- 203 - 8 Conclusion The approach defined by ASN for the complementary safety assessments (CSA) is to study the behaviour of nuclear facilities in severe accident situations caused by an off-site natural hazard or, independently of any hazard, according to accident scenarios with characteristics (duration, number of facilities concerned, seriousness of the situation, etc.) exceeding the current baseline safety requirements. The CSAs thus also consist of a verification of the preventive measures and the steps taken to mitigate the consequences using the defence in depth principle: initiating events (earthquake, flooding), resulting loss of safety systems (loss of heat sinks, loss of electricity sources) and severe accident management. This approach, carried out with the aim of avoiding serious consequences for the environment and the populations as the result of a hazard or accident situation exceeding the baseline safety requirements, can be broken down into two main phases: conformity with the current design, which is necessary for the robustness of the facilities; an approach to the beyond design-basis scenarios built around the principle of defence in depth. ASN considers that EDF has carried out considerable work in the time available, in submitting its CSA reports, which comply with the spirit of the ASN specifications and which allow an analysis of the robustness of the facilities. EDF also presented proposals for improvements; ASN considers that these proposals provide a satisfactory answer to the objectives set for the CSAs. Owing to the short time ASN allocated to EDF in which to carry out these studies, the evaluation produced in 2011 is simply the first step in the process aimed at integrating the experience feedback and lessons learnt from the Fukushima accident. This approach will be continued in the coming years. 8.1 Steps to increase the robustness of the facilities (already implemented) In the light of the safety approach and the design methods used so far in France, along with the ten-yearly periodic safety reviews, the nuclear power plants look robust to the hazards considered in the baseline safety requirements. As a matter of fact, the periodic safety reviews of the NPPs require that EDF not only conducts a detailed conformity check of its facility, in order to maintain its level of safety over time, but also makes modifications to its facility in order to improve the level of safety of the installation. The level of the design-basis hazards are thus periodically reassessed on the occasion of the periodic safety reviews, to take account of operating experience feedback from France and abroad, plus the best international practices. Conformity of installations The conformity of nuclear installations with the safety requirements applicable to them is a key component of their safety and their robustness to the accident initiating events or hazards. For ASN, this conformity must be managed over the long-term and be based on a systematic search for any deviations which must then be processed in a way commensurate with the safety implications. The detection, notification and processing of non-conformities are now therefore the subject of ASN requirements as defined in the order of 10th August 198457 and in the general operating rules for nuclear power plants, which for example specify how quickly the reactors must be temporarily shut down according to the safety significance of the nonconformities. The CSAs confirmed that the processes put into place at EDF to detect non-conformities, in particular via the periodic tests, maintenance and periodic safety reviews, were satisfactory. The CSAs were also an opportunity for EDF to carry out specific investigations into the condition of its facilities. EDF has undertaken to complete these by the end of 2012. 57 Order of 10th August 1984 concerning the quality of the design, construction and operation of basic nuclear installations.
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