- 317 - In the event of core meltdown, the "normal" nuclear ventilation would be stopped manually and the safeguard ventilation would take over (by static containment), enabling the reactor containment to be kept at slight negative pressure. The safeguard ventilation is designed to withstand the reference earthquake. The CEA has examined the potential risks of containment degradation after core meltdown. It considers that there is no risk of containment damage by hydrogen explosion, even if ventilation is lost. Moreover, the pressure rise in the reactor vessel would be very slight and would not lead to its destruction. The CEA rules out the risk of a criticality accident, even in the event of an earthquake. In addition, it has evaluated the dose rate in the facility in the event of exposure of the fuel elements. If channel 2 were to become exposed, the dose rate would be 13.5 Sv/h at the edge of the channel and 0.7 Sv/h at 1 metre from the edge. The CEA indicates that if necessary, the FLS will be able to make the required water make-ups using a remotely-controlled robot. It should also be noted that the availability of the means necessary for the intervention of the FLS on the facility for the management of a severe accident will be analysed in 2012. Identification of the factors potentially hindering accident management and of the resulting constraints With regard to the fire risks induced by an earthquake, the CEA takes the envelope case of a fire in the equipment room affecting one of the electrical power supplies to the reactor. Yet it does not indicate whether the fire protection means are designed to seismic standards, nor does it indicate the vulnerability of the essential equipment items to fire. The licensee has undertaken to assess the induced hazards internal or external to the facility (global CEA commitment). Conclusion on the planned organisational measures for accident management The licensee has proposed replacing the FLS equipment shed doors with flexible doors to facilitate access to this equipment for post-accident operation. Existing severe accident management measures The CEA has undertaken to assess the robustness of the instrumentation considered important for monitoring the situation of the facility, namely: the position of the natural convection valves; the core outlet temperature or the reactor pool temperature; the water level in the reactor pool. Conclusion on the planned measures to mitigate the consequences (radioactive or chemical releases) in the event of a severe accident ASN will request the submittal of a complementary safety assessment for the Saclay site in which the question of environmental instrumentation can be addressed. JHR The feared severe accidents studied in the CSA report for the JHR are those corresponding to loss of fuel cooling leading to fuel meltdown. Such situations can be initiated in different ways (loss of off-site and on-site electrical power supplies, loss of cooling flow, breaches, etc.) and be compounded (loss of containment, criticality, fire, etc.)
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