Advanced Thermal Hydraulic Simulations For Human Reliability Analysis

Human reliability analysis (HRA) is an important part of Probabilistic Safety Assessment of nuclear power plants. For a number of reasons there is a growing interest in more accurate HRA. There exist several methods to evaluate reliability of operator actions in nuclear power plants. These methods may have different approach to evaluate the reliability but all of them use transient (thermal hydraulic) data to evaluate the reliability of a needed operator action. The quality of the transient data is crucial to perform a realistic HRA. In this work we demonstrate how uncertainties in thermal hydraulic plant response can be merged with the traditional HRA methods. We analyze a Small Break LOCA (break size below 2" diameter) initiating event for a 4 loop Westinghouse type PWR plant for on-power and shutdown states. Safety injection (SI) is necessary to mitigate the core damage. The reliability of the operator action "manual safety injection" was analyzed by an EDF HRA method MERMOS. We used system analysis code MAAP4 coupled to uncertainty propagation software DAKOTA to study the variability of the parameters used in the existing HRA MERMOS analysis as a function ofTH uncertainties. We found that we can significantly reduce the conservatism of initial HRA analysis.