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NKS Programme Area:NKS-R
Research Area:Risk analysis
Report Number:NKS-171
Report Title:NPSAG/NKS: Interpretation and Evaluation of the Technical Specification Criteria
Activity Acronym:RiskEval
Authors:Ola Bäckström, Anna Häggström, Kaisa Simola
Abstract:The use of risk-informed methods has been discussed since the late 1980s in the Nordic countries. However, at that time the industry and authorities were not ready for the use of these methods and the use of them have been limited. The common understanding right now is that the industry and authorities are ready for adoption of risk-informed strategies, and the use of risk informed methods in daily operation at the nuclear power plants (NPPs) as well as for long term evaluation and definition of rules and regulations is increasing. The authorities are strengthening the rules and regulations with regard to redundancy and diversification in the safety systems. There are several ongoing projects at the NPPs, such as modernization, power upgrade etc. These projects will require modification of the Technical Specifications (TS). The requirements on a risk analysis to verify exceptions will be a natural part of the TS update. To summarize; there are both activities and trends at the plants that will result in TS changes (modernizations, increase of electrical power, risk informed strategies). At the same time, authorities are increasing the requirements on risk informed evaluation of the TS. TS evaluation from a risk point of view raises several questions: - How shall the TS conditions be evaluated? - What aspects shall be taken into consideration? - Can a prolonged/shortened surveillance test interval (STI) or allowed outage time (AOT) affect the experienced importance of the equipment? -What do the conditions in the TS with regard to AOT really represent? Are they conditions that shall be used when spare part storage and/or maintenance strategies are developed or do they represent how a real situation (unavailable component) shall be managed? To form an idea of the opinion on these questions phase 1 of the project is based on a literature study and interviews with persons at the Swedish and Finnish utilities and authorities. 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 STI and AOT analyses respectively are presented. Together this serves as a background for the recommendations for phase 2 of the project.
Keywords:Risk Informed Decision Making; Technical Specifications; TS Evaluation
Publication date:01 Jul 2008
ISBN:ISBN: 978-87-7893-237-2
Number of downloads:1332
Download:pdf NKS-171.pdf
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