NPSAG/NKS: Interpretation and evaluation of the technical specification criteria

The use of risk informed methods in daily operation at nuclear power plants as well as for long term evaluation and definition of rules and regulations is increasing. Risk informed methods have been applied on a case by case basis during the past few years, but it is expected that these methods will be applied in a quite different manner in the coming years. The report summarises a literature study and interviews with persons at the Swedish and Finnish utilities and authorities on risk-informed approaches to evaluate Technical Specifications (TS) at nuclear power plants. A short background to the current TS is also given and the role of PSA in the TS evaluation process is briefly discussed. Methods, discussions and comments with regard to surveillance test interval and allowed outage time analyses respectively are presented.