- 128 - 4 Other extreme natural phenomena related to flooding Flooding can be accompanied by other climatic phenomena. This is why, in its resolution of 5th May 2011, ASN asked EDF to conduct an analysis similar to that performed for flooding and earthquakes. As an example, one could mention the storm which swept across France in December 1999, characterised by both high tide and strong winds, which led to partial flooding of the Le Blayais NPP platform and electrical disruption of the Nogent and Le Blayais sites. 4.1 Design of the facilities With regard to the extreme meteorological conditions related to flooding (storm, torrential rain, etc.), ASN asked EDF to clarify: The events or combinations of events taken into account and the reasons they were (or were not) selected for the design of the facilities; The weak points, specifying any cliff-edge effects, as well as an identification of the buildings and equipment that would be affected; Whether steps could be envisaged to prevent these cliff-edge effects or reinforce the robustness of the facility (modification of the design, modification of procedures, organisational measures, and so on). EDF devoted a chapter of the CSA reports on each of its sites to the extreme meteorological conditions related to flooding. In its CSA reports, EDF considered four phenomena: the direct effects of wind on the facilities; the effects of projectiles generated by extreme winds; the effects of hail; the effects of lightning. Equipment design for these extreme climatic phenomena Wind The structures were designed in accordance with the latest revision of the Snow and Wind 65 rules available for the construction of each plant series. On the occasion of each periodic safety review, EDF checks that the buildings important for safety (IPS) and the buildings housing IPS systems or equipment were able to withstand winds with characteristics conforming to the updated Snow and Wind rules (1999 and 1984 editions, amended in 2000). EDF also checked the design of the buildings, in particular in the light of operating experience feedback concerning the storms which swept across France in December 1999 and more recently (Klaus in 2009 and Xynthia in 2010). EDF considers that these storms led to no damage to the nuclear island buildings and the civil engineering structures of the pumping station. The systems and equipment performing the reactor safety functions are chiefly located in these buildings and structures and the effects of wind had no impact on safety. On the occasion of the latest periodic safety reviews of the 900 MWe and 1300 MWe series, EDF checked the wind-resistance of the equipment classified IPS-NC30 located outside these civil engineering structures. The CSA reports, however, fail to mention this equipment. Projectiles were also generated by the extreme winds (gravel, antennas, parts of roofs, etc.) during the three storms mentioned above; EDF evaluated their energy at a speed of about 200 km/h. EDF considers that this is 30 Equipment important for safety but not safety-classified, that is: equipment for which a failure is liable to prejudice compliance with the safety objectives (integrity of the pressure envelope of the main primary system, shutting down the reactor and keeping it in a safe state, preventing and mitigating the radiological consequences of accidents), equipment for which correct operation is only necessary in the long-term to achieve these objectives, certain equipment required in the event of a hazard (fire, flooding, etc.). Since the design stage, the IPS-NC class has been extended to include other equipment necessary for the safety demonstration.
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