Assessment with Coupled Thermo-Mechanical Creep Analysis of Combined CRGT and External Vessel Cooling Efficiency for a BWR

Abstract

In this paper we consider in-vessel stage of a severe core melt accident in a Nordic design Boiling Water Reactor (BWR). Decay-heated pool of corium melt inflicts thermal and mechanical loads on the lower-head vessel wall. Performed thermo-mechanical creep analysis identified two different modes of vessel wall failure: (i) a ‘ballooning’ of the vessel bottom and (ii) a ‘localized creep’ concentrated within the vicinity of the top surface of the melt pool. Next, given the mechanical and thermal loads from the decay-heated melt, external vessel cooling is applied at a specified time. It is found that combined CRGT and external vessel cooling was able to suppress the creep and subsequently prevent vessel wall failure.