Summary on integrated deterministic and probabilistic safety assessment development and case studies

Integrated deterministic and probabilistic safety assessment (IDPSA) combines two methodologies to support risk-informed decision making in nuclear power plant safety considerations. In IDPSA applications, information on physical phenomena is obtained from deterministic analyses, and probabilistic risk models are constructed based on that information. In this report, IDPSA is applied to the analysis of severe nuclear power plant accidents and level 2 probabilistic risk assessment (PRA). Level 2 PRA analyses how large and probable are radioactive releases after core damage. Severe accidents involve complex physical phenomena of which information can be best gathered by performing deterministic analyses. This report summarises case studies conducted on passive reactor cooling systems, hydrogen recombinators and explosions, steam explosions, and the coolability of an ex-vessel debris. These systems and phenomena, except passive reactor cooling system, were modelled in level 2 PRA based on supporting accident progression simulations. The studies provided useful insight on the phenomena and their modelling in level 2 PRA