Abstract
The purpose of this paper is to present an assessment of the BWR MARK III steel containment under severe accident conditions. The accident follows a station black-out with the unavailability of the emergency cooling system, core melting and RPV rupture. The performance of the containment vessel has been evaluated with and without a possible flaw in the most stressed regions of the shell. The accident conditions assumed in the analysis derive from the rise of the March 3 model. The response of the containment to those conditions has been evaluated by means of the elastic-plastic finite-element computer code MENTAT-MARC with large displacements. The flow-stress is locally achieved under a differential pressure of about two times the calculated severe accident maximum pressure and about eight times the design LOCA pressure. It appears that the BWR steel-containment vessel of the MARK III type can withstand high loads deriving from a severe accident even if the presence of a flaw is assumed. Penetrations represent the most limiting areas which may lead to a leakage well before instability.
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