Technetium-99m Transport and Immobilisation in Porous Media: Development of a Novel Nuclear Imaging Technique
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Technetium-99m Transport and Immobilisation in Porous Media: Development of a Novel Nuclear Imaging Technique Claire L. Corkhill1, Jonathan W. Bridge2,3, Philip Hillel4, Laura J. Gardner1, Steven A. Banwart3 and Neil C. Hyatt1 1
The Immobilisation Science Laboratory, Department of Materials Science and Engineering, The University of Sheffield, UK. 2 The Centre for Engineering Sustainability, School of Engineering, University of Liverpool, UK. 3 Kroto Research Institute, Department of Civil and Structural Engineering, The University of Sheffield, UK. 4 Department of Nuclear Medicine, Sheffield Teaching Hospitals NHS Foundation Trust, Sheffield, UK. ABSTRACT Technetium-99, a β-emitting radioactive fission product of 235U, formed in nuclear reactors, presents a major challenge to nuclear waste disposal strategies. Its long half-life (2.1 x 105 years) and high solubility under oxic conditions as the pertechnetate anion [Tc(VII)O4] is particularly problematic for long-term disposal of radioactive waste in geological repositories. In this study, we demonstrate a novel technique for quantifying the transport and immobilisation of technetium-99m, a γ-emitting metastable isomer of technetium-99 commonly used in medical imaging. A standard medical gamma camera was used for non-invasive quantitative imaging of technetium-99m during co-advection through quartz sand and various cementitious materials commonly used in nuclear waste disposal strategies. Spatial moments analysis of the resulting 99m Tc plume provided information about the relative changes in mass distribution of the radionuclide in the various test materials. 99mTc advected through quartz sand demonstrated typical conservative behaviour, while transport through the cementitious materials produced a significant reduction in radionuclide centre of mass transport velocity over time. Gamma camera imaging has proven an effective tool for helping to understand the factors which control the migration of radionuclides for surface, near-surface and deep geological disposal of nuclear waste. INTRODUCTION In Europe and the US, the preferred long-term disposal solution for nuclear waste is burial in a deep geological disposal facility (GDF) [1]. During the operational lifetime of such facilities (~106 years) the influx of groundwater will occur, leading to the deterioration of the engineered barrier system (composed of a cement backfill or clay, and the canisters in which the waste are stored). This will lead to the release and transport of low concentrations of long-lived radionuclides from the GDF and into the near-field (the surrounding host geology). It is not yet fully understood how radionuclide species will be transported from these engineered facilities when the containment is breached. In a failure scenario, it is expected that the transport of most radionuclides will be inhibited by the backfill material, which provides alkaline conditions to suppress the solubility of cationic radionuclides and a high surface area to enhance radionuclide sorption [2]. However, it h
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