Secondary-side depressurization during PWR cold-leg small break LOCAs based on ROSA-V/LSTF experiments and analyses

The effectiveness of an operator-initiated steam generator (SG) secondary-s ide depressurization on the core cooling performance during small-break los s of coolant accidents (SBLOCAs) in a pressurized water reactor (PWR) with total failure of the high pressure injection (HPI) systems is studied. The study is based on experiments conducted in the ROSA-V Large Scale Test Faci lity (LSTF) and analyses with the RELAP5/Mod3 code. The sensitivity of the core minimum liquid level and peak cladding temperature (PCT) to the second ary side depressurization rate and the initiation time of the depressurizat ion is evaluated analytically for various break sizes. It is shown that the PCT takes a maximum value for break areas between 1.0% and 1.5% of the col d leg cross-sectional area. The conditions which the depressurization rate and the initiation time should satisfy to limit the maximum PCT are derived .