The clean-up method today preferred by the ASN for nuclear installations is based on a waste zoning methodology. Using a demonstration based on the design of the installation, its operating methods, an analysis of its history (incidents, modifications, periodic radiological checks, etc) or any other empirical type of demonstration, the licensee must determine the waste zoning in its installation by accurately defining the boundary between conventional waste zones and nuclear waste zones.

With regard to complete clean-up of the structures in the nuclear waste zones, a policy note was prepared by the ASN in 2005. The first line of defence to be used must be based on a comprehensive picture of the condition of the installation and an understanding of the physical phenomena involved (activation, migration of contamination for example). Modelling of these phenomena enables a minimum clean-up thickness to be defined, with addition of a fixed safety margin. The total clean-up thickness thus obtained then corresponds to the limit between a nuclear waste zone and a conventional waste zone. The licensee then removes all nuclear waste from the nuclear waste zones, before implementing an appropriate inspection programme on the remaining elements, to confirm that there is no contamination or activation (2nd line of defence). It then proposes to the Director General of the ASN, that this zone be downgraded to a conventional waste zone. After approval of this final waste zoning modification, the remaining conventional waste is disposed of in conventional channels and can be dealt with in the same way as normal industrial waste.

On the basis of this policy, the licensee of the Monts d'Arrée plant in Brennilis defined a general clean-up methodology based on determination of a minimum depth of concrete to be removed from the walls of the building, by analysing the operating history of this building, combined with modelling of migration of radionuclides through the concrete. After removal of this concrete thickness, a programme to confirm the conventional nature of the remaining walls was implemented.

In 2003 and 2004, EDF used this methodology to clean-up several nuclear buildings: the spent fuel building (BCI) and the effluent treatment station (STE) on the Monts d'Arrée site and all the hillside buildings at Chooz A. The requests for downgrading the nuclear waste zones in these buildings to conventional waste zones were approved by the ASN in 2004. These buildings were demolished using conventional demolition techniques and the resulting products are considered as conventional waste. Furthermore, in the current context of managing industrial sites being dismantled, the need became apparent for conservation of a trace of the past existence of a basic nuclear installation on a site, along with any utilisation restrictions appropriate to the condition of the site. A conventional encumbrance on behalf of the State is established by the ASN, together with the local State representatives concerned, and proposed to the owner of the land. This constraint is recorded in the mortgage register to guarantee its permanence. These procedures were implemented for the first time in the case of the FBFC installation in Pierrelatte in 2003: the licensee and state representatives signed a conventional encumbrance on behalf of the state, affecting the land within the BNI boundary, at the same time as the decision was signed to remove the installation from the list of BNIs. The same type of encumbrance was put in place in 2005 at delicensing of the SATURNE installation (BNI 48) in the CEA Saclay centre.