The analysis of fire ignition frequency calculation for small modular light water reactors

With the release of reports such as NUREG/CR-6850, the calculation of ignition frequency concerning general large-scale Pressurized Water Reactors (PWRs) has matured. However, there is currently a lack of methods for calculating the ignition frequency in the case of Small Modular Light Water Reactors (SMRs). By studying the calculation of ignition frequency reported in NUREG/CR-6850, we propose a method for calculating the ignition frequency in SMRs, which is based on the generic ignition frequency at the component level. The problem of counting ignition sources is discussed in detail, and we determine the component-level ignition frequencies due to different types of ignition sources. In order to improve the calculation of the ignition frequency in SMRs, this paper provides two methods, which are based on the prior lognormal distribution and the prior Gamma distribution, respectively, for updating ignition frequency. We also consider the effect of the accumulation of fire events on the posterior mean determined by both methods. In this paper, we suggest that the method based on the prior lognormal distribution should be used in the initial stage of updates of ignition frequency. As data for plant-specific events accumulate, the approach based on the prior Gamma distribution should be considered.