Sensitivity studies for the station blackout accident with crash-cooldown at a generic 900MW CANDU reactor

In the early stage of a Station Blackout (SBO) in a CANDU reactor the operators will initiate crash-cooldown by opening the main steam safety valves (MSSVs) to depressurize the secondary side and allow water supply to the steam generators (SGs) thereby extending natural circulation on the primary side. This work examines the effectiveness of SGs heat removal after crash-cooldown and that of several water make-up options for a generic 900MW CANDU using RELAP5/MOD3.3. Severalcases on SBOsequence with/without crash-cooldown and with different water make-up options are simulated. The sensitivities to various parameters such as the nodalization/grouping of fuel channels/U-tubes, Counter Current Flow Limitation (CCFL) correlations, the timings of crash-cooldown and pressurizer isolation are investigated.