Long-lived radionuclides in residues from operation and decommissioning of nuclear power plants

Abstract

Radioactive residues, in order to be classified as Low-Level Waste (LLW), need to fulfil certain conditions; the limitation of the maximum activity from long-lived radionuclides is one of these requirements. In order to verify compliance to this limitation, the abundance of these radionuclides in the residue must be determined. However, performing this determination through radiometric methods constitutes a laborious task. In this work, 129I concentrations, 239+240Pu activities, and 240Pu/239Pu ratios are determined in low-level radioactive residues, including resins and dry sludge, from nuclear power plants in Spain. The use of Accelerator Mass Spectrometry (AMS) enables high sensitivities to be achieved, and hence these magnitudes can be re determined with good precision. Results present a high dispersion between the 129I and 239+240Pu activities found in various aliquots of the same sample, which suggests the existence of a mixture of resins with a variety of histories in the same container. As a conclusion, it is shown that activities and isotopic ratios can provide information on the processes that occur in power plants throughout the history of the residues. Furthermore, wipes from the monitoring of surface contamination of the José Cabrera decommissioning process have been analyzed for 129I determination. The wide range of measured activities indicates an effective dispersal of 129I throughout the various locations within a nuclear power plant. Not only could these measurements be employed in the contamination monitoring of the decommissioning process, but also in the modelling of the presence of other iodine isotopes.