Human reliability evaluation method covering operator action timing for dynamic probabilistic safety assessment

Dynamic probabilistic safety assessment (PSA) has been introduced due to the limitations of static-based PSA such as the difficulty to analyze dynamic sequences caused by stochastic random events. While various research has been performed to achieve this integration, quantifying risk in dynamic PSA is still challenging because operator response models that can provide a branch probability according to the timing of operator action in dynamic scenarios have not yet been addressed. Existing human reliability analysis (HRA) models only consider the time given to operators for actions insofar as it can impact the failure probabilities of the human actions, despite the timing of the actions being a vital element of HRA for dynamic scenarios. This paper proposes an operator action timing-based human reliability evaluation method for dynamic PSA to evaluate the distribution of operator action timing. The method covers operator action timings with a model that convolutes two time distribution functions to provide the probability of the success or failure of an operator action. To demonstrate the practicality of the proposed method and its effectiveness, a case study and uncertainty analysis for a small break loss of coolant accident with two operator tasks were conducted.