- 131 - Hail Most IPS equipment is situated indoors, which offers it protection from hail damage. With regard to the robustness of the buildings themselves to the effects of hail, EDF considers that the maximum impact could be pitting of the cladding, but without penetration. No incident related to a hailstorm has been observed on the reactors in service. The targets identified with respect to hail are primarily those already considered in the analyses covering windgenerated projectiles. Piping and tanks are considered to be able to withstand the impact of hail. The consequences of blockage of the rainwater drainage networks, which could be caused by hail, are dealt with in § 3 of this chapter. ASN considers that the elements presented by EDF concerning hail are succinct: in particular, no hail loading value (intensity, diameter of hailstones, etc.) was mentioned. ASN will ask EDF to propose a more precise definition of extreme hail loading and to conduct a more detailed analysis of the resistance of the equipment. Lightning EDF considers that there is no plausible cliff-edge effect liable to be created by lightning, given: the high robustness of the facilities required for management of an accident situation with regard to the lightning risk and its effects; the confirmation from operating experience feedback of the effectiveness of this robustness, up to high levels; the functional redundancy and the diversity of certain systems, especially those linked to the electrical power supplies. To reinforce the robustness of the facilities, EDF nonetheless states that a preventive maintenance programme for the "Hot non-IPS structures" and a maintenance programme for the "turbine hall" are currently being drafted. They will cover the metal cladding. EDF considers that maintenance of the cladding will limit the risk of it being damaged by a storm, for the buildings within the scope of these maintenance programmes, thus increasing the protection of the facilities against the lightning-related risks. With regard to lightning-induced cliff-edge effects on PWRs in operation, ASN observes that EDF bases its position solely on arguments related to the design or to positive operating experience feedback at high intensity levels, but without mentioning any values which clearly indicate the absence of a cliff-edge effect. During the examination in preparation for the meeting of the advisory committees in November 2011, ASN noted that on the EPR (Flamanville 3, Penly 3), EDF mentioned analysis of operating experience feedback which revealed the occurrence of lightning strikes of an intensity of up to 454 kA (Chooz in April 2011). EDF specified that a study will be conducted on the EPR to assess the consequences of a lightning strike in excess of 200 kA for the equipment installed outside the "mesh cage". This feedback from Chooz and this study are not mentioned in the CSAs for the PWRs in operation. ASN considers that an "extreme lightning" loading, defined on the basis of the available operating experience feedback, should be defined and taken into account for the PWRs in operation, concerning the equipment needed to manage H1, H3 and severe accident situations. ASN will ask EDF to conduct such studies. Combination of extreme climatic phenomena and loss of heat sink (H1) and loss of electrical power supply (H3) situations Contrary to what ASN requested in its decision of 4th May 2001, EDF does not include these extreme natural phenomena in the H1 and H3 analyses presented in the CSA reports (see § 5 of this chapter). However, during the examination preceding the meeting of the advisory committees in November 2011, EDF indicated that it would be including them in the analyses of the action to be taken for H1, H3 and severe accident situations.
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