Secondary-Side Depressurization during PWR Cold-Leg Small Break LOCAs Based on ROSA-V/LSTF Experiments and Analyses

Abstract

The effectiveness of an operator-initiated steam generator (SG) secondary-side depressurization on the core cooling performance during small-break loss 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 Facility (LSTF) and analyses with the RELAP5/Mod3 code. The sensitivity of the core minimum liquid level and peak cladding temperature (PCT) to the secondary-side depressurization rate and the initiation time of the depressurization 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 cold leg cross-sectional area. The conditions which the depressurization rate and the initiation time should satisfy to limit the maximum PCT are derived.