- 253 - Measures envisaged to reinforce robustness of the facilities to the seismic risk Structures resting on elastomeric supports The behaviour of these structures (ponds of pools C, D and E, cooling towers of pools and fission product storage areas) is governed by that of the elastic supports which provide great flexibility in the horizontal directions. Consequently the robustness of the structures resting on these supports should be evaluated not by considering the ductility of the structure itself, which behaves like a "rigid body", but by a specific analysis of the behaviour of the supports considering their distortion for the horizontal earthquake effects and the vertical earthquake effects, which they do not attenuate. For the La Hague site structures resting on neoprene supports, ASN will ask the licensee to make a specific analysis of their behaviour beyond the design-basis level, considering the vertical earthquake effect and examining their conformity with respect to the aging phenomenon. Furthermore, constructing pools on elastomeric supports favours sloshing phenomena (formation of waves on the free surface) in the pools (influence of the structure's low frequency response), which can lead to significant water overflows. ASN considers that the licensee must assess the consequences of the risks of pool water overflowing depending on the earthquake levels considered. It will issue a request in this respect. Auxiliary structures The backup structures ensuring the cooling of the pools and fission product storage tanks feature several civil engineering structures (cooling tower supporting structure, diesel generator set buildings, electrical rooms, etc.) and are linked by trenches or racks to the buildings containing the spent fuel pools or fission product storage tanks. AREVA has not presented an analysis of the earthquake behaviour of these racks and trenches, nor has it analysed the effects of differential movements of the structure in an earthquake, particularly with regard to the routing of pipes and cables. ASN considers that the licensee must analysis the robustness of the connecting structures designed to earthquake design standards (racks, trenches, etc.) and the equipment items they support, considering all the induced effects (inertial and kinematic effects). It will issue a request in this respect. Structures that have been reinforced and/or justified by redistributing seismic loads Some structures, such as the NPH and T4 buildings, required reinforcement, considering areas of cracking with load redistributions determined by an elastic calculation to ensure their stability in an earthquake considering the DSN 79 spectrum. These reinforcements, while preserving the resistance of the structure, do not confer robustness comparable with that of a structure built from the outset to earthquake design standards. ASN considers that the licensee must analyse the seismic behaviour of the T4 workshop using the methodology applied in the CSA report, considering the areas that have been justified by load redistribution. It will issue a request in this respect. 2.3.3 Other facilities in the fuel cycle (Mélox, FBFC) Mélox Design of the facilities The functions important for safety are: maintaining the containment of radioactive materials, preventing the criticality risk. The equipment and structures whose loss further to an earthquake could lead directly or indirectly to either an unacceptable dispersal of nuclear substances into the environment, or to a criticality accident, are designed to earthquake design-basis methods. Similarly, the equipment items likely to damage, following an earthquake, an equipment dimensioned to earthquake are also dimensioned to earthquake.
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