Safety issues, in other words protection of persons and the environment, can be significant, during clean-up or decommissioning operations, as well as during passive surveillance phases. The rapidly changing nature of the installation is a non-negligible risk factor in that it is harder than for an operating installation to guarantee that all potential risks have been consistently and exhaustively taken into account.

The above figure attempts to summarise the main risks encountered when decommissioning an installation and the periods during which these risks are highest.

The risks linked to waste management (radioactive waste disposed of inappropriately in a conventional channel, etc.) are present throughout all phases producing large quantities or a wide variety of waste.

As decommissioning proceeds, the risks identified during operation of the installation, primarily linked to the radioactive nature of the materials handled, are gradually replaced by risks more linked to radiation protection and conventional safety (decommissioning requires that the workers go into areas they were not used to visiting during operation) or risks linked to the technologies used for decommissioning and cutting the structures (often involving hot points with the concurrent risk of fire or explosion). The risks linked to the problem of the stability of partially decommissioned structures must also be taken into account, along with those linked to the obsolescence of the equipment (in particular concerning the possibility of fires breaking out in ageing electrical installations).

For complex nuclear installations, decommissioning work often lasts more than a decade, frequently coming after several decades of operation. There is thus a considerable risk linked to loss of memory of the design and operation of the installation, especially when the former licensees leave the installation, and it is vital to be able to collect and record the recollections of the persons involved in these phases, all the more so as the traceability of the design and operation of old installations is frequently less than rigorous.

With each subsequent phase in decommissioning, arises the question of the surveillance of the installation being at all times appropriate to its state and the risks entailed. It is often necessary to replace the in-service surveillance systems with other (radiological, fire) more appropriate means, either temporarily or more permanently. As it is hard to constantly check that surveillance is appropriate to the constantly changing state of the installation, there is a risk of failure to detect an incipient hazardous situation.

Once the final installation state is reached, there is still the risk of pollution being inadequately or not at all identified or poorly characterised, having a significant long-term impact on the site or its environment.

The decommissioning scenario (immediate or deferred) is selected by the licensee on a case by case basis, generally in the light of comparative studies. The strategies today adopted by the licensees, CEA or EDF, are presented in points 3.1 and 3.2.

Similarly, the various technical provisions chosen for each stage in decommissioning of a nuclear installation are chosen by the licensee on a case by case basis. However, to avoid splitting up the decommissioning projects and to improve overall consistency, the ASN asks that as of final shutdown of an installation, a file be submitted, explicitly presenting all the various works envisaged from final shutdown until the target final state is reached, and demonstrating at each step the nature and scale of the risk presented by the installation and the steps taken to control it.

Finally, in the current context regarding management of industrial sites being decommissioned, it seems necessary in most cases that there should be a means of preserving the memory of the past existence of a BNI on a site, along with any utilisation restrictions corresponding to the condition of the site. The procedures for delicensing after clean-up are mentioned in chapter 16.

The ASN specified the regulatory framework for BNI decommissioning operations in a note signed on 17 February 2003, following extensive work to clarify and simplify the administrative procedures, while improving the extent to which safety and radiation protection are taken into account.

New practical measures for application of article 6 ter of the above-mentioned amended decree of 11 December 1963 are now in place in order to:
- clarify the definition of the leading technical and administrative stages in decommissioning to ensure that it is better tailored to the diversity of nuclear installations;
- to encourage complete decommissioning either immediately or after slight postponement;
- encourage presentation and justification by the licensee of the decommissioning scenario chosen before initiating the regulation process, from the decision to cease operations up to complete decommissioning;
- to clarify the administrative notion of delicensing of a basic nuclear installation and the related criteria.

This revision leads to a clearer definition of the two main phases in the life of an installation, each of which is associated with a single authorisation decree, the authorisation decree for the operating phase and the final shutdown and decommissioning decree for the decommissioning phase. This creates a more balanced picture, both technically and administratively, between the importance given to the decommissioning phase and that given to the operating phase.

All these requirements are detailed in the ASN note of 17 February 2003, entitled: "regulatory procedures concerning decommissioning of basic nuclear installations". This note is available on the ASN website, www.asn.gouv.fr