Dynamic approach for scenario quantification of combined event of internal flooding and earthquake in nuclear power plant

The study aims to develop probabilistic risk assessment (PRA) methodology for the combination event of an earthquake and internal flooding. The seismic impact on the safety-related systems is taken into account by considering seismic fragility under various ground accelerations and implemented in a fault tree to evaluate failure probability of safety-related equipment. The internal flooding impact is considered by evaluating the probability of loss of safety function based on a calculation of water level in rooms where safety equipment is installed. The water level in each room is calculated by a flood propagation model. Based on the Markov process, the probability of loss of safety function in next time step is calculated based on current water level. Monte Carlo method is used to evaluate uncertainties in initial leak rate, and broken area of the water barrier. As a result, combined event of seismic and internal flooding is evaluated. A new methodology is a useful approach for quantification of interactive accident scenarios which consider event progression. (author)