Novel method of dynamic event tree keeping the number of simulations in risk analysis small

Conducting a risk analysis on nuclear plants using the dynamic event tree (DET) to improve the accuracy of consequence analysis of the system state significantly increases the number of event tree (ET) branches. Several methods have been developed to reduce the number of branches and event sequences of DET. In this study, we developed a new risk analysis method using a relatively small ET to estimate risk considering time changes in the system state of a target system, in a drastic short time. The main features of the proposed method are: to set some headings which cause the same branches on every event sequence outside of the ET for keeping it small; to set the probability distribution function or cumulative distribution function of the time to activating each of safety measures which have the monotonous relation to the risk; and to estimate the maximum and minimum risk values of every event sequence using these probabilistic distributions.The proposed risk analysis method can drastically reduce the time required for consequence analysis, i.e., the number of simulations are drastically reduced. Furthermore, conducting risk analysis by this method is proved to be equivalent to that using a DET in principle.

Automated summary

In this study, a new risk analysis method is proposed to estimate the risk of a target system by using a relatively small event tree, considering the time changes in the system state. The method utilizes probability distribution functions to estimate the maximum and minimum risk values of each event sequence. This approach greatly reduces the time required for risk analysis and is equivalent to using a dynamic event tree in principle.