Application of FIRE PSA in case of modifications for post-operational shutdown states

This contribution presents results of recent research and development activities in the field of Hazards PSA (HPSA). The reactor accidents at Fukushima Dai-ichi in March 2011 gave reason and indications for checking the risk assessment approach for internal and external hazards as currently described in the German PSA Guideline and its supplementary technical documents. A standardized approach for performing a comprehensive HPSA has been developed emphasizing the complete consideration of all potential failure dependencies induced by hazards. The systematic extension of the given plant model of Level 1 PSA is the real crux of the new HPSA approach. The extension is carried out for each hazard H using the corresponding Hazard Equipment List (H-EL) and the corresponding Hazard Dependency List (H-DL). Parts of the approach have already been tested. In the paper a successful application for the plant internal hazard fire is presented. A German licensee plans a system modification of the spent fuel pool cooling, therefore a Level 1 PSA has been carried out to compare the fuel damage frequencies for the existing and the modified version. It is described how the systematic (and partly automatic) extension of the fault trees is performed using the Fire Equipment List (F-EL). The F-EL contains a compartment assignment for all relevant components and cables. The probability of a room failure by fire must be determined for any mapped room. This is the conditional probability that the components and cables within the room are destroyed by the fire. (orig.)