Application of STPA in Probabilistic Risk Assessment of the Loviisa Nuclear Power Plant

Probabilistic risk assessment (PRA) of nuclear power plants requires the use of hazard analysis methods. System-theoretic process analysis (STPA) is a relatively new hazard analysis method based on systems-theoretic accident model and processes (STAMP) causality model. This paper studies the use of STPA in the context of probabilistic risk assessment. This is achieved by conducting a case study of the refueling pool backup cooling system of the Loviisa Nuclear Power Plant in Finland. Results of the case study are compared with an existing risk model of the system. The results of the study indicate that STPA is a promising method for hazard analysis. It can identify all hazard scenarios that were previously identified using multiple techniques, such as failure mode and effect analysis (FMEA) and human reliability analysis (HRA). In addition, the method has been found to be useful in communicating results within a multidisciplinary team of subject-matter experts. However, the incorporation of a new method into the well-established PRA methodology requires further research.

Keywords: System-theoretic process analysis, Probabilistic risk assessment, Hazard analysis, Spent fuel pool, Nuclear safety.