The general principles for the protection of the Nuclear Power Plants against flooding of external origin are defined in the French Basic Safety Rule I.2.e. Nevertheless, the partial flooding of « Le Blayais » Nuclear Power Plant in 1999 has called into question the design bases used for the protection against external flooding and the existing measures, especially the warning systems, the site protection measures, the protection of safety-related equipments, the procedures and the emergency organization.
In addition to the rush through protection measures implemented on the Blayais site, the utility Electricité De France has reassessed the maximum design flood level at all the plants and has launched a wide "review project" of investigations aiming to ensure that the installations would be effectively protected against external flooding. The paper presents the main safety and technology issues to be further examined in the framework of this "review project", incorporating the lessons learned from the flooding in Le Blayais.
The "review project" principles were submitted to the judgment of the French Safety Authority in December 2001 after being analyzed by its technical support IRSN (Institut de Protection et de Sûreté Nucléaire). In general, they were considered as satisfactory. Therefore, the safety analysis of the protection of all French nuclear plants against external flooding should be performed in compliance with both Basic Safety Rule I.2.e and the methodology developed after the incident occurred in Le Blayais.
In practice, the reassessment of the maximum design flood and the application of the new methodology have brought about many modifications and improvements on the sites. Some practical examples of improvements are given in the paper.