Application of Phoenix Human Reliability Analysis Methodology to Model External Operation with FLEX Strategies Consideration

This paper examines the application of the Phoenix Human Reliability Analysis (HRA) methodology to model external operations in nuclear power plants during Beyond-Design-Basis External Events (BDBEEs), incorporating Diverse and Flexible Coping Strategies (FLEX). BDBEEs, such as those observed during the Fukushima disaster, challenge conventional safety systems and HRA methodologies due to extreme conditions like seismic events and station blackouts (SBOs). FLEX strategies, which leverage portable equipment and multi-phase operational protocols, are critical in addressing these scenarios.
The Phoenix HRA methodology integrates Event Sequence Diagrams (ESDs), Fault Trees (FTs), and Bayesian Belief Networks (BBNs) to quantify Human Error Probabilities (HEPs) and model operator performance. This paper conducts a case study of an SBO caused by an earthquake. First, the operation of mobile power supply vehicles, a key FLEX equipment, is modeled alongside conventional SBO recovery operations. Second, critical tasks, failure modes, and performance-influencing factors (PIFs) are identified. Third, the methodology quantifies HEPs for securing FLEX equipment and evaluates overall recovery operations under environmental challenges such as road inaccessibility.
Quantitative results demonstrate the impact of environmental factors on HEPs, providing insights to enhance human reliability during FLEX operations. This study advances human-system interaction modeling under extreme scenarios and offers practical guidance for integrating FLEX strategies into the Phoenix HRA methodology. The findings aim to support the HRA community in addressing the unique challenges posed by BDBEEs.

Keywords: Human reliability analysis, FLEX Strategies, BDBEEs, Station blackout, Phoenix HRA.