Application of NUREG/CR-6850 to the fire risk quantification of a High Temperature Gas-Cooled Reactor

NUREG/CR-6850 provides a universal process to conduct fire Probabilistic Risk Analyses (PRAs) of Nuclear Power Plants (NPPs). A three-step procedure among the report's findings is proposed for quantifying fire-induced risks of potentially risk-significant fire scenarios: i) Estimation of the compartment fire ignition frequencies associated with the fire ignition sources; ii) Estimation of the frequency of occurrence of the compartment fire scenario; and iii) Quantification of the fire PRA model induced by the fire scenario, to generate the fire risk results. The procedure supported by operational records of traditional Light-Water Reactors (LWRs) also can be applied to the new-type reactors, provided that the challenges of the new imbedded features and equipment can be legitimately tackled. In this study, three key issues manifested in the applications of the three-step fire risk quantification procedure to new-type reactors are discussed, namely, ignition frequency estimating approaches of the new-reactor-specific fire compartments in i), applicability analysis of the fire modeling tools and uncertainty treatment in ii), and updating fire PRA models in iii). The feasibility of the analysis is illustrated to a switchgear room fire scenario of the first demonstration NPP of High Temperature Gas-Cooled Reactor (HTR-PM) in China.