Instrumentation for decommissioning and dismantling of nuclear installation

Philippe Girones 1
1 LMN - Laboratoire de Mesures Nucléaires
SMTA - Service Mesures et modélisation des Transferts et des Accidents graves : DEN/DTN
Abstract : Today, facility cleanup, dismantling and decommissioning activities (D&D²) represent a mature industry. For CEA facilities in France, the results obtained on the Grenoble site $^1$ are proof of this, and technological advances such as the implementation of the Maestro system $^2$ confirm it. Process efficiency is based on mastering the three generic phases (high level functions) of any manufacturing industry: storage management, treatment (physical and radiological reduction) and then waste conditioning (product). The procedures have been deployed in complex situations and are adapted to meet the challenges of different technical configurations: reactor, research laboratories, spent fuel treatment plants, etc. The point in common is the management of a source term (Bq). Each step in a D&D² procedure is controlled depending on the evaluation of the radiological levels involved. Nuclear instrumentation is therefore a major function in the deployment and the mastery of D&D² processes. During facility operation, most of the radiological and physical-chemical characterization equipment for materials at the end of the life cycle is concentrated on the waste packages. These devices are maintained during the D&D² phase. Further measurement and checking apparatus are distributed throughout the facility, from the components in their original positions to the storage of final packages. The functional and logical architecture of this instrumentation is in the form of an instrumentation diagram where the first apparatuses are adapted to characterizing the scenes to dismantle, then on to control cleanup and dismantling procedures, and at the end of the line, to demonstrate that the packages or the facility are free of radiological constraints. Measurements of gamma and neutron rays dominate the non destructive analysis techniques. Gamma spectrometry is the reference technique in D& D². Its deployment has been facilitated by the arrival of detectors which function at ambient temperature (CdZnTe, LaBr3, etc.). For complex scenes, the gamma spectrum processing result is combined with techniques for the localization of concentration points (hot spots). The combined processing of measurement results is carried out by the use of digital methods for drawing up curves for the yield and the estimation of the uncertainty associated with the quantity of interest. Overall, the characterization of D&D² waste has reinforced the use of coupled methods: physical and chemical analysis, gamma spectrometry, gamma camera and neutron counting.
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Philippe Girones. Instrumentation for decommissioning and dismantling of nuclear installation. Efmmin, Jul 2016, Marseille, France. ⟨cea-01690360⟩

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