| 摘要 |
Nuclear fuel is employed for a first cycle in a light water reactor and thereafter subjected to reprocessing for the removal of fission products, for the removal of higher actinides, for the recovery of plutonium, and for the recovery of uranium. Such recovered uranium includes about 0.1 to about 0.7 per cent uranium 236. Higher concentrations of U-236 in subsequent cycles are plausible. The difficulties attributable to the U-236 isotope are managed by separately enriching the recovered uranium to provide an upgraded fraction containing from about 1.0 to about 3 per cent U-235. From 30 to 60 per cent of U-236 initially present can be shifted to the tails fraction, with only about 40 to about 70 per cent of the U-236 in the enriched fraction. The U-236 tends to follow the U-235 in the enrichment step so that the U-236 concentration (as distinguished from distribution of total U-236) in the upgraded fraction is greater than initially. Such enriched upgraded recovered uranium is mixed with plutonium to provide a mixed oxide fuel containing from about 1 to about 7 per cent plutonium oxide. No enriched uranium derived from virgin uranium is mixed with or diluted with recovered uranium because of the significant penalty attributable to the presence of the U-236 isotope, particularly in the dilute parasite range.
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