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Conference Article: Reprocessing and refabrication of thorium-based fuel

Zimmer, E.; Ganguly, C. (Kernforschungsanlage Juelich G.m.b.H. (Germany, F.R.). Inst. fuer Chemische Technologie der Nuklearen Entsorgung)

Abstract

In the last decade extensive R and D has been carried out at our institute on the thorium fuel cycle, particularly on reprocessing and refabrication of High Temperature Reactor (HTR) fuel. For reprocessing thorium-based spent fuel, the dual cycle THOREX process has been thoroughly investigated. The study demonstrates that there are no significant differences between the two extraction modes with either acid or acid deficient feed solution. The investigations have also shown that the feed solution of the second extraction cycle need not be acid deficient since the history of zirconium does not play a role for its decontamination. For re-extraction, the original flow-sheet has been changed such that the Th/U partition is already achieved in the first cycle. The formation of a crud produced by a Th(DBP)4 precipitate can thus be avoided. For refabrication of U-233 bearing HTR fuel kernels, the EGT sol-gel process has been developed. The process starts with a solution containing Th(NO3)4 and UO2(NO3)2. The kernel production is completed in a few steps and besides ammonia and water no other chemicals are necessary. In conjunction with the chemical process, equipment for continuous and remotely controlled operation was developed, e.g. a particle transport system, a belt drier, a sintering furnace, etc. On the basis of the EGT process a gel pelletization route for the production of (Th,U)O2 pellets has been developed. Two important changes were necessary for the sol-gel process: the sol must contain carbon black as well as Ca(NO3)2. The pores remaining after burning off the carbon black improve the compactability and provide for closed porosity in the pellets whereas calcium improves the sinterability. At a pressing load of 350 MPa and a sintering temperature of 1773 K, pellets with a density of >= 96% TD and an excellent microstructure can be produced.

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key words: experimental data; fabrication; fuel pellets; sintering; sol-gel process; spent fuels; thorex process; thorium cycle; thorium oxides; uranium dioxide
Reference:
Proceedings of a technical committee meeting on utilization of thorium-based nuclear fuel: current status and perspectives held in Vienna, 2-4 December 1985
International Atomic Energy Agency, Vienna (Austria)
IAEA-TECDOC--412, pp:89-111