Simulation on Reactor Coolant System Pump Coastdown Transient of PWR and Test Criteria Optimization

The Reactor Coolant System (RCP) pump coastdown test is an important part of RCP pump performance test before core loading. This test requires to verify the decrease in primary flowrate following a synchronized trip of all RCP pumps meets the safety analysis requirements. The test criteria, which includes rapid decrease curve and slow decrease curve, are determined according to the fault analysis of Loss Of Off-site Power (LOOP) event. Research on the criteria of RCP pump coastdown test is conducted by performing the analysis on pump inertia and thermal-hydraulic characteristics on the very beginning of idling transient including LOOP, partial loss of core coolant flow and overpressure transient. The research results show that the influence on core safety and overpressure risk is limited if the first several seconds of test criteria is released. The optimization of RCP pump coastdown test criteria helps to mitigate the problem of small upper and lower limit space of the early stage criterion of idle transient, which is beneficial to the on-site test performing. The assessment of RCP pump coastdown test criteria in this research provides theoretical and statistical supporting for the following optimization of test criteria and safety analysis.