Primary coolant drainage level response analysis and optimization of CPR1000 units

Highlights: • The primary drainage process is divided into 4 stages. • The usual drainage operations during primary drainage and the level gauge response tendency for different level measuring zones are described. • Analysis of the cause of level deviation in different stages is given. • The optimization solution for the primary drainage process is proposed in the aspects of deviation criteria setting, drainage process optimization, system design improvement and volume assisted judgement. - Abstract: During primary coolant drainage operation of CPR1000 units in maintenance shutdown mode (MCS), the high deviation of level gauge often directly influences the actual indication of primary coolant inventory, and greatly threatens the monitoring of nuclear fuel uncovering and core safety. According to the inventory arrangement characteristics and drainage level response tendency of the primary circuit, the drainage process is divided into 4 stages, i.e., single cavity drainage zone, dynamic deviation zone, bundle drainage zone and stable consistence zone. With the typical examples of primary coolant drainage of CPR1000 units, the usual drainage operations during primary coolant drainage and the level gauge response tendency for different level measuring zones are described, and analysis of the cause of level deviation in different stages is given on the basis of fluid mechanics principle and level gauge measuring characteristics. Additionally, the optimization solution for the primary coolant drainage process is proposed in the aspects of deviation criteria setting, drainage process optimization, system design improvement and volume assisted judgement.