The Application of Time-Related Event Tree During the HTR-PM Design Phase

The Probabilistic Safety Assessment of HTR-PM, the demonstration nuclear power plant of High-Temperature Gas-Cooled Reactor in P.R. China, started in 2005, in order to offer supplementary support to the reactor design. Four critical initiating events families such as water-ingress, primary depressurization, loss of primary cooling etc. have been selected for the accident sequence analysis during the preliminary reactor design phase. Due to the special characteristics of doing PSA in the new reactor design phase, such as insufficient information, unavoidable iterations, complicated communications among multiple specialties and so on, efficient measures shall be developed to further the projects. A time-related Event Tree approach presented in this paper is one of them. Compared with ordinary event tree, the time-related event tree intends to illustrate not only the accident propagation processes, but also the key time points when safety systems, signals and operator actions are challenged and the durations. It seems to be a good bridge between designers and PSA engineers for the consistent understanding and more efficient information exchanging.