Reprocessing Thorium-Based Fuels

XI-3] ANANTHARAMAN, K., RAMANUJAM, A, KAMATH, H.S., MAJUMDAR, S., VAIDYA, V.N., Thorium based fuel reprocessing refabrication technologies and strategies, INSAC-2000, Annual Conference of the Indian Nuclear Society (Proc. of Annual Conf, Mumbai, 2000). 

A Nonaqueous Reprocessing Method for Thorium-Based Fuels... 

A conceptual pyrometallurgical method for the reprocessing of thorium-based fuels is presented in Fig. 1. It is responsive to the constraints described previously, being operable with either oxide or metal alloy fuel, and producing product streams consisting of enriched uranium/thorium and plutonium/thorium. 

The Idaho Chemical Processing Plant is a versatile, multipurpose facility used for recovering highly enriched uranium from a variety of fuels in naval propulsion, research, and test reactors. Materials processed [Al] include aluminum-alloyed, zirconium-alloyed, stainless steel-based, and graphite-based fuels. The West Valley plant, although designed primarily for low-enriched uranium fuel from power reactors, also processed plutonium-enriched and thorium-based fuels. It is the only U.S. plant to have reprocessed fuel from commercial nuclear power plants. 

Np, and fission products. The Thorex solvent extraction process is generally used to reprocess spent Th-based fuels. As in the Purex process, the solvent is TBP diluted in an appropriate mixture of aliphatic hydrocarbons. Figure 12.9 shows the Thorex process flow sheet used by Kuchler et al. [41] for reprocessing high-burn-up thorium fuel. 

Liquid-liquid extraction (LLE) systems using neutral phosphorus-based organic compounds have been the subject of extensive study since Warf (1) first reported the use of tributyl phosphate, TBP, as a useful extractant for cerium(IV), uranyl and thorium nitrates. After more than twenty years, liquid-liquid extraction systems (such as the Purex and Thorex processes) employing TBP dissolved in a suitable diluent versus an aqueous HNO3 phase remain the most widely accepted systems for reactor fuel reprocessing. 

Fission energy can be obtained from uranium, using the uranium once-through option and the uranium-plutonium fuel cycle, and from thorium, by the thorium-uranium fuel cycle. Each fuel cycle offers a number of alternative routes with respect to reactor type, reprocessing, and waste handling. Although the uranium based cycles are described with special reference to light water reactors, the cycles also apply to the old uranium fueled gas cooled reactors. 

The evaluated concepts foresee partly different fuel cycles. Rssion reactors can be operated in principle on the basis of eittier a Uranium-Plutonium-cycle or a Thorium-Uranium-cycle, while combinations of these cycles among them or with other reactor concepts than proposed are possible. With t(xja/s nuclear park (comprising mainly LWRs), the world-wide plutonium excess increases annually by about 1001. Besides strategies based on reprocessing like... 

In parallel with the work done in collaboration with the European partners BNFL has conducted studies of the potential role of fast reactors in the UK and elsewhere. It is important to consider the fuel cycle as a whole and to make use of fast reactors in the optimum way to maximise safety and economic advantage while minimising environmental impact and proliferation risks. To this end accelerator-based systems as alternatives to critical reactors, and the thorium cycle as an alternative to the uranium-plutonium cycle, have been examined with particular reference to the implications for fuel fabrication, reprocessing and waste disposal. This work continues but the initial conclusion is that the critical Pu-fuelled fast reactor, properly integrated with reactors of other types, and with optimised arrangements for Pu recycling, has many attractive advantages. 

As far as reprocessing in the U/Pu fuel cycle is concerned, several chemical separation techniques have been proposed and developed in the past few decades. The most efficient process to date remains the PUREX process (Plutonium and Uranium Recovery by Extraction). This process uses nitric acid HNO3 and organic solvents to dissolve and extract selectively U and Pu, resulting in two separate product streams (U on one side and Pu on the other side of the process chain). As far as reprocessing in the Th/ U fuel cycle is concerned, THOREX (Thorium Oxide Recovery by Extraction) technology must be used, also based on dissolution in nitric acid and solvent extraction (however, with special care for the extraction of Pa, for the separa-tion of U and U, and for the dissolution of thorium dioxide in pure nitric acid). 

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