Developments in reprocessing technology for high-temperature and fast-breeder fuels

The paper reports on the comprehensive long-range programmes in the USA to develop fuel-cycle technology for high-temperature gas-cooled reactors (HTGRs) and liquid-metal fast-breeder reactors (LMFBRs) which are being planned and implemented. In each case, the fuel cycle is an essential integral part of the power-reactor system, and the technical problems in the fuel cycle are being solved in parallel with the reactor development programme. For the LMFBR, the end point of the technical development will be a demonstration in a hot pilot plant to be operated with fully irradiated fuels from the Clinch River Breeder Reactor (CRBR) in the late 1980s. The programme is at present addressing process R and D problems, equipment development, and conceptual design of the pilot plant. The basic process will use a modified chop-leach head-end followed by Purex solvent-extraction cycles. Although a large base of experience will come from the early LWR plants, the significant differences between LMFBR and LWR fuels - sodium contamination, more complex fuel hardware, higher fissile and fission product content - introduce new problems requiring substantial development work. Increasing public concern and more stringent emission limits have prompted considerable effort toward retention of the gaseous fission products. For the HTGR, development is directed primarily toward the 233U-Th fuel cycle with a final goal of operation of a HTGR Fuel Recycle Demonstration Facility that can support the recycle requirements of 20-GW(e) installed capacity. The reference fuel element is a prismatic graphite block containing coated fissile and fertile particles bound together by a carbon matrix. Start-up is with 235U, which is replaced on subsequent cycles with the bred 233U. Spent fuel elements are crushed and burned, and the fuel particle oxides are dissolved and processed by solvent extraction. Refabrication must be done remotely because of γ-activity from 232U daughters, and the programme includes extensive development of the specialized equipment for forming and coating particles, preparation of fuel rods, and assembly of the elements. (author)