Tsunami flooding analysis graded-approach framework for tsunami probabilistic risk assessment

A tsunami probabilistic risk assessment (PRA) is an effective tool that reviews the safety margins for beyond-design-basis events and strengthens the application of the defense-in-depth philosophy. It is recognized that tsunami hazard levels, assumed margins, and assumed risks differ significantly between sites. This paper proposes a framework of risk-based graded approach for a tsunami PRA. Since the predominant sources of uncertainties in an overall tsunami PRA may stem from tsunami hazard analysis, the framework selects a methodology for incorporating the uncertainties of tsunami hazard analysis in subsequent analyses, by grade. The framework provides five grades depending on the level of detail in the assessment. This graded approach framework was experimentally applied to the tsunami PRA for a virtual nuclear power station.