- 294 - ILL will examine the possibility of performing tests on the reactor with appropriate instrumentation, in addition to the computer simulations. If demonstration difficulties should arise, the ILL will examine the benefits of considering the shutdown cooling system (CRA) and its electrical power supply as a "key" SSC; consider the emergency shutdown system as a "key" SSC, on account of its role in serious accident risk prevention in the event of heat sink loss. On completion of its review of the ILL's complementary safety assessment, ASN considers that the improvement proposals presented by the licensee, and in particular the installation of two wells to draw water from the water table in the immediate vicinity of the reactor building to reinforce the robustness of the facility to the loss of the heat sink, are satisfactory. ASN will issue formal requests with respect to these proposals. Loss of the main cooling system combined with total loss of the off-site and emergency electrical power supplies For the HFR, loss of all the electrical power supplies forcibly means loss of the primary heat sink, as none of the secondary pumps are powered any more. This scenario is therefore exactly the same as those described previously for loss of the electrical power supplies and loss of the heat sink. The core is cooled by forced convection for about one hour by the CRAB pumps, thanks to the autonomy of their batteries. After this the core is cooled by natural convection, the ultimate heat sink being the reactor pool. This totally "self-sufficient" cooling can continue for at least two weeks. The point raises no particular remarks from ASN. 5.2 Facilities in the nuclear fuel cycle (La Hague, Tricastin, Mélox, FBFC) 5.2.1. Tricastin site Loss of the electrical power supplies Although the electrical power supply is not a safety function for the facilities on the AREVA Tricastin platform, its reliability does contribute to the overall safety of the facilities. The Georges Besse I plant The facilities of the GB I plant are supplied from 5 independent 225kV sub-assemblies supplied by the NPP and RTE. Each normal train is designed to be able to satisfy, alone, all the power demands of the consumers that can be connected to it. Eurodif Production also has an uninterruptible power supply by batteries and inverter to supply the control stations (autonomy 1 h), electrical cabinets of the security network (autonomy 12h), safety lighting (autonomy 1h30), local diesel generator set control station (autonomy 5h) and sensors and control loops of annex U (autonomy 10h). Comurhex The plant is supplied from the distribution substation of AREVA NC Pierrelatte via 2 redundant 15kV lines, each of which can provide the necessary power alone. Comurhex also has an uninterruptible power supply by batteries and inverter to supply the control stations (autonomy 1h), the automatic fire detection (DAI) safety networks (autonomy 12h) and the safety lighting (autonomy 1h). Total loss of the electrical power supply automatically leads to the process equipment being placed in safe position. Prolonged loss of power would lead to slow heating up of the storage building of the 100HF structure. If the temperature of 20°C were to be exceeded, the tank pressure would rise. The licensee nevertheless considers that the 3 days necessary for this rise in pressure (high and very high thresholds at 100 mbar and 1 bar respectively) would leave it sufficient time to deploy a mobile diesel generator set. Furthermore, the tanks are equipped with pneumatic and manual valves connected to the vents manifold.
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