RADIOLOGICAL PROTECTION OBJECTIVES ASSOCIATED WITH NUCLEAR FACILITY DISMANTLING OPERATIONS

A large number of decommissioned (or soon to be decommissioned) nuclear facilities are currently undergoing dismantling. This concerns various types of facilities (laboratories, GCR or PWR reactors, front-end nuclear fuel cycle facilities, etc.), with multiple radiological protection objectives associated with their dismantling (radiological protection of workers, radioactive materials and waste handling, site rehabilitation after dismantling). These past years, the CEPN has conducted various studies on the application of radiological protection principles and best practices during the dismantling phase. The results of these studies are presented in this article.

Generally speaking, the progress of work throughout the dismantling phase leads to changes in radiological conditions for workers (rupture of containment barriers, evacuation of radioactive materials, etc.). These changes in radiological conditions need to be predicted and monitored to ensure optimal radiological protection (radiation monitoring equipment, individual protective gear, etc.) under actual working conditions. In addition, the predictive assessment of radiological protection requirements is sometimes made more complicated by issues such as the partial loss of historical facility records, source term characterization problems, and the absence of operating experience feedback after facility decommissioning. There is often a strong temptation to overestimate source term values so as to avoid exceeding a target dose, but this is unnecessary and sometimes even in contradiction with the application of radiological protection optimization principles, as it may lead to poor resource allocation. The often-observed lack of radiological protection culture is particularly apparent in dismantling projects, with operators often resorting to subcontractors without solid experience in nuclear work. The present article provides guidelines for improving the preparation of dismantling work.

Nuclear facility dismantling operations produce very significant volumes of radioactive waste (with a very broad range of activity levels) and conventional waste, requiring the availability of waste management outlets (disposal, storage or partial recycling facilities). In France, the National Radioactive Materials and Waste Management Plan (PNGMDR) identifies the waste management outlets available or planned for each type of waste considered. In the case of very low-level waste (VLLW), which represents a significant amount of the waste generated during dismantling operations (for example, the dismantling of the George Besse 1 uranium enrichment facility is expected to generate approximately 150,000 tons of very low-level radioactive scrap metal), the PNGMDR stipulates transfer to the Morvilliers VLLW disposal facility. This approach is different from that adopted by a large number of countries on the basis of IAEA and EU basic safety standards authorizing the disposal of radioactive waste as conventional waste if the radionuclide content falls below the stipulated threshold. Nevertheless, the PNGMDR allows for the possibility of recycling very low-level radioactive materials, under certain conditions.

Finally, a site released by the operator after the completion of nuclear facility dismantling operations will require rehabilitation. The scope of the rehabilitation work required is strongly dependent on the site’s operating history (presence of contamination patches) and raises questions regarding the site’s future and the involvement of local actors intending to use the rehabilitated site.