Coolability Evaluation of the Debris Bed on Core Catcher in a Sodium-Cooled Fast Reactor With a Whole Vessel Model

This paper describes coolability evaluations of a debris bed with a variety of decay heat removal system (DHRS) operating conditions with a whole vessel model assuming fuel accumulation on the core catcher in a short term. The DHRS consists of two circuits of direct reactor auxiliary cooling system and one circuit of reactor vessel auxiliary cooling system. The evaluation tool is a one-dimensional plant dynamics code, Super-COPD, with a debris bed module. The coolability evaluations have indicated that the current core catcher design secures sufficient natural circulation flows around the core catcher to ensure the debris bed cooling when at least one circuit of DHRS was activated. Sensitivity analyses under a pessimistic condition have shown that the debris bed is coolable with at least one circuit of improved DHRS even if most fuel accumulates on the core catcher in a short term.