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Progress in development of Fluoride reprocessing technology

Jan Uhlíř, Martin Mareček and Martin Přeček*

Nuclear Research Institute Řež plc, CZ-250 68 Husinec – Řež 130, Czech Republic [email protected] *Present address: Oregon State University,Corvallis, Oregon, USA

Abstract – Fluoride Volatility Method is based on direct fluorination of powderized spent fuel with gas in a flame fluorination reactor, where the volatile fluorides (represented mainly by UF6, partially NpF6) are separated from the non-volatile ones (e.g. PuF4, AmF3, CmF3, fluorides of majority of fission products). The method is regarded to be a promising advanced pyrochemical technology mainly for selected spent oxide fuels of advanced LWRs or GEN IV fast reactors. The technology should be chiefly suitable for the reprocessing of advanced oxide fuels with inert matrixes of very high burn-up and short cooling time, which can be hardly reprocessed by hydrometallurgical technologies. The current research and development work in the area of Fluoride Volatility Method is focused to the experimental program carried out at the semi-technological line called FERDA placed in radiochemical labs of the Nuclear Research Institute Řež plc.

INTRODUCTION reprocessing of spent fuel from thermal reactors. They are caused, for example, by higher burn-up, Fluoride Volatility Method (FVM) is regarded as shorter cooling time resulting in a higher amount a promising advanced pyrochemical reprocessing of energy released by the fuel, higher technology, which can be used for reprocessing concentration and amount of , different mainly of oxide spent fuels coming from future cladding material, presence of metallic sodium, LWRs or GEN IV fast reactors. The technology different fission products composition etc. should be chiefly suitable for the reprocessing of Therefore, countries that were planning the advanced oxide fuel types e.g. fuels with inert introduction of fast reactors also were attempting matrixes and/or fuels of very high burn-up, high to develop suitable methods for reprocessing, content of plutonium and very short cooling because the industrial hydrometallurgical time, which can be hardly reprocessed by PUREX process, employing organic extractants hydrometallurgical technologies. and solvents, was not suited for the fast reactor spent fuel. Hence, the most intensive effort in the Fluoride Volatility Method is based on a development of the FVM was in 1960s, 1970s separation process, which comes out from the and in 1980s together with the development of specific property of , and fast breeder reactors. [1, 2, 3, 4] plutonium of forming volatile whereas most of fission products () Nowadays, the renewed interest in the dry – and higher transplutonium elements present in pyrochemical reprocessinging methods is irradiated fuel form non-volatile trifluorides. motivated by requirements on the development of advanced fuel cycle technologies devoted to Original intentions of the development of this the planed Gen IV nuclear reactor systems. dry reprocessing method of spent fuel were Among the pyrochemical technologies under motivated in the past by the assumed commercial present development, the Fluoride Volatility utilization of fast breeder reactors. Their Method is almost the only one, which is not application in the power industry can be based on the use of molten salt techniques. economically efficient only in the case of a closed fuel cycle. However, reprocessing of fast The reprocessing technology based on the reactor spent fuel brings about a number of Fluoride Volatility Method consists of the specific difficulties in comparison to the following main operations:

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1. Removal of the cladding material from spent fuel elements 2. Transformation of the fuel into a powder form of a granulometric composition suitable for the fluorination reaction 3. Fluorination of the fuel (the purpose of this operation is the separation of the uranium component from plutonium, minor and most of fission products) Fig. 1. Process flow-sheet of Fluoride Volatility 4. Purification of the products obtained Method

CURRENT STATUS OF R&D ON FVM The first two steps represent preparatory stages for FVM itself and they can be realized The Nuclear Research Institute Řež plc has been separately from the FVM. Whereas the early developing FVM in the frame of fuel cycle fluorination techniques of the FVM were devoted to Molten-Salt Transmutation Reactor. fluidized bed processes, now the direct flame Here, the present day R&D represents the fluorination of powderized fuel is considered as follow-up of the former long-lasting R&D the most promising unit operation for future activities in FBR fuel reprocessing. The current industrial application. This method of R&D program is focused mainly to the fluorination in the frame of the FVM, which was technological verification of individual unit firstly used in 1980s, is now under development operations, apparatuses and material research in the Nuclear Research Institute Řež plc. and to the process control.[5,6,7] The

experimental semi-technological line called

FERDA, shown in Fig. 2, was manufactured and FVM PROCESS DESCRIPTION placed in the alpha-radiochemical laboratory of

the NRI Řež plc. The technology consists of Flame fluorination reaction of a spent oxide fuel flame fluorinator, series of condensers and is a basic unit operation of the whole process. sorption columns and from distillation column. The reaction between the fuel powder and pure The short-run capacity of flame fluorination fluorine gas is spontaneous and highly reactor is 1 – 3 kg of fuel per hour, but the exothermic. Usual temperature of ignition is over process, as a whole, has a batch character. 250 °C. Subsequently the temperature in the flame can reach in the reactor the range of 1500 – 1700 °C. Based on the fluorination reaction, the main partitioning of spent fuel is realized directly in the fluorination reactor. Whereas the volatile products of the fluorination reaction (typically UF6, PuF6, NpF6 and minority of fission products) leave the apparatus, the non- volatile fluorides (majority of fission products and and fluorides) remain catched in the fluorinator bottom in the form of ash. Further individual separation of uranium, plutonium and neptunium from those fission products forming volatile fluorides is generally possible by sorption, condensation and Fig. 2. Experimental line FERDA for R&D evaporation of volatile fluorides, thermal on FVM decomposition of plutonium and finally by distillation processes. A total process The main present experimental effort is oriented flow-sheet of the Fluoride Volatility Method is to the mastering of the flame fluorination process shown in Fig. 1. and to the elimination of some bottlenecks of the technology. After the tests done with the

ATALANTE 2008 Montpellier (France) May 19-22, 2008 2 P1_21 uranium fuel, the present day program is focused REFERENCES to the verification of the main unit operations with simulated spent oxide fuel constituted from 1. J. J. SCHMETS, Atomic Energy Review, a mixture of uranium oxides and non-radioactive 8(1970), 3. oxides representing selected fission products (mostly lanthanides, Cs, Sr etc.). The next series 2. M. BOURGEOIS, B. COCHET-MUCHY, of experiments should verify the suitability of Bulletin d’Informations Scientific et the technology also for reprocessing of oxide Technoques, 161(1971), pp. 41-50. fuels with inert matrixes.

3. M. A. DEMJANOWICH et al., RIAR report No. 50(565), 1982, RIAR Dimitrovgrad, CONCLUSIONS USSR (Russia). The Fluoride Volatility Method has a good 4. P. NOVÝ et al, NRI report No. 9062Ch, potential to be used within the fuel cycles of 1989, NRI Řež, Czech Republic (in Czech). several current or advanced reactor types for reprocessing of current or future oxide fuel 5. M. MAREČEK, F. LISÝ and J. UHLÍŘ, types. The main attractiveness of technology can Technological development of fluoride be found in the reprocessing of fast breeder volatility method for front-end of molten salt reactors spent fuel owing to the extreme transmutation reactor fuel cycle, Proc. radiation resistance of the used chemical agents InWor for P&T and ADS 2003, Mol, (fluorine gas, inorganic fluorides), which allows Belgium, October 6 – 8, 2003. to reprocess the spent fuels after the cooling time 6. J. UHLÍŘ and M. MAREČEK, R&D of of about six months only. Also the attractiveness pyrochemical reprocessing technologies to use FVM as the “Front-end” technology of dedicated to MSR fuel cycle, Proc. of Molten-Salt Transmutation Reactor is high due GLOBAL 2005, Tsukuba, Japan, October 9 – to the conversion of oxide form of original spent 13, 2005. fuel into fluorides – the chemical form of Molten-Salt Reactors. Another attractiveness of 7. J. UHLÍŘ, M. MAREČEK and M.PŘEČEK, the process comes out from the possibility to R&D on fluoride volatility method for process those oxide fuel types, which are reprocessing of LWR and FR oxide-type insufficiently soluble in used in fuels, Proc. ICAPP 2007, Nice, France, May PUREX process, like oxide fuels with inert 13 – 18, 2007. matrixes (ZrO2) or with high content of plutonium. Further advantages of the technology come out from the achieved compactness of the whole process and from the exclusion of any moderating agent. However to reach the separation efficiencies similar those, achieved by current hydrometallurgical processes will require further intensive research and development.

The research and development of Fluoride Volatility Method is realized in the Nuclear Research Institute Řež plc thanks to the financial support of the Ministry of Industry and Trade of the Czech Republic, the Czech Power Company ČEZ and the Radioactive Waste Repository Authority. The R&D has a close connection to the national Partitioning and Transmutation program.

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