- 250 - For the La Hague site, the DSN79 spectrum (DBE 1979) used for the design of the facilities after that date is higher than that resulting from application of the RFS 2001-01 (reference spectrum for the La Hague site: DBE 2001). However, the DSN 76 spectrum (DBE 1976) used for the design of BNI 33 on the La Hague site is higher than the spectrum determined by application of RFS 2001-01 only for frequencies below 2 Hz. Measures to protect the facilities against the seismic risk / design-basis earthquakes The licensee indicates in its report that the foundation soil of the La Hague site was a hard rocky soil (first category envisaged by RFS 2001-01) which it therefore considered very suitable for building earthquake resistance. Regarding the quality of the paraseismic design, concrete buildings are usually braced by face walls with few openings and a gridwork of internal walls that are generally rise from floor to ceiling, subject to low shear stress, and floors forming horizontal webs. They are founded on basemats. The height-to-width ratio is usually low, which means that the walls function predominantly in shear mode. The licensee stated that experience feedback indicated that this category of structure tended to remain stable and only suffered limited structural damage at earthquake intensities higher than that considered in the design. These buildings have undergone three-dimensional calculation simulations taking into account the ground flexibility to give a good estimate of the natural frequencies and load distributions. The quality control of the La Hague nuclear constructions was based on technical requirements and a site organisation that complied with quality assurance principles. The licensee considers that the inspections performed by the prime contractor assisted by an approved inspection agency as from the 1980's are worthy of confidence. Conformity of the facilities with the current frame of reference As was said earlier, the design-basis earthquakes considered vary from one facility to another on the La Hague site. The oldest buildings are not designed to earthquake design standards. Most of the more recent buildings are built to earthquake design standards as from design-basis spectrum DSN 79, and in some cases the DSN 76 spectrum. The DBE 79 encompasses the reference spectrum of the La Hague site, derived from RFS 2001-01, and the DBE 76 encompasses the reference spectrum up to frequencies of 2 Hz. The most recent buildings therefore comply with the design standards currently in effect. However, the durability of facility conformity with the design hypotheses, particularly with respect to the effects of aging, has not been truly examined.
RkJQdWJsaXNoZXIy NjQ0NzU=