1,30 1enH S5 44 3«37 1«30 149 707D Da-““f) 1401 Ta630 E)ofj’_’ 30“37 1.#6 SIND DIRECYIOND ARL NUMPAIRED COUNTERCLOCK R ISL STARTINMG AT 1 FUR DUF NITH i 71-1v Appendix 2 DIFFUSION EQUATION USED FOR THE ESTIMATION OF RADON-220 EMISSIONS AZ-3 An equation developed by Culot and Schaiger (ref. 2, Sect. 4.3) was used to estimate the “20Rn release from the open-pit mine, the ore pile, and the tailings pile. This equation was also used in the ERDA-1541 (ref. 1, Sect. 4.3) study. This equation, which describes the steady- state diffusion of radon from porous, uniform solids containing the radium parent, is - g fE _L Jg = D tanh( - ) . (1) where Jo, = radon flux at the surface of the solids, Bq/m?-sec, S = production rate of radon in a unit volume of the solid, Bq/m3.sec, k = effective diffusion coefficient of radon in the interparticle void space, m?/sec, p = void fraction: the fraction of total volume which is not occupied by solid particles (this is often called porosity and should not be confused with the porosity of an individual particle), A = radon decay constant, sec‘l, L. = depth of the solids medium, m. The term vk/Ap is called the relaxation length. If the depth, L, of the so0lids is 22 or 3 relaxation legnths, then tanh L ') approaches 1, i/ Ap and radon flux from the solid surface is described by J =8 vk/Ap . : (2) O In the present study the depth of the ore body, the ore storage pile, and the tailings pile was sufficient to use Eq. (2). A2-4 The production rate of radon, S, is calculated by the following equation: 8§ = Cp Eo) , (3) where CRa = concentration of radium parent, Bq/kg, E = emanation factor, dimensionless (this factor represents the fraction of radon which escapes from the solids particles and reaches interparticle void space), o = bulk density of solids, kg/m3, A = radon decay constant, sec” !l. By combining Egqs. (2) and (3), Egq. (4) is obtained: Jo = Cp Eor/2 (pmh)1/2 (4) In all our estimates of “20Rrn release, we assumed that the emanation factor, E, was the same for 220Rn (t1/2 = 55.6 sec) as it is for 222Rn (3.30 x 10° sec). Values of E have not been measured for 220Rn. 1If the release mechanism of 220Rn is primarily a vesult of recoil energy of decay, this may be a good assumption. However, if the rate-controlling process is governed by gaseous diffusion through the solid, along grain boundaries, or from intraparticle porosity, the assumption would make our estimates of 22URn release much too high. Reported values of E for *?ZRn range from about 0.01 to 0.23. We used a value of 0.23 in all of our calculations so that a conservative estimate was obtained. Clearly, measurements of E values for 220Rn from thorium—-containing solids are needed. In calculating the radon flux from the mine, ore pile, and tailings, the only wvalues which change for the different media are (kp"l)l/2 and p. Therefore, we substituted £ = 0.23, Cry = 17.7 x 103 Bq/kg, and the value AZ2-5 for A of 220Rn (0.0125/sec) in Eq. (4) and obtained Eq. (3), which was utilized as the general equation for an estimation of 220Rn release from thorium~containing solids: 3, = 4550 (k/p)1/2 (5) Appendix 3 RADON-220 RELEASE FROM THE OPEN-PIT THORIUM MINE A3-1 A3-3 The “?0Rn flux was estimated using Eq. (5) (Appendix 2) after making the assumption that the in-place ore density was 2.25 x 103 kg/m3 and the value of k/p was identical with that of 2??Rn from the Ambrosia Lake deposit (1.65 x 107°% m?/sec): J, = 455 x 2,25 x 103+(1.65 x 1076)1/2 = 1,32 kBq/m?-sec . Therefore, for the 1.21 x 10%m? (3-acre) mine surface the source term ST is ST = 1.32 x 1.21 x 10% = 16 MBq/sec . The value of k/p of 222Rn from the Ambrosia Lake deposit was cal- culated using Eq. (4) (Appendix 2) and the following values for the constants in Eq. (5): Jq 19.9 Bq/m?-sec , il 2,25 x 103 kg/m3 o i Aopp = 2.097 x 107% | ] i Ra 20.7 kBq/kg , E=0.23. Appendix 4 RADIOACTIVITY CONTAINED IN DUST GENERATED BY MINING OPERATIONS A4-1 A4-3 The principal traffic in the mine area will be due to front-end loaders and the ore trucks plus activity of rippers and bulldozers, Front-End Loaders [3 m3 (4 yda) capacity] The fractured ore will have an apparent density of about 80% of theoretical or 1.8 Mg/m3 (1.8 metric tons/m3). 3m3 x 1.8 mg/m3 Capacity of loaders = 5,4 Mg/load Moo+ " i = 1.6 G /d& Trips"/day for 1.6 Gg (1600 metric tons) of ore gtzffi§7IE§g = 296 loads/day Round—-trip distance of front~end loader = 30 m x 2 = 60 m Distance traveled/day by front-end loaders = 296 trips x 60 m = 18 km = 11 miles/day Ore Trucks [35 Mg (35 metric tons) capacity] 1.6 Gg 35 Mg capacity it "Trips'"/day for 1.6 Gg (1600 metric tons) of ore i 46 loads/day Round trip out of pit and return = 300 m x 2 600 m i (Assumes 10% grade out of pit of average depth of 23 m plus 75 m travel in pit. Does not include travel distance from mine to mill.) Ab—4 ii Distance traveled/day by ore haulers = 600 m x 46 trips ii 28 km/day 17.4 miles/day Observations made by PEDCO-Enviroomental Specialists, Inc.,* show the rate of dust generation relates to vehicle speed as follows: E = (76)(1.158)° , where E = dust emission in mg/vehicle-meter from dry rvoad, s = vehicle speed, m/sec. An equivalent vehicle speed of 8.9 m/sec (20 mph) was selected for the mine vehicles, This is probably too high but is justified on the basis that heavy equipment is operated at high engine speeds with an attendant increase in dust from air blown by the engine cooling fan. Therefore, E = 0.285 g/vehicle~meter (1.01 1b/vehicle-mile) Dust generated by loaders and ore trucks = (17.7 km/day + 28 km/day) (103) (0.285 g/vehicle- meter) il 13 kg dust/day i 29 1b dust/day Other mine activities such as ripping, bulldozing, drilling, and selective blasting will double this value. However, routine wetting with water should reduce dust generation by 50%,* resulting in an estimate of % PEDCO-Environmental Specialists, Inc., "Investigation of Fugitive Dust — Sources, Emissions, and Control," PB 226 693, Cincinnati, Ohio, May 1973. A4~5 13 kg/day (29 1b/day) of fugitive dust from mine operations. Although thorium-bearing rock will become spread around the pit, it is assumed that dust containing no thorium will dilute the fugitive ore dust to a concentration of about 0.25% ThO,., The isotopic content of the fugitive dust is given in Table 4.1 of the report text. Appendix 5 ORIGEN CODE CALCULATIONS OF RADIONUCLIDES IN EQUILIBRIUM WITH THORIUM IN THE ORE AND IN THE MILL TAILINGS A5~1 A5-3 Thorium Ore The radionuclide concentrations of the ore were computed from ORIGEN code calculations of the quaatities of a daughter in equilibrium with 1 g of thorium (Table A.5.1). The wvalues listed in Table 4.3 (Sect. 4.2) were computed by multiplying the values in Table A.5.1 by the factor 4.39 x 10”3, which is the weight fraction of Th in a thorium ore of 0.5%Z ThO, content. For example, 228Th concentration is 228Th = 4,39 x 10~3 x 4.03 x 103 = 17.7 Bq/kg . Table A.5.1. Calculated values of radionuclide activities and masses in equilibrium with 1 g of thorium (by ORIGEN code) Buclide Activity (kBq) Mass (g) 2327h 4.03 1.00E0% 2287y 4.03 1.33E-10 228p¢ 4.03 4. 8BE-14 2283q 4,03 4.67E~10 224p4 4.03 6.83E-13 220gn 4.03 1.19E-16 216pg 4.03 3.14E~19 212pg 2.59 3.95E~25 212py 4.03 7.47E~15 217pg 4.03 7.84E~14 20871 1.46 1.35E-16 Read as 1.00 x 100, Dry Tailings The radionculide concentrations of the tailings were computed from ORIGEN code calculations of the quantity of thorium daughters remaining after extraction of 1 g of thorium from an ore with a 91% extraction efficiency (Table A.5.2). Removal of 1 g of thorium with an extraction efficiency of 91% from the thorium ore (0.5% ThO,; 0.4397 Th) produces about 250 g of tailings. This quantity is calculated as follows: mass of tailings per g of Th = 1 + (0.91 X 4.39 x 1073) = 250 g . A5-4 Tahle A.5.2. Adtivity of tailings left from the extraction of 1 g of thorium: 91% extraction (from ORIGEN code calculations) Activity (Bq) Nuclide Discharge 1yr 3 yr 10 yr 100 yr 300 yr 30,000 yr 2327 4.00E24 4.00E2 4.00E2 4.00E2 4, 00E2 4.00E2 4 ,00E2 2281p 4.00E2 1.56E3 2.64E3 2.26E3 5.85E2 4,00E2 4 .00E2 2284¢ 4.44E3 4.03E3 3.36E3 1.84E3 5.81E2 4.00E2 4.00E2 22Bpg 4,44E3 4.03E3 3.36E3 1.84E3 5.81E2 4 .00E2 4.00E2 224pa 4. 44E3 1.57E3 2.64E3 2.26E3 5.85E2 4.00E2 4.00E2 229Rn 4.4L4E3 1.57E3 2.64E3 2.26E3 5.85E2 4.00E2 4.00E2 216pq 4. 44E3 1.57E3 2.64E3 2.26E3 5.85E2 4.00E2 4.00E2 212p, 2.84E3 1.C00E3 1.69E3 1.44E3 3.74E2 2.56E2 2.56E2 212p4 4.44E3 1.57E3 2.64E3 2.26E3 5.85E2 4.00E2 4 .00F2 212pp 4, 44E3 1.57E3 2.64E3 2.26E3 5.85E2 4.00E2 4.00E2 2087y 1.60E3 5.62E2 9.51E2 8.14E2 2.10E2 1.44E2 1.464E2 aRead as 4.00 x 102. The values for tailings listed in Table 4.3 (Sect. 4.2) were obtained by multiplying the appropriate values listed in Table A.5.2 by the factor 4. At discharge, of course, the daughter concentrations in the tailings are equal to those of the original ore. Note from Table A.5.2 that after about 100 years, the daughter activity, originally associated with the separated thorium, has about completely decayed. In comparison with uranium mill tailings, which contain an 226Ra daughter (t1/p = 1622 years), this is a relatively short time. Appendix 6 MODEL TAILINGS IMPOUNDMENT Ab-1 A6-3 The model used for impoundment of the tailings is a natural wedge- shaped basin (Fig. A.6.1). The upstream face of the dam slopes 27° (about 2:1) with the horizontal. The walls of the basin are assumed to be perpendicular to triangle ABD in Fig. A.6.1. The tailings surface slopes downward 1° with the horizontal along line AC, and the bottom of the basin slopes upward 1° from the upstream face of the dam along line BD. The length of dam, d_ , necessary to contain a given volume of > tailings at a fixed dam hiight, dy, can readily be calculated from the triangular area of the tailings represented by triangle ACD. In this study we choose to let the maximum value of dj be 30.5 m (100 ft). The cross-sectional area of the tailings (triangle ACD) can easily be cal- culated in terms of dj, using a Hewlett-Packard model HP-67 programmable calculator and the Triangles Program Card (Standard Pac SD-07-07). Relationships of the triangular areas to d, and the relationships of dy, to the various sides of the triangles used to calculate the surface areas of the tailings and the pond, are given in Table A.6.1. The calculated value of dy required to contain the 20-year accumulation of tailings (5.86E6 m?®; 207E8 ft3) is 441 m (1450 ft). 1In this study the evaporation rates of water from the pond were sufficiently high to permit ORNL DWG 78-5028 26° POND AREA I78° 2e /7 ¢C SOLID TAILINGS AREA DAM 152° 27° € 0 Fig. A.6.1. Cross section of the natural wedge-shaped basin. Ab-4 Table A.6.1. Relationship of triangular areas and sides to the dam height (dh) . a Geometric term Relation to dh Triangular areas ACD 14.3057dh2 ABC 15.3206dh2 Triangle sides AB 59.2526d AC 29.6308d: BC 29.6308dh CD 27.6679dh AD 2.2027dh adh = AE (in Fig. A.6.1). the dy and dy values for containment of the tailings to also be sufficient to contain all of the pond liquor. Since this calculation is only approx- imate, no contingency was allowed for abnormal weather conditions. Once the values of dj and d; have been determined for containment of the 20-year accumulation of tailings, it is a relatively simple matter to calculate the surface area of the tailings. The surface area, A, presented by the rectangular top of the tailings pile is proportional to the one-half power of the volume of tailings, V., in the impoundment basin: AL =k, V2 (1) where ky, = a constant that is calculated from the geometric constants in Table A.6.1. A sample calculation of k, is as follows: V. = 14.306d,°dy , (2) A= de - (AC) , (3) AC = 29.631dy, . (&) A6~5 Combining Eqs. (2), (3), and (4), Eq. (5) is obtained: A_ = 1.645 x 102 v 1/2, (5) Therefore, k, is equal to 1.645 X 102 m}/2., Since there is a fixed addition rate of tailings (9.29 x 10-3 m3/sec), Eq. (5) is more useful if time is substituted for Vt in Eq. (5): A_ = 8.906 x 10* g1/2 (6) where the units of A, are m? and those of t are years. The calculated values of A, at yearly intervals of the 20~year mill operation are given in Table A.6.2. The value of AC is also listed, since it is used in Appendix 7 to calculate the area of tailings covered by pond liquor. Table A.6.2. Characteristics of model tailings pile Time (years) Surface area (m? x E5) AC (m) 1 0.9% 202 2 1.3 286 3 1.5 350 4 1.8 404 5 2.0 451 6 2.2 495 7 2.4 334 8 2.5 562 9 2.7 606 10 2.8 639 11 3.0 670 12 3.1 700 13 3.2 728 14 3.3 756 15 3.5 782 16 3.6 808 17 3.7 832 18 3.8 as7 19 3.9 880 20 4.0 903 Average 2.8 623 TRead as 0.9 x 10° m?. Appendix 7 CALCULATION OF AREAS FOR DRY TAILINGS BEACH AND POND DURING THE 20-YEAR OPERATION OF THE MILL A7-1 A7~3 Calculation of the volume of the pond and its surface area as a function time is more complicated than is the same calculation for the tailings, by virtue of the fact that the water is continuously lost by evaporation at a variable rate until the volume becomes constant at steady state. An equation for calculating the volume of the pond as a function of time was derived with the assistance of H. W. Godbee of ORNL. The calculated volume in tura could be used to calculate the surface area of the pond. We assumed no loss from the pond by seepage. The derivation is as follows: Let I = input of liquid to the pond, 0 = output of liquid from the pond by evaporation, de = change in volume of pond: then 1 -0 = de . (1) Because there is a fixed rate of addition of liquid to the pond, R, the increase of I with time is described by Eq. (2): 1 = Rdt . (2) Since it was shown in Appendix 6 that surface area of the top of a triangular wedge is given by > I o = ko Vpl/2, (3) Ap = surface area of pond, m2, = volume of pond, m3, < o] | geometric constant, ml/z; O??‘ I A7~4 therefore 0 =k ko V72, (4) where k] = evaporation constant, m/sec. After combining the two constants, Eq. (5) is obtained: 0 = RV,? . (5) By substituting for I and 0 in Eq. (1), Eq. (6) is obtained: Rdt - KV,1/? dt = avy . (6) Integration of Eq. (6) yielded Eq. (7), which was named the Bond-Godbee equation: _ 2R . R 2. 31/2 2R R Ko/ \ t 2 1n 5 % Vp 2 1n (2 > Vp . (7) It is relatively easy to solve this equation by "trial and error," using a programmable caleculator such as the Hewlett-Packard model HP-67. Programs were written to evaluate Vp at time t and for the value of R necessary to yield a given value of Vp at time t. Note that the Bond- GCodbee equation is only valid for volumes of VP less than that at steady state. The steady-state volume is given by Eq. (8): (Vp) steady state = K% K=? (8) Values of k,, K, and the calculated value of Vp at steady state are given in Table A.7.1 for the water addition rate (1.94 x 1072 m3/sec) to the model tailings impoundments. The calculated rate of addition of water to keep the tailings completely covered during the 20~year operation of the mill is given in Table A.7.2. For the evaporation rate of 1.93 x 1078 m/sec A7-5 Table A.7.1. Constants used in Bond-Gedbee equation and the calculated steady-state volume of the tailings pond Evaporation Location rate (m/sec) ko(ml/z) K (m3/2/sec) Vp at steady state (m3) Montana 1.93E-84 3.179E2 6.133E-6 9.97E6 Coelorado 2.90E-8 3.179E2 9.218E-6 4.43E6 %Read as 1.93 x 1078, Table A.7.2. Calculated values of the minimum water addition rate required to keep tailings under water over the 20-year life of mill Location Evaporation Minimm rate (m®/sec) Ratio of calculated rate rate (m/sec) to the rate for model mill Montana 1.93E-82 2.13E-2 Celorado 2.90E-8 2.77E-2 1.4 “Read as 1.93 x 1078, (2 ft/year), a 10% increase in the flow rate (obtained by adding water to the mill discharge) would keep the tailings covered over the 20-year operation. However, at an evaporation rate of 2.90 x 1078 m/sec (3 ft/year) an increase in flow rate of about 407 would be required. Calculated values of the pond volume at yearly intervals are shown in Table A.7.3 for the model pond at the Montana and Colorado sites, where the respective evaporation rates are 1.93 x 107% and 2.90 x 1078 m/sec. At an evaporation rate of 1.93 x 10~% m/sec, the pond volume after 20 years reaches about 557 of its potential steady-state value; whereas at 2.90 x 10~% m/sec, it reaches about 80%. From the geometric relation- ships (Table A.6.1, Appendix 6) and the pond volumes (Table A.7.3), values of the area of exposed tailings, the area of tailings covered by the pond liquor, and the total surface area of the pond were calculated. Results of these calculations are shown in Tables A.7.4 and A.7.5. A7-6 Table A.7.3. Change in volume of pond (V) with time as a result of evaporation Water input rate (R) = 1.94E-2 m?/sec 3 , Time (years) VP (m” % B6)" Montana Ceclorado 1 0.52% 0.48 2 0.96 0.85 3 1.36 1.17 4 1.74 1.45 5 2.08 1.70 6 2.40 1.92 7 2.70 2.12 8 2.99 2.30 9 3.26 2.46 10 3.51 2.61 11 3.75 2.74 12 3.98 2.87 13 4,21 2.98 14 4.41 3.09 15 4.61 3.19 16 4.80 3.27 17 4.99 3.36 18 5.16 3.43 19 5.33 3.50 20 5.49 3.57 Average 3.41 2,45 aRead as 0.52 x 10% m3. Table A.7.4. Evaporation surface area of tailings pond (Ap) and values of AC used to calculate area of tailings underneath the pond Time (years) 1 2 3 4 5 10 15 20 av? A, m? x E5 p Montana 2.31b 3.12 3.72 4.17 4.57 5.95 6.84 7.45 5.71 Colorado 2.19 2.91 3. 44 3,84 4.13 5.14 5.67 5.99 4.86 ac,%m Montana 259 354 421 475 521 677 774 844 646 Colorado 249 332 390 433 469 582 643 680 552 aAverage of values calculated at yearly intervals for the 20-year operation of the mill. bRead as 2.13 x 10° m?. “Area of tailings covered by pond liquor is equal to AC x da. A7-7 Table A.7.5. Calculated values for the area of taillings covered by water and of the dry tailings beach Time (years) 1 2 3 4 5 10 15 20 Av? Tailings beach, m? x E3 Montana 0 0 0 0 4b 24 4 Colorado 0 0 0 20 60 160 40 Tailings under water, m? x B4 Montana 9c 13 15 18 20 28 34 37 27 Colorado 9 13 15 18 20 26 28 30 24 aAverage of values calculated at yearly intervals for the 20-year operation of the mill. bRead as 4 x 103 m2, C'Read as 9 x 10% m?2. Appendix 8 EVAPORATION OF THE TAILINGS POND AFTER MILL CLOSING AND EXPOSURE OF DRY TAILINGS SURFACE A8-1 A8-3 The equation used to calculate the evaporation area of the pond as a function of time was obtained by integrating Eq. (6), Appendix 7, with a water input rate of zero (i.e., R = (Q): thl/2 = vpill2 - 2Kt , (1) Vpi = volume of liquid in the pond at mill closing, m3, Vpr = volume of liquid after evaporation time t, m3, K = evaporation constant, m3/2/sec (values for Colorado and Montana sites previously given in Table A.7.1, Appendix 7), t = time, sec. Volumes of the ponds at the two locations as a function of elapsed time are given in Table A.8.1. From these volumes, values of the areas of the dry beach and of the pond were calculated by the same method used in Appendix 7. The values obtained were listed in Table 4.5 (Sect. 4.2). Table A.8.1. Volume of liquid in the tailings pond (V) as a function of elapsed time after closing the thorium mill Elapsed time Vp (m3 x E6) (years) Montana Colorado 1 3.8ER4 9.7E5 2 2.5Eb 1.6E5 3 1.4E6 0P 4 6.2E5 0 5 1.6E5 0 6 2.8E2 0 @Read as 3.8 x 10° m3. bCalculation by Eq. (1) estimates the pond is completely evaporated after 2.7 years, Appendix 9 RADON-220 FLUX FROM THE DRY TAILINGS AND FROM THE POND SURFACE A9~1 A9-3 Dry Tailings Surface The 220Rn flux from the dry tailings surface during mill operations was calculated using Eq. (5) from Appendix 2 as follows: Jo = 445p(kp—1)1/2 , Jo = 455 x 1.64 x 103 x 103 x (5 x 1078)1/2 | Jo = 1.67 kBq/m? » sec (or 4.51 x 10" pCi/m? « sec) . 1 The following values of p and kp ' were utilized: 1.64 x 10° kg/m3 , P kp~! = 5 x 107¢ m?/sec These values were utilized by previous investigators (ref. 4, Sect. 4.2.8) as being applicable to uranium mill tailings. A factor of 0.6 was applied for decay of 224pa in calculating the flux after shutdown of the mill. This factor was determined from a graphical plot of the data listed in Table A.5.2, Appendix 5. Surface of Pond It was assumed that radium daughters of the thorium decay chain had the same solubility as that observed in the pond liquor of a uranium mill. Using Eq. (4), Appendix 2, the source term is as follows: i J 5.14 x 10% x 103 x (0.0125)1/2 (1.13 x 107%)1/2 | O Jo = 19.3 Bq/m? « sec (or 522 pCi/m? + sec) The following values for Cgg of 224Ra, p, and kp~! were utilized: Cra = 5-14 x 103 Bq/kg of 22%Ra , 1 x 103 kg/m3 , p= i 1.13 x 107° m?/sec , P;-I lUI facd i = 0,0125/sec . > ) ro o ! A9-4 This calculation probably yields a source term that is optimistically low. The action of the prevailing wind on the surface of the pond would cause mixing of the upper liquid layer and hence enhance diffusion of the 220Rn, However, we were unable to locate a model in the literature which took such a mixing process into account. ~ Pl Ln I [ O W X 11. 12. 13-17. 18-20. 21. 22. 23. 24, 25. 26. 27. 28. 29. 30. 31. 32. 33. 34. 35. 36. 37. 38-40. 41. 42. 43. 44, 45. 180-181. 182-183. ORNL/TM-6474 Dist. Categories UC-79b,~c INTERNAL DISTRIBUTION Central Research Library Document Reference Section Laboratory Records Department Laboratory Records, ORNL RC ORNL Patent Office R. L. Beatty B. G. Blaylock J. 0. Blomeke E. S. Bomar W. D. Bond R. A. Bradley R. E. Brooksbank W. D. Burch J. A. Carpenter A. G. Croff W. Davis R. G. Donnelly J. I. Federer D. E. Ferguson D. W. Fitting R. B. Fitts M. H. Fontana E. J. Frederick W. R. Grimes W. O. Harms R. F. Hibbs G. §. Hill M. R. Hill A. R. Irvine R. R. Judkin P. R. Kasten S. V. Raye G. G. 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