Mechanistic modelling of station blackout accidents for a generic 900MW CANDU plant using the modified SCDAP/RELAP5 code

To quantitatively study the effect of pressure-tube ballooning and sagging on accident progression in CANDU reactors, the previously developed and benchmarked mechanistic channel deformation models have been integrated into RELAP/SCDAPSIM/Mod3.6 as new SCDAP subroutines. In this paper, this modified SCDAP/RELAP5 code is used to simulate the station blackout accidents for a generic 900MW CANDU plant. The main focus of this paper is on the impact of these new CANDU-specific models on the predicted event timings. The sensitivity to decay heat portioning especially the fraction of heat directly deposited to the moderator is also investigated.