Once nuclear reactors or nuclear facilities enter the decommissioning phase, large amounts of radioactive materials are produced requiring proper waste management. In view of an efficient separation of the different waste types, it is very important to radiologically characterize these wastes. This implies to identify the different relevant radionuclides and to determine the level of radioactivity. Based on this radiological characterization, materials can be sorted in different categories (low, intermediate and high radioactive) for final disposal (landfill, near surface or deep-geological repository) or for conditional or free release. In Belgium, and across Europe, many nuclear installations are planned to be decommissioned in the near future or are currently being decommissioned (e.g. BR3 at SCK•CEN).
So called ‘difficult-to-measure’ radionuclides challenge radiological characterization. These are beta- or alpha-particle emitters that are produced as fission or activation products during the life-time of a nuclear reactor and have a long half-life. The quantification of these challenging radionuclides may also be required in context of site monitoring and the associated analyses of environmental samples (soil, sediment, vegetation, water).
Determination of the ‘difficult-to-measure’ radionuclides employs destructive methods that are based on complete dissolution of the sample followed by laborious radiochemical separation procedures (e.g. by extraction chromatography) in order to have a pure fraction of the analyte of interest to be measured by beta and/or alpha-particle spectrometry or by mass spectrometry. These analytical methods are continuously being improved as new extraction chromatographic resins, sequential separation methods and the application of automatic systems for radiochemical separations are being developed (Hou et al., 2016).
In this PhD study, we will develop novel analytical methods and improve existing methods for chemical separation and subsequent measurements for a selection of ‘difficult-to-measure’ radionuclides (79Se, 36Cl, 129I, 151Sm, 147Pm, 41Ca) in different matrices. These radionuclides were selected because of an actual need for these analyses for decommissioning purposes and because of the scientific challenges in the development of the quantification procedures. The matrices considered in this project include real samples resulting from the decommissioning of the BR3 reactor (e.g. concrete from the bioshield). In addition, via participation in the INSIDER project (http://www.insider-h2020.eu/) we have access to additional relevant sample materials from decommissioning scenarios. The methodologies to be developed concentrate on fusion and combustion as sample dissolution techniques, extraction chromatography separation methods and LSC (liquid scintillation counting) and/or mass spectrometry (ICP-QQQ) as measurement techniques.
This work is co-promoted by Dr. Jixin Qiao of the Denmark Technical University.