Criticality Safety Evaluation of Shutdown Diffusion Cascade Coolers

Abstract

A criticality safety study of diffusion cascade coolers in a shutdown state is presented. The coolers represent six typical cascade coolers at a gaseous diffusion plant with accumulated deposits of UO₂F₂. The study involves k_eff calculations for the coolers with various distributions of UO₂F₂, which are assumed as part of several hypothetical accident scenarios. The results show that at least two independent failures must occur in order to have a criticality. Additionally, the distributions chosen represent the upper bounds for k_eff. Individual results show that the k_eff values for the cascade coolers designed for 80 and 97% enriched UF₆ with deposit amounts <2.409 and 2.185 kg, respectively, will not exceed 0.9 for the accident scenarios modeled. All other coolers require shell-side flooding with H₂O in order to cause a criticality, which is possible only if two or more independent failures occur.