Design Improvement of the Discharge Proposal Preventing SG Overfill After SGTR in HPR1000 PWR

Base on the result of full scope accident analysis for HPR1000,which is a third generation localized PWR with combination of initiative and passivity, the secondary side pressure of the damaged SG should be controlled by the steam generator blowdown system (TTB) during the retreat process of SGTR accident. In order to response the safety criteria of DBA function, the proposal of post accident discharge pipeline of TTB system should be improved. The part of secondary side fluid are discharged through the pipeline after SGTR, to realize the decrease of water level of damaged SG and preventing SG overfill. The paper suggests a proposal of post accident discharge pipeline for TTB as a mitigation measure of SGTR accident. The discharge flowrate with two phases flow condition in the discharge pipeline must be verified by theoretical calculation to evaluate the mitigation capability of the proposal. Now the performance test has been finished in the first unit of HPR1000, The achievement indicate the discharge capability of the proposal conform to the relative safety criteria for the SGTR accident.