SAS4A analysis of unprotected loss of flow accidents in a metal fuel reactor

摘要

This paper discusses the SAS4A code system which is used to analyze the core behavior under beyond-design-base transient conditions for various Advanced Liquid Metal Reactor (ALMR) designs. The results of these analyses provide help in assessing the outcomes of various accident sequences, and provide guidance for future experimental needs and mathematical model development. This paper describes the thermal-hydraulic and neutronic events that occur in a low void worth metal fuel core (2) during a very rapid unprotected Loss of Flow (LOF) accident, with a flow decay half time t(sub 1/2) = 0.3s. This LOF was selected because it leads to fuel pin failure and subsequent fuel relocation. The only mechanistic initiator that can lead to such a rapid LOF is, possibly, a severe earthquake. For slower LOFs pin failure and fuel relocation do not occur, as negative reactivity from other core feedback effects has enough time to counteract the positive reactivity introduced by the early sodium boiling.