The objective of this workshop is to discuss recent research and the regulatory, utility and industry issues associated with PSHA. The results of PSHA studies undertaken to date in regions with low to moderate seismicity exhibit large areas of uncertainty. Participants in this workshop will therefore discuss how to improve knowledge and reduce uncertainty associated with the lack of strong-motion data and regional-specific attenuation relations. Material presented at the November 2006 specialists' meeting on the seismic probabilistic safety assessment of nuclear facilities will be used to support these discussions.
The deliverables and expected results from the workshop are as follows:
Information obtained as a result of this workshop should provide the key to understanding and interpretating potential differences and discrepancies, from which methods to address them can be proposed.
The NEA held a Specialists' Meeting on Seismic Probabilistic Safety Assessment (SPSA) of Nuclear Facilities, in Jeju, Korea on 6-8 November 2006, at which about 75 specialists from 15 countries participated. One of the main issues raised at the meeting concerned probabilistic safety hazard analyses conducted in areas with low to moderate seismicity.
Results of properly conducted PSHA studies for regions with low to moderate seismicity typically exhibit large uncertainty. One reason is that there are very few strong-motion earthquakes in such regions, so that attenuation relationships must start with those taken from other regions with available strong motions. Analysts typically select regions with analogous tectonics and structure and may also rely on simulations using seismological models based on regional geophysical features.
A proper PSHA in such cases must reflect the uncertainty due to insufficient knowledge of the regional ground motions. This can lead to inconsistencies or to large uncertainties, depending on experts' choices. In such situations, a strategy to improve knowledge and to reduce uncertainty should involve improving strong-motion data collection, and research to improve regional-specific attenuation relations.
The CSNI and its Working Group on Integrity of Components and Structures (IAGE) considered that there was a need to clearly understand how PSHAs were performed in the different NEA member countries with different seismicity, including the handling of epistemic and random uncertainties. Furthermore, recommendations on improvements or on a common basis that could be adopted were found to be very valuable. Consequently, in June 2007 the CSNI approved an activity aimed at understanding and assessing potential differences and discrepancies in PSHA methodologies and results and to propose a method to address them.
The International Atomic Energy Agency has launched an extrabudgetary project (EBP) on the seismic safety of existing nuclear power plants with the participation of various OECD member and non-member countries. The main objective of the EBP is to investigate available methods and practices for resolving current seismic safety issues affecting design and operational aspects of existing nuclear power plants. The results obtained from the proposed EBP will also support in more detail the application of the recommendations of related IAEA safety guides on this subject. The activities of the IAGE subgroup on the seismic behaviour of structures and components and the conclusions of this workshop will provide inputs to the EBP.
Last updated: December 9, 2009