ORNL experience and perspectives related to processing of thorium and ²³³U for nuclear fuel

Thorium-based nuclear fuel cycles have received renewed attention in both research and public circles since about the year 2000. Much of the attention has been focused on nuclear fission energy production that utilizes thorium as a fertile element for producing fissionable ²³³U for recycle in thermal reactors, fast reactors, or externally driven systems. Lesser attention has been paid to other fuel cycle operations that are necessary for implementation of a sustainable thorium-based fuel cycle such as reprocessing and fabrication of recycle fuels containing ²³³U. This paper first identifies recent literature that has resulted from the renewed interest in thorium-based fuel cycles. Next, differences in the radiation characteristics of nuclear materials associated with thorium-based and uranium-based fuels are discussed, and the generic implications of the differences to nuclear material processing are identified. Then, experience at Oak Ridge National Laboratory concerning processing of thorium and ²³³U is described in terms of the processing projects and campaigns undertaken and the facilities in which the processing was implemented. This experience then provides the basis for a generalized discussion of processing nuclear materials associated with thorium-based fuel cycles as compared to uranium-based fuel cycles. This comparative discussion focuses on key out-of-reactor fuel cycle operations: reprocessing of metal-clad oxide and graphite-matrix oxide used nuclear fuels (UNFs) including head-end processing (shearing and dissolution), solvent extraction, product conversion, fuel fabrication, and waste management. It is concluded that the recycle of thorium-based UNF constituents (²³³U and thorium) is more technically challenging than the recycle of uranium-based UNF constituents (plutonium and uranium) based on the radiation, chemical, and physical characteristics of nuclear materials in thorium-based fuel cycles as compared to uranium-based fuel cycles.