RECEIVED BY DTIE MAR 6 1970 ‘ ' y 1 ) OAK RIDGE NATIONAL LABORATORY operated by UNION CARBIDE CORPORATION m NUCLEAR DIVISION for the U.S. ATOMIC ENERGY COMMISSION ORNL- TM- 2743 L] THIS DOCUMENT CONFIRME UNCLASSIFIED 0 AS COPYHE. - ngfim’ CLASSIFICATION DATE — December 22, 1969 il Z DAIRL Yl 2D . DESIGN AND CONSTRUCTION of CORE TRRADIATION-SPECIMEN ARRAY FOR MSRE RUNS 19 and 20 - MASTER v Abstract A new MSRE core specimen array was designed and fabricated to replace the type of metallurgical surveillance specimen array that was used in the MSRE through Run 18. The main purpose of the new array is to measure the capture-to-absorption ratio of 2337 and to determine the effects of salt velocity, turbulence, and surface finish on the deposition of fission products on graphite and on Hastelloy-N. Two additional test specimens were included, one of pyrolytie graphite to determine if there is permeation of fuel salt or its constituents into the graphite and one of Hastelloy-N to ex- pose a serles of electron microscope screens in a trapped gas pocket. .. The new specimen array was installed on July 31, 1969 and was ex- posed in the reactor core for 12,9’+3 Mwhrs of reactor operation during Runs 19 and 20. Keywords: MSRE, core-irradiation-specimens, design, fabrication, uranium-233, capture-to-absorption ratio, cross sections, . fission products, adsorption, nickel-molybdemum-chromium ' alloy, graphite, o w NOTICE This document contains information of a preliminary nature and was prepared primarily for internal use at the Oak Ridge National SOy Laboratory. It is subject to revision or correction and therefore does P,l%{_; - not represent a final report. - DISTRIBUTION OF THIS DOCUMENT 1S UNLIMITED LEGAL NOTICE This report wos prepored os an eccount of Government sponsoroa work, Neither the United VSf-utas,r nor the Commission, nor any person acting on behalf of the Commission: A. Makes ony warronty er representation, expressed or implied, with respect to the accuracy,- completeness, or usefulness of the informotion contained in this report, or that the use of 7 ony informotion, epparatus, mthod or process disclosed in flus report may not in!rmge privately owned rights; or B. Assumes any liabilities with respect to the use of, or for damages resulting from the use of - any information, opparatus, method, or process disclosed in this report. . As used in the above, "‘person acting on beoholf of the Commission®® includes any employee or contractor of the Commission, or employes of such contractor, to the extent that such smployee or contractor of the Commission, or employes of such contractor prepares, disseminotes, or provides access to, any information pursuant 1o his cmpioymen! or contract with the Commission, or his employment with such contractor. . |’ s o CONTENTS Introduetion « o 4 o o 4 6 0 b e e e e e e e e e e e e e e e e e . Mechanical Design of the Cage and Basket Assembly. . o . ¢« o o o & Description and Design of Test Specimens . . . . . . . « . . . . . FlowTube & , & ¢ 4 o ¢ ¢ o o o o o o o o o s o o o o s o o s Uranjum Capsules. . + ¢ « o o « « . ; . ; e e ¢+ o s o s s« & 10 Pyrolytic Graphite, . . & o ¢ ¢ v ¢ ¢ ¢ o o ¢ o o o o o« o« o « 14 Graphite Tube with Turbulence Wire... . » ¢ « ¢ o« « ¢ o o o . 1b Hastelloy-N Tube with Turbulence Wire . . . « o v o o » » » . 18 Gas Trap and Electron Microscope Screen Holder. . . . . . . . 18 DispoSition of the Specimen Array . . 4 v« ¢« ¢ ¢« ¢ ¢ o « o =« » 21 Acknowledgements ., . . . . . 4 . v 0 4 4 s 4 b s s e e e e e ... 22 LEGAL NOTICE - -] “This repnrt whRs wepu-ecl as an account of Government -pomred work. uen.her the Uafted “§ "Biates, »or the Commission, nor any person acting on bebalf of the Commisaion: © - A. Makes sny warrenly or representation, sxpressed or imptied, with respect io {he accu- racy, completenees, or usefulness of the information contalned in this report, or that the use ‘o any tnformation, apparatus, ietbod, or process dtlcloud in thia report may mot lnfringe prinuly owned rights; or . . . B Assumes any liabilities with rupact to the use ot or for dzmages regulting from the -} nse of sy iniormation, appnnml method, or process disclosed in this report. - An unsed in the sbove, "‘person scting on behnlf of the Commisasion’ includes any em- | ‘ployee or contractor of the ¢ ar empl of such , to the -mm that such employse or contracior of the C or employee of such ¢ . .1 7] disseminates, or provides access to, sny information purseant to his cupioymml er contract o r 'ma the Gommlnuiou or his nuploymanl with lm:h mtructor * ') DISTfiIBUTION_OF THIS DOCUMENT IS UNLIMITED " » o« p. 87. Introduction During nuclear operation of the MSRE through May 1969, the graphite sampler assembly contained. ‘semples of graphite and Hsstelloy -N which were used to determine the effects of the reactor enviromment on these materials, including corrosionvand_theVeffectsfof irradiation on the physical proper- ties and to determine the deposition of fission products on the materials,?! Assemblies of this type were removed.in July 1966, May 1967, April 1968, and June 1969, After the latter removal, the same type of array was not reinstalled because the relatively short exposure'that‘would occur before the planned'final shutdown'of the MShE would add little to the information obtained during the previous long exposures., lnstead a different sample 'assembly was designed to utilize the existing space in the core. This new assembly is ‘described in this report The new assembly contained several experiments for fission product : deposition studies and four graphite capsules containing uranium isotopes for measuring nuclear properties of 233, Two of the uranium capsules :contained about l-gr total of 3% and 2%y and the other two contained about 1l-gr total of 23%U and 22y, The other specimens of graphite_and Hastelloy-N were.designed'to study the effects of flow, surface finish, and turbulence on the fission product deposition. A specimen of pyrolytic graphitegwasvincluded forsaltipermeation studies and the final specimen formed a gas trap. where electron microscope screens were exposed to detect - the presence of colloidel materials. The design details of the individual specimens and of the assembly are shown on ORNL Drawings M?lOSSl-RB—OOl M-10551 RB-002, and M-10551-RB-003 (Footnote 2). | The new specimen array was installed ‘into the MSRE core on July 31 : 1969 and was exposed during.Runs 19 and 20. Teble I summarizes the ex- > posure histbry of the,arrayo,;Thedspecimen,array vas scheduled for removal ~sbout December 15, 1969. | ;MSR Program Semiannual Progress Report, August 31, 1965, ORNL-3872, EThese drawings are available 1n Reactor Division Design Department or Laboratory Records. Table 1 Exposure History of the MSRE Core - Irradiation-Specimen Array for Runs 19 and 20 Time above 900°F a - 2,815 hrs Time exposed to flush salt | 120 hrs - Time exposed to fuel sall | 2,262 hrs Integrated Power - - . - 12,943 Mwhrs Mechanical Design of the Cage and Basket Assembly In order to keep the assembly as simple as possible, each capsule or specimen was made cylindrical with an outside diameter of l—l/h inches, This was the largest diemeter that could be held in & removable eage in- side the existing basket design. The individual experiments within the assembly are more completely deeeribed later in the report. Figure 1 shows the completed cage and basket assemblies., The new basket assembly is generally the same size and shape as the previous ones, but is made from 2-in, OD by 0,062-in., wall Hastelloy-N tUbing (control rod thimble material) because the perforated sheet used previously was not available, The large slots in the lower part of the basket assembly were to reduce the metal volume and the neutron flux depression to.a minimum in the vicinity of the uranium-containing capsules. The smaller slots at the top of the basket are to ensure an adequate salt flow through the upper portion of the basket | | The cage assembly consists of three vertical 3/16 in.-diameter rods held by end fittings and with spacer rings welded at intervals along the length, The 1ower-end fitting was welded to the vertical rods and forms . & flow passage which directs about half of the salt flow from the 1nlet tfibe of the basket into the center of the first test specimen. The top Ll y : . ey ¥ 8 end fitting, which was removabie_to facilitate loading and unloading the test specimens, slips over the three rods and was held in place by 1/16-1n.-dia. wire clips. | The bottom test specimen was pinned to the lower end fitfing to re- sist any pressure drop effects. The other specimens were loose in the cage and were free to expand and cofitract aérnecessary. Thé total length of test specimens was adjusted during assembly by machining the length of the top metal filler plug to provide end clearance with the cage assembly. At operating temperature the end clearance increased to about 0.42 in, due to differential fhermal ekpansibn. The graphite speciméhs, which would normally float in salt, were held down by the weight of the top - metal specimens and the filler plug. The assembly procedure of the cage into the basket and the installa- tion of the basket into the reactor vessel were the same as for the previous - graphite sampler assemblies, The assembly of the cage and basket was sim- plified by the use of all new parts. However, a previously used "Ball-Lock assembly" was used to complete the basket assembly, and the radietion level of this part required the final pinning operation to be completed in a hot cell, | ' The radiation from the ball-lock assembly was sufficiently low that the completed assembly couid be carried from the Hot Cell to the MSRE in | a pipe carrier with relafiively light shielding on one end. An argon at- - mosphere was maintained 6n the uvranium capsules and on the completed assembly as much of the time as possible., The total exposure of thé uranium capsules to atmosphere was about one hour or less, A : Description and Design of Test Specimens Flow Tube - The first test specimen at the bottom of the assembly is the flow | tube. Figure 2 is a photograph of the parts and the completed assembly of this specimen, The metal core inside the graphite body formed a l/l6-in. thick flow anmulus so a direct comparison between the deposition on Hastelloy-N and on graphite will berpossible. The salt flow through the ol ¥ Flow Tube Assembly 2 Fig. 10 annulus was introduced through the lower end fitting of the cage assembly and wés driven by the pressure drop across the graphite lattice-bar grid at the bottom of the reactor vessel. The salt velocity through the 1/16-in. annulus was estimated to be 2.5 ft/sec as compared to 0.8 ft/sec on the outside of the specimen, The effect of salt velocity on deposition can be obtained by comparing inside and outside surfaces of the graphite. Different surface finishes'wefe“used on both the internal énd the ekternal surfapes so that the effeét'of'surface,finish can be determined. The external surfaces will also be used as a reference for the graphite speci- - men with the turbulence wire. The graphite parts were made:of POCO.grade AXF-5Q. This grade of graphite was selected because of its uniform pore size, Grade CGB graphite, such as constitutes the MSRE core, was not used for this specimen because the pieces of this graphite still in stock all had numerous cracks that ‘would cause misleadingly high indications of apparent surface deposition. Uranium Capsules The next section of the sbecimen assembly contains four graphite capsules that contain mixtures of uranium isotopes in a NaF-ZrF, carrier salt., The purpose of these capsules is to determine, for the energy spec-' trum at the capsules, the capture-to-absorption ratio of 23X and to de- termine the absorption cross sections of the other uranium’isotopés relative to 23%3, Two sizes of capsules_were provided, the long capsules containing primarily 233 and 233U‘and the short capsules containing 234y and 239y, After exposure the salt mixtufés will be analyzed for uranium 233, 23&, 235, 236, and 238 and for ®*°Pu, The production or depletion of £hese .isotopes will be obtained by comparison with.similar analyses 6f unir- radiated samples of the salt miXtures. The isotopic'concentfations of uranium in the original salt mixtures as calculated from the analyses of the source materials are shown in Taeble II. The total weighté of salt for the long and short capsules were_h9.h and 25.0 grams respectively giving a total uranium content of 1 gram per éapsule; Since the analyses will be done on the basis of isotopic ratios the exact quantity of salt or uranium is not important, The NaF-ZrF, » " ' C 11 Table IIT Caléulated;;sotopic Concentrations - of Original Salt Mixtures rams Long Capsule - ~ Short Capsule U-232 0.4 ppm of U 0.03 ppm of U 233 0.1000 - 0.0081 234 0.00k42 ~ 0.0263 235 0.008L - 0.0566 236 ~ 0.000k 0.0033 238 - 0.8870 0.9056 carrier salt was selected so*that any leakage of MSRE fuel or flush salt into the capsules could be detected by an analysis for lithium, The heat geheration rates within The salt miktures were estimated to be 170 and 100 watts respectively for the long ‘and short capsules. The total temperature rise in the capsule was estimated at about 300°F, but most of this is in the salt mixture and in the outside convective film, The high thermal conductivity limits the temperature gradients within the graphite so that thermal stresses are not a problem, ‘Each capsule_cofitainsiafsEriesrof flux and temperature monitors lo- cated on the vertical center line. The flux monitorsiconsisted_of'302 "stainless -steel wire and a silver-copper alloy. These'monitors will give ~en indication of both the thermal and fast fluxes, The temperature moni- tors are small rods of 8ic 1/2 in, long which sustain a dimensional change under irradiation. The irradiation temperature is the temperature at which this dimensional change can be annealed out, The design details of. the capsules are shown on Drawing‘M-10551~RB-002 '_(Reference 1) and in Figure 3.i The annular salt cavity 3/h~in.-OD by _l/2—in. ID reduced the’ centerline temperature of the capsule and also 1This drawing is available in Reactor Division, Design Department, ‘or Laboratory Records, Y-94127 Ry Ty g Fig, 3. Uranifim Capsule 281 Y-94728 g s T » w “y ..phere.' 13 provided a convenient location for the flux ‘and temperature monitors in the central graphite core, POCO graphite grade AXF-5QBG Be was selected to avoid the neutron depression- that would occur with Hastelloy N and to pro- vide a satisfactorily low salt permeability.‘ The capsules were sealed by welding the ends of two molybdenum rings that were each vacuum brazed to the graphite body or cap with a.85Cu-10Ni-5Cr brazing alloy at 1250°C and 1075 torr. A direct braze between the graphite body and cap was not used because of the high. temperatures that would have been required on the com- pleted and salt-filled assembly - The integrity of the brazed joint between the molybdenum rings and graphite was the most important mechanical problem. The metallographic examination of the test braze indicated that the braze'was'satiSfactory, but-the initial production brazes leaked helium when subjected to 10-psig - pressure. The brazing procedure was revised to include coating the gra- phite surfaces with Cr3ce to facilitate wetting of the graphite by the. brazing alloy. Subsequent brazes were satisfactory, but one cap was re- ~ jected because of a large. pore in the graphite. : Following the brazing operation, the capsules were leak-tested in an alcohol bath with 10-psig helium, Since the graphite is porous to helium, the leak test was used-dnly?to screen out any parts with abnormally large pores or any parts with a poor braze. The capsules were then cleaned in an untrasonic alcohol bath and vacuum-dried at 300°C. The flux and temperature monitors, which had been previously cleaned, dried and assembled into glass tubes, vere installed and the capsules were delivered for salt £11ling. The salt mixtures were prepared and loaded into the capsules by the Chemical Technology Division. The salt was prepared in one melt for each of the two compositions.~ The salt in each melt was crushed and weighed into batches for the indiv1dua1 capsules. The crushed salt was loaded '1i-into the capsules as dry powder and then melted_down under an argon atmos- After the loading and meltdown of the salt was completed the capsules were sealed by TIG welding the exposed ends of ‘the molybdenum rings. The | weldlng was done 1n an argon atmosphere W1thout the use of filler wire, 1k The welds were inspected visually and by liquid penetrant, The completed capsules and the excéss éalt;mixtures contained in small glass Jars were sealed in plastic with an argon atmosphere until ready for use. "~ The original'plans'were to load the salt mixtures into four capsules of each type, but one cépsule_of;each type‘was.rejected during fabrication. Two of each type were assembled into the core specimen array and the third, -'along with the excess salt, is being held to develop the salt recovery and analytical’procedures and to prOvide the isotopic concentrations of the un- irradiated salt. | o Table IIT shows the monitor data and core location for each capsule. Pyrolytic Graphite A rectangular specimen of pyrdlytic'graphite as shown in Figure y is,immediately above the uranium cgpsules. The test‘specimen is,O.S?in. X 0.687-in, x 6,0-1in. long and is held in the cage assembly by circular pieces of POCO AXF-5Q graphite pinned to each end, The layer planes of the graphite are parallel to the 0.687-in. x 6-in. surfaces. The depth of any penetration of salt or 1tsrconstituénts into the graphite both parallel and perpendicular to the layer planes, will be determined by proton acti- vation technique. The specimen will also be analyzed for the penetration of fission products both parallel and perpendicular to the graphite layer planes, The weight of the test specimens above the pyrolytic graphite is transferred from the outer diameter of the top end ring to the central region by a 1/8-in. thick Hastelloy-N disk. | Graphite Tube with Turbulence Wire The next specimen is a graphite tube machined from'POCO AXF-SQ. _The test section is a 1-in.-diemeter cylinder with three 2-in,-long sections with different surface finishes (5, 25, and 125 RMS). The bore diemeter is 1/2-in, with surface finish bands of 5 and 125 RMS. The OD of the test section has a coil of 1/16-in. Hastelloy-N wire wound on a 1/2-in, pitch and with a 20-mil radlal clearance between the graphite surface and the wire.rrThe‘original design called for spacers between the wire and the "graphité,rbut these were.eliminated because of welding problems with the thin spacers, The wire céil is to promote turbulenceron the outside sur- face of the graphite. Figure 5 is a photograph os this test specimen, - - » ’ L) 3 Table IIT Urenium Capsule Location and Monitor Data ~ Location | Weight (Top to - o Capsule U-Mixture of Salt. Bottom) Monitor Array (Top to Bottom) | | §8-302-1 /4" | (116" o o ‘ Ag-Cu Spacer = SiC Holder) Sic s-1 234238 25.0 gn MSRE-3 .Mi36 em 5/32" .U99%0" 9.700 mg .50046" s-2 234-238 ‘25éOém;?f'M$RE‘l--hth“gm 5/32" ,4g988" 9.382 mg .50024" S-3 234-238 24,5 gm Storage JLLLE gm - 5/32" .k9992" 9,387 mg .50050" SS-302-1/4" 5S~-302-3/8" (1p/16" - B | (11/16" Holder) Spacer Sic Spacer Ag-Cu Holder) sic L~2 233-238 Lok MSRE-4 9,505 mg 1-1/16" ,L9998" 1-1/16" Lb38 gm 16,046 mg ,50025" | ‘ ‘ - (Bottom) | | O . L~3 233-238" _hg.hf Storsge 9.58L mg 1-1/16" 49992" 1-1/16" .L435gm 15,60k mg .50046" L-b 233-238 49,4 MSRE-2 9.46l mg 1-1/16" .ho999" 1-1/16" .Lk22 gm 15.321 mg .50019" Analysis of 302'Stéi-n]..éSS:Ste‘e.l FE T1.30 | SRR Ni 8.51 Cr 0.080k e Y-94928 ‘ R i Graphite Fission Product Deposition Specimen Fig. 5. 18 The salt flow rates on both the internal and external surfaces are somewhat more uncertain than on the bottom flow-tube specimen because the pressure drop is not well defined, However, both the internal and ex- ternal velocities should be about the same as outside the Sample basket or about 1 to 2 ft/sec. | 'Thé quantity of fission-product depbsition as é function of surface finish will be determined for both the inside and outside surfaces. The effect of the tfirbulence wire will be determined by;comparisoh'with the graphite flow tube at the bottom of the assembly. ‘ | Hastelloy-N Tube with Turbulence Wire This test specimen, shown in Figure 6, is a duplicate of the graphite specimen just described except that it is constructed of Hastelloy-N. Both of these specimens will be subjectéd to about the same conditions and will provide the same type of information. The effect of the turbulence wire will be determined by comparison with the surface of the electron microscope screen holder, | The double well design of this specimen, and the next one above, pre- vents contamination of the surface under study from the exposure of the opposite surface, The test specimen will be sawed into individual rings for each surface finish and then each ring will be dissolved for analysis, This procedure eliminates the necessity for machining off the surface for analysis, 7- | Gas Trap and Electron Microscope Screen Hbiéer The last test specimen will trap a sample of gas that may be circu- lating in the core and expdse several electron microscope screens to this gas so that any colloidal or particulate material can be collected and examined. Figure 7 is a photograph of this specimen with the central rod, which holds the microscope screens, removed. The drilled holes in the rod slope downward and will trap salt so that the maximum salt level during operation can be determined. The sealed cavity formed by the double wall was filled with helium to improve the heat transfer and to reduce the temperéture of the central rod to about 100°F above the salt temperature. ) Fig. 6. Hastelloy-N Fission Product Deposition Specimen. "y 61 20 . s en Holder Gas Trap and Electron Microscope Scre T Fig o L] 4y 21 Disposition of the Specimen Array - The specimen array waé,removed from the MSRE core on December 18, 1969 and delivered to the hot-cell on the 19th., The assembly was free of salt and was in good mechanical condition. The individual specimens were removed‘from the.assembly Qn December 22, 1969. The detailed examination and analysis of the fission-product deposition specimens will be directed and reported by S. S. Kirslis and the analysis and results of the uranium capsule experiments will be directed and reported by G. L. Ragan, 22 ' ACKNOWLEDGMENTS The author is indebted to a large number of individuals whose co- operation and assistance was required to complete the design, fabrication, and installation of the specimen array on the time schedule that was available., The following individuals in particular contributed directly ' to the design and fabrication of the assembly. S. S. Kirslis: G. L. Ragan: Conceptual design of fission-product deposition experiment and specimens. Formulation of the 233 capture-to-sbsorption ratio experiment. \ W. J. Werner and coworkers: Graphite to molybdenum brazing and final seal welding of the uranium capsules. J. C. Mailen and F. J. Smith: Preparation of the salt mixtures and W. H. Cook: fl. G. Kern: filling the uranium capsules, Design and fabrication of the pyrolytic graphite specimen and general assistance on the design and fabrication of the overall assembly. Scheduled and supervised the fabricatlion of the parts and assemblies through the various shops. l’; 23 ORNL-TM~27k43 Internal Distribution l. G. M. Adamson _ 39. R, N. Lyon 2. J. L. Anderson | . 40.. R, E. MacPherson 3. C. F. Baes | - 41, J. C. Mailen L, S. E, Beall k2, H, E, McCoy 5. E. S. Bettis | 4L3. H. C. McCurdy 6. F. F, Blankenship kh-L5, T, W. McIntosh (AEC) 7. E. G. Bohlmann - h6. L. E. McNeese 8. G. E. Boyd - 47. J. R. McWherter 9. R. B. Briggs ' L8, A, J. Miller 10. E, L. Compere : 49, R, L. Moore - 11, W, H, Cook : 50. E. L. Nicholson 12-13. D. F. Cope (AEC) 51. A. M. Perry 14, W, B, Cottrell 52, B. E. Prince 15, J., L. Crowley o 53 G. L. Ragan 16, F. L. Culler , 5k, M. Richardson 17. S. J. Ditto 55-56. M. W. Rosenthal 18. W. P. Eatherly ? - 57. A. W, Savolainen 19. J. R, Engel , , 58, Dunlap Scott - 20. D, E, Ferguson 59. M. Shaw (AEC) 21, L. M, Ferris - | 60. M, J. Skinner : 22, A, P, Fraas o 61. L. A. Smith, ORGDP 23-27. C. H. Gabbard , 62, F. J. Smith - 28. G. Goldberg , 63. I. Spiewak 29. W. R. Grimes | 64. D. A, Sundberg 30. A. G. Grindell : 65. R, C. Steffy 31. R. H. Guymon , 66. R. E. Thoma 32, R. W, Harvey o ' 67. D, B. Trauger 33, P. N, Haubenreich 68. J. R. Weir 34, P. R. Kennedy ' 69, W. J. Werner 35. Re J, Kedi , ' T0. M. E. Whatley 36, C. R, Kennedy | 71. J. C. White 37. S.S. Kirslis 72. G. D. Whitman 38. M, I, Iundin S 73. Gale Young Th-T75. Central Research Library (CRL) 76-7T. Y-12 Document Reference Section (DRS) 78-80. Laboratory Records Department (IRD) ‘81, Iaboratory Records Department — Record Copy (LRD-RC) 82. ORNL Patent Office | External Distribution 83-97. Division of Technical Information Extension (DTIE)- 3 o8. | Laboratory and University Division, ORO