As part of its nuclear installations safety supervision role, the ASN can make certain reactor operations dependent on its prior approval. In certain cases, prior authorisations were imposed on the licensee following significant incidents. Generally however, the ASN considers that the prior authorisation system must remain limited to the cases which specifically require it, either because stipulated in the regulations or because of the safety, radiation protection or environmental protection issues. Actually, such a system could encourage the licensee to shift the burden of validating its operations or documents onto the ASN and thereby pay less attention to their quality, which runs contrary to the principle of the licensee's prime responsibility for nuclear safety.

According to experience feedback in recent years, the ASN considers that some of the prior authorisation requirements could be lifted, provided that EDF reinforces monitoring of the activities and implements an appropriate supervisory organisation:

• lowering the primary system water level to the "low operating range" of the RRA system with core loaded (transient commonly called "mid-loop operation");
• reactor restart after outages without significant maintenance.

Since January 2005, the authorisations in these two areas have been issued by the DPN management or by the management of the plant concerned, after review by an internal commission independent of the decision-making chain and comprising safety and quality experts. EDF also checks the working of these processes and reports on them to the ASN.

During the course of 2005, the ASN conducted an inspection within the DPN to check compliance with the new provisions. In 2006, the ASN will conduct an inspection in each plant on the subject of internal authorisations.

In recent years, a number of anomalies have been detected in EDF nuclear power plants, to a large extent as a result of the systematic conformity checks required by the ASN, but also because of the questioning attitude of the licensee, which tracked down these anomalies at its own initiative. The ASN requires that those anomalies with potential safety consequences be corrected within a time commensurate with their significance.

The ASN considers that the checks conducted are the guarantee that a good safety level is maintained and that a facility on which nothing is done to find anomalies would only give the illusion of being safer than one on which the licensee looks for, finds and corrects conformity discrepancies.

Systematic checks: conformity reviews

The ASN requires that conformity reviews be conducted as part of the periodic safety reviews. The conformity reviews consists in comparing the state of the facility with the design safety requirements, taking account of changes made since construction, and listing any anomalies. These anomalies can be of various origins: design errors, construction defects, discrepancies introduced during maintenance, deterioration due to ageing and so on.

This review includes a check on the conformity of the steps taken to protect against external hazards, including extreme weather conditions and earthquakes, and against internal hazards such as high-energy pipe breaks, as well as a check on the ability of the equipment to operate in the degraded ambient conditions likely to exist in the event of an accident (known as "qualification for accident conditions"). To this must be added a "programme of additional investigations", the aim of which is to check the parts of the facility which are not covered by maintenance schedules because access to them is too difficult.

The conformity review on the 900 megawatt reactors ran from 1997 to 2001, while that for the 1300 megawatt reactors started in 1999 and ended in 2003.

Real time" checks

In addition to the process of systematic anomaly searches, a questioning attitude on the part of the licensee's staff is another means of detecting conformity discrepancies: routine field inspections or even a critical review of older design studies in the engineering centres can contribute to this. Several anomalies were discovered in this way and the ASN considers EDF's attitude in this area to be positive.