An Evaluation of Operator's Action Time for Core Cooling Recovery Operation in a loss of Component Cooling Water

Operator's action time in the success criteria of a Probabilistic Safety Assessment (PSA) is generally derived from Thermal-Hydraulic (T-H) analyses. It serves as a type of input in Human Reliability Analyses (HRA) which eventually impacts PSA. For the successful implementation of risk-informed application, more realistic T-H analyses in PSA are necessary. In existing PSA of KHNP, T-H analyses are conducted using the MAAP4 code. However, the results of MAAP4 analysis are too conservative to perform a realistic PSA, because it is simplified simulation code. Also, ASME PRA standard recommends the use of best-estimate code to improve PSA quality. The MARS code is more useful for realistic and plant specific analyses, as it provides best-estimate results for the thermal hydraulic behavior of a Nuclear Steam Supply System (NSSS). In this paper, under a loss of component cooling water, equivalent break size depending on four cases of RCP leakage rate are calculated and corresponding operator's action times to mitigate accidents are evaluated. Consequently, the Human Error Probability (HEP) and Core Damage Frequency (CDF) are compared with previous results