- 277 - Measures to protect the facilities against the flood risk The main design measures to protect against the risk of external flooding are as follows: the building has a waterproof lining in the basements, supplemented by a peripheral drain connected to the storm water drainage system, allowing partial lowering of the storm water; in the areas likely to be flooded in heavy rainfall events or by a rise in the water table to the 280 m NGF level, appropriate gradients (or steps) have been provided at the building access points, which are therefore raised with respect to the outside ground level. The storm waters are collected by downpipes, gutters, ditches and area drains, then channelled towards the Ravin de la Bête stream into which they are discharged. These design measures are supplemented by other actions such as maintenance and servicing of the storm water drainage system, inspection and monitoring (periodic inspection of the leak-tightness of the roof, walls, openings, monitoring of piezometric levels, flood alarm) and interventions (pumping, positioning of inflatable tubes, etc.) with the aim of limiting water ingress into the premises in the event of a flood. The licensee points out that no significant rainfall event has jeopardized the safety of the ATPu facility since it was built. Conformity of the facilities with the current frame of reference The licensee indicates that conformity of the facilities with the frame of reference is regularly checked through the facility's periodic inspection and test program. More specifically, this includes annual testing of probe remote alarm transmission and annual maintenance of the sump pumps that pump water up to the tanks. Evaluation of the safety margins The equipment present in the basement of the main ATPu building essentially comprises one of the two electrical power supply stations and the facility ventilation and filtration systems. A flood in this basement would cause total loss of the electrical power supplies and shutdown of the facility's entire ventilation system. The licensee considers that these events are not such as to induce a cliff-edge effect. Likewise, the radioactive materials present in the basement of the main ATPu building have several containment barriers, thereby preventing the risk of dissemination and of criticality in the presence of water. Consequently, there if no risk of a cliff-edge effect associated with the flood risk. The licensee considers that as the basement of the main ATPu building has a waterproof lining, the facility can withstand a flood level of 280 m NGF - the level of the ground floor of the building - without losing containment integrity. Above this level the water would infiltrate by the facility's ground floor access points. The flood alarm detectors on the basement of the building would be activated, triggering calling of the response teams. Measures envisaged to reinforce robustness of the facilities to the flood risk Given that there is no significant risk associated with flooding, the licensee does not propose any measures to reinforce ATPu robustness to the flood risk. On completion of its review, ASN considers that it is not necessary to reinforce the ATPu facility's robustness to the flood risk. 3.4.2 Masurca Design of the facility When designing the Cadarache site facilities, the CEA calculated a flood safety margin level of 265 m NGF, based on failure of the Serre-Ponçon dam. The Cadarache site is moreover crossed by the Ravin de la Bête stream, which is at level 297 m NGF at the Masurca facility, then channelled at the ATPu in an oval drain dimensioned to discharge the 100-year storm flow estimated for this part of the watershed. Given the margins available between the levels of the platforms and the two watercourses (which reaches several tens of meters), or between the extreme flow of the stream and the discharge capacity of its channel, the CEA
RkJQdWJsaXNoZXIy NjQ0NzU=