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NKS Programme Area:NKS-R
Research Area:Risk analysis
Report Number:NKS-153
Report Title:Probabilistic Safety Goals. Phase 1 ? Status and Experiences in Sweden and Finland
Activity Acronym:Safety Goals
Authors:Jan-Erik Holmberg, Michael Knochenhauer
Abstract:The outcome of a probabilistic safety assessment (PSA) for a nuclear power plant is a combination of qualitative and quantitative results. Quantitative results are typically presented as the Core Damage Frequency (CDF) and as the frequency of an unacceptable radioactive release. In order to judge the acceptability of PSA results, criteria for the interpretation of results and the assessment of their acceptability need to be defined. Ultimately, the goals are intended to define an acceptable level of risk from the operation of a nuclear facility. However, safety goals usually have a dual function, i.e., they define an acceptable safety level, but they also have a wider and more general use as decision criteria. The exact levels of the safety goals differ between organisations and between different countries. There are also differences in the definition of the safety goal, and in the formal status of the goals, i.e., whether they are mandatory or not. In this first phase of the project, the aim has been on providing a clear description of the issue of probabilistic safety goals for nuclear power plants, to define and describe important concepts related to the definition and application of safety goals, and to describe experiences in Finland and Sweden. Based on a series of interviews and on literature reviews as well as on a limited international over-view, the project has described the history and current status of safety goals in Sweden and Finland, and elaborated on a number of issues, including the following: • The status of the safety goals in view of the fact that they have been exceeded for much of the time they have been in use, as well as the possible implications of these exceedances. • Safety goals as informal or mandatory limits. • Strategies for handling violations of safety goals, including various graded approaches, such as ALARP (As Low As Reasonably Practicable). • Relation between safety goals defined on different levels, e.g., for core damage and for unacceptable release. A number of important issues have been identified for continued studies in the next project phase. The results from the project can be used as a platform for discussions at the utilities on how to define and use quantitative safety goals. The results can also be used by safety authorities as a reference for risk-informed regulation. The outcome can have an impact on the requirements on PSA, e.g., regarding quality, scope, level of detail, and documentation. Finally, the results can be expected to support on-going activities concerning risk-informed applications.
Keywords:Safety Goals; PSA; Safety Targets; ALARP; Decision criteria; Risk informed decision making
Publication date:01 Mar 2007
ISBN:ISBN: 978-87-7893-216-7
Number of downloads:1667
Download:pdf NKS-153.pdf

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