- 304 - 5.3 Other facilities (ATPu, Masurca) 5.3.1. ATPu Loss of the electrical power supplies The ATPu is supplied by two 15 kV looped three-phase lines passing via the facility's 2 transformer stations. Each of these lines can supply the entire loop. The transformer stations are equipped with cut-off means upstream of each HV/LV transformer. If the building's main electrical substation should fail, all the ATPu facilities can be taken over by the second substation, subject to load-shedding. In the event of a loss of power lasting more than 2 seconds further to a voltage drop of more than 15% at the main transformer station, a relay control gives the diesel generator set starting command. The backed-up circuits are energised about 15 seconds after start-up. The two 1000 kVA diesel generator sets are located in an auxiliary technical building. The supply and storage tanks are linked by an overflow tube. Furthermore, mobile generator sets can be made available from the Centre's general resources, to resupply certain parts of the electrical distribution network depending on the context. One of these generator sets is intended for power supply redundancy of the fixed generator sets' electrical panel, during maintenance in particular. A second generator set is intended to backup the facility monitoring systems, the auxiliaries of the substations and of the fixed diesel generator set plant, and the safety lighting circuits. A third and final generator set is intended to resupply the normal system coming from the PU2 station. The remote alarm, interphone, criticality, radiation protection and emergency shutdown networks, powered with low voltage (24 V or 48 V), are backed up by a 100 kW group of dry batteries permanently connected to charging units. Feared situations in the event of loss of the electrical power supplies In the event of loss of the off-site electrical power supplies, without off-site backup, electrical power is supplied by two fixed diesel generator sets of 1000 kVA each, located in an auxiliary technical building. Each generator set is fuelled from a 500-litre diesel fuel tank, supplied by pump from two external tanks of 8,000 litres. If one of the two diesel generator sets should fail, the generator set remaining in service is capable of taking over powering of the facility, subject to load-shedding. The equipment that supplies the power for all the functions important for the safety of the ATPu facility requires 1,250 kVA of power. Considering the hourly fuel consumption of the diesel generator sets and the quantities of fuel present on the Centre at all times, the licensee estimates that these generator sets have 37 hours of autonomy. If the facility's ventilation is shut down, the diesel generator sets can supply the other equipment of the facility for 225 hours. Loss of the off-site electrical power supplies and the conventional emergency power supplies If the two fixed diesel generator sets are lost, the licensee places the ATPu facilities in safe condition, stops any glove box activity and evacuates the cells. If the ventilation is not taken over by the emergency system, the sealed doors upstream of the exhaust stacks are intentionally closed. If there is a total loss of electrical power for more than one hour, the personnel is ordered to evacuate the main building. In the event of loss of the off-site electrical power supplies and the conventional emergency supplies (fixed generator sets), the remote alarm, interphone, criticality, radiation protection and emergency shutdown networks are backed up by dry batteries permanently connected to charging units. The autonomies of the chargers and inverters supplying the different equipment items vary between 10 minutes and 5 hours, depending on the equipment. There is also a mobile emergency battery/battery charger unit located in an auxiliary technical building that can be connected to and supply the consumers.
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