INTEGRATION OF AFIRE INITIATING EVENT DECISION TREE INTO A FIRE PRA

摘要

Enhancements in the Fire PRA modeling (due to MSO scenarios etc.) identify additional fire induced initiating events that would result in more challenging initiating event sequences in comparison to the standard turbine trip sequences. This paper explores how to utilize a fire initiating event decision tree (FIEDT) in a Fire PRA analysis. The initiating events modeled in the FIEDT are arranged so that the more detrimental fire induced initiating event sequence nodes (i.e. ISLOCA, LLOCA) are reached prior to the least harmful sequence nodes (turbine trip). Additionally, this paper explores an approach of using the complement initiating event nodal values in scenario-specific situations. This proves to be beneficial as the fire induced initiating event nodal values can be non-minimal (closer to 1.0 compared to the result of the random failure events). This complement approach uses either FRANX or PRAQuant to calculate each fire scenario's conditional probability for each of the fire induced initiating event logics modeled in the FIEDT. For a given fire scenario that proves to have a high conditional probability for a given fire induced initiating event (LLOCA initiator for example), the complement conditional probability value is applied to the fire induced initiating events reached later in the FIEDT for the same fire scenario (turbine trip initiator).