- 205 - Definition of a hard core Following the complementary safety assessments (CSA) carried out on the nuclear installations after the Fukushima accident, ASN considers that the safety of nuclear facilities must be made more robust to improbable risks which are not currently included in the initial design of the facilities or following their periodic safety review. These facilities must be given the means to enable them to deal with: a combination of natural phenomena of an exceptional scale and which exceed the phenomena used in the design or during the periodic safety review of the installations ; very long duration loss of electrical source or heat sink situations capable of affecting all the installations on a given site. ASN will therefore require that by 30th June 2012, EDF define and then deploy a "hard core" of material and organisational measures able to manage the basic safety functions in these exceptional situations and stipulate what steps have been taken. These steps would thus guarantee ultimate protection of the installations, with the following three objectives: Prevent a severe accident or limit its progression, Limit large-scale releases in an accident scenario which could not be controlled, Enable the licensee to perform its emergency management duties. To define the requirements applicable to this hard core, EDF shall adopt significant fixed margins compared to the current baseline safety requirements. The systems, structures and components (SSCs) which are included in these measures shall be maintained in a functional state in the extreme situations studied by the CSAs. In particular, these SSCs shall be protected against the on-site and off-site hazards induced by these extreme situations, for example: falling loads, impacts from other components and structures, fires, explosions. The proposals to be transmitted by the licensees will be reviewed by ASN and its technical support organisation. Regarding the EPR reactor of Flamanville 3, EDF proposed several measures to increase its robustness. ASN estimates that these propositions are relevant, and considers that they should be implemented. Similarly to other reactors, ASN will require EDF to identify the equipments to be included in the hard core, including the existing or complementary systems to ensure control of the pressure in the containment building in case of severe accident. Earthquake The complementary safety assessments demonstrated that the current seismic margins on the EDF nuclear reactors are sufficient to avoid cliff edge effects in case of limited exceeding of the current safety requirements . These CSAs confirmed the interest of he periodic review of the seismic risk on the occasion of each ten-yearly periodic safety review. Following the analysis of the CSAs and the targeted inspections it carried out in the summer of 2011, ASN identified a number of areas for improving safety, linked to the seismic robustness of the facilities. With regard to the earthquake risk, ASN will thus be requiring that EDF: ensures that the equipment capable of managing the basic safety functions is protected against fire in the event of an earthquake. The main measures to protect the facilities against fire are not today designed to withstand the earthquake in the facility's baseline safety requirements; increases the way this risk is taken into account in the day-to-day operation of its reactors: enhanced operator training, improved consideration of the "event-earthquake" issue, compliance with the basic safety rule regarding seismic instrumentation (maintenance, familiarity of the operators with the equipment, calibration). In a number of NPPs, ASN observed deficiencies in application of the safety requirements in force for the seismic risk.
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