The reactor main primary and secondary systems (CPP and CSP), collectively referred to as the nuclear steam supply system (NSSS) and presented in point 1.1.3, are fundamental components of a reactor. They operate at high temperature and high pressure and as they contribute to all safety functions - confinement, cooling, reactivity control - they are the subject of extensive supervision and maintenance by EDF and in-depth monitoring by the ASN. Surveillance of the operation of these systems is regulated by the order of 10 November 1999, mentioned in point 2.2.1 of chapter 3.

In 2005, the ASN's actions primarily concerned assessment of the EDF demonstration of the 900 MWe reactor vessels' service life. On the whole, the ASN considered that the condition of the CPP and CSP in the French nuclear power reactors gave no cause for concern in the short term but that the known ageing and deterioration phenomena needed to be taken into account and it asked for appropriate measures in preparation for the third ten-yearly outages of the 900 MWe series.

When designing the systems, the manufacturer must assess how the NSSS will be damaged by the situations it will experience during operation. Sufficient margin must therefore be designed-in so that the various types of damage identified, particularly fatigue-related phenomena, do not impair NSSS safety.

In order to ensure that the licensee operating a nuclear power plant has assimilated the manufacturer's recommendations and adapted its operating conditions accordingly, the regulations require the creation of "reference files" for the systems.

The licensee must also supervise the systems during operation and set up a documentary system containing the reference files and all events marking the life of the NSSS.

The reference files

The above-mentioned order of 10 November 1999 thus requires that the licensee gather and update all system design, manufacturing and operating data which contribute to justifying system integrity. For reactors already in operation at the time the order was published, a time was allocated for compilation of these files.

Owing to the uniformity of the French reactors, EDF chose to create "plant series" reference files for all the reactors of each series (900 MWe, 1300 MWe and 1450 MWe) with separate "unit" files for each individual reactor. These "unit" files particular contain data concerning maintenance, faults and events which have occurred on this reactor. In 2005, through inspections or meetings, the ASN was able to check that nearly all the plants had set up an organisation and created a plan of actions for compiling and updating these files.

In May 2005, the ASN asked the Standing Nuclear Section (SPN) of the Central Committee for Pressure Vessels for its opinion on the first part of the "plant series" reference files. The SPN considered that on the whole these files were satisfactory but did state that additional data was needed. EDF will in particular be required to guarantee that the operating parameters considered encompass all possible values, and to classify the system zones with respect to the risk of fatigue or sudden failure. These data will need to be provided in time for the next maintenance document update.

ASN review of a second part of the reference files will continue in 2006.

Situations counting

The purpose of situations counting is to ensure that the NSSS design margins are maintained throughout the life of the reactor.

During reactor operations, the licensee must therefore check that the NSSS components do not encounter conditions harsher than those provided for in the design. It must in particular record in its documentary system those situations effectively encountered by the systems.

Counting of these situations is important to the ASN because it is a key factor in demonstrating the robustness of the equipment over its entire lifetime. The ASN carries out periodic inspections on this subject. The points tackled concern plant organisation, verification of activities, records and associated resources, archival, experience feedback, situations counting contractors, etc.

The ASN considers that this situations counting activity was not sufficiently stringent until 1997, at which point it asked EDF to take corrective measures. In 2002, the ASN began a tour of inspection, to be completed in 2006, to obtain an overview of how EDF now carries out this situation counting. The ASN has already observed an improvement but considers that further progress is still required. The level of quality differs from one site to another and much could be gained from harmonising the practices employed.