- 125 - In its CSA reports, EDF also proposes other measures to reinforce the robustness of the facility: a study of the consequences: o of a rise in the groundwater level on the structural resistance of the buildings of units 1 and 2 on the Penly site; o of a karst28 flood on the lack of buoyancy of the buildings on the Paluel site; studies to confirm the ability of the protective embankments to withstand a CBMS+1m under the effect of wave swell; studies on the seismic behaviour of the protections in the event of an earthquake initiating dam bursts and studies concerning multiple dam bursts; study on the seismic resistance and electrical backup of the SEO lifting29 pumps. For the Tricastin site, EDF proposes carrying out studies on seismic strength and electrical backup of the SEO rainwater lifting device. ASN considers that the approach proposed is satisfactory. For three sites (Tricastin, Fessenheim and Bugey), on which the heat sink is at a higher elevation than the site platform, there is a risk of a major leak in the event of rupture of the cooling systems (CRF) for the facilities connected to them. Although in the examination EDF stated that the valves can isolate the system from the heat sink in all circumstances, a study programme was initiated to improve the robustness of these isolation valves up to a level beyond design-basis, yet to be defined. EDF also states that: "appropriate reinforcement of the door counterweight arms will then be implemented". EDF concludes that as things currently stand, this point does not compromise the safety of the facilities. However, given the risk of the channel emptying, ASN considers that all the elements (sensors, automation, valves, part upstream of the valves, etc.) preventing the channel draining to the site in the event of a rupture of the cooling system, must be included in the above-mentioned study. With regard to the consequences of the various scenarios, IRSN indicated that the orders of magnitude of the water levels obtained on the nuclear island platform are of a few centimetres for the maximum rainfall and flooding scenarios induced by an earthquake beyond design-basis, and up to about two metres on the site platforms for the maximum river flood scenarios. ASN considers that neither the CSA reports, nor the complementary data presented by EDF during the examination clearly describe EDF's strategy with regard to the cliff-edge effects identified and that the solutions envisaged by EDF to reinforce the robustness of the facility are primarily solutions that would be such as to mitigate the accident (strengthening of the equipment necessary for operation in an H1 or H3 situation). ASN estimates that this approach does not offer a satisfactory response to the requirements and that the prevention of cliff-edge effects needs to be strengthened. For example, ASN considers that sufficient raising of the VP would, in most cases, be able to prevent H1/H3 cliff-edge effects for the maximum rainfall and flooding induced by an earthquake beyond design-basis scenarios. ASN will require that EDF present the modifications it envisages in order to reinforce the protection of the facilities against the risk of flooding beyond the current baseline safety standards, for example, by raising the volumetric protection, to prevent the occurrence of total loss of heat sink or electrical power supply situations for the maximum rainfall and flooding induced by an earthquake beyond design-basis scenarios. In particular on the occasion of the targeted inspections, ASN noted the vulnerability to flooding of the diesel halls on certain sites. For example, on some sites, EDF claims that there are kerbs of about ten centimetres in front of the diesel hall access points. However, on the site, ASN observed that these kerbs are not always present. ASN will be formulating a request on this subject. Case of embankments on the Tricastin site EDF states that the seismic resistance of the embankments on the Donzère Mondragon canal are significantly robust beyond the SSE. Given the time available, EDF presented the results of an existing study concerning failure of the embankments along the Donzère-Mondragon canal. According to EDF, the potential 28 Flood from the karst (limestone formation in which water has excavated numerous cavities) 29 Pump transferring fluid from one elevation to a higher one.
RkJQdWJsaXNoZXIy NjQ0NzU=