**1.2. Objective of the Chapter**

Objective of the recent Chapter is to provide practical insights to the re-evaluation and upgrading of seismic safety of operating plants.

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 under the condition of an operating plant.

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 the design basis earthquake.

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 of the application of seismic design methods combined with those developed for the reevaluation of existing plants is demonstrated.

New areas of the seismic safety evaluation of operating plants are also addressed in the Chapter that were triggered by recent events, the Kashiwazaki-Kariwa plant and the Fukushima Dai-ichi plant, that are focusing on the assessment and assurance of the beyond design base capability of the nuclear power plants, periodic review of safety, etc.
