- 111 - EDF also took account of certain hazard combinations taking account of the degree of interaction between these phenomena, the order of magnitude of the frequency of occurrence and the potential risks associated with the various hazards or combinations thereof. The following were thus taken into consideration: 1. For river sites: Thousand-year flood and chop; High-intensity rainfall and medium discharge river; Regular and continuous rainfall and hundred-year flood level; Intumescence and various flood situations. 2. For coastal sites The CMS (as defined by RFS I.2.e for coastal sites and recalled previously in this report) and a hundred-year wave swell; High-intensity rainfall and mean tide high water level (coefficient 70); Regular and continuous rainfall and overall hundred-year sea level (including storm surge and tide); Intumescense and various flood situations. EDF has also taken into account the possible damage to structures (located above the sites or on the platform, such as channel embankments, reservoirs, dams, tanks, etc.) as well as damage to systems or equipment (mainly those associated with the pumping station, the circulating water intake and discharge channel and the CRF18 system) which could lead to the presence of large volumes of water on the site platforms. For the channel embankments and reservoirs, EDF is studying their behaviour in response to the following hazards: earthquake, airplane crash and off-site hydrocarbon explosion. This method complementing RFS I.2.e was evaluated by IRSN. After obtaining the opinions of the advisory committees19 in December 2001 and March 2007, ASN considered this methodology to be on the whole satisfactory. However, ASN did ask EDF to revise its studies concerning a system or equipment break and to supplement the methodology for characterising the high-intensity rainfall hazard, to ensure that the protection measures for these two hazards are sufficient. Additionally ASN has submitted specific requests concerning the sites of Belleville and Tricastin: The Belleville CMS considered by EDF does not cover the significant influence of the Strickler coefficient20. If the calculation does take account of this influence, then it leads to a higher water level, estimated at 47 cm by EDF. However, EDF did not update the CMM value accordingly. ASN asked EDF to update the Belleville CMM value to take account of the uncertainty surrounding the Strickler coefficient. The Tricastin CMS needs to be revised to take account of failure of the Vouglans dam. EDF presented new studies in 2008 giving the water level at the Tricastin site in the event of failure of the Vouglans dam. In its hypotheses, EDF postulated a median water level (in other words reached 50% of the time) in the Vouglans dam at the time of its failure. ASN considers this hypothesis to be insufficiently conservative and asked EDF to take account of a higher water level in the Vouglans dam at the time of its failure in its CMS calculation for the Tricastin site. 18 CRF: circulating water system 19 See Introduction of this report 20 Coefficient representative of the roughness of the river bed.
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