Application of the CFAST zone model to the Fire PSA

Abstract

The integrity of the cables located in the target room is very important in the Fire PSA, because the CDF and CCDP are changed according to the results of a cable integrity that depends on the surrounding gas temperature. The conservative assumptions used in the Fire PSA typically specify that all of the equipment and cables of a room would fail when a fire happens in the room. But the realistic assessment of a fire risk by using a fire simulation tool has become necessary in the Fire PSA as described in the ANS Fire PRA Standard. This paper evaluates the cable integrity of eight pump rooms in the nuclear power plant by using the CFAST zone fire model. The upper layer gas temperature of each room is estimated, and an analysis based on the results of model simulations is used to judge the cable integrity. According to the analysis results, the integrity of the cable located in the upper layer in the pump rooms is maintained without any thermal damage, and the CCDP is reduced to about the half of the original CCDP. A fire safety assessment for dominant pump rooms by using a fire modeling tool is seen capable of evaluating the consequences of a fire scenario, of reducing the uncertainty, and of developing a more realistic Fire PSA model. It is considered that the fire modeling can satisfy the requirements of the ANS Fire PRA standard related to a fire modeling, and improve the quality of the Fire PSA.