Model, Method, and Data Issues in Human Reliability Analysis (HRA)
Authors: Ujita Hiroshi 
Published: June 2024

According to the results of the HRA comparison study by USNRC and Halden, the evaluation results are significantly different when comparing the method calculations alone, comparing the experiments alone, and further comparing the method and experiment trends [1]. It is considered that human correspondence characteristics have a large context dependency in plant behavior and operator cognitive mechanism variety, however they are not properly captured. It is said that experiments are required to understand cognitive processes and contexts, and models are required to develop evaluation methods that take cognitive mechanisms and context dependencies into consideration. These data and conclusions, which must be true, are still startling facts. Here, we will examine three comparative studies1.Cognitive Process Analysis Experiment (in House): Joint study of Japanese BWR utilities and vendors. When we estimate Human Error Probabilities including Time Reliability Correlation, we must remind its dependency of accident scenario, culture, crew type, etc. Some insights are useful for HRA method consideration [2].2.Three HRA Model Comparison (in House): Two representative HFEs from two types of reactors in Japan, Pressurized Water Reactor (PWR) and Boiling Water Reactor (BWR), were chosen [3]. HRA method to be used are THERP method, Electric Power Research Institute (EPRI) method, and IDHEAS method [4-6] For both PWR and BWR examples, different HEPs were obtained by different HRA methods also. The scenario analysis, qualitative analysis, and task analysis must be reflected into HEPs.3.USNRC & Halden Model & Experiment Comparison: The model is judged to be underestimated compared to the experiment in one accident scenario and another case, to be overestimated. The dispersion of the calculation results by the method and experimental results are close to three digits [1, 7]. The importance of qualitative scenario analysis was widely recognized, and it became clear that the level of analysis depends largely on the knowledge and experience of analysts. This is because the lack of clear guidance in the HRA methodology has led to discrepancies in the analyst's approach [7].References[1] U.S. Nuclear Regulatory Commission, The International HRA Empirical Study, Lessons Learned from Comparing HRA Methods Predictions to HAMMLAB Simulator Data, NUREG-2127, August 2014. [2] Ujita, H., Kawano, R., Yoshimura, S., An Approach for Evaluating Expert Performance in Emergency Situations, Reliability Engineering and Systems Safety, Vol.47, pp.163- 173, 1995.[3] Hiroshi Ujita, Yoshihiro Ide, ASRAM2020, Asian Symposium on Risk Assessment and Management 2020 Online Virtual Conference, November 30 - December 2, Ideal Way of Method and Data Issues in Human Reliability Analysis (HRA) (1) Extraction of HRA Method Issues by Comparison Analysis & (2) Extraction of Method and Data Issues from Research Survey.[4] A. D. Swain, H. E. Guttmann, “Handbook of Human Reliability Analysis with Emphasis on Nuclear Power Plant Applications Final Report”, NUREG/CR-1278, August 1983. [5] S. Lewis, et. al., “EPRI/NRC-RES Fire Human Reliability Analysis Guidelines Final Report”, NUREG-1921, July 2012. [6] USNRC, EPRI, “An Integrated Human Event Analysis System (IDHEAS) for Nuclear Power Plant Internal Events At-Power Application”, NUREG-2199, March 2017. [7] Taylor, Claire. Improving scenario analysis for HRA. Probabilistic Safety Assessment and Management, PSAM. 2012.