Comparison between RELAP/SCDAPSIM/MOD3.4 and MOD3.6+ in Simulating a CANDU6 SBO

Romania, as a country that currently operates two CANDU 6 (CANada Deuterium Uranium reactor) units, has extensively investigated the severe accident progression, including studies on the severe accident management measures to be accounted in order to limit the core damage. Most analyses of CANDU 6 SA were performed using RELAP / SCDAPSIM / MOD3.4 a thermalhydraulic and nuclear safety analysis code which was initially designed for Light Water Reactors. A new version of the code has been developed, MOD3.6+, which includes mechanistic models specific to CANDU reactors core degradation under severe accident conditions. In this paper we introduce the best-estimate analysis results from the SA accident analysis for a CANDU 6 reactor using MOD3.6+ with the mechanistic models for fuel channel failure and core disassembly in comparison with the previous results from conservative analyses using conservative assumptions for the phenomena during a Station BlackOut accident.