Calculational criticality analyses of 10- and 20-MW UF(sub 6) freezer/sublimer vessels

摘要

Calculational criticality analyses have been performed for 10- and 20-MW UF(sub 6) freezer/sublimer vessels. The freezer/sublimers have been analyzed over a range of conditions that encompass normal operation and abnormal conditions. The effects of HF moderation of the UF(sub 6) in each vessel have been considered for uranium enriched between 2 and 5 wt % (sup 235)U. The results indicate that the nuclearly safe enrichments originally established for the operation of a 10-MW freezer/sublimer, based on a hydrogen-to-uranium moderation ratio of 0.33, are acceptable. If strict moderation control can be demonstrated for hydrogen-to-uranium moderation ratios that are less than 0.33, then the enrichment limits for the 10-MW freezer/sublimer may be increased slightly. The calculations performed also allow safe enrichment limits to be established for a 20-NM freezer/sublimer under moderation control.