Advanced design of PWR through probabilistic safety analysis

The KWU NPP is designed on the basis of deterministic oriented criteria, requirements and on a licensing procedure with a well-established set of rules, e.g. safety criteria by the German Ministry of Interior, guidelines of the German Reactor Safety Commission. Safety is achieved by carefulness of plant design, quality assurance, operation and surveillance of plant. The assurance of normal operating conditions and the prevention of incidents through control result in extraordinary plant load factors of KWU-PWR. With this background there would be no need for probabilistic analysis in licensing or for a fundamental review of the design. Nevertheless PSA are very useful to demonstrate and quantify safety margins of engineered safety features. Furthermore PSA can be used to check the existing design with respect to a balanced concept or any possibility for streamlining the concept. For this purpose a systematic reliability analysis of each active or passive function has to be performed. Then the result of these analyses have to be evaluated in connection with those incidents and accidents which influence the design. This procedure is illustrated at the following examples: accumulator injection, steam generator feeding, and reactor building design