- 238 - The earthquake behaviours analysis of the facility's civil engineering structures is based essentially on an opinion of experts who evaluate a permissible earthquake level by referring to the minimum fixed spectrum (SMF) of RFS 2001-01. On completion of its analysis the CEA judges that the overall behaviour of Osiris is satisfactory for an earthquake acceleration level equivalent to 1.3 times the fixed earthquake level. With regard to conformity, the CEA indicates that performance of conformity examinations during preceding periodic safety reviews, combined with periodic inspections and tests, enables this to be checked. These periodic tests and inspections concern the automatic shutdown system on earthquake detection, and the civil engineering (measurement of leakage rate, visual inspection of the condition of the sealed cladding of the reactor coolant pump and heat exchanger bunkers, of the penetrations, and monitoring the development of a number of cracks in the reactor containment dome). Facility protection measures The CEA has identified the key structures, systems and components necessary to place and maintain the Osiris reactor in a safe shutdown condition. These SSCs are: the Osiris reactor emergency shutdown system; maintaining the leak-tightness and the water inventory of the reactor pools and canals, and at least canal No.2, ensuring in this case the availability of sluice gates 1 and 2 and a means of handling them; the operation of the natural convection valves of the primary cooling system. It is noteworthy that in 2010 as part of the Aménophis project, the CEA equipped the Osiris reactor with an automatic shutdown system on earthquake detection system. Evaluation of the safety margins and measures envisaged to reinforce robustness of the facilities to the seismic risk Although the CEA considers that the occurrence of earthquakes significantly higher than the site SSE on the Saclay site is not realistic, it thinks that work to improve the stability, particularly of the anchorings, can be envisaged on the metallic structure situated at level +8 m of the reactor building, which can represent a hazard, its stability being guaranteed up to an earthquake of 0.7 SF (fixed earthquake). According to the CEA, the mechanical equipment items on the whole have significantly higher margins than the civil engineering structures. For example, the margin evaluated for the equipment items varies from 1.3 to 2 whereas that for the infrastructures and superstructures varies from 0.7 to 2. The CEA has evaluated the overall margin relative to radioactive material containment integrity at 1.3. The CEA has also examined the risk of coolant leakage and loss, and indicated the measures envisaged to counter this type of event (installation of sluice gates, water movements within the facility, external water make-up, etc.). Measures to improve the safety of the facility, and opinion of ASN The examination showed that the safety margin coefficients put forward by the CEA required consolidation. Based on the information provided, ASN considers that the CEA must take the following measures, some of which were already identified in the CSA report: perform scheduled works to improve the seismic behaviour of the metallic structure at level +8 m with respect to the risk it represents for the pool; supplement the analysis of the risk of the pool liner and canal No.2 being damaged by superstructures or equipment items situated nearby; ensure seismic qualification of core and spent fuel cooling water make-ups to prevent them becoming uncovered; check the operability of the travelling crane (sluice gate movements).
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