- 254 - Paraseismic design rules have been applied to the Mélox buildings and civil engineering structures. The initial design of the structures used the spectra established in application of RFS 1981: a fixed spectrum (type I) PGA 0.3 g corresponding to a near earthquake, two spectra (types II.1 and II.2) PGA 0.21 g corresponding to two distant earthquakes of intensity VIII MSK. These spectra taken as a whole are called "DBE 1981 Mélox" (RFS 1981 design-basis spectrum of Mélox). The modifications to building 500 were justified with the spectra established in application of the provisional 1998 version of RFS 2001-01: a spectrum corresponding to a near earthquake of magnitude 5.3 and focal distance of 7 km, PGA 0.25 g, a spectrum corresponding to a paleo-earthquake of magnitude 6.5 and focal distance of 13.5 km. These spectra taken as a whole are called "DBE 1998 Mélox" (design-basis spectrum of the 1998 version of RFS 2001-01 of Mélox). The update of the Definitive Safety Report revision B in 2003, approved by ASN, consolidated the justification of the encompassing nature of the spectra used for the design of the structures with respect to the RFS 2001-01 spectra. Measures to protect the facilities with respect to the seismic risk / design-basis earthquakes The civil engineering essentially fulfils a containment function, but it also contributes to criticality risk prevention, particularly by helping support the equipment necessary for maintaining storage area geometry. The structural elements have been designed to bring together all the conditions necessary to preserve their condition with respect to: the general balance of the building; the stability of form of the building; the integrity of the walls (little cracking). Nuclear buildings tend to have a low height-to-width ratio to minimise their mechanical stresses in the event of an earthquake. Furthermore, the surface layers of the ground on which the buildings are located has been replaced by noble foundation materials resting on consolidated gravelly-sandy alluvial deposits. The various inspections carried out in the substitution backfill put down after excavation revealed satisfactory overall uniformity and high compactness with, on the whole, mechanical characteristics equal to or higher than the subjacent gravellysandy alluvial deposits. Conformity of the facilities with the current frame of reference Industrial commissioning of the Mélox plant was declared in May 2000, and the licensee has carried out the first periodic safety review of the facility. It submitted the corresponding report to ASN at the end of September 2011, in accordance with the regulations. The conformity review, for which the licensee can be held liable, is based on the analysis of the Elements Important for Safety (EIS), and consisted in verifying the conformity of: the facility with respect to its design requirements, considering questions of equipment aging and obsolescence, the operating practices with respect to the applicable frame of reference.
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