A large number of nuclear plant systems contain pressurised fluids and are consequently subjected to general pressure vessel regulations (see chapter 3, point 2.2.1).

At central government level, responsibility for supervising application of the regulations lies with the ASN for nuclear pressure vessels containing radioactive products inside BNIs, and the Directorate for Regional Action, Quality and Industrial Safety (DARQSI) for other pressure vessels.

Of the BNI pressure vessels subject to ASN supervision, the main primary and secondary systems of EDF's 58 pressurised water reactors are particularly important systems. Since under normal conditions they operate at high temperature and pressure, their in-service behaviour is one of the keys to nuclear power plant safety.

ASN supervision of these systems is consequently very specific. It is based:
- with regard to the design and construction phase, on the order of 26 February 1974 for the main primary system (CPP) and on basic safety rule II.3.8 of 8 June 1990 for the main secondary systems (CSP);
– with regard to the operations phase, on the order of 10 November 1999 concerning supervision of the operation of the main primary system and the main secondary systems of pressurised water nuclear reactors, which gives the requirements for these two types of systems.

The ASN has prepared a new regulatory text, the order of 12 December 2005 concerning nuclear pressure vessels, which was published at the end of 2005. It will apply as of 2006 to the construction of nuclear pressure vessels, in particular reactor main primary and secondary systems (see chapter 3 point 2.2.1).

Pressure vessel operation is supervised. This supervision in particular applies to the in-service surveillance programmes, non-destructive testing, maintenance work, disposition of nonconformities affecting the systems and periodic post-maintenance testing of the systems. The principal PWR main and secondary system files currently being dealt with are discussed below in chapter 12.

In BNIs, as in any industrial firm, compliance with regulations concerning health and safety in the workplace is the responsibility of labour inspectors. In the case of EDF's nuclear power plants, supervision is carried out by DRIRE agents under the authority of the Directorate for Energy Demand and Energy Markets (DIDEME) at the Ministry for the Economy, Finance and Industry, by delegation of the Ministry for Labour. At the DRIREs, the agents carrying out this activity may also be BNI inspectors and could in the future be radiation protection inspectors.

Nuclear safety supervision, radiation protection and labour inspection actions have common concerns, notably the organisation of work sites and the conditions governing use of subcontractors. Whenever necessary, the ASN and the DIDEME therefore aim to co-ordinate their respective actions.

Finally, exchanges with the labour inspectors can also be a valuable source of information on the employment relations situation, in a nuclear safety and radiation protection context more attentive to the importance of individuals and organisations.

The operator is required to provide the ASN with all data required to enable it to carry out its inspection functions. The volume and quality of this data should enable the technical demonstrations presented by the operator to be analysed and the inspections to be targeted. It should also allow identification and monitoring of the key events marking BNI operation or a TMR.

When ASN supervisory actions reveal failures to comply with safety requirements, penalties can be imposed on the operators concerned, in some cases, after service of formal notices. Penalties in such cases may consist in prohibiting restart of a plant or suspending operation until the requisite corrective measures have been taken (point 1.2.3).

Finally, to ensure that supervision is as effective as possible, by checking that adequate resources are allocated to its duties, the ASN is developing an approach involving transfer to the operator of certain decisions for which it was hitherto responsible. This is the principle of "internal authorisations" (see point 1.2.5).