HRA-Methodology Comparison on a Practical, Realistic-NPP Model Implementation: Sensitivity Analysis on a Plant-Level Risk Contribution

This paper addresses the performance of human reliability analysis (HRA) as part of the development of a new plant-specific, full-scope industrial-scale L1/L2 PSA-model at the NPP Goesgen-Däniken (KKG), Switzerland. The focus of the paper is aimed at conducting sensitivity analysis on designated plant-level risk metric contribution (delta CDF) given two different HRA-methods for modelling the cognitive part of selected post-initiator operator actions (OA) - the Technique for Human Error Rate Prediction (THERP) and the Human Cognitive Reliability/Operator Reliability Experiments Method (HCR/ORE) method.
KKG, together with their supplier Framatome GmbH, embarked on the substantially thorough project - PSASPECTRUM - of migrating KKG's existing PSA model from Riskman\circledR to RiskSpectrum\circledR environment. The conduction of an updated, plant-specific HRA using the RiskSpectrum\circledR HRA Tool as well as a relatively new RiskSpectrum\circledR feature - the Conditional Quantification tool - is one constituent part of this project. The preferred HRA-method, used for the internal events analysis, is the THERP practical method of predicting human reliability - both for the cognitive as well as for the execution part of the human error probability (HEP). Although this method is well established and being applied worldwide, it has its strengths and limitation. Especially, the use of simple, generic time reliability correlation (TRC) for addressing diagnosis errors is an over-simplification for addressing cognitive causes and failure rates for diagnosis errors when used, by itself. On the other hand, the HCR/ORE method would ideally use plant specific TRCs based on simulator measurement but may rely on expert judgement or generic data to derive the TRCs, hence making use of empirical data to support the HRA is a strength for this method. Once the relevant parameters have been identified, the derivation of the HEP using the TRC is straightforward and traceable.
Selected post-initiator OAs are used as basis for this comparative study. The results of the sensitivity analysis on the plant-level risk contributions are studied and discussed.

Keywords: PSA, HRA, Event sequence diagrams, RiskSpectrum, HCR, OA, THERP.