Methodologies For Seismic Safety Evaluation Of Existing Nuclear Installations

Experience shows that an assessment of the seismic capacity of an existing operating facility can be required for a number of reasons, for example identification of potential seismic vulnerabilities based on operating experience events or the periodic safety review programme. This publication covers the seismic safety evaluation programmes to be performed on existing nuclear installations in order to ensure that the required fundamental safety functions are available, with particular attention to the safe shutdown of reactors. It includes lessons learned based on the IAEA Action Plan on Nuclear Safety following the Fukushima Daiichi accident, and updated methodologies for seismic safety evaluation of nuclear installations.

Experience shows that an assessment of the seismic capacity of an existing operating facility can be required for a number of reasons, for example identification of potential seismic vulnerabilities based on operating experience events or the periodic safety review programme. This publication covers the seismic safety evaluation programmes to be performed on existing nuclear installations in order to ensure that the required fundamental safety functions are available, with particular application to the safe shutdown of reactors. It includes lessons learned based on the IAEA Action Plan for Strengthening Nuclear Safety, following the Fukushima accident, and updated methodologies for seismic safety evaluation of nuclear installations.

This Safety Guide provides recommendations on the seismic safety evaluation of nuclear installations. It addresses all types of new and existing nuclear installations. This Safety Guide presents three assessment methodologies: the deterministic approach, generally known as seismic margin assessment (SMA), seismic probabilistic safety assessment (SPSA), and a combination of SMA and SPSA known as ‘probabilistic safety assessment (PSA) based SMA. This Safety Guide provides specific recommendations on applying a performance-based graded approach to the seismic safety evaluation of nuclear installations other than nuclear power plants. It also covers the relation between seismic safety margins and defense-in-depth (DiD) level 3 and level 4. For new nuclear installations, this Safety Guide provides recommendations to assess adequacy of seismic margin to avoid cliff edge effects considering DiD level 3 and level 4. This publication is intended for use by regulatory bodies, operating organizations, and designers of nuclear installations.

This Safety Guide provides recommendations regarding the criteria and methodologies to be used for seismic safety evaluation of existing nuclear installations, including installations whose purpose and associated radiological risks have changed, installations where longer term operation is under consideration and installations where comprehensive seismic safety reassessments have become necessary. Two methodologies are discussed in detail: deterministic seismic margin assessment (SMA) and seismic probabilistic safety assessment (SPSA).

This Safety Guide provides recommendations on the seismic safety evaluation of nuclear installations. It addresses all types of new and existing nuclear installations. This Safety Guide presents three assessment methodologies: the deterministic approach, generally known as seismic margin assessment (SMA), seismic probabilistic safety assessment (SPSA), and a combination of SMA and SPSA known as 'probabilistic safety assessment (PSA) based SMA. This Safety Guide provides specific recommendations on applying a performance-based graded approach to the seismic safety evaluation of nuclear installations other than nuclear power plants. It also covers the relation between seismic safety margins and defense-in-depth (DiD) level 3 and level 4. For new nuclear installations, this Safety Guide provides recommendations to assess adequacy of seismic margin to avoid cliff edge effects considering DiD level 3 and level 4. This publication is intended for use by regulatory bodies, operating organisations, and designers of nuclear installations.

This Safety Guide supersedes the 2010 edition of IAEA Safety Standards Series No. SSG-9. It takes account of recently gained knowledge and practices developed by Member States related to seismic hazards, especially lessons from the Fukushima Daiichi accident. It also addresses concomitant events associated with earthquakes, such as tsunamis. The revision provides a clearer separation between the process for assessing the seismic hazards at a specific nuclear installation site and the process for defining the related basis for design and safety assessment of the nuclear installation. Thus, it bridges gaps and avoids undue overlap of the two processes, which correspond to and are performed at different stages of siting of the nuclear installation.

This report provides guidance for conducting seismic safety evaluation programmes for existing nuclear power plants in a manner consistent with internationally recognized practice. It will be useful for regulatory organizations and other organizations responsible for the implementation of seismic safety evaluation programmes.

The response of a nuclear installation's structure during an earthquake depends on the characteristics of the ground motion, the surrounding soil and the structure itself.