- 320 - cliff-edge effect, as their consequences are limited to possible problems with light vehicle movements, isolation of the planned diesel generator set on the platform in front of the BMR, and potential water ingresses in the BMX building. Although it has not identified any cliff-edge effect, the CEA proposes additional measures to prevent and mitigate the consequences of the risk, which are described in the section dedicated to the analysis of other extreme natural phenomena, namely: movement of the standby diesel generator set to an area outside the water runoff area; local adaptations of the second-phase roads and utilities networks in order to improve water discharge towards the le Ravin de la Bête. Other risks The following risks have also been examined: the risk of containment degradation after core meltdown by hydrogen explosion or basemat meltthrough, the exclusion of which is substantiated in the CSA; the re-criticality risk, even though it is excluded in the safety frame of reference. With regard to the management of this risk, the CEA puts forwards a system of emergency poisoning by injecting soluble neutron poison via a line of the core backup cooling system (RUC) which can be manoeuvred from the auxiliary building and energised by the normal electrical power network; The CEA has also assessed the radiological conditions in the premises with a potential requirement for operator inputs (control room, fall-back centre, quick-connect coupling external to the nuclear unit, diesel generator premises) and considering that the nuclear materials stored in the auxiliary building are exposed. These conditions confirm those set for "controlled areas in the sense of the labour code". For the JHR, with regard to mitigating the consequences of severe accidents, ASN will ask the CEA to examine the possibility of including the equipment items involved in the "control of environmental releases" in the hard core of reinforced provisions, and to verify their robustness to an earthquake exceeding the reference earthquake for the facility. Phénix The feared serious situations are: loss of sodium containment that could lead to a sodium fire or a sodium-water reaction; a criticality accident in the spent fuel assembly storage tank; collapse of the hot cells. The CEA therefore analysed in its CSAs the robustness of the means available in the following situations that could lead to a cliff-edge effect: cumulated leaks of the main vessel, of the double-walled vessel and the primary containment vessel , which could lead to a sodium fire; a leak in the fuel storage tank vessel combined with failure in integrity of the fuel storage tank vessel pit lining, which could lead to a sodium fire; a sodium fire affecting the in-service primary cold trap; a large-scale sodium-water reaction; an accident mobilising the radiological source term of the cells. Licensee's accident management organisation The CEA's means for detecting a sodium fire include monitoring the oxygen content and atmospheric relative humidity, as well as televisual monitoring of the primary containment vessel. The CEA specified that if the normal sodium fire detection systems malfunction, and given the scale of the fires considered for cliff-edge effects, the quantity of fumes released would be such that fire would be detected visually. In the event of a sodium fire, some premises can be inerted, and the facility has appropriate means for this (Marcalina powder). If a sodium fire occurs in the fuel storage tank vessel pit or in the primary cold trap, only inerting of the
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