- 274 - Conformity of the facilities with the current frame of reference It is noteworthy that the licensee performed an elevation measurement study in 2009 which revealed that the settling has slowed down since 1996 and that the maximum settling value does not call into question the existing margins with respect to the reference floods. Evaluation of the safety margins The licensee has studied the robustness of the facilities and in particular the key SSCs mentioned above (cooling units, emergency and backup generator sets) with respect to floods beyond the reference level. The margins were evaluated with respect to the maximum design flood level (CMS). The following table summarises the results of the licensee's study Key systems and components NGF level Margin with respect to maximum design flood level (CMS) 2 provisional emergency diesel generator sets(*) > 38 m(*) > 1.35 m (*) 2 backup diesel generator sets (train A/train B) 41 m 4.35 m 2 safeguard electrical rooms 40.60 m 3.95 m 2 safeguard control stations (train A/train B) 40.30 m 3.65 m 41.05 m 4.4 m 2 STE cooling units (train A/train B) 51.46 m 14.81 m 40.70 m 4.05 m 2 TAS cooling units (train A/train B) 40.80 m 4.15 m (*) The replacement of the provisional emergency diesel generator sets is planned for early 2012 after obtaining regulatory authorisation. The final generator sets will be situated at 40.05 m NGF, i.e. with a margin of 3.4 m with respect to the maximum design flood level (CMS) In the framework of the CSAs, the licensee envisaged a progressive flood of a level exceeding: firstly, that of the 100-year flood combined with failure of the Vouglans dam; secondly, that of the platform (40 m NGF) on which the plant is built. According to the licensee, the first equipment impacted would be the provisional emergency diesel generator sets; their loss has no impact on placing the facility in safe condition. In the definitive configuration (2012) of emergency diesel generator sets (40.05 m NGF) would also be the first to be impacted. The safeguard control stations would be the next impacted (40.30 m NGF), but local operations still remain possible. Upwards of a flood level of 40.40 m NGF, the criticality risk prevention conditions are modified. Nevertheless, criticality risk prevention is ensured as long as the fuel assemblies and rods remain in place. From level 40.80 m NGF, fuel assembly cooling is no longer ensured, and upwards of level 51.46 m NGF, cooling of the fuel rod storage area is no longer ensured. The backup diesel generator sets are flooded upwards of the flood level of 41.00 m NGF. To summarise, the flood levels necessary to damage the key SSCs are very difficult to reach given the width of the plain. Consequently the licensee considered that only the loss of the emergency diesel generator sets should be taken into account. With regard to the risk relating to torrential rain events, the values updated by Météo France are: Duration 6 mn 15 mn 30 mn 1 h Reference rainfall (mm) 21.5 41.7 67.0 112.1 Nîmes-Courbessac rain-gauge station - Maximum adjusted precipitation over the 1964-1992 period
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