- 300 - 5.2.3. Other facilities in the fuel cycle (Mélox, FBFC) Mélox Electrical power is distributed to the Mélox buildings by three networks: the "normal" network, connected to the RTE grid by two redundant trains; the "redundant" network comprising two redundant trains, each supplied by a diesel generator set (GE); the "backup" network, designed to earthquake design standards and comprising two redundant trains, each supplied by a specific diesel generator set (different GE to the redundant network). In the event of loss of the off-site power grid, switchover to the redundant network occurs automatically. If the normal automatic mechanisms should fail, safeguard automatic mechanisms start the backup generator set (at the end of 2012, two permanent fixed generator sets will be installed) and the supply of the emergency and backup electrical panels. Several measures have been taken to ensure the starting (automatic or manual) of the emergency diesel generator set(s): redundant fuel supply pumps, redundant starting systems, control panel on batteries, etc. The licensee indicates that these measures enhance the reliability of the emergency electrical power supply for the Mélox facility. Loss of the off-site electrical power supplies and the conventional emergency power supplies In the event of loss of the off-site and emergency power supplies in a non-earthquake situation, the consumers whose shutdown could jeopardise the integrity of the first containment system are taken over by the backup network. In the event of an earthquake, the consumers whose shutdown could have consequences on the environment are taken over by this network. Automatic mechanisms start the backup diesel generator sets and the supply of the backup electrical panels. The backup network is designed to the DBE. Loss of the off-site electrical power supplies and the conventional emergency power supplies and any other on-site emergency electrical power source Total loss of the electrical power supplies leads to loss of the following safeguarded functions: safeguarded dynamic containment (stopping of fans), cooling (stopping of fans, cooling units and recyclers) and safeguard operating control of the facility. In the event of total loss of the power supplies, radioactive material containment is maintained by the key SSCs associated with static containment. Damage to the key SSCs further to an earthquake or a rise in temperature can lead to feared situations. Conclusion on the measures planned to protect the facilities against the risk of loss of the electrical power supplies The licensee considers that the loss of the normal and emergency electrical power supplies does not lead to feared situations. However, the total loss of electrical power supplies in an earthquake situation and the impact of the associated loss of the cooling function must be examined (see below). The feared situations are loss of containment and criticality accidents. The safety of the Mélox facility in the event of loss of the electrical power supplies is dependent on its capacity to maintain containment of the materials. These are fail-safe systems. ASN judges these systems sufficient to ensure the safety of the facility in electrical power supply loss situations. ASN will issue formal demands concerning the licensee's capacity to manage the loss of the cooling function, further to loss of the electrical power supply or not (see following section). Loss of the cooling systems / heat sink The thermal risk is due to the heat released by the fissile materials, which can induce degradation of the constituents of the first containment barrier, of the radiological protections or neutron-absorbing screens. This risk is high in the fissile material storage areas and in the homogenisation facilities.
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