1- Fontenay-Aux-Roses CEA Clean-up methodology
For the denuclearisation of the first French nuclear research centre (CEA), the centre of Fontenay-aux-Roses started developing in 1999 a clean-up methodology to rehabilitate places that have been contaminated by radioactive materials. The structure of this methodology is comparable to the one that the Prevention of Pollution and Risks Management Direction published: “Management of areas that are potentially contaminated by radioactive substances”.
This methodology is based on a remediation objective and relies on four phases:
- Phase 1 corresponds to the collect of historical data about the radiological life of the place.
- Phase 2 corresponds to the constitution of a radiological assessment file for each area where the contamination has been confirmed. A study of the vulnerability of the environment is performed to determinate the most ambitious remediation level that is possible considering acceptable costs and technical constraints.
- Phases 3 and 4 are made up of realization of the clean-up process as defined in phase 2 with the requirements and the waste zoning. The radiological monitoring of the whole process is also an important task of these phases. At the end of these, the final radiological evaluation will validate the achievement of the clean-up objective and the final sanitary impact can be calculated.
2- Tools developed for soils characterization
To address the issues regarding the different phases of the clean-up methodology, the CEA-FAR developed vehicles equipped with measurement devices.
One of them, the VEgAS, is a four-wheel-drive vehicle with speed control system dedicated to the radiological characterization of soils. The vehicle is equipped with various devices to perform exhaustive radiological γ and β measurements of the ground (β energy > 900 keV). Furthermore, 0.5 ha per hour can be characterised with a 137Cs detection limit below 100 Bq/kg.
This vehicle is equipped with Kartotrak, a software platform which includes several tools, including Kartotrak RT, dedicated to real-time acquisition and monitoring of soils. All collected data are then processed through geostatistics in order to perform a radiological cartography, complemented by uncertainty map and probability maps. This method helps to highlight quickly areas of interest that need further in-situ gamma measurement to be able to identify the exact radionuclides.
VEgAS and these on-board tools are an efficient answer to the various needs in radiological evaluation of contaminated sites and soils, particulary concerning the optimization of measurement costs, remediation process and waste volumes.