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 Alternative Energies and Atomic Energy Commission (CEA) of Fontenay-aux-Roses, established an important feedback and developed over the last 10 years a sound methodology for radiological characterization. This approach is based on several steps: - historical investigations; - 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 using geostatistics. This approach is now used to characterize soils under facilities. The paper presents the radiological characterization of soils under a facility basement. This facility has been built after the first generation of nuclear facilities, replacing a plutonium facility which has been dismantled in 1960. The presentation details the different steps of radiological characterization from historical investigations to optimization of excavation depths, impact studies and contaminated volumes.

In France, the nuclear industry has developed a substantial program for decommissioning plants and nuclear installations, and for remediating and rehabilitating industrial sites. The Commission for the Establishment of Analysis Methods (CETAMA) is a unit of the French Alternative Energies and Atomic Energy Commission (CEA) whose main objective is to improve the quality of analysis and measurement results in the nuclear field. Analysis is the primary tool for monitoring the spread of nuclear material. This document shows that sampling, in close relation with measurement techniques, is a factor of potential gain and risk reduction for site remediation, decommissioning, and rehabilitation projects.

The presented methodological study illustrates a geostatistical approach suitable for radiological evaluation in nuclear premises. The waste characterization is mainly focused on floor concrete surfaces. By modeling the spatial continuity of activities, geostatistics provide sound methods to estimate and map radiological activities, together with their uncertainty. The multivariate approach allows the integration of numerous surface radiation measurements in order to improve the estimation of activity levels from concrete samples. This way, a sequential and iterative investigation strategy proves to be relevant to fulfill the different evaluation objectives. Waste characterization is performed on risk maps rather than on direct interpolation maps (due to bias of the selection on kriging results). The use of several estimation supports (punctual, 1 m 2 , room) allows a relevant radiological waste categorization thanks to cost-benefit analysis according to the risk of exceeding a given activity threshold. Global results, mainly total activity, are similarly quantified to precociously lead the waste management for the dismantling and decommissioning project.