- 108 - For each of its sites, EDF also studied the plausibility of the scenarios leading to cliff-edge effects. EDF examined the consequences of the collapse of all the tanks and pipes leading to spillage of the entirety of their contents. Conservatively, EDF considered the tanks to be filled to their maximum capacity and evaluated the total volume poured onto the nuclear island platform on each site and compared the water level reached with the building access and platform access thresholds. EDF concludes that the off-site flooding risk created by an earthquake exceeding the level for which the facility is designed cannot be ruled out for several sites. For those sites on which the off-site flooding risk created by an earthquake and exceeding the level for which the facility is designed, cannot be ruled out, EDF proposes a study to determine how real is the water risk on the nuclear island platform. In the light of the results, EDF will determine whether or not additional protection is necessary. In addition, for the Gravelines site, the retaining walls along the sides of the intake channel need to remain stable in order to guarantee the heat sink flow. This point was evaluated on the occasion of the VD3. ASN however considers that additional studies going beyond the SSE need to be carried out by EDF. 2.2.4 Measures envisaged to reinforce the robustness of the facilities to the seismic risk With regard to earthquakes, the complementary safety assessments concerned an evaluation of the conformity of the facilities with their safety requirements and a study of their robustness beyond the design-basis earthquake, up to 1.5 SSE. Beyond the current safety requirements, EDF proposed additional measures to prevent the serious consequences of extreme situations, on a deterministic basis, regardless of their plausibility. EDF proposed defining a hard core of reinforced equipment such as to prevent severe accidents and avoid significant radioactive releases into the environment, over and above the current safety requirements, for the deterministic situations studied in the complementary safety assessments. EDF intends to draw up a list of the main hard core items and the robustness requirements to be applied to them, according to the following calendar: For the power plants in operation: June 2012 For the EPR, according to a calendar included in the Flamanville 3 commissioning file review schedule. ASN considers that the approach proposed by EDF is appropriate and will require that EDF rapidly submit for approval the requirements associated with this hard core (see § 8) which shall include significant fixed margins in relation to the design-basis earthquake.
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