SITE REHABILITATION

The final step in the dismantling of a nuclear facility is to rehabilitate the site. The IAEA has issued recommendations for the release of sites that have accommodated activities involving radioactive materials. These recommendations address the contamination levels to be achieved prior to the release of a site, and the cleanup tools and methods to be implemented in order to achieve these levels. For the unconditional release of a site, the IAEA recommends a maximum individual dose limit of 300 µSv/year after the cleanup phase, regardless of the manner in which the site is to be reused. This limit is considerably higher than the dose limit of 10 µSv/year often recommended for unconditional disposal of radioactive materials. The IAEA justifies this difference based on the fact that the uncertainties associated with the future use of radioactive materials are much higher than those associated with the future use of a site, hence the more conservative approach for materials. The IAEA recommends the implementation of a four-step strategy for the release of a site that has accommodated a nuclear facility:

• Site characterization (natural environment and contamination level), i.e. data needed to assess the radiological impact of the site.
• Assessment of site compliance with unconditional release criteria, i.e. use of generic or specific threshold values (construction of scenarios taking into site-specific characteristics).
• Definition of final objective: cleanup work or implementation of restrictions regarding future use of the site.
• Development of a cleanup plan.

In Germany, the new radiological protection order specifies the conditions for the unconditional release of nuclear sites. The order proposes specific thresholds for each radionuclide. These thresholds are based on an individual dose limit 10 µSv/year, which is more constraining than the limit recommended by the IAEA.

In the United Kingdom, the former National Radiological Protection Board (ex-NRPB) issued a set of recommendations in 1998 regarding radiological protection objectives for soils contaminated with radionuclides. These recommendations indicate that the cleanup of soils contaminated with radioactive substances must be performed in such a manner so as to ensure that potential exposure levels for site cleanup personnel and future site occupants will remain as low as reasonably possible, in keeping with the economic and social context. Public expectations must be taken into account. Optimization considerations must not be limited to cost-benefit analyses, but instead must encompass all aspects of the problem. In terms of release conditions, these recommendations indicated that public exposure to ionizing radiation resulting from residual soil contamination be limited in such a manner that the associated risk factor does not exceed 10-5/year. It should be noted that this risk constraint corresponds to an effective dose limit of approximately 0.3 mSv/year, similar to that recommended by the IAEA.

In France, no individual dose limits or maximum permissible activity concentrations are defined in regulations concerning the release of nuclear sites. An industrial operator wishing to clean up and release a site contaminated with radioactive substances must first submit a report to the National Authority, specifying the planned cleanup strategy and the final radiological state sought. An impact assessment must be provided, addressing the final radiological state and future use of the site, and indicating the individual risk of exposure to ionizing radiation due to residual site contamination.

The National Authority insists on the fact that the operator in charge of contaminated soil cleanup operations must be able to demonstrate the application of radiological protection optimization principles under all conditions. In addition, it is essential that all potential risks (chemical risks in particular) be taken into account in the impact assessment. A facility decommissioning report may be acceptable even in cases where the final radiological state sought contains residual activity. Public utility servitudes should nevertheless be systematically requested. These servitudes may involve a number of limitations and restrictions (site surveillance, reserved access, etc.) whose implementation and duration are determined on a case by case basis.

The proper consideration of radiological protection objectives within the framework of dismantling projects poses a significant number of challenges. It appears necessary for the CEPN to capitalize on initial national and international experience feedback so as to ensure a continuous improvement of radiological protection performance benefiting all those involved in nuclear facility dismantling activities. Experience feedback will be used to ensure better consideration of radiological protection objectives during worksite preparation and monitoring, better training of relevant personnel, and better integration of the specific characteristics of dismantling activities into radiological protection procedures.

Reference Documents

P. Fayolle, C. Rappet, F. Drouet, M. Michelet, C. Schieber, L. Vaillant, Guide to enhance reliability of the dose estimates in dismantling, ISOE Symposium in VIENNA, 13-15 October 2009.

C. Badajoz, F. Drouet, L. Vaillant, T. Schneider, Réglementation et pratiques en matière de gestion des déchets radioactifs de très faible activité, CEPN Rapport N° 307, Juillet 2009.

AIEA, Release of Sites from Regulatory Control on Termination of Practices, Safety Guide N° WS-G-5.1, 2006

AIEA, Remediation of Sites with Mixed Contamination of Radioactive and Other Hazardous Substances, Technical Reports Series N° 442, 2006

NRPB, Radiological Protection Objectives for Land Contaminated with Radionuclides, Volume 9 N° 2, 1998.