Novel method for the determination of radionuclides and their precursors in concrete using LA-ICP-MS

Abstract

During the decommissioning of nuclear facilities, a range of materials are generated and need careful characterisation in order to segregate them into their appropriate waste stream. The procedures involved demand significant time and investments to accurately determine the radionuclide inventory necessary to proceed. Methodology requires sampling, homogenisation, dissolution and sometimes a separation step to measure radionuclides using their decay properties. The approach proposed here is to spatially resolve the distribution of major and trace elements in concretes, and by inference important neutron activation-induced radionuclides, using laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). The technique offers the possibility of an onsite sampling tool for the different concrete constituents such as aggregates and sand/cement mixes at the micron scale, with typical detection limits in the ng.g-1 range for most elements. Several shielding concrete samples from Windscale (Cumbria) and CONSORT research reactor hosted by Imperial College (Silwood Park campus) are investigated. Initial work focussed on the identification and main chemistry of the aggregate types involved, using a set of chemical characteristics to fingerprint the ablated phases. Subsequently, available and manufactured calibration materials are evaluated for direct quantification purposes, together with wet chemistry reference values obtained for each concrete constituent for validation. Typical chemistry can thereafter be linked to each phase and build the overall bulk information. Finally, the potential to measure 3H directly using ICP-MS is investigated. This theoretical approach describes the conventional analysis methods and problems with ICP-MS analysis and considers several technological advances from the original instrumentation to overcome these, including the latest instrument available and figures of merit based on practical data.