- 276 - Measures envisaged to reinforce robustness of the facilities to the flood risk On completion of its review, ASN considers that the FBFC facility requires no reinforcement of its robustness to flood risks other than those caused by rainfall on the site. ASN will however demand reinforcements in the protection of any buildings identified in the periodic safety review as being vulnerable to the risk of flooding by rainfall further to the results of the study due in mid-2012. 3.4 Other facilities (ATPu, Masurca) 3.4.1 ATPu Design of the facilities The majority of the Cadarache Centre is located on the watershed of the Ravin de la Bête, a perennial stream fed by springs in its "downstream" section, and which flows into the river Durance. The flood situations considered by the licensee are: flooding from the upstream watershed The watershed upstream of the ATPu facility covers a small surface area and is entirely vegetated. The 100year flow rate provided by this watershed is less than 1m3/s. The storm water drainage infrastructure situated on the periphery of the ATPu facility protects it against the risk of flooding from the upstream watershed. storm water The large majority of the Cadarache Centre storm water drainage system was built in the 1960's 70's on the basis of the conventional design rules for urban environment road and utility networks. The design model of the drainage systems is the Strickler flow model that takes the roughness of the pipes into account, and is conventionally used in open channel hydraulics. This model enables the evacuation capacity of systems to be evaluated by associating them with a filling rate. rise of the water table The highest level recorded at the ATPu facility reached 273.5 m NGF (1993-1994). The basement of the main building is at level 275.5 m NGF. The building has a waterproof lining. The ground floor is at level 280 m NGF. overflow of the Ravin de la Bête The ATPu facility is situated near the Ravin de la Bête stream in an area where it is entirely channelled in an oval drain with a capacity of about 40 m3/s, which is subject to special maintenance and periodic inspection after each rainfall event. Its capacity is consistent with the 100-year flow adopted for this part of the watershed. The licensee therefore considers that the ATPu facility is protected against the risk of flooding caused by overflow of the Ravin de la Bête stream. damage to hydraulic structures. The licensee considered the case of an extreme flood of the Durance and failure of the dams situated near the Cadarache Centre (EDF dam of Serre-Ponçon, dams of Sainte-Croix and Esparron-sur-Verdon) and breaching of the Canal de Provence. The calculations showed that the most pessimistic dam break flood wave in terms of height of the reservoir surface would correspond to failure of the Serre-Ponçon dam situated more than 95 km from Cadarache. The dam break flood wave would result from the total but progressive failure of the dam. It was calculated that this wave would reach Cadarache 5 h 40 min after dam failure and lead to a peak flow of some 60,000 m3/s with a mid-height width of a few hours. The case of a simultaneous 100-year flood would represent an additional flow of 5,000 m3/s, which would not significantly alter the maximum level reached by the dam break flood wave. The maximum level reached would be 265 m NGF. The licensee considers that no nuclear facility would be concerned and that the Centre would remain accessible via the auxiliary doors.
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