Extensive repository system performance analyses have been carried out in the course of evaluating the feasibility of the proposed Yucca Mountain repository. These studies have shown that the primary contributors to public radiation dose as a consequence of release of radionuclides from the repository are isotopes of iodine, technetium and neptunium (129I, 99Tc, and 237Np). The United States Department of Energy is presently conducting a science-based R&D program, the Advanced Accelerator Applications Program, that addresses the technical issues associated with the transmutation of transuranic elements and long-lived fission products contained in the U.S. inventory of commercial Light Water Reactor (LWR) spent fuel. One of the main issues is the recovery and transmutation of iodine. The two fuels from which the iodine must be extracted are quite different, one (the LWR fuel) being an oxide fuel with zirconium alloy cladding, and the other most likely being a dispersion of metallic transuranics in a metallic zirconium matrix with stainless steel cladding. An aqueous solvent extraction process similar to the PUREX process will probably be used for LWR spent fuel processing, while a pyrochemical process seems to be most appropriate for the transmuter fuel. An overall system recovery target for iodine of 95% has been set as an initial goal of the program. Prior experience with iodine recovery in the PUREX process, both domestic and international, suggests that a satisfactory means can be developed for recovering the iodine contained in the LWR spent fuel. Iodine recovery in the less well-defined pyrochemical process for transmuter fuel appears to be feasible, but experimental verification and validation of the recovery steps is required. It is possible that the form of the recovered iodine from the two fuel types will be different, so it then remains to develop processes for incorporating the iodine in a standard target form, expected to be sodium iodide. Target design will also take into account means for accommodating the products of iodine and sodium transmutation.
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