Approach to assess fire risk for nuclear power plants

The results of the first fire risk assessments on an international level have shown that fires are one major contributor to the risk of a nuclear power plant depending on the plant specific fire protection concept. Therefore, fire risk assessment has today become an integral part of the probabilistic safety assessment of nuclear power plants in addition to deterministic analyses. Based on existing guidance documents a state-ofthe-art approach for performing probabilistic fire risk assessment has also been developed in Germany. This approach has been exemplarily and completely applied to a German nuclear power plant with boiling water reactor for the full power states PSA. The general approach outlines the steps necessary for performing fire risk assessment and the prerequisites for a sound and traceable database

Methods to assess effects of cable failures caused by fire

It is state-of-the-art that a Level 1 PSA also includes a fire PSA for all plant operational states. In performing Fire PSA not only the malfunction of the components has to be assessed but also all supply systems and cables have to be traced for a given component. In the past it was assumed in the case of a fire in a compartment that all components and cables in that compartment are not functional anymore. However, this is in many cases a too conservative approach and could lead to overestimated fire induced core damage frequencies. Therefore, a method is necessary to assess in a more realistic manner the effects of cables failures caused by fire. Such a procedure requires a sound data base on equipment, list of cables and their properties as well as cable routing. Two methods are described which are currently developed. One of them is a cable failure mode and effect analysis which is easier to apply in practice