Analysis of single failure criteria and operator action effect for different SGTR mitigation strategies of HPR1000

•Single failure criteria and operator mitigation intervention after HPR1000 SGTR were investigated.•VDA stuck open and AFW isolation failure was conservative single failure criteria for two strategies respectively.•Strategy 1 can provide multiple redundant engineered safety features from T-H safety aspect. Establishment of a unified single failure criteria hypothesis and operator action for Steam Generator Tube Rupture (SGTR) accident in Deterministic Safety Analysis (DSA) is not an easy thing due to the complexity of the transient and the various operator actuations. Also, it’s very difficult to finish leakage in 30 min without operator action. In HPR1000 type nuclear power plant design, two kinds of mitigation strategy to cope with SG overfill risk and radioactive release risk can be adopted. In this paper, behavior of HPR1000 under different operator actions and single failure criteria hypothesis for this two mitigation measures were investigated. System response featured by primary pressure, SG level, break mass flow rate, safety injection mass flow rate was obtained to investigate single failure criteria and operator manual intervention effect. For strategy 1, if VDA stuck open was chosen as single failure criteria, primary loop would be over cooled and accumulator safety injection would increase with more drastically fluctuation. In strategy 2, AFW isolation failure was chosen as single failure criteria from SG overfill risk aspect. Affected SG would overfill if AFW isolation failure lasting over 5 min. Combined manual PRZR spray and SIS termination can obtain faster depressurization and leakage termination rate within controllable core boiling and acceptable radioactive release in strategy 1. However, in Strategy 2, manual PRZR spray depressurization and manual SIS termination have little effect on accident mitigation due to VDA comparatively large cooling ability and early intervention. From T-H safety aspect after SGTR, operator manual intervention has more obvious effect in strategy 1 than in strategy 2, which can provide multiple redundant engineered safety features.