- 303 - three particular cases must nevertheless be noted, as they require electrical power for a few minutes to place the equipment items concerned in safe condition: o the conversion autoclaves (building C1): in the event of loss of the electrical power supplies, autoclave heating is stopped. The fluid supply valves (nitrogen, compressed air) and the solenoid valves of the UF6 circuit are fail-safe valves and should therefore close automatically on loss of power. The injection of steam into the conversion ovens is stopped automatically by the valves moving to the closed safety position; o the sintering furnaces (building AP2): these furnaces serve to "bake" the uranium pellets, a process that produces hydrogen. It is absolutely vital that this hydrogen gas be burned at the furnace outlet to avoid any risk of explosion, and this is achieved by flares. Consequently, in the event of loss of the electrical power supplies while the sintering furnaces are functioning, these furnaces are placed in shutdown position by automatically introducing an inerting gas (nitrogen), while maintaining a minimum gas flow inside the furnaces to ensure sufficient internal pressure, by closing the furnace doors, and guaranteeing combustion of the hydrogen by maintaining a hot wire supplied by an inverter at the flare outlets. Lastly, the furnaces are cooled by a water cooling circuit which is energised by the backed-up electrical network. The transient phase of furnace cooling stoppage lasts about 3 minutes; o the HF station: in the event of loss of the electrical power supplies, the HF station must continue to scrub the HF discharges from the conversion autoclaves, until the autoclaves are completely stopped. The duration of this operating transient is not estimated in the CSAs. Conclusion on the measures planned to protect the facilities against the risk of loss of the electrical power supplies The licensee estimates that the measures it has provided for are sufficient. The foregoing raises no particular comments from ASN. Loss of the cooling systems / heat sink The licensee indicates that only a few equipment items in BNI 98 require cooling: In building AP2: o the grinding machine wheels cooling with demineralised water; o the BTU sintering furnaces cooling water in closed circuit, which is itself cooled by 2 cooling towers backup water supply from public water system; o the DEGUSSA sintering furnaces cooling with recycled water; o the exit area of the roasting furnaces, called "Ripoche furnaces" - cooling with recycled water; In building R1: o calcining / reduction furnaces cooling with recycled water. The only cooling functions whose loss could impact the safety are those of the BTU and DEGUSSA sintering furnaces. According to the licensee, their loss would lead to: possible slight contamination in the environment of the furnace concerned; very slight hydrogen leaks in the furnace hall during the furnace inerting time. The licensee identifies no feared situation in the event of loss of the ultimate cooling system. Likewise, it identifies no feared situation in the event of loss of the main cooling system combined with total loss of the off-site and emergency electrical power supplies The foregoing raises no particular comments from ASN.
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