- 290 - Loss of the off-site electrical power supplies In the event of loss of the off-site electrical power supplies, that is to say the 225 kV supply and the two 20 kV supplies, the site relies on two diesel generator sets, D1 and D2, for the supply of electrical power. Each diesel generator set can supply all the auxiliaries necessary to safeguard the equipment and ensure the permanence of the monitoring sources. The licensee states that the estimated operating time of the generators exceeds 3 days. Loss of the off-site electrical power supplies and the conventional emergency supplies If diesel generator sets D1 and D2 are lost, electrical power must be supplied by the ultimate backup diesel generator sets DE and DW, which are earthquake qualified. Their estimated operating time exceeds 8 days. Some safety auxiliaries are powered by dedicated storage batteries. In the event of total loss of the off-site and on-site power supplies, one or more generator sets from outside the facilities can be procured and connected at generator sets DE and DW level. The impact of a total loss of the electrical power supplies (failure of the normal and inverted power supplies and non-starting of the diesel generator sets) on the safety functions is presented below. Removal of residual power According to the CEA, loss of the current means of removing the residual power remaining in the reactor, the drums or the cells in which the fuel assemblies transit, has no impact given the current residual power levels. Containment of radioactive and hazardous materials In the event of loss of the electrical power supply, the general and process ventilation systems ensuring dynamic containment are stopped. Containment of the materials is then guaranteed by the static containment barriers. With regard to the risk of deterioration of the barriers if the sodium in the reactor and the drum freezes, the CEA states that the temperature levels reached do not call into question the long term integrity of either the tubes or the reactor block structures, and particularly the structures supporting the core. Control of reactivity and sub-criticality According to the CEA, total loss of the electrical power supplies has no impact on the control of reactor reactivity, given the definitive shutdown of the reactor (rod drop being in any case assured passively by gravity if the electrical power supply fails). Moreover, the CEA indicates that the loss of the electrical power supplies has no impact on the geometry, the moderation or the mass in the places where a criticality accident risk is identified. The method of monitoring fissile environments is not modified by loss of the electrical power supplies. Likewise, the lines of defence implemented to ensure equipment sub-criticality are also maintained in the event of electrical power supply loss. Specific risks associated with sodium Regarding the specific risks associated with sodium, the "nitrogen production and distribution" functional assembly remains operational in the event of a total power supply loss. Monitoring of the facility The radiation protection equipment that permanently monitors the radiological environment of the premises is connected to battery-backed busbars. In the event of loss of the off-site electrical power supplies or generalised loss of power, the CEA indicates the power supply to this equipment remains ensured by diesel generator sets DE or DW. If these generator sets should be lost in turn, the equipment would be supplied by batteries for about 8 hours.
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