... , 1 I OFI ORNL P 899 . 4 7 . PN 1 Ć : . . . A + . .. . i . * SI, . . . . EHF 3.6 . . _ . . . : TE . :: . 01:25 1.1.4 LG MICROCOPY RESOLUTION TEST CHART NATIONAL BUREAU OF STANDARDS - 1963 man eristica de This paper was submitted for publication in the open literature at least 6 months prior to the issuance date of this Micro- card. Since the U.S.A.E.C. has no evi- dence that it has been published, the pa- per is being distributed in Microcard form as a preprint. . ... litor : V A STS " 1: . . . 4 ........ . .. . - . , --- - meneri .. - . LEGAL NOTICE This report was prepared as an account of Government sponsored work. Neither the United States, nor the Commission, nor any person acting on behalf of the Commission: A. Makes any warranty or representa- tion, expressed or implied, with respect to the accuracy, completeness, or usefulness of the information contained in this report, or that the use of any information, appa- ratus, method, or process disclosed in this report may not infringe privately owned rights; or B. Assumes any liabilities with respect to the use of, or for damages resulting from the use of any information, apparatus, method, or process disclosed in this report. As used in the above, "person acting on behalf of the Commission" includes any em- ployee or contractor of the Commission, or employee of such contractor, to the extent that such employee or contractor of the Commission, or employee of such contractor prepares, disseminates, or provides access to, any information pursuant to his employ- ment or contract with the Commission, or his employment with such contractor. .. . in... - . .. . wice ::' '...::'-.. . .... ' , ... ... ;'.'. .- nicio , , T T . R . ORTL-P_899 ARIES CONF-650502-2 MOLTEN FLUORTANS AS MASEAR REACTOR FUSS* , F. F. Blankenship, H. F. McDuffie, R. E. Thoma, and W. R. Grimes Oak Ridge National Laboratory Oak Ridge, Tennessee Molten mixtures of ?LiF, BeF2, ZrF4, and UF4 show nuclear properties, chemical stability, and phase behavior required of circulating fuels for high temperature nuclear reactors. The liquids are adequate heat transfer media and are compatible with moderator graphite and with INOR-8. The fluoride-graphite-metal system withstands radiation, fission of uranium and accumulations of fission products without appreciable damage. The Molten Salt Reactor Experiment, fueled with such & fluoride mixture, will begin operation during the summer of 1965. *Research sponsored by the U. S. Atomic Energy Commission under contract with the Union Carbide Corporation. -LEGAL NOTICE Tu roport we pompared un account of Communal pound worth, Naldor the United H ., por dhe Comminaton, nor ny pornoo actting on behall of the Countessor.. A. Want wy nrruty or repeatadou, prosed or lapued, wuh ruspect to the cor- noy, completenes, of wafale dhe laborator contatoed la o report, or that we al my taformation, appunto, w ad or proces ducloud ba je roport may not latria primately oned rights; or B. der Ray Habudas mil repect to the woof, or for dumugue monditoy trou the w of any belorustion, apparibus, method, or process dixcloud la is report A wood on the woma, "perman scthar an Delall of the corralaston" including my nae plogna or contractor of the winton, or employu al medio atractor, to the extent dat tech plogus or contractor at De Coundation, or employee al wat oorector properes, dominatra, o provides acowbo, w babondion par to wo employment or contract va te Counterton, of we reployment will recha contructor. unui ruinnrånXN1133INITO KUULIOKITWAN: :10 am 093INITI Wann eer een COWI KUTINIu. ROOGDOM UN ULEIURIREWING VIMUI. . APPROVED FOR' PUBLIC RELEASE This paper was submitted for publication in the open literature a. least úlonths prior to the issuiincr, date of this Micro- card. Since the 1.8..E.C. has no evi- dence that it has been published, the pa- per 18 being distributed in Microcard form as a proprint. MOLTEN FLUORIDES AS NUCLEAR REACTOR FUELS* F. F. Blankenship, H. F. McDuffie, R. E. Thoma, and W. R. Grimer Oak Ridge National Laboratory Oak Ridge, Tennessee A circulating liquid fuel for a thermal nuclear reactor must satisfy the following minimum requirements: The fuel must consist of elements of low capture cross section for neutrons and must contain the critical con- centration of fissionable material. The mixture must be thermally stable, must have & low vapor pressure, and must be an adequate heat transfer fluid. It must be nonaggressive toward some suitable structural metal and toward some useful moderator. The fuel must be stable under reactor radiation, must survive fissions of the fissionable material and must tolerate accumula- tion of fission products without serious deterioration of its useful proper- • - -. ties. In addition, an effective and economical decontamination and repro- -. .. .* - - - - - - in a cessing scheme must be possible. A considerable study, lasting many years, at the Oak Ridge National Laboratory has demonstrated that molten mixtures of 'LiF, BeF2, ZrF4, and 235UF4 can meet these stringent requirements and can be used as fuels for high temperature thermal reactors. The Molten Salt Reactor Experiment (MSRE), designed to operate at about 650°C, will begin operation in the summer of 1965. MSRE is a 10-Mw reactor constructed of a nickel alloy containing 17% Mo, 7% Cr, and 5% Fe and moderated with unclad graphite. The molten fuel flows *Research sponsored by the U. S. Atomic Energy Commission under contract with the Union Carbide Corporation. . om upward through a graphite matrix in a cylindrical reactor vessel. At the design power level (<20 W/cm3 of fuel in the core), the salt enters the saphite at 635°C, leaves at 663°C, enters the centrifugal punp, and 16 discharged through the heat exchanger shell to the reactor vessel inlet. The coolant, a mixture of Li’F and BeF2 (66 mole % L1F), flows through the heat exchanger tunes and an air-cooled radiator. When the reactor is not operating, the sa].58 is draineá to dump tanks held at temperatures above the melting points o: the salt mixtures. MSRE will demonstrate a class of reactors capable of development into thernal breeders; its fuel system, chosen primarily for neutron economy, consists principally of Li’F and BeF2. Some 27F4 is added to insure that . . . . . . . . VO2 will not precipitate if the fuel is inadvertently contaminated by oxide ion. The MSRE fuel composition will be about 65 L1F, 29 BeF2, 5 ZrF4, and 1 UF4 (in mole %). The fuel mixture begins to freeze at 450°C; the coolant begins to freeze at 455°C. The fuel as charged to MSRE will contain about half the required 235U concentration; it will be brought to critical and operating concentration by addition of molten Li?F-UF mixture (27 mole % UF2). Although the MSRE will use no blanket, the system LiF-BeF2-ThF4 has been shown to offer low-melting mixtures with the high ThFe concentrations needed for the purpose. In the absence of irradiation, compatibility of molten fluoride fuel- mixtures, INOR-8, and graphite is well demonstrated. Attack upon INOR-8 by molten fluorides similar to MSRE fuel at temperatures up to 750°C approaches 0.5 mil per year and is independent of fluid flow rate. Graphite does not react chemically with the fuel mixtures and is not wetted by them. mo: . . . - Reaction of fuel with sorbed geses that cannot readily ve removed from the moderator before operation seems inconsequential, and carburization of INOR-8 by carbon dissolved or suspended in the fuel has been shown to be no problem in long-term tests. The salt-graphite combination has been irradiated in several types of INOR-8 capsules at realistic temperatures and at power densities from 12 to 250 Kw/liter of fuel (to uranium burnups of 1.3 to 11.5%), Early experi- ments, in which the fuel mixtures cooled to room temperature during reactor shutdowns, showed that F2 was released when the solid salt was irradiated by its contained fission products. Irradiation in capsules which permitted sampling of cover gas during irradiation has shown that fission product Kr and Xe, an appreciable fraction of the iodine, (perhaps) a trace cf CFA, and no other gases are released under irradiation at elevated temperature; Fa begins to evolve when the temperature drops below 100°C. Recent tests in which the high temperature was maintained until disassembly of the . . . . . . . . . - - - - - - capsules show no evidence of F2 evolution and no detectable damage to the . materials. CF4 generation at high temperatures, if real, is too small to be of consequence to MSRE. Four fluoride ions are released, along with the fission fragments, when uranium in UF4 fissions. The fission fragments must achieve steady state valences such that cation-anion equivalence is maintained in the liquid and redox equilibria are established among components of the melt and between ssione interessanthathu the melt and surface layers of the container metal. The data from many ... in-pile tests suggest strongly that these requirements are met (the fluoride .'*. a ions are satisfied) without oxidation of the container. Kr and Xe, which a ch servono .zrin M ILL monogram .* ri alta ES 21: * we quite insoluble in the fuel, should be easily removed if the graphite 18 reletively impermeable and if a gas-stripping mechanism (not provided in MSRE) 18 included in the design. The fission products that are active metals (Hb, C8, Sr, Ba, Zr, Y, and the lanthanides) will exist as fluorides in their ordinary valence states; solub111ties are sufficient to permit operation of MSRE for several years without precipitation of these materials. The less active metals (Mo and Ru, for example) should exist at least, in, part as metals. In MSRE, which contains no provieion for their removal, they must be expected to plate on the INOR-8 surfaces and, perhaps, cü the graphite. Methods of localization or removal of these materials must be provided for large reactors of this type to avoid protilems of local over- heating (especially upon shutdowns) or even blockage of flow in the heat exchanger. Recovery of unburied uranium from the fuel (or of 233U bred in a blanket) by volatilization of UF6 upon fluorination of the melt has been demonstrated. Complete schemes for reprocessing the fuel remain to.be demonstrated, but vacuum distillation of the fuel constituents from the most important fission product poisons shows promise.. --- Lit t le Withers t...... . . . . . . . END . . - - - - . DATE FILMED 9/ 18 / 65 - - I. TWI