ORNL-TM-3832 ublve7% DESIGN STUDIES OF A " MOLTEN-SALT REACTOR DEMONSTRATION PLANT E. S. Bettis L. G. Alexander H. L. Watts This report was prepared as an account of work sponsored by the United States Government., Neither the United States nor the United States Atomic Energy Commission, nor any of their employees, nor any of their contractors, subcontractors, or their employees, makes any warranty, expréss or implied, or assumes any legal liability or responsibility for the accuracy, completeness or usefulness of any information, apparatus, product or process disclosed, or represents that its use would not infringe privately owned rights. Fi ) ORNL-TM-3832 Contract No. W-T405-eng-26 Reactor Division DESIGN STUDIES OF A MOLTEN-SALT REACTOR DEMONSTRATION PLANT E. S. Bettis, L. G. Alexander, H. L. Watts Molten-Salt Reactor Program JUNE 1972 —— e —— - — NOTICE This report was prepan‘ed as an account of ‘jvork sponsored by the Unitad States Government, Neither their contractors, subcontractors, or their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, com- ‘| pleteness or usefulness of any information, apparatus, _product or process disclosed, or represents that its use would not infringe privately owned rights. the United States nor the United States Atomic Energy |- .| Commission, nor any; of their employees, nor aay of NOTICE This document contains information of o preliminary nature ond was prepared primarily for internal use ot the Qaok Ridge National Laboratory. It is subject to revision or correction and therefore does not represent o finol report. OAK RIDGE NATIONAL LABORATORY Oak Ridge, Tennessee 37830 operated by UNION CARBIDE CORPORATION for the U. 5. ATOMIC ENERGY COMMISSION BISTRIBUTION GF THIS DOCUMENT 1S UNL AR AP TR TR e+ 21 o, e ai a) o i i iii CONTENTS Page List of Figures =e-ec-ecceccec=a- - o e B e e iv List of Tables =~eemww-v-wncne=- crmmme——— - o e v ADSETBCE m—mmcmcccmemcmmeememmeemeesesemmesmee—s—sesseme-meeee-——e 1 SUMMBYY ==meee e oo nm e e e e e o o e o o o e e e e e e 1 Introduction e e e e e e 3 General Description -—-----eccccccmcccrcccceccrmrrmrmc e e e 5 Primary Systell e~eeeecccecmcccccmcccccacccccmcncccccccccenseeenan- 10 Reactor ~--ecececcccccccnaccccecnaaaax - 2 40 e o i e 10 Primary Heat Exchangery ---e-ewcwcceccecorrorcccccacccccccena- 26 Primary Pumps =-mee-c-cer-cccccccccccccccscncssrcmmmanen e 32 Secondary Circuits ==-eeesccccccccccnucaccrcerccorarcrcrccmecnaaea 33 Tertiary Salt Circuit e-ccce=c-- - o o o e o o e e e e 35 Steam SysStel mec-ceccemeccccccccccsscnsnsser e e — e — e e e —— e 37 Reactor Building ~==-==- e EscmcsRsceceRREre e, — e - ———————————— 38 Cell Heating and Cooling -=--w=eveccmccecreccrcrcacecsmcrccncaecax 39 Drain Tank System ewe-cmeececccccccccccccerrcrrccmcccccrerr e e ee e 45 Off-Gas System -------- e ——————————— .---_ ..................... 57 Control Rods =emmmros—emcessecosemeoscsosoeoe ;-----_----------;- 60 Instrumentation =---===--= S S ——— 61 Maintenance —eomemmmiem—- --------f;-;-;-----_-f----, _____ ——————— 62 Performance ------~ssceev-- rermecssrmessssscsmmseeeee e —————————— 62 » *) y 2 6 Fig. 7. 8 9 Fig. 1. Fig. 2. Fig. 3 Fig. h; Fig. Fig. Fig. Fig. Fig. 10. Fig. 11. Fig. 12. Fig. 13. Fig. 1k, Fig. 15. Fig. 16. Fig. 18. Fig. 19. Hgo 20. Fig. 2l.. Figo 220 Fig. 23. Fig. 2k. LIST OF FIGURES Simplified Flowsheet for 300-Mi(e) Molten-Salt Demonstration Reactor ~==-mweccna-- —————— - o o o o Reaétor Vessel Elevation =seeccrcrmccmmmcmccmcmmcacnamce0- Reactor Vessel PLAN =ommmemmmmc-—————————————————————— Axial Reflector Mounting =-----s=-----==mmou-mun e Reflector Attachment -s---cemmeccccmammccmcmcmccocaccmana Reactor Core and Reflector Plam —-s-=-mw--mco-cmmeooooooe Core‘Cell Plan ==weee m-—————— e eemeem—m— e e ——————— Core Peripheral Cell Plan m=-m=--=--ccecmomoccaomocooonoao Bottom Graphite Grid ------r--ccomomcmmcmoom oo Graphite Collar - mmmemer—e——oee .- e o o om0 o e Co:e Orificing end Tie Plates --------------- —mmmm————— Control Rod Cell —cemmmmeccescmccmccccamemocammaaaacacan Primery Heat Exchanger --=---- meme— e —————— ———— - Primary Heat Exchanger Head Closure Detail «=wmcecceaca-- Reactor Building Flevation eemrmumcwccvccvccmwncccconnnaan Reactor Building Plag, --------- o o e Reactor Ce11 and Heat Exéhanger‘Cell Elevafion --------- Drain Tank Cell‘Elevationv----;---.a;--.-; ...... e PrimaryHeat'EXchangerSupport.-Q-;-----;-;-;----; ...... Drain Tank Plafi.—--»--g—;----;---5-_---.--_-----__ ______ Drain Tank_Elevafion_—---;w--a-w --------- -——— m———— DraifiTafik Heat_sink---;-gé---------------------------- Dréin Valve ;--------;------;-------,__--_-u---w--;-_--_ Drain Tank Jet Pump Assembly =weeememmcccccocccmcncnaea- 12 13 15 17 19 20 43 LL L8 52 53 55 Fig: 25. Fig. 26. Table 1. Teble 2. Table 3. Tableh.:_ Table 5. Table 6 '“"‘ ‘ Table 7. Table 8. Table 9. | | Page Processifig-afid Stbrage’TanksPlan_#é——a ------------- mmm—= 58 Processing snd Storage Tenk Elevation —------mm--------= 59 LIST OF TABLES Axial Reflector'Hydfaulicfinat&;ff--*"'? """"""" ----- 16 AMSDBIPrimary‘Heat Exchanger Design Date --e=e-=-mee--e--- 28 'uPh&sicalPrbperties of the Fuel and Coolamt . = Salts Used in the MSDR ==-e-=--ecc—amcca-—- mmmmcecmeeem== 29 MSDR Secondary Hest Exchanger Design Date -c-ommesmmmene 3% Stean Generating Dabte -----smmmmmmemmmmmemcmmmmmmemamin 37 ‘Hoater Design Dats for MSDR Contaimment Cells —m-m-nmen-= 46 ée1i Cooling System e meem e LT Dump Tenk Heat Sink Data cmmmcmemmemmmemmememmmmmmmsen 50 “,Lifetimé Averaged Performance of & 750-MW(t) | ‘. | | Molten-Salt Demonstration Reactor =—------c--escecacaaa- 63 E ) uf o | DESIGN STUDIES OF A MDIEEN-SALT REACTOR DEMDNSTRATION PLANT E. S. Bettis, L. G. Alexander, H. L. Watts ' ABSTRACT The MSDR, a 350-MW(e) Molten-Salt Reactor Demonstration Reactor, is based on technology much of which was demon- strated by the MSRE. The cylindrical vessel (26 ft diam by 26 ft high) houses a matrix of graphite slabs forming salt passages having a volume fraction in the core of 10%. The flow of fuel salt is distributed so that the temperature rise along any path is the same — from 1050 to 1250°F., 1In the primary exchanger, heat is transferred to barren carrier salt (in et 900°F, out at 1100°F). 1In the secondary ex- changer, heat is transferred to a stream of Hitec salt (in at 800°F, out at 1000°F). The Hitec oxidizes tritium to tritiated water which is removed and disposed of. The Hitec generates steam at 900°F, 2400 psi in a boiler, super- heater, and reheater. Electricity is produced at an overall efficiency of 36.6%. Soluble fission products are removed by discarding the carrier salt every 8 years after recovery of the uranium by fluorination. Volatile fission products are removed by sparging the fuel salt with helium bubbles in the reactor primary system. The fuel cycle cost was estimated to 0.7 mill/kWhr for inventory, 0.3 mill/kWhr for replacement and 0.1 mill/kWhr for processing, giving a total of 1.1 mllls/kWhr - The" purpose of this study was to describe & semi- commerC1al-sca1e molten-salt reactor and power plant that would be based on the technology, mich of whlch was demonstrated by the Molten-Salt Reactor Experlment. The plant'was-designed to produce 350 electrioal megawatts."The nuclear | onversion ratio is about 0 9, and the speclfic power is about 0.5 MW(e) per kilogram flssile. : . ; . - The "reactor consists of a cylindrlcal vessel ebout 26 ft in diameter and about 26 ft high filled with a matrix of graphlte slabs forming flow passages 0.142 in. thick by 9-3/8 in. wide and with a volume fraction in the core of about lO% ‘The reflectors consist of graphlte slabs cooled by a small flow of fael salt.; Flow through the core and reflectors is regulated by orlflces 80 that the temperature rlse of the fuel with minor exceptions, along any flow path is- approx1mate1y the same. The fuel salt consists of a mlxture of the fluorides of 71i, beryl- 1ium, thorium, and uranium. (inltlally 235U) Salt leauing the reactor at 1250°F flows through the tubeside of & shell-and-tube exchanger where heat-ls,transferred-to_a secondaryrsalt stream composed:of barren carrier salt. The°fue1 salt exits'at°10505F:and'is recirculated to the reactor. Secondary salt enters the - exchanger at 900°F and- leaves -2t 1100°F. It flows to a secondary exchanger, also shell-and-tube ~where the heat is transferred to a tertlary salt stream, a. mixture of KNOa, Nanoa, and NaNOz known as Hitec. The purpose of the Hitec loop is to trap tr1t1um formed -in the reactor and which- dlffuses through the exchangers in the direction of the steam system Tritlum is ox1d1zed by the Hitec to trltlated water, which is readlly removed for safe dlsposal The Hitec enters the exchanger at 800°F and leaves at lOOO°F. ; - The heat exchangers are arranged SO that after the removal of shield plugs, the heads may be removed and 1eaky tubes may be plugged off by remotely manipulated equipment. , Heat is transferred from the Hltec tofwater in_thevsteam“generator which consists-of a boiler, a superheater;'and.a_reheater, all shell- and-tube types. Steam at 900°F and 2400 psi is produced which, after being expanded through high, intermediate, and low-pressure turbines, generates electricity with an overall efficiency of 36.6%. In the event that there is anvinterruption in the generation of power, the reactor is drained through a freeze valve into a drain-tank _provided with an NaK cooling system. The NaK system dumps heat to-a free-flow1ng water stream.by thermal convection. Hence, the system is reliable even. when all power fails. | | Xenon and other noble gases. are removed from the fuel stream by sparging it with helium in a bubble generator located in a bypass loop -from pump discharge to pump inlet. After contacting the salt to absorb noble-gases,;the-bubbles are removed in a centrifugal gas separator. Following & holdup of about 6 hours in the drain tank, the gases pass .l ) 0 ¥ through & particle trap for remofial of solids. About half the gas is recycled to the bubble'generator.‘ The other half is routed to a cleanup system consisting of charcoal beds where the effective holdup time is about 90 d&ys,'alldwing for almost completé decay of radioactivity. The effluent is recycled to pump'shaft seals and other purge points. Removal of fission products from the fuel stream is effected by discarding'éarriér’salt every 8 years'after fluorination to recover uranium. The spent salt 1s stored for future recovery when a complete molten-salt processing plant is available. Although the main control of the reactor consiéts in adjusting‘the concentration of fissile uranium in the fuel salt, auxiliary control is achieved by means of 6 cruciform control rods loaded with By C and clad with Hastelloy N. h Fuel Cycle Costs Inventory : | Mills/kWhr Fissiles | - 0.62 Salt 0.07 Replacement Fissiles 0.18 Salt ' 0.13 Total 1.0 Processing (estimated) 0.1 Total fuel cycle cost. = 1.1 .aj'INTRoDUCTIoN-‘ The prlmary objective of the Molten-Salt Reactor Program at ORNL is ~to develop a hlgh—performance thermal breeder reactor that utilizes a molten salt fuel and breeds on the th0T1Uflk'33U fuel cycle. Conceptual de31gns for such reactors have been studled for several'years. A ref- ‘erence design for a lOOO-MW(e) plant ‘end the uncertalntles that must be resolved to achieve a commercial thermal breeder plant were described recently 1n report ORNL-h5hl and 1n Nuclear Appllcatlons and. Technology The Molten-Salt Reactor Experlment (MSRE)a - a 7,5- MW(t) reactor — was operated from December l96h to December 1969 to demonstrate ‘the feasibll- 1ty and 1nvest1gate some aspects of the chemlstry, englneerlng, and operatlon of molten-salt reactors. Although successful operatlon of the MSRE was a notable achlevement _the power denS1ty was low, the heat was reaected to alr, and the experlment lacked meny other complexztles of & power breeder plant | The next step 1n the Program plan for devel- oping the breeder is the constructlon of a Molten-Salt Breeder Experlment (MSBE) .4 | The MSBE would be & lBO-MW(t) reactor that Would have all the “tech- | n1cal features of a hlgh-performance breeder The maximum temperature ‘(1300°F) and peak power density (llh W/cc) Would be as high or hlgher‘,- than in the reference breeder design. Supercritical steam'would be generated in the reactor steam supplyrsystem, and the plant would have the fuel reprocessing facilities required for a breeder. The purpose of the MSBE would be to demonstrate on an intermediate scale the solu- tions to all the technical problems of a hlgh-performance Molten-Salt Breeder Reactor (MSBR). An alternatlve approach to the development of a commercial MSBR has also evoked 1nterest This approach emphasizes more rapid attain- ment of commerclal smze but more gradual attainment of high performance. The step beyond the MSRE is construction of a_300-MW(e)_Molten-Salt Demonstration Reactor (MSDR). The purpose of the MSDR would be to 1Molten-Salt Reactor Program Staff, Roy C. Robertson, ed., Conceptual Design Study of a Single-~Fluid Molten-Salt Breeder Reactor, ORNL-L5L1 (June 1971). 2g, §. Bettis and Roy C. Robertson, "The Design and Performance Features of a Single-Fluid Molten-Salt Breeder Reactor," Nucl. Appl Tech., 8, 190 . (1970) , , | ®p. N. Haubenreich and J. R. Engel, "Experience with the Molten-Salt Reactor Experlment " Nucl. Appl. Tech., 8, 118 (1970). ! "‘J ‘R. McWherter, Molten Salt Breeder Experiment Design Bases, ORNL- TM-3177 (Nov 1970). -t ¥ &) £ ot demonstrate the molten-Salt reactor concept on & semi- commercial scale while requiring 1ittle development of basic technology beyond that demon- strated in the MSRE. The objective of the study reported here was to prepare a conceptual design of an MSDR'plant. The overall engineering deSign of the plant and the details of some aSpects of the:deSign”are described in this report. Basic information7on chemistry, materials,_neutron physics, and fuel reprocessing waS'reported recentl& in'ORNLéhshl and is not repeated here. The problem to which this study was addressed concerns design of a firstgof-aAkind'reactor plant which could be built with & minimum of development'and from which higher performance breeder plants could evolve, Concepts which could not be used in future breeder plants were to be aVOided | Two maJor 51mp11f1cations were made in the design of this demon- stration plant as compared to the de31gn of the breeder plants. First, the MSDRVhas only such chemical processing as was demonstrated in the MSRE and has no proviSion for removing fission product poisons on a short time cycle. This results in a much less complicated chemical processing plant, although it means that'the reactor has a breeding ratio less than one and is therefore a converter. The second major simplification is that the poweridensity was made low enough for the graphite core to last the 30-year design lifetime of the plant,xthus simplifying the reactor vessel and eliminating the eqhipment for replacing the core. Other areas of design were also simplified by the very low power denS1ty of the reactor as will be noted in the description of the plant that follows. ' 'We believe that the design described here’ represents a molten-salt reactor plant which is feas1ble to build will produce a significant amount of electrical power, and would be a major step toward a useful family of breeder reectors f ‘7' o GENERAL DESCRIPTION ThlS plant is designed to produce 750 thermal. megawatts in a single- fluid molten-salt reactorr. Tho_r:Lum in the prlmary, or_,fuel, salt is converted to fissile uranium. Because of the simplified salt processing, the conversion ratio is of the order of 0.9. _The heat generated in the reactor is transported to the primary heat exchangers as the salt is “clrculated through the reactor and heat exchangers by the prlmary pumps. Figure 1 is a simplified flow dlagram of the system In the prlmary heat exchangers the prlmary salt glves up. its heat to the secondary salt which is c1rculated between the prlmary and ~secondary heat exchangers by the , secondary salt pumps. The secondary salt has the same compos1t10n ‘ (7L1F-BeFa) as the prlmary carrler salt Slnce it contalns no f1ss1le or fertlle materlal it is very much 1ess radloactlve than the prlmary - salt. . , _ , . The secondary salt 1s cooled in the secondary heat exchanger by a f thlrd molten salt whlch circulates between the secondary heat exchangers - and the steam generatlng equlpment This third salt is a eutectlc mix- ture of nitrite and. nltrate salts (KNOa-NaNOg-Namoa) The prlmary purpose - of thls th1rd salt loop is to capture trltlum.which is generated in the prlmary salt and dlffuses through the heat exchange surfaces of the pri- mary and secondary systems and 1nto the third salt system. It would migrate into the steam system if this thlrd salt, having oxygen avall-,. able to tie up the tr1t1um, were not present. The nitrite- nltrate salt cannot be used as a secondary coolant for reasons that will be dlscussed later. _ The steam system is conventlonal. It has high-, 1ntermed1ate-' and 1ow-pressure turbines, coupled to a generator, whlch take steam from the steam generator-superheaters, and reheaters at a temperature of 900°F. The high-pressure turbine throttle pressure is 2HOO psia. The b011ers and superheaters are of the once-through type with rec1rculation of water through the boiler for flexibility in control. The condenser, deaerator, water. treatment and feedwater heater chains are conventlonal and Wlll not be descrlbed The steam.condltlons were chosen somewhat arbltrarlly as be1ng sultable for & first-of-a-kind plant. R One of the essential auxiliary systems for a molten-salt reactor is the cover-gas system for the prrmary salt circuit. Since salt must be kept free from oxygen, an inert atmosphere (helium) must be maintained “in the gas space associated with the fuel-salt system. Many of the fission products are volatile and these highly radioactive gases must be “cooled, stored, contained, and safély disposed of by either radioactive o !fi'i!.lm - SEPARATOR o) ' .. § 24,450 gem T ‘wearpemcy T - ' ; mimasy RAN TANK 5 . Fig. 1. Simplified Flowsheet ) " [ ] » ( ORNL DWG T2-3586 for 300-MW(e) Molten-Salt Demonstration Reactor. decay or permanent storage. This,off-gas:system,.which,will'beAdescribed -in detail later, must have a guaranteed heat removal system, fission product-absorber.system, pressure regulating system,.and meenS[of sepa- rating 1iquid~(salt) entrainment. The off-gas system is quite involved and.must ‘have an extremely high degree of dependablllty'— a- requlrement that makes & certain amount of redundancy necessany A second auxiliary system.whlch is extremely 1mportant is the after- ‘heat removal system. Because ‘the fuel can be drained from the molten- salt reactor and because of the low power dens1ty,there is no need for anremergencygcore cooling system,,but the drsln_tank for the prlmary salt nust have a cooling systefifthafsis posiiiveVend independent of the -power~sfipply or operating machinery3 if possible. The afterheat removal system ‘is thus one of the essential auX1liary systems.‘ ' | The fact that -there are no solid fuel elements to be fabrlcated 1oa.ded, reprocessed, and refabricated makes the molten-salt reactor unique. Many advantages accrue from this fact, but it 8150 mskes neces- sary an on-site chemical processingfplant'for'maintaining.the”salt in a cleen\and:operating condition. This chémical processing plant is another auxiliary system which is essential to the plant.. When a molten- salt reactor is to be used as a breeder, the chemlcal processing system becomes relatively involved. In addition to keeping the salt clean and low 1n,oxygen, and adjusting the uranium inVentory,~fihe fission product -poisons must be removed from the primary sjstem on,a%fairly short time cycle;i If, on the other hand, the plant is designed only as a converter having & breeding ratio of less than unity, the‘fission producfis can _‘ be removed on a long time cycle and: the chemical plant becomes much more 31mple o 3 Even in a converter reactor it 1s uneconomical to allow the fission product p01sons to remain in the prlmary salt for the 11fe of the plant. The fuel carrier salt with the fission product poisons is therefore dis- carded after about 8 years of operation. Provision must be made for recOvering.the.fissile material and for disposing of the radioactive carrier salt. Such a chemical processing plant is an integral part of this reactor power plant design. The'processes inVolved are those which were used successfully to process the salt in the MSRE. » .y n 3 & 9 A nuclear power plant requireslother 1 . ot T t.h 7 . ' 0 - ! /\ * B Y . ¥ g . LR ) Fig. 2. Reactor Vessel Elevation. £} n v 36 - A 2t k - ¢ ek ke r————— e s - . Fig. 3. Reactor Vessel Plan. 4% 14 of the axial reflectors. Top and bottom heads are exactly alike and have ribs welded on their convex surfaces to form bearing surfaces that fitvagainst the reactor vessel heads. The concave surfaces bf these - heads are machined to form concentric‘rings having flat "lands" or | surfaces about 12 in. wide to which gfaphiteISectors are attached. Thei graphite sectors, having radii corresponding to the radius of the ring to fihich they fasten, are mounted on these'heads with gaps of’varying widths between the concentric rlngs formed by the graphite. Spaces .equal to the gap width between rings are also left between the ends of adjacent graphlte sectors in each ring as they are assembled on_the head. The method of mounting fihé*Séctors*bn the:héédsfis?shbfifi infiFig, L. Three holes are drilled in each graphite sector fram-the.Cénter of»the. surface that is to be in contaét with the head. One is at the center . “of the séétor and'one is near the end. Into these holes aré]placed Hastellqy plugs 2 in. in diameter bjjh inI lbng. These'plugs are are. - drilled end tapped axially for 3/h~in, cap screws, They also hévé 3/h—in.-d1am‘transverse holes at a distance of 3 in. from the tapped " end. The graphlte sectors have horizontal holes so that 3/h~in.-d1am pins 1nserted through those holes will pass through the transverse holes . in the metal plugs and fix them in the_graphite. Holes in the hgads ' permit the graphite sectors to be fixed to the heads by cap screfis that engage the metal plugs in the graphite. The holes for the screws that engage the plugs in the ends of the graphite sectors are slight1y overg size to permit differential expansion between the graphite and the metal head. | | o e The widths of the slots between the concentric rings of reflector were computed to provide salt flow to the core in accordance with the radial power distribution in the core.men making these computations, the AP across the reflector was assumed to be 5 psi.' The AP across the holes in the head under the slots was also assumed to be 5 psi and the number of holes required to furnish the required flow was calculated with the results shown in Table 1. After the graphite has beeh installed in the reflector head the complete bottom assembly is lowered into the reactor vessel. Worklngr through the bottom hole in the vessel, the center gussets of the ( ', “ - v - Borrorn Llrescroe Sawe - Locaay M LogucormG Coo Ao o8 »” " Axial Reflector Mounting. ) ORNL DWG T2-4030 _IPERE T AN LIETikord o I“l s* - . 138.68 — 1.456 x 1072T (°F) Viscosity, 1b h_r-]- 71 | ' | 0.2806 exp E%TFT Specific heat, Btu 1b7} (°F)7 | 0.57 Thermal conductivity, Btu hr™* ft~* (°F)™* 0.58 Nitrate-Nitrate Coolant Salt Composition (eutectic) - KNOg -NaNOg - NaNOg- (44-49-7 mole %) Density, lb/ft® | 130.6 — 2.54 x 10727 (°F) : i -1 1 3821.6 Viscosity, 1b hr * ft | 0.1942 exp 557 5 T (°F Specific heat, Btu 1b~* (°F)7? 0.37 Thermal conductivity, Btu hr t ft ! (°F)? 0.33 62 30 ORNL DWG T1-5032 . PIeIMtARy Sasy MKET ~ A | s28” Almot Tronsrer Pdk - SEE MW . AB. Fubes - IFE8. . Tube Sice-Y 0.0 <.035 woll Tube Btct -.67 4 Fig. 13. Primary Heat Exchanger. 31 ORNL DWG T72~358) ~SELL WELO R JOBE SHsEy v //////// //// //// - Fig. 14. Primary Heat Exchanger Head Closure Detail. “ The heat exchangers are mounted hbrizontally, one leg of the "U" being under the other. The tubesheet’endseof the exchanger are access- ible through a hole in the cell wall by removing a shield plug from the hole. The head is flanged and bolted with metal "O"-ring seals backed up by a thin’éeal weld. This permits relatively easy removal of the heads for plugglng a tube in the event of a 1eak g ' Primary,ggggsl ‘Sump-type centrifugal pump5jfpr-eircfilatingemblteneSaits?haVe'been' employed for many years in experimental rigs and he#e been used success- fully in two molten-salt reactors, the ARE® and the-MSRE,_ Theselmolten— salt pumps are described in the 1iterature,§ and tnep-material will not be repeated here. - In the MSDR the pumps are mounted symmetrlcally on the top of the reactor vessel. Each pump is submerged in a tank that has excess gas volume to accommodate expansion of the salt. This volume commnicates with the primary sysfem.by & 6~in. line from each pump bowl to the center dome in the_top'of the reactor vessel. During normal operation, flow down these lines returns the fountain purge flow from each pump to the top head of the reactor. The pump suction line commnicates with the pump sump through a small leakage path in order to drain the sump when the primary system is drained. Each pump has a capacity of 8100 gpm end develops a 150-ft head. In order to pfirge xenon from the salt; about 10% of the flow from each pump is bypassed directly from pump outlet to inlet. The bypass line | contains a bubble generator for admitting gas to the salt and a bubble stripper'for rembving'gas. The gas stripper removed about two volumes of salt with each volume of gas removed, and this mixed stream is directed into the drain tank. A venturi in this line is provided with 5J'am.es A. Lane, H. G. MacPherson, and Frank Maslan, eds., Fluid ‘Fuel Reactors, Chapter 16, "Aircraft Reactor Experlment " Addison- Wesley Publishing Company, Inc. (Sept 1958). : ®Molten-Salt Reactor Program Staff, Roy C. Robertson, ed., Conceptual Deszgn Study of a Single-Fluid Mblten-Salt Breeder Reactor, ORNL o541, ' 58 ff (June 1971). » L1 33 a l-in. connection to the gas space 1n the pump bowl. This arrangement “makes 1t pos31ble to mix the. pump. seal purge gas with the stripped gas and to send it to the drain tank and thence into the off-gas system. This line also serves as a syphon break to prevent draining the system through the gas separator discharge line in the case of a stopped pump in any of the primary circuits. ' | In addition to providing the primary selt flow and the bypass flow, a line from each pump discharge is manifolded into.a line which drives two jet pumps in the drain tank. Each of these lines has a ball check valve inserted in it-npstream of the manifold. The jet pumps in the drain tankfreturn_the_entrained liquid in the gas ‘separator discharge to the primary circult, as will be described in the discussion of the drain tank. ) SECONDARY CIRCUITS Heat from each primary clrcuit is transferred to a secondary salt system. The salt in each\secondary loop is circulated through the shells of the primary heat exchangers and the tubes of the secondary heat ex- - changers by a pump similar‘to the primary pump. The secondary circuit is designed'to contain arrelatively small volume of salt. o The salt used in the secondary loop is 7LiF-BeFs (66-34 mole %). Although it would be possible to use a different salt in the secondary circuit, it was believed that the advantages accuring from using the 7LiF_‘--BeF‘z salt Justifies its useuin the first demonstration plant. By using this salt, any primary heat'exchanger_leak will be much less troublesome'than-if5a”different-secondary salt were used. Als6, the - LiF-BeF: salt will remain°nonradioactive, except for very. Short-lived' activities, and’ thus maintenance of the secondary heat exchangers will : be less complicated. There are +two secondary heat exchangers per secondary.loop. These - are "U" tube exchangers of the same design as- the primary exchangers. ;Because of the differences in the salt heat transfer properties, they . are slightly. larger than +the primary exchangers.-_Table L gives the design data for these exchangers. e - It may be noted that the secondary circuit isolates the primary cir- cuit from the rest of the system. Because of the sensitivity of the 3k ‘Teble 4. MSDR Secondary Heat' Exdhanger De51gn Date Iype . Rate of heat transfer per unit MW | : “Btu/hr Tube-side conditions Hot fluid L s Entrance temperature, °F Exit temperature, °F Lo Pressure drop across exchanger, psi - Mass flow rate, 1b/hr Shell-side condltlons Cold fluid Entrance temperature, °F Exit temperature, F ' o Pressure drop across exchanger, pSl Mass flow rate, 1lb/hr Tube material Tube OD, in. Tube thickness, in. Tubesheet- to-tubesheet dlstance, £t Shell material Shell thickness, in. Shell ID, in. Tubesheet material - Number of tubes Pitch of tubes, in. Total heat transfer area, ft° . Basis for area calculation Type of baffle Number of baffles -Baffle“SPacing. in. Disk -OD, in.. - Doughnut ID, in. Overall heat transfer coefficient, U, Btu hr™* £t72 Volume of 2L1F-BeFa salt in tubes, ft3 . U-tube, U-shell counter- ' current, one-pass shell = and tubes_W1th disk-and- doughnut baffles .., . 1z ook, 3 X 10 ;2LiF-BeF3,§alti,e' 1100 . 900 80 3. 7 X 106 - Hitec T00 1000 80 3.8 x 10° .. Hastelloy N - L 0375 . ' .0.035 - 37.5 Hastelloy N - - 015_ ’ Hastelloy N . - 160k | - 0.7188 (trlangular) OutSide.offtubeg_;fl,*;‘ - Disk and doughnut. - - 8.6 o2.0 . - 500 305 1 35 primary salt to oxygen, this is a desirable, if not necessary, feature. Also, the secondary and tertiary salt circuits provide a double barrier - between the low-pressure fuel-salt system and the relatively high-pressure steam system. 'TERTTARY SALT CIRCUIT - The primary purpose of the tertiary salt c1rcu1t is to prov1de a tritium trap to prevent diffus1on of tritium.from the primary circuit into the steam system v1a the circulating salt systems The tertiary circuit uses a eutectic mixture of KNOa—NaNog-NaNoa (hh 2-48.9-6.9 mole %), which has the commercial name of "Hitec " The oxygen in this salt comblnes with the tritium to form tritiated water, Whlch can be recovered from the system, . o Although the primary function of the tertiary saltiloop is to trap tritium, it also has certain advantages which offset, at least to a degree, the complication of the additional pumps and heat exchengers required for the third loop. The advantages derive chiefly from the fact that the liquidus temperature of the nitrite-nitrate eutectic is 288°F, which relieves cons1derably the poss1ble problems of salt freeze- up in the steam generators. An additional advantage concerns the fact thet water‘will simply vaporize from the nitrite-nitrate salt‘and_the_ consequences of a steam leak ere thus much less severe In fact, this salt could possibly be used with steam. as & cover gas. ~ The nitrate-nitrate salt cannot be used as a secondary coolant _because 1t would react W1th the primary salt to precipitate thorium and uranium oxides in. the event of a primary heat exchanger leak. 'There 1s the additional danger of a reaction W1th the graphite of the ”core should nitrite-nitrate eutectic get into the primary system..w The nitrite-nitrate salt will remain nonradioactive, except for some tritium, and thus the tertiary loop can penetrate the building containment. This permits the location of all the steam system equipment outside the containment and makes it access1ble for direct maintenance It also removes the possibility of a pressure rise within the contain- ment due to a leak in the steam systen. The corrosion resistance to Hitec is a consequence of the estab- lishment of a passivating film on the containment metal. Cheaper 36 materials can be used for the piping'andeteamegenerating equipment of this~loopthan is reQuired inithefprimaryfand secondary systems. ~It:is ‘intended to make the secondary exchangers out of 316 stainless steel - because of the secondary,salt in the tubes. The shells and piping, - however, could be made of Croloy. ?he‘tertiary;pumps could also be fab- ricated of Croloy. As preViously mentioned the low melting pOint (228 F) of the Hitec permits ‘the feedwater to enter the boiler at temperatures that are in line with current steam plant practice Since the wall At must be held to a reasonable value (< 200 F), the salt temperature at the ex1t of the bOiler must be of the order of 700 F if the feedwater enters at about | 500°F.f This 700 P salt cannot be returned to the secondary heat exchanger because the freezing point of the secondary salt is 856°F.- To av01d o this low temperature and still maintain an acceptable At across ‘the tubes in the bOiler, a bypass stream.of hot tertiary salt is mixed‘With the' cool (700°F) salt to raise the temperature of the mixture to an accept- able level before returning it to the secondary heat exchanger The‘"‘fi total flow 1n the tertiary system is about hO 500 gpm of this, 27 OOO gpm flows through the steam generating equxpment and is cooled to 700 F. The bypass loop mixes 13 500 gpm of lOOO F salt With the 27 OOO~gpm o T00° F stream and raises its temperature to 800°F before it enters the | secondary heat exchanger A throttle valve in this bypass 1ine permits temperature control for partial loading and trans1ent conditions 'y o Data on the decompos1tion and corrosion of Hitec are insufficient | to be absolutely certain of the highest temperature that is allowable | and the type of cover gas required over the salt It is intended to limit the temperature to 1000 F and to prov1de an Ng overpressure until more experience is gained Indications are that a tenperature of 1100 F is tolerable, and, if this is verified steam conditions for & molten- salt plant could be Significantly improved A report ORNL-TM-3777,_ o which is in preparation, Wlll present the known information on’ Hitectygm temperature limitations. » v 37 - STEAM SYSTEM . The steam system condltions at the turblne throttle Were chosen to be 900 F/2h00 ps1 ‘with 900°F reheat but the steam system was riot specialky designed or optimized for the demonstratlon plant. Steam flows and tem- peratures are shown on the simplified flowsheet of Fig. 1. The steam generatlng equipment is, of course, quite different fram | that in a f08811-fired plant in that the heat 1s extracted from a circu- lating nciten salt On a completely arbitrary bas1s the steam 1oad for the turbine-generator is diV1ded between 6 b01ler units 6 superheater units,'and 6 reheater unlts A1l these units are heated by the three salt circuits’ comprislng the tertiary salt system of the plant The boilers are divided into two units each simply because this results in units of a size more eas1ly handled. The entire steam c1rcuit is a ‘once-through system where both the water and salt s1des of the preheater, boiler, and superheater are in series. Feedwater from the conventional feedwater chain enters the tube side of a ULtube preheater at a temperature of h80 F and a pressure of 2600 psi. It passes from this unit first 1nto a similar U~tube boiler and from that into the U-tube superheater. These three units each have 100 tubes in shells about 12 in. ID. Additional data are given in Table 5. Table 5. Steam Generating Data No. of Length Diameter Wall Steam AP Salt AP Duty tifunit; Tubes ‘ (ft):_ | (in ) (in ) L (psi)'u (PSl) (Btu/hr) Preheater —€100 V'¢32%7'-‘ 50:5—15* 0.050 7.2 . 23.8 :451,x:106a- " Boiler 100 32 j-o ‘50,050 17.6 23.8 68 :106 - Supérheater 100" 3h;8.z;a?o;5*ff 0:.050 . 73.8 " -:23.8 57 X 10° Reheateri Jér16o_;tfh3;5'”’u50551c*~f0;050--v'*6O-rx1*5'3h5"1**7.2'x 108 At the'side—stream eXit'of'the ‘boiler secticn‘there is a bypass through a recirculator pump: to the inlet of the preheater.» ‘This. bypass is for the purpose of .control for partial load operation and for such _38. contingencies as a breaker trip!from.fulléload. The shell sides of all ‘these units (preheater, boiler, superheater) are also connected in series 8o that the 1000°F tertiary salt flows countercurrent to the water and leXits fram the preheater at 700 F at des1gn load._: L e The steam generating cells are outside the reactor containment ;(3 building but are closely adgacent to provide close coupling._ The 1nterlors of the steam.cells are not heated 1ike the reactor cell but heaters and 1nsulation are, 1nstalled on the piping and components. All steam.and ‘ water 11nes are run from each piece of equipment in the steam.cells from manifolds, stop valves etc 3 located outs1de the steam cells. The | -rupture disecs on the tertiary salt system for relieving steam.pressure . in the event of a leak are installed in the steam cells 1n order to _con= tainthe saltw:Lthinthe cell. ', o S . The turbine-generator 1s shown as a tandem.unit with one high-pressure, one 1ntermediate~pressure, and two low-pressure caSings on one shaft drivang a single generator unit The Specific turbine-generator has not been des1gnated As has been stated the usual extraction p01nts and | conventional feedwater handling are emplqyed. No effort has been made :_ to detail the regenerative feedwater heating system or other aspects of the steam system REACTOR ‘BULLDING The. reactor building follows what has come to be a rather traditional containment structure. Bas1cally it is a cylindrical reinforced concrete structure with a hemispherical - dome. - A sealed steel membrane, 1f2-in. - thick, lines the entire building and provides the containment. The con- crete provides. protection‘againSt-missiles.resulting*frumttbrnadic‘winds. The building is about 150 ft tall and about 112 ft in diameter. - - - - The building is suspended from a large concrete ring about 176 £t in outside diemeter and sbout 8 £t thick. This arrangement gives & low center of gravity to the building. Although seismic analyses_have not been made, it is believed that this method of construction may be more stable'to'a*seismic disturbance. The same basic design?of‘thepbnildinga* could be used if subsequent-analyses-or considerations related to:agpar-fi ticular site indicate that the building should be set on a foundation » £ " 39 at the bottom of the structure. Figures 15 and 16 show the elevation and plan of the reactor building. The steam cells are appended symmetricélly outside the containment and rise from the concrete ring. Also mounted on the ring and external to the contaifiment are the three water tanks which provide the heat sink for the drain tank cooling system. The control room is also built on this ring outside the containment building. Inside the reactor building are the cells containing the radioactive portions of the plant. There are 5 sealed cells which have a common atmosphere: the reactor cell, the 3 heat exchanger cells, and the drain tank cell. These cells have water-cooling coils embedded in the concrete walls with water plena at the ends of the cells for removing the heat that leaks through the thermal insulation. Each cell is completely lined with;a;l/2-in.-thick—30h stainless steel membrane Wfiich seals the cells from the remainder of the buiiding;..PenetratiOns into the cells have been kept to a minimum and the'interconnecting sleeves between cells have bellows which permit differential movement between the membranes of the various cells. These sleeves provide the necessary passages for the salt piping. Flgure 17 is an elevation of the resctor cell and one of the 3 heat exchanger cells. Figure 18 is an elevation and plan of the drain tank cell. : a The reactor is hung from a ledge by means of a large flange near the top of the vessel. This is seen in the elevation section of the building, Fig. 15. In the heat exéfianger cells all units are mounted from & superstructure.rising from the floor of the cell. This mounting method is shown in Fig. 19. The drain tank sits on the floor of the drain tank cell, therload being.carfied through a skirt and 8 lugs which transmit the load through the seal membrane and insulation to the con- crete botfam.of the cell. . CELL HEATING AND COOLING All 5 cells are heated by 01rculat1ng the cell atmosphere (mostly nitrogen) over electrical heaters. The c1rculation is accomplished by 3 large blowers,'eaCh of which discharges 32,500 cfm of gas at a tem- perature of 1050°F into the reactor cell. The reactor cell has 4 gas outlets, one to each heat exchanger cell and one into the drain tank Lo ORNL DWG 72-3578 Fig. 15. Reactor Building Elevation. (‘ f iv » & TLlaek ;Vara& LTI HETOf CHLL O\ £ // o~ 3 g7y ok .. . ‘-l’ 1 . A /7 B ] /1 7 / 4 -~ ’; - ‘; - -~ . 7 < A -~ ‘ s \ ' e \ 1 \‘ .\ \‘ + ® NN . 1 ) SN A\ 1 . - ‘ “ i ' ‘ = 2 /7 .! . . N i , . . \ - - = ~ ConTROL A0oA a SN A ES o Lpuip, ~ - - . A CBELow ] - e e e . fi—e . — o - . X hY . \\ e L 1 N . \\ ~ - \\\ . " . ] S ’ . ) o SN ‘“\ . . CELL Fig. 16. Reactor Building Plan. A (FESERAT AN s ORNL DWG 72-3581 s 2RI MY E SECON OO KEA] XM GER (Etn NAH - WG TER C HEAT ExcadigER (S) T PHOTO 79084 Cowcotrd Cookrv'G Marae Oufc.or\ FRLALL Sints s s g Aoclss sy o Jies. : Couyhn w By Aoas Lk 2 8 Supr08” LoD .\ Bevcong Harae L ASAIRTI O COuT ol WSAL T TS oSLA, P Hooass Ferg O Psaz.' of Case Wores Mors ¢ | S COUT A MEST HELT LXCMINGER CEit * ! = n . ArsrcaFron f BOrte’F FomTEE Su B 2 ) . e Ry T . . . Coocrurg fia,*.'efip@; Coocsng ;’ 4’44)34 Cll eyl D Coocary Whyrek Povust - . /l/l‘"df £re. Syseo£rs . ' Lot i I 1 ' ! : e . m_' fi;:-:.iéy’ f e, T e 7B Sraany GavdoR7mG S rlay e ' Cow o by ‘ Afimuaxr Daww Pocrs - Coocivg Wazse @ OCurcey &) st By VR s BT a ,"“ e . - Fig. 17. Reactor Cell and Heat Exchanger Cell Elevation. ‘) Dedms & dox. . Lwles TEEvE. Zursegancy DRt Lrsid SLLLre L3 PHOTO 79090 = - - n . g I’“\\ N N , w I /, \\ ': l’ ’ "W h " / O\ “ P N N 14 "\ ‘Q}\ \\\ II ,,; y u\ 4 S w i 7 A 3 W u } -~ 2\ iy T, O o .2\ i Nt o M - 14— e e ey A . e . ' =} ) --: 1 - -— ' ! “' i : fooo i zod ° g it i/ A\ o o e o \ . S .\ \\L/{\ o 3 e Y TN . 4 " ,/ ' \\ . - ~ /'y 1 \‘ . S ~, . || N r - |' f‘_’ _— ‘i - . » SRECTION Fosry . \-\.-/' » - DR’ S CLid Corcw Fey JE28 Brests z) VIV ~PINE loa‘,' pag”] Fig.rlB. Drain Tank Cell Elevation. Cged £ - N A NS N Scark: K520 Fig. 19. -~ i HoRrTowyw8 Jeors w Svppoer i Scacas ¢ L0° Sewsac g%yt Primary Heat Exchanger Support. ORNL DWG T2-3585 it " L5 cell. Return ducts frdm each of these cellsrto the blower suction make a closed circulation system which is part of the cell containment. Perti- nent data for this cell heating system are shown in Table 6. | Heating the cells by forced circulationNgreatLy reduces the number of cell penetrations necessary when compared to heating by space heaters in the cells. In addition to heating, it is desirable to cool the cells at times. The data for cooling,'nsing the same circulation system, are shown in Teble 7. The circulation duct is divided into two sections, and a simple'butterfly'type damper directs the'air-through either the heater section or the cooling section. | | The electric heaters and the reentrant tube cooling water units each fit into thimbles which are welded into the top of the duct. In each case (heating or cooling), heat transfer is by radiation. Neither the heaters nor the water piping penetrate the ducting so that repairs can be made without breaking the containment. DRAIN TANK SYSTEM One of the most important systems in the molten-salt reactor plant is the fuel-salt drain tank with its cooling system and provisions for gas holdup. (It is somewhat analogous to the emergency core cooling system of a solid fuel reactor.) It provides automatic removal of.the afterheat in the event of g failure of the main circulation sy stem. Also during normal"operation the volatile fission products and the stripping gas are held up for about 6 hours in the drein tank. The . decay heat from this operatlon 1s removed by the natural convection ' coollng system. . | | | - The drain tank con31sts of two separate tanks. Theiprimary_tank 81ts 1n31de & secondary tank or. crucible. The drain tank has a flat top with thimbles located in a symmetrlcal pattern. Sixty'anits of 6 tubes each cover the top of the drain tank. Flgure 20 is a plan view shOW1ng the arrangement of these thlmbles W1th the cooling headers 1n place Figure 21 1s an elevation of the drain . tank ‘In: order to stabilize these thimbles against seismic shock they are interlocked at the bottom in such & way as to allow differential axial movement but no individual vibration. The 360 thimbles, therefore, act together Table 6. Heater DeSign Data for MSDR Contairment Cells ,Estlmated normal containment heat loss (total), KW Design heat 1oss, KW Number of heater cells Capacity of each heater cell, kW éirculétigg gas fGaSginiet-outlet temperatures at heaters, c"F Gas flow rate through each heater'cell, cfm Heater element Heater length, ft Number of heater elements per heater cell Heater element arrangement per heater cell Pressure drop in circulating gas, in. HgO Heater cell width and depth, ft Thermal conductivities for cell wall (k), Btu hr -1 f£7r (°F)7? 1/2-in. stainless steel cell liner ~5=in.-thick fiber glass cell insulation Prestressed concrete with 2-in. sched LO carbon-steel watér cooling pipes on 6 in. centers located L in. from inside concrete face Assumed heat transfer coefflclent 1n'water plpes, Btu hr™t Tt -2 (°F) R :Maximum.concrete temperature, °F 600 1200 3 hoo N3 _ 1000~1100 32,500 (at 1050°F) 1-in.-0D cartridge with Incoloy 800 cladding g oo o 150 | 12 rows of 12 or 13- elements on 3-in. A'pitch 9. 6 - | 3.25_x'2.61 12.4 0.034 - 1.12 (concrete) 25.9 (steel) - 1_5'0 . M b7 Table 7. Cell Cooling System Tnitial heat rate, Btu/hr Number of cooler cells Number of thimbles per cell Length of thimbles, £t Diameter of thimbles, in. Pitch of tubes in squgre arfay, in. Temperature of cooling water, °F Gas flow'rate per cell, cfm AP acrst_thimbles;_in..fléQ | Bmissivity of thimble Volume of'gas.tobe quléd;ftaz Temperatfire.N§ at stért, °F | Tem@eratfiie Né after 2.75 hr, °F Temperature reactor atsfart;ffF\ Temperature reactor after'2f75_hr, °F 3.5 % 10° 225 4 2 3 225 32,500 10 0.7 150,000 1000 740 11000 998 'i ORNL DWG 72-3582 — — — —— — 0 ] A Q /N g a AELD ZATEaTas "Tfi"'r YT - ‘. TR/ :jr' 'QM“II’:§/1; buge. Porrs ZTciqrir Liwvd& g , Fig. 20. Drain Tank Plan. ko PHOTO T9085 Bd 4P AL 0 Moy L L Lo /T, | SLOW SEREAT S CRUCUBLE CoomlY - - - Copcirr S $ BTz r Tk T VS 'l‘.},q, Ltb'._"_\') Paad S . 8 & 2T .l IS L 2 L Ll ks ol d oottt dodndlnd o d y e o r 3% \ : LW & e e g = " = N3 b e e A et [ A UL S .. { r e e —— e - —— UH — —— T o m M o ! ¢. L . == _. . me W ,”u Q- |-y e — X9 & == = e e e % d. il 1l - el - - R fl, \ ! . e C [ oo o J ] — . ."rll..fln” puin § T - T .IIIL ———r e e e 1 ” _ LT T S N e m—— 3 tflfl 1 “. i g e = L ) -t . . b 5 . [ . . " /.’ - , - N . = ! d ” m,- M RN = —_ fl? Y M. 4 m ™ N3 ? E pa m oy 4 g - ! : ”5 .” P 3., U~ 3 ] U X JC s — = g v § 3 e o ] ¢ v 18 . §7 % P —~— . - CL ' D,H. n, r.\.- ] ‘ ,rm - N 7 . . N .. 1 ] . oy J nr. . N\ I R R, 3 - 2 L~y I T N T R P T T T T > 2 4 .8 \ S Y E S R S O T S T Q : . , L 17.. v ‘ . . . " o~ §" : s 0 , ; ’ =L ‘ - - -C . 4 -0 . o —— e . i — e e . ammee s - .. N . — 8 ' 8 ion. Tank Elevat ain Dr - Fig. 21.- 50 'e*asia%unit as far as vibrationis:concerned,andthe.natural frequency‘_ ) of this-Structure is high enough to provide protection against,earthquake damage ., - e o B A cooling module. cons1sts of & manifold and 6 reentrant tubes for - each of the 60 groups of thimbles which penetrate the draln tank. Each “of these cooling modules is connected by two h-in pipes to a section of pipe . in the Water heat dump outside ‘the building containment - These cooling modules contain NaK as the clrculating heat transport fluid Each module has an expans1on tank and shutboff valve so that each can . act independently of the others. ' Three water tanks 25 ft X'25 £t X 12 ft deep are located outS1de " | the reactor building. Water flows through these tanks in an open cireuit. .JThe water is taken from ‘the same source as the turbine condenser cooling water and, after going through the tanks, it is returned to ‘the stream, Data on these water tanks are given in Table 8, and the tank arrangement Table 8. .Dump Tank Heat Sink Date Size of tank, ft 25 X 25 X 12 Depth of water over tubes, ft 5 _ . Number of tubes ' 576 for each of 2 tanks, 672'for‘third Arrangement of tubes 418 tubes per row, 12 rows for 2. tanks, . | and 48 tubes per row with 1h rows for _ - , third tank. Total volume of water for 12,920 all tanks, £t° | - - S Thimbles tn row =~ 3-in. sched-10 pipe on 6-in. centers " Row spacing, in. 1 - “ NeX pipes in thimbles . 2-in. sched-lLo pipe 'NaK entering temperature, °F 532 | NaK exiting. temperature, °F 450 Water enterlng temperature, °F 80 Water exiting temperature, °F 100 Nak flowfrate,~gpm S - 2800 - Water flow rate, gpm 39 " 51 is shown in Fig. 22. Two of the 3 tanks are sufficient to provide cool- ing under maximum heat load conditions. Heat is transferred from the drain tenk to the NaK, and from the NaK to the water by radiation. Thus the NaK has a double barrier between it and the contents of the drain tank and also between it and the water in the cooling water tanks. The crueible in which the drain tank is suspended is a double-walled tank. It is also cooled by NaK, having its own independent lines to the water tanks. The crucible cools the drain tank walls by radiative transfer. - The drain tank connects with the primary system in three completely different ways in order to perform the three distinctly different func- tions for which it is used. The first of these functions is to provide a receptacle into which the prifiary salt may be drained whenever it is necessary for any reason to remove the salt from the primary system. A 6-~in. line runs from the bottom of the reactor in a generally horizontal direction into the drain tank pit. At this point a drain valve is installed and a vertical line connects the drain valve to the drain tank. The drain valve is a critical paft of the system since it operates but infrequently and yet must operate when requlred To provide some redundancy, the drain valve is bypassed by a rupture disc valve which can be used in an epergency if the drain valve fails to open. Both the drain valve and the rupture disc valve are replaceable by remote maintenance methods after the prlmary system is drained. The drain valve is a comblnatlon mechanical valve -fTeeze valve.‘ As shown in Fig. 23, the poppet does not seal mechanlcally'but relies on a frozen salt film to seal. Thls seal is frozen by czrculation of a coolant in the body of the poppet . It is thawed by c1rculat10n of hot fluid. The poppet is actuated by a posztive electrlc drlve and the movement is sealed by & bellows which cannot be contacted by salt but only by - the cover gas. o o , The second use for the draln tank 1s one whlch 1s extremely unlikely but nevertheless must be provided for safety considerations. If there is any leak of"primary salt from the primary system,‘the salt must be put into the drain tank. Therefore, the reactor cell, heat ORNL DWG T72-3583 L A, Tau. o =22 . - JANMS ‘/_f fz L2725 e CPomwi 876 Lass/ G540 #? Tanse 23 r S, P47 /¥ Ao s °8 JuA G 7. -JLmEs 92 63850 frd warse 0 P.irE " r— 3 Stk ! ::_..._.._“ Fintdtier i 1 1 et noonn. i by ittt 1 ' 1 . et Pttt e Vi it Vi . fPhelita Prid et b betiding ity gt ._‘___..“ __...,-.__ _:.,_::::&f SV p e e Prett b 1i 14 @ Fitil i Vitilp1-@ - ’ 3 9 By ____..__ue __I:..mo‘e_ T IT it T E Y P—LELITLIILIITTITL 1i 33-34:1-:.- n-nunnHH§§§§§1 FIIIIITTAL 13141 EATIINITL LTS eI GO I I O LI I HUUUUULG %gaaflfldg --.anaqqifl :-.44.141‘......11111-.1:1 é}i*flgagaug Ukl IOICINIRT ol L ik ud L ULULUU m dflgfl_ NITULNN _.Eg»-gflagghrg I L O TR PR T AT T L M LI LT T DT S O O T T S o e e T e 2 L Y T A N AT R TR VA AL 24 5 e R LR T LS LR D T T AT L L L R L LR IILTReLittau E—h.firflég CIHHE—H_.EE:E:::: B O R L e Ve EELENLT UL LT VT L O T T T . L LTSI LA, e L R AR AL AL EEQE_EE LiLIiJLIUh .LUJ-J.LJ...HLL....U 25'-0° Drain Tank Heat Sink~ Fig. 22. e ! * » ORNL DWG T2-3587 JAL/’ FAOK/ | g/ o / V7L V/:,M///Z/ ZZ77 frrz %5_ ” s ! . ! i « - " i ' LTI T T 77 g o Jffhe/ -'//// "/\//////J//A \ Poppzs 7 ‘Fig. 23. Drain Valve. €S 5h exchanger cells, and the salt piping above the drain tank celi are equip- ped with catch pans which eommunicate with the drain tank through a rupture disc in the top of the tenk | The third use of the drain tank ¢oncerns the holdup of the fission gagses and the separation of entrained liquid from these gases. About_8 MW of heat from these fission products must be disposed of and the drain;tank cooling system is used to dissipate this'heat. This is a continuous func- tion of the drain tank while the plant is in operation. - As has been mentioned, the primary salt is SParged with helium to remove xenon from the salt. This sParglng is accompllshed by introducing ga.s bubbles into a salt bypass loop around each pump of the primary cir- cuit. In this bypass ercentriffigalrseparatof extracts the gas from the salt. The separator constantly extracts about 10 gpm of salt along with the gas. This two-phase stream from each?pump is sent to the drain tank where, because of the size.offthefdraifi éenk, the salt separates from the gas by gravity, and, after an average residence time of about 6 hours, the gas passes through a partlcle trap. About half the gas is returned directly to the bubble generator and the other half passes through a cleanup system and is returped to the pump purge system by means of & gas compressor. o The flow of liquid to the draln tank may vary over & range from O to about 32 gpm. A means must be‘provldefi for returning this salt -to the primary system without returning any,bf5ffie’radioactive gas. A system of jet pumps with automatic flow control is used to_accomplish this. This jet pump system is installed as a unit in the center of the drain tank and can be removed for replacement or repair shofild any of the unit become defective This unit is shown in p;en and elevation in Fig. 2h. A 19-ft -long by 6-1n -diam pipe, closed afi'the'bottom end and open at the top, acts as a sump in the center of the drain tank. On the out- side of thls sump there are two jet pumps whlch are driven by a common -salt source taken from the output of the three primary pumps. A line from the dlscharge of each primary pump, after passing through a ball check valve, is manifolded into one common line which feeds these two jet pumps. PHOTO T9087 %‘ TR Pl AT n,’* Ly -*y.;‘,'& "y - L : | e S i Pin SO Letmn 58 2" J f . ) r<} i i Pos: Bace Jop-] . "\ AT ity Ly ) & - 3 i 3~ iy R 4\ Fore Frmee s S f, o | S . ‘ . ‘—-;_‘ -,e:‘:‘l fn.g .[Q; -—"‘:’-Jfl: . FJ . . / Y 7B Fe *er & : > -fl,c‘flfll ' ‘ | ! : » LA> SO ODScH ARSI . . ,&a - s Srwo Loy ./:r...____* \ s " T s . o= SNy fm Pa-sw”/ L 2, ST Sdapy Sy Syaraer . &"-..:fll" . ‘ / vo dace Jef , . ; o 5 ~ e vay ~ IV Y : . \» ' - Rayues Jo Lpmressy A S BT T 7 ST . o I [ ¥ fu.&’.fifimd_—g" S v Thagsy /s ] . Scmety {01 Fig. 24. Drain Tank Jet Pump Assembly. 6§ 56 One of the jet pumps has its suction in a small sump in the bottom of the drain tank and discharges tangentially into the 6-in.-diam.sump near the top. This pump has a capacity greater than the flow of liquid into the tank so it keeps the drain tank sump-empty. Because.the“Capacity of the pump exceeds the liquid flow, this pump at times pumps‘gas, but the gas simply discharges back into the drain tank atmosphere. | The second jet pump is located about mi dway up the 6-in.-diam sump and sucks out of the bottum of this pipe. The discharge of this;pump goes into one of the pump .bowls. of the: prlmary system. The jet pump suction can change from about plus 14 £t to a mlnus 5 ft. Therefore," the pump dlscharges salt at a rate proportlonal to the suction head and this rate can be anythlng between O and 32 gpm Thus only liquid and . never hot gas is returned to the primary system. This automatic regu- lation takes care of the liquid pumpback for all condltlons-of operation. A third jet pump is mounted with this assembly, but it 'is used only for filling the primary system or for transferring the contents of the drain tank to the chémical processing cell. This operation is described below, along with the chemical processing system. ' | Because this plant is operated as a converter having a breeding ratio less than unity, the chemical processing reqfiired is very much less involved than that required for a breeder. Three things are re- quired of the chemical treatment: TFirst, means must be provided for removing oxygen from the primary or secondary salt in case either becomes contaminated. Second, when the fuel salt has accumilated enough fission products to cut significantly into the neutron economy, this salt mist bé'replaced with unconteminated carrier salt. The uranium must be extracted for return to the reactor before the old salt is discarded.. Third, there must be provision for storing the discarded carrier salt, at least as long as cooling of this salt is required. In addition to these three primary functions there is a further requirement for.a storage faéilityuwhere primary salt may be placed if it is necessary to do maintenance of any kihd on the drain tank. Since this storage tank is required in any event; it was decided to use it as the chemical pro- cessing tank for fluorination of the priméry salt to remove uranium. [} a* 27 The cooling system.for the storage tank can be quite simple since the salt can be held in the drain tank until the heat rate is of the order of 1 Mi. This situation exists after approximately 30 days of cooling. The 1 MW can be successfully transferred from the surface of ‘the storage tank by radiation to the NaK-cooled jacket surrounding the storage tank. ‘ After removal of the uraniumg the contaminated carrier salt must be put into disposable cans. These cans, about 2 ft in diameter by 10 ft long, are'placed in tanks located in an ennulus around the top part of the storage tank. Figures_25 and 26'are plan and elevation of-the stor- age tank and the disposable cans. These cans—haVe interconnecting l-in. lines so that salt can:he'transferred to them frdm.the_storage tank by gas pressure. After cooling, the lines can be cut-and welded, sealing the spent salt permanently in the disposable,oans. After the cans have been sealed they can be stored under the reactor in the storage vault or transported to salt mlnes or other permanent storage facility. New cans can be installed by dlrect malntenance once the full cans have been re- moved from the location FF-GAS SYSTEM Helium.is used as & .cover gas over ‘the prlmary and secondary salt. It is also used as a purge, flowzng inwerd eround the pump seals, and as & sparge for remov1ng xenon from the primary salt. Thls gas system is a closed system, and storage and cleanup eqnlpment must be provided. The bubble injection and separation and the holdup of the gas in - the drain tank have already been descrlbed When the gas leaves the drain tank it goes to one of two partlcle traps “These traps can be isolated by valves for removal from the systam for repair. The purpose of these partlcle traps is to catch the solid daughters and granddaughters of the noble gases and also such noble metal particles as are carried by the gas as it leaves the drain tank.: These particle traps have adequate size to accumulate solid particles for about three months before excess- “ive pressure drop would require replacement of the trap. To remove the heat generated by these particles, the traps have NaX cooling; The heat load is of the order of 400 kW. These particle traps have not been A - DU SOOSAL, CAn e rei 8s. L) 273 |Lrsro sS4 i 29 ORNL DWG T0-12199 - DrsposaL Cau ——3 Ccocav/ S Y = Essnvg TunE - " Loorans Srofage & LROCESSNG JANK '/ z&az Z J | = LOOLING ’i./d:r'r_/,f," A5 -~ Al EROMAL LIS AT, D Y e -~ JACKET _CoOeANT Fig. 26. . Processing and Storage Tank Elevation. 60 designed since the exact calculations on which a design is based have notiBeen made. Past experience with MSRE shows that the design is not complex and the configufetion does not present a problem. | The gas line downstream of the particle trap divides into two equal branches. About 1 cfm of the gas goes directly to the bubble generators in each of the three pump bypass lines. When this gas is removed by the bubble separators, it recirculates to the drain tank, through the particle trap,‘and to the bubble generators again., This gas is very radioactive, the only loss in radioactivity being that which has decayed in the approximately 6-1/2 hr transit ‘time for the loqp. | The other gas stream from the partlcle trap enters one of two char- coal absorber beds. The two beds are valved so that either can be used. It is imperative that the krypton and xenon in this part of the gas be held up for 90 days because it must be essentially clean before it goes to the gas compressor and storage tank for recirculatlon to the pump ‘seals. The head end sectlon of the holdup bed is cooled by NaK while the downstream sections of the bed can be cooled by natural convection of the gas atmosphere in the off-gas cell. These beds are in the form of calandria with the charcoal surrounding the tubes. The aotual design ‘of the charcoal beds, as in the case of the particle trap, has not been done. Again, there has been enough experience with such absorber bede at ORNL to show that they are feasible and are not excessively large. For details concerning gas cleanup systems, reference is made to ORNL~ 45kl (ref. 6). CONTROL RODS There are 6 control roanpenetrations'in the reactor core. These are T=-in.-diam holes in graphifeiblooks