Impact Analysis of Airlock Seal Fragility From a Psa Perspective on Reactor Building Overpressure Protection at Wolsong

Abstract

According to the Level-2 probabilistic safety analysis (PSA), the probability of a late breakdown of a reactor building (RB) has mainly changed depending on the weakness in overpressure protection capability of the RB. A review of the ultimate pressure capacity of containment penetrations and airlocks for the Wolsong station identified that an airlock door blow-by may occur at a lower pressure than the cracking pressure through a concrete wall. Specifically, the pneumatic seal area for mechanical door seals is highlighted as the primary weakness of the RB pressure boundary. This paper shows the change characteristics in containment failure modes and their probabilities under severe accidents due to the airlock seal fragility. In the previous analyses, the RB damage probability was only 5% at the RB pressure of 38 psig, but the failure probability based on the new fragility curve increased to 50%, which has a negative impact on existing PSA results, such as an increase in failure frequency at a late timing before calandria vessel failure.