Safety analysis of bleed-and-feed operations for Maanshan power plant

Thermal-hydraulic calculations using RELAP5/MOD2 are performed to simulate the responses of the Maanshan pressurized water reactor (PWR) power plant when the secondary heat sink is lost. The loss of heat sink transient of primary interest in this study is the loss of off-site power coincident with a loss-of-all-feedwater event. This transient is selected because it is one of the risk-dominant sequences leading to core damage for the Maanshan PWR power plant. The initiating event for the transient is assumed to be loss of offsite power, which trips the turbine, the reactor coolant pumps, and the main feedwater pumps and generates a signal to scram the reactor. Neither the motor-driven nor the turbine-driven auxiliary feedwater system supply make up water to the steam generator secondary on demand. According to the emergency operation procedures (EOPs), the operator should make every effort to restore the function of the auxiliary feedwater systems. If such efforts cannot succeed in the recovery of the secondary heat sink before the secondary inventory dryout indicated by 6% readings of the wide range water-level measurements, bleed-and-feed (B and F) operations should be executed in time to prevent damage to the integrity of the reactor core. Once the operator decides to take the B and F action, the EOP requires the operator to open at least two out of three pressurizer power-operated relief valves to depressurize the primary system and at the same time, manually, introduce HHSI with at least minimum flow capacity to cool down the reactor core. The major purpose of this study is to identify the effectiveness of the B and F operation in mitigating the consequences of the event