- 18 - 1.12.1 Protection of facilities against off-site flooding 2.1.1 Introduction Context Flooding is a risk that is designed into the facilities and reassessed on the occasion of the periodic safety reviews or in response to certain exceptional events, such as the partial flooding of the Le Blayais nuclear power plant during the storm on 27th December 1999. This reassessment in particular concerns the maximum water level considered in the design of the site protection structures, called the flood safety margin level (CMS). The method for calculating this CMS is given by fundamental safety rule RFS I.2.e. The revised CMS takes account of the additional causes of flooding, such as high intensity rainfall, failure of water retention facilities, rising ground water or, for coastal sites, tidal waves. Following the partial flooding of the Le Blayais power plant in December 1999, EDF complied with ASN's request for an overall reassessment of the flooding risk for each of its nuclear sites. Initially, the platform elevations were set according to the water level calculated upstream of or at the site, taking account of margins, in particular with respect to future settling. Embankments were built in certain cases (Le Blayais). On the occasion of the CMS reassessment following publication of RFS I.2.e, mobile protections (cofferdams) were put into place on sites with a CMS higher than the platform elevation (Belleville for example). Following the Le Blayais incident, protection improvement actions were decided on. They have been completed on some sites and are either in progress or planned for others. Stakes The risks caused by flooding and high water are primarily: the loss of the water supply by flooding of the pumping equipment or large-scale arrival of detritus; the loss of off-site power supplies by flooding of the switchyard; flood-related loss of equipment important for safety; prolonged isolation of the site, in particular making it impossible to relieve the shift crews, refuel the emergency generator sets or bring in mobile emergency resources. Inspection frame of reference EDF describes the results of its assessments and the protection against the resulting off-site flooding risks in each of its safety reports and also in the flood files produced (also called "stage 3 site files"), updated to take account of ASN's requests following the advisory committee meetings of 21st and 22nd March 2007 devoted to examining the protection of the pressurised water reactors in service and the other nuclear facilities against the risks of off-site flooding. The sites also rely on operational documents, in particular to anticipate and manage a flood situation. This for instance concerns the flooding special operating rules (RPC) specific to each site and used to ensure early initiation of measures to limit the risks (example: reactor shutdown) or the effects of flooding. The purpose of the inspections on this topic was to verify the conformity of the facilities with this frame of reference. Field visits were carried out to check the progress of the action plan implemented by EDF and check the availability and condition of the equipment contributing to protecting the site in the event of flooding, especially the equipment participating in volumetric protection (PV) and the mobile pumping resources. A number of exercises were held related to the deployment of protection equipment. 2.1.2 Organisation The ASN inspectors investigated the organisation put into place for management of the flooding risk. The EDF head office departments established a set of documents for each of their sites, presenting the off-site flood risk protection measures (systems and procedures) tailored to the specificities of the site. Most of the sites have a flood coordinator, which was found to be satisfactory by ASN, although their roles and duties are not always described (Bugey, Saint-Alban, and Cruas). Depending on the site-specific flooding vulnerability, some sites are covered by an on-site emergency plan (PUI) specific to management of this type of crisis, referred to as a "flood safety PUI" (for example Belleville or Le Blayais) used in the event of an alert. Some sites hold flood safety PUI deployment
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