DS522 - Evaluation of Seismic Safety for Nuclear Installations

The revised Safety Guide will provide guidance to re-evaluate seismic safety for existing nuclear installations, supporting applicable requirements from GSR Part 4 (Rev. 1), SSR-2/1 (Rev. 1), SSR-2/2 (Rev. 1), SSR-3 and SSR-4.

The current Safety Guide NS-G-2.13 issued in 2009 needs an update addressing the following issues:

• Changes in the requirement documents in higher hierarchy (GSR Part 4 (Rev. 1), SSR-1, SSR2/1 (Rev. 1), SSR-2/2 (Rev. 1), SSR-3 and SSR-4);
• Considerations fulfilling the gap between the existing publication and the current state of practice in IAEA Member States;
• Evolution of the techniques and methodology in seismic safety assessment of nuclear installations.

The changes mentioned above include the issues highlighted in the Director General’s Report on the Fukushima Daiichi Accident (2015). For instance, the new Safety Guide needs to address provisions on seismic hazard severity higher than the one used in design, methodologies that consider explicitly the uncertainties, provisions for a site with multiple nuclear facilities, etc.

The revision will also take into consideration feedback from existing operating experience, technical safety review services, advisory services and the current state of practice

The process to evaluate seismic safety for existing nuclear installations consists of the following steps:

• define the purpose of the seismic safety evaluation,
• define the Review Level Earthquake (which is different from the Design Base Earthquake), based on site-specific seismic hazards results,
• select the suitable methodology,
• define the implementation programme and expected outputs,
• peer review,
• document the results in a manner that facilitates decisions concerning safety.