- 279 - Regarding the effects of a gradual rise in the water table beyond the levels considered for the design of the facility, the licensee highlights firstly the protection measures which, as is the case with the storm water, evacuate the flows towards the Ravin de la Bête, and secondly the margins before the low points of the sensitive buildings are reached. Typically, in the case of the BSM, the level of 317 m NGF is to be compared with level 321.6 m NGF of the low point of the nuclear material storage area, which represents an additional margin on a rise in the water table of almost 5 m, and corresponds to a rise return period of more than 50,000 years. Furthermore, if the water were to rise beyond the level of the BSM building basement slab (321.3 m NGF), the topographic configuration of the facility and the area around it favours passive defence. This is due to the fact that the "basement" of the facility opens directly onto the external ground level via the delivery hall door. Subject to a slight alteration in the truck manoeuvring area gradient, water will run off naturally by gravity towards the Ravin de la Bête as of an elevation of approximately 321 m. On condition that the doors are opened to allow water evacuation, and given the geometry of the storage areas, the water could not reach the fissile materials for which the low point is 25 cm higher than the coamings (5 cm high) of the loading hall access doors. Measures to improve the safety of the facility - Opinion of ASN Apart from the proposals and commitments associated with the flood risks, such as the reversing of the gradient of the truck manoeuvring area and giving it a diamond-like shape, the CEA proposes upgrading the storm water collection and drainage systems if this should be revealed necessary by the external flood risk reassessment currently in progress on the basis of the on-site measurements taken in July and August 2011, and the design-basis "flood" hazard. ASN considers that licensee's proposals to reinforce the robustness of the Masurca facility to the flood risks must be applied. ANS will give the proposals formal request status.
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