Systematic selection method for probabilistic fire analyses. Final report

A PSA for the plant internal fire hazard is carried out in several steps. First step is a selection process ('screening'). The screening can be performed qualitatively or quantitatively or by means of a combined qualitative and quantitative approach as developed by GRS in the frame of a research project. During the revision of the PSA guidance documents it turned out that the GRS screening approach needs further automation and developments, in particular regarding the systems specific part to reduce the effects of expert decisions as far as possible. Therefore, the combined approach has been further improved. The improved screening approach as outlined in this report provides estimated values for damage frequencies. By this means, it is possible to identify relevant fire scenarios and to apply the cut-off criteria defined in the PSA for fire analyses. The approach corresponds as far as possible to the existing PSA models. The event and fault trees of these models describe in detail the correlation between component failures and the occurrence of damage states. The screening process combines fire and compartment specific information for estimating fire induced component failures with the PSA models for determining damage frequencies. The screening process is carried out in three steps starting with an as far as possible automated fire specific screening based on a comprehensive plant specific information collection. In a second step, qualitative PSA specific information is considered. The rooms and/or plant areas not screened out and ranked by fire specific ranking criteria are subject to a quantitative systems specific selection. (orig.)