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Nuclear Waste Management
Published in William J. Nuttall, Nuclear Renaissance, 2022
High level wastes are intensely radioactive. The primary defining characteristic of HLW in the United Kingdom is not actually based upon radioactivity but rather on thermal properties. HLW is defined by the attribute that it is self-heating from the radioactive decay of the waste itself (primarily of the fission products in the waste). The main radioactive components of HLW are the long-lived fission products such as technetium-99, caesium-135, and selenium-79 and minor actinides such as americium-241, neptunium-237, and curium-242. The most active output of reprocessing is a liquid solution of the fission products and minor actinides dissolved in nitric acid. The conditioning of this liquor to HLW consists of a series of processes: chemical reduction, evaporation, vitrification with boron (to absorb thermal neutrons), and the preparation of large sealed steel flasks containing the HLW in a solid glass form. The flasks are placed in air-cooled channels in a special vitrified product store at Sellafield.
Iron-induced association between selenium and humic substances in groundwater from deep sedimentary formations
Published in Journal of Nuclear Science and Technology, 2023
Motoki Terashima, Takashi Endo, Shingo Kimuro, Hikari Beppu, Kazuaki Nemoto, Yuki Amano
Selenium-79 (79Se) is a key radionuclide in safety assessment (SA) for a system of geological disposal of high-level radioactive waste (HLW), because it is a long-lived fission product with a half-life for 2.95 × 105 years [1] and can be mobile in geosphere due to its anionic form [2–4]. The presented SA for the disposal systems [5–7] concluded that the radiation impact of 79Se on the biosphere could be limited by retardation via the formation of precipitates such as elemental selenium [8–10] and/or iron selenide [11,12] and slight sorption to host rocks [13–15] and bentonite as an artificial barrier [16]. However, this conclusion was derived by assuming only inorganic Se species, although organic Se species such as those associated with natural organic matter (NOM) could occur in groundwaters at considerable levels [17,18].