A radiological characterisation method using in-situ nuclear measurements for a facility prior to decommissioning

Within the framework of nuclear facility decommissioning, a radiological description of the premises and of the process elements that it contains remains essential. It enables us well in advance to: - guide and provide assistance in the definition of dismantling scenarios; - optimise the work site with regard to radioprotection; - know ahead of time the volumes and conditioning of the waste according to the possible or specifically envisioned disposal methods (HLW, LLW). This approach enables us to optimise dismantling procedures from both the technical and economic standpoints. The CEA (DEN/DED/SCCD) has a methodology for carrying out the radiological characterisation of a nuclear facility undergoing dismantling. This method, based on in-situ measurements was perfected thanks to feedback obtained from many measurement campaigns carried out over the past few years on different types of facilities (reactors, hot cells, ventilation ducts, etc). Such a procedure can establish all source terms of a facility. It therefore provides the operator with complete data concerning the distribution of activities (contamination and activation) in his facility. This methodology is based on well-identified stages, to be carried out chronologically. The instrumentation and the calculation codes used are based on known principles but necessitate in certain cases a specific adaptation. Its originality resides in the combination of the different tools and techniques (instrumentation, calculation codes, radio-chemical analyses). Based on this structured procedure, we may examine a piece of data as complex as the global source term of the facility. Furthermore, it enables us to assist, step by step the work master in the complex process of dismantling a nuclear facility. This global characterisation method has been applied successfully on very different types of facilities