**1.3. Scope of the Chapter**

80 Nuclear Power – Practical Aspects

plants are still of great practical importance.

upgrading of seismic safety of operating plants.

under the condition of an operating plant.

the design basis earthquake.

**1.2. Objective of the Chapter** 

one.

probability of damage is not zero even if the loads are less than the design base one. The seismic PSA provides the core damage frequency as the output of the analysis, which is a measure of the seismic safety. The PSA is generally failure oriented. The seismic PSA shows the weak links. This knowledge can be very useful for the planning of the postevent inspections. Similar information is provided by the seismic margin analysis, which quantifies the capability of the plant to survive an event greater than the design basis

After the severe accident at Fukushima NPP the operators in European Union, U.S. and some other countries including Japan performed comprehensive safety and risk evaluation of operating nuclear power plants, see e.g. (European Commission, 2011). These tests/reviews will launch different re-evaluation and upgrading programmes with regard to seismic safety and for improvement of the capability to cope with the beyond design base earthquake and associated events (fire, flood) at the existing plants. This process includes at some sites the re-assessment of the site hazard motivated by recent events and/or new scientific evidences, for example in the U.S. (NRC, 2011). These lessons learned will also affect the projects under preparation and/or implementation. For the new plants, it has to be demonstrated that the plant has sufficient margins with respect to the design basis extension earthquake loads of and avoiding the cliff-edge effect. Consequently, the lessons learned from the former projects for evaluation of the seismic safety and upgrading of operating

Objective of the recent Chapter is to provide practical insights to the re-evaluation and

Evaluation of seismic safety and re-qualification of operating plants require specific approach; the safety goals have to be ensured in reasonable manner, avoiding unnecessary conservatism, contrary to the design that is ab'ovo conservative. State-of-the-art methodologies have to be implemented in every aspect of the re-evaluation and upgrading process. The optimisation of the measures from logistics point of view is very important

International Atomic Energy Agency developed a comprehensive Safety Guide on "Evaluation of Seismic Safety for Existing Nuclear Installations" (IAEA, 2009a). The supporting document of this Guide is the Safety Report Series No 28 on "Seismic Evaluation of Existing Nuclear Power Plants" (IAEA, 2003) that summarises the before 2003 experience in the seismic evaluation and upgrading of the operating plants. These documents focus mainly on the methodologies for seismic safety evaluation that do not involve a change in

In this Chapter the case of seismic evaluation and upgrading methodologies and solutions are presented. The Chapter includes the case for upgrading of an operating nuclear power plant originally not designed for earthquake. Based on the graded approach, the feasibility Scope of the Chapter covers


## **1.4. Structure of the Chapter**

Section 2 of this Chapter defines the basic principles of seismic safety. Section 3 provides an overview of the methodologies applicable: Section 3.1 outlines the objective and scope of the seismic safety programmes. Section 3.2 provides an overview of applicable methodologies. Sections 3.3 address the issues of restart after earthquake. Section 3.4 outlines the questions of accident management. Sections 3.5 to 3.7 address the walk-down, design of upgrading and role of the peer-review. Section 4 is devoted to the pre-earthquake preparedness and post-earthquake actions. The practical and full scope example of seismic re-evaluation and upgrading is shown in Section 5. Section 6 and 7 are related to the maintenance of the seismic qualification during operation and periodic safety reviews. Extensive list of references is provided to the Chapter in Section 8.
