- 235 - For the feared situations considered, the licensee postulates failure of the successive lines of defence and identifies the barriers whose robustness is examined with respect to the elements in the ASN specifications (earthquake, flooding, extreme climatic events, loss of electrical power supplies or loss of cooling). A list of key SSCs was established from this, either "structural" (civil engineering and mechanical structures) or "functional" (items fulfilling active functions). The key SSCs analysed were: the third static barrier of building 500 and its extension (walls of laboratory premises on the edge of the buildings, doors, filters, ventilation valves and adjustments); the backup electrical systems, including the backup diesel generator sets and their fuel supplies; the STE storage area and its cooling units, recyclers and chilled water system. ASN considers that the identification of feared situations for the Mélox plant is globally satisfactory, but must be supplemented to include failure of the seismic detection systems and the mechanisms they control. FBFC Romans The licensee took the accidents catered for in the FBFC Romans on-site emergency plan (PUI) as the "feared situations", that is to say: a criticality accident in buildings C1, AP2 and R1; leakage of HF solution in the HF station; fire in buildings C1, AP2 and R1; a radioactive material transport accident; a chemical transport accident; aircraft crash hitting the UF6 container storage yard (scenario outside the context of the CSAs). According to the licensee, the processes involving the largest quantity of dispersible material (hot UF6, that is to say in liquid or gaseous form, and HF) are situated in building C1 (conversion area) and in the HF station (two 20m3 tanks of concentrated HF (50%)). The feared situations identified by the operator are: leakage of UF6 in the conversion area further to multiple failures leading to the feared situation (loss of the 1st containment barrier (cylinder, hose and internal valve), loss of the 2nd containment barrier(autoclave), malfunction of the ambient environment purification column, structural damage with loss of static containment). The consequences would be a direct discharge of UO2F2 and HF into the environment, corresponding to a source term of 6 cylinders each containing 2277 kg of UF6 (highly pessimistic estimate); an HF leak in the HF station further to loss of the containment of the 2 tanks of concentrated HF, malfunctioning of recovery in emergency retention pit, malfunctioning of the ambient environment purification column or loss of containment though serious damage to building. The consequences would be a large release of HF directly into the environment (source term of 34 m3 of concentrated HF). The key SSCs identified for the feared situation of "UF6 leak in the emission area" are: building C1 (earthquake); the autoclaves, the hoses and isolation valves and the UF6 cylinders (earthquake, flooding); the potential hazards for the autoclaves (earthquake). The key SSCs identified for the feared situation of "HF leak in the HF station" are: the building (earthquake); the tanks (earthquake, flooding); the potential hazards for the tanks (earthquake). ASN considers that the identification of feared situations for FBFC is satisfactory, but the licensee must make a complementary study of the potential hazards for the HF station.
RkJQdWJsaXNoZXIy NjQ0NzU=