Radiological characterization for decommissioning - methodology, approach and example of a nuclear facility - 13096

Nowadays, nuclear industry is facing a crucial need in establishing radiological characterization for the appraisal and the monitoring of any remediation work. Regarding its experience in this domain, the French Atomic Energy Commission (CEA) of Fontenay-aux-Roses, established an important feedback and developed a sound methodology for radiological characterization. This approach is based on several steps: - historical investigations and functional analysis, - assumption and confirmation of the contamination, - surface characterization, - in-depth characterization, - rehabilitation objectives, - remediation process. The amount of measures, samples and analysis is optimized for data processing through geo-statistics. Geo-statistics allow to understand if the pollution phenomenon is structured or not and quantify uncertainties regarding to the characterization. This innovative approach, first developed for soils characterization, is now also used to characterize civil engineering of facilities. According to feedbacks concerning facilities structures characterization, it appears that the perfect command of the initial state is a crucial step to carry out an efficient decommissioning strategy. Indeed it is essential to know the thickness of floor and wall to remove in order to take the right decision. For instance, a wall removal of 5 centimetres could be impossible without weakening the structure or could involve underpinning or important work. In this context the initial characterization is a decisive step which involves efficient methods, tools and optimization. The original approach and methodology developed at CEA for soils characterization is now transferred to nuclear facilities. The aim is to provide a suitable framework to address a tremendously increasing demand about the characterization of contaminated concrete structures and facilities. The essential step is the perfect command of the initial radiological state in order to propose a sound and viable dismantling strategy. Indeed it happens that the characterization calls completely into question the initial strategy scheduled for decommissioning.