Seismic assessment of French nuclear power plants

In the the last seven years, Electricite de France has been evaluating the seismic safety of some of its older operating nuclear power plants as part of the periodic safety review program. The methodologies developed in the United States by Seismic Qualification Utility Group (SQUG) and the Electric Power Research Institute (EPRI) for seismic adequacy evaluation and seismic margin assessment (SMA) are employed in these studies. In the first study, EDF's objective was to examine the applicability of SMA methodology to French nuclear power plants. Tricastin Nuclear Power Plant was selected for this exercise. A review level earthquake was chosen for the site by considering the effects of the median NUREG/CR-0098 spectrum shape and the RFS spectrum anchored to 0.3 g peak ground acceleration. In this way, the impact of both the near-field and far-field earthquakes was considered. More recently, EDF has evaluated the seismic adequacy of Fessenheim and Bugey following the requirements of Generic Implementation Procedure (GIP) developed by SQUG. This was proposed by EDF to complement the ongoing VD2 periodic safety review of the plants. Although GIP recommends use of a single success path for safe shutdown following the design earthquake, EDF chose to use two alternate success paths required in a seismic margin assessment. Further, the safe shutdown equipment list (SSEL) was expanded to cover systems needed to assure containment performance. SSEL items were inspected at these three plants following the GIP and SMA walkdown procedures. Seismic adequacy and margin evaluations were done taking into account the specific design, testing and anchorage features of EDF plants. These studies assisted in the validation of seismic upgrades of certain items (e.g., block walls and anchorage of electrical equipment) implemented as a result of other EDF programs. (author)