Effects of Break Location and Time Uncertainties in Small-Break and Medium-Break LOCA Sequences With Unavailability of HPSI

The Integrated Safety Assessment (ISA) methodology, developed by the Spanish Nuclear Regulatory Body, consists of a dynamic methodology of probabilistic safety assessment. It has been applied to a thermal-hydraulic analysis of small-break and medium-break LOCA sequences without HPSI, for different break locations, in a three-loop PWR. ISA methodology allows to obtain the damage domain, defined as the region of the space of uncertain parameters where the damage condition is exceeded, for each sequence of interest. In this work, damage domain relates two uncertain parameters (starting time of secondary-side depressurization and break size) to damage exceedance condition (PCT > 1477 K). Several damage domains have been obtained, each one for each break location of interest (cold leg, hot leg, vessel upper head and vessel lower head). Simulations have been performed with TRACE v5.0 patch 1 code, and the results show the capability and convenience of ISA methodology, in order to obtain accurate results that take into account time uncertainties.