- 234 - o stopping of rotation of the pendulum type centrifugal decanters in the R1 and T1 units (estimated time lapse before ruthenium release: 50 hours); o loss of cooling of the storage tanks containing concentrated solutions of fission products from units R2, T2, T2C, T2D, SPF5, SPF6, R7 and T7 (estimated time lapse before solutions boil: between 17 and 35 hours depending on the equipment); o loss of cooling of the fission product solution concentrating evaporator condensers of units R2 and T2 (estimated time lapse before boiling: 44 hours); o loss of cooling of the plutonium oxide (PuO2) container storage areas of the BSI and BST1 units (estimated time lapse before concrete reaches a temperature of 160°C: about 20 hours); For the risk of radiolysis hydrogen explosion: o loss of the air supply sweeping the tanks storing the solutions of concentrated fines and the alkaline rinsing solutions of units R1, T1, T2, R7 and T7 (lower flammability limit (LFL) of hydrogen reached in 7 to 48 hours); For the loss of containment risks: o loss of sealing of the so-called "HAO" waste storage silos and the STE2-A unit; these feared situations were not studied in greater depth, as AREVA considers that appropriate means will soon be implemented as part of the "waste recovery and conditioning" operations (water table lift pumps). The licensee has identified the spent fuel pools and the storage tanks for the concentrated fission products of unit SPF6 as the target perimeter for the feared situations study. For the La Hague site, AREVA identifies the following as key SSCs: the SSCs relating to cooling of the fuel assembly storage pools (outside perimeter of UP2-400 plant) in abnormal situations (safeguard or consequence mitigation mode); the SSCs relating to the cooling of the storage areas for fission products from the UP2-800 and UP3-A plants in abnormal situations (the file only examines the robustness of the SSCs associated with the SPF6 unit, as this is considered to be representative of the other units); the two backup diesel fuel tanks (necessary for the refuelling of the generator sets). ASN considers that the feared situations assessment for the La Hague site must be supplemented, in particular to take the possible aggravating factors into consideration (fire, etc.). Other facilities in the fuel cycle Mélox The feared situations analyzed are: those described in the safety frame of reference (transport accident of the LR47 tanker truck containing medium-activity (MA) effluents, criticality accident (in the homogeniser), uncontrolled fire in an area containing radioactive material (primary dosing room), loss of containment caused by an earthquake); a scenario involving simultaneous loss of the first and second static containment barrier and the dynamic containment of the Powders units in building 500 with maintaining of the third static containment barrier made up by the outer shell of the building (basemat, walls, roof, doors and penetrations); a scenario of total loss of the electrical power supply or of the STE fuel rod storage unit cooling leading to a criticality accident due to the deterioration in the storage geometry. The licensee defines the safe states guaranteeing safety in all situations; they are based on the control of the two major risks, namely dissemination of radioactive materials (corresponding to the Important Safety Function (FIS) relative to the containment of radioactive materials) and the criticality risk (FIS: prevention of the criticality risk). The FIS's are divided into safety functions: the overall stability of the civil engineering structures, maintaining the integrity of the third containment barrier (minor cracking), cooling of fissile material, prevention of the criticality risk and the associated auxiliary functions.
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