An integrated modeling approach for event sequence development in multi-unit probabilistic risk assessment

• A general MUPRA framework is developed based on HTR-PM.
• An Integrated Modeling approach for event sequence modeling is proposed.
• The integrated sequence modeling approach is illustrated in detail with a LOOP case study.

To obtain a complete site risk profile for multi-unit nuclear power plants (NPPs), the existing single-unit probabilistic risk assessment (PRA) model needs to be upgraded to address both intra-unit and inter-unit dependencies. The high temperature gas cooled reactor-pebble bed module (HTR-PM), with two reactor-steam generator modules and one shared steam turbine-generator set, is a ready-in-hand pilot for multi-unit PRA (MUPRA) studies. In this paper, a general framework for MUPRA is firstly developed based on HTR-PM PRA methodology. An Integrated Modeling (IM) approach is then proposed for multi-unit event sequence modeling. The approach is discussed in detail and illustrated with a loss of offsite power (LOOP) case study. Also, the limitations of the current analysis are put forward for open discussion.