Validation study for the determination of in-depth contamination in concrete structures using in-situ gamma spectroscopy

The decommissioning of Belgian Reactor 3 (BR3) approaches its final phase, in which the building structures are being decontaminated. Certain radionuclides, as Cs-137, might be present due to contamination. The costs for radwaste are forcing the producers to minimise its amount and to invest in decontamination and characterisation methodologies. This report describes a validation study for the determination of in-depth contamination in concrete structures using the ISOCS (In-Situ Object Counting System), a nondestructive measurement technique. The study consisted of three main objectives: • identification and quantification of the main sources of standard uncertainty, • optimisation of the main parameters of standard uncertainty towards a decrease in expanded uncertainty, • verification of this method with a destructive method. Before this study, the expanded uncertainty seemed to largely exceed 100%. After adjusting several parameters, the expanded uncertainty is estimated at 80%. Optimising still more parameters in the near future, might lead to a reduced expanded uncertainty of about 60%. Results obtained using the non-destructive method have been compared with the traditional destructive method based on core drilling, sample preparation and standard gamma spectroscopy. For the one spot that has been tested, results obtained from both methods were in agreement.