Application of a gamma spectrometric method for in situ determination of surface and volume activity of radioactive waste using a CeBr3 scintillation detector: Metallic waste case

We propose a method for the in situ determination and discrimination of surface and volume activity in metallic or mixed (metallic/concrete) radioactive waste. Owing to its ability to evaluate the specific activities of radionuclides, such as 60 Co and 137 Cs, this method is particularly suitable for characterizing radioactive waste produced by the decommissioning of reactors and surrounding structures, including buildings. The method was tested under laboratory conditions and during the characterization of training stands with nuclear reactors at a former military site in Paldiski, Estonia. The method combines in situ measurements using a portable CeBr 3 scintillation detector and MCNP6.2 modelling of gamma-ray interactions, incorporating the exact geometry of the sample and the detector analyzing both the Compton edge-to-peak and Compton backscatter-to-peak ratios. The method uncertainty was generally below 30%, which is within the acceptable range for radioactive waste characterization. The procedure takes approximately 10 min, depending on the sample configuration, provided that an MCNP model of the sample is available. • Discrimination of surface and volume activity in metallic radioactive waste. • Use of a CeBr₃ detector and MCNP6.2 modelling for in situ waste characterization. • Spectrometric method based on analysis of Compton scattering and photopeak ratios. • Method tested at the Paldiski site on reactor compartment structures.