RELAP5 Analysis of Integral Test of the Loss-of-RHR Event During the Mid-Loop Operation

Abstract

We are developing a statistical safety evaluation method using the RELAP5/MOD3.2 code for the loss-of-RHR (Residual Heat Removal) event during the mid-loop operation. To confirm the code prediction performance for gravity injection which is a one of the mitigation measures for this event, the Bethsy 6.9a test was analyzed using RELAP5/MOD3.2. In the analytical results, water mass flow rate into the pressurizer in the early period of the transient event was overpredicted. But water mass flow rate into the pressurizer was able to be decreased by artificially giving the circulation flow between core and the core bypass region.