Structure determination of compounds for the immobilisation of Iodine-129 and Technetium-99

99Tc (half life 2.13 x 105 years) and 129I (half life 15.7 x 106 years) are abundant and long lived products of nuclear fission, with yields of 6% and 0.7% respectively for thermal fission of 235U. These radionuclides are of particular concern in closed nuclear fuel cycles, since the long half life and high production rate, combined with solubility and bioaccumulation. Future advanced nuclear fuel recycle strategies demand disposition of 99Tc and 129I in a robust wasteform, and isolation from the bio-sphere, in a deep geological disposal facility for 10E6 - 10E7 years. We have endeavoured to address this challenge, exploring the synthesis, structure and properties of ceramics for 129I and 99Tc disposition. Here, we propose to determine the structures of seven such ceramic compounds, within three families, using neutron powder diffraction, with natural isotopic abundance I and 99Tc.

99锝（99Tc，半衰期2.13×10^5年）与129碘（129I，半衰期15.7×10^6年）均为核裂变（nuclear fission）产生的丰度较高且长寿命的产物；在铀-235（235U）的热中子裂变中，二者的产额分别为6%与0.7%。这类放射性核素（radionuclides）在闭合核燃料循环（closed nuclear fuel cycles）中受到格外关注，因其半衰期极长、生成量可观，且兼具溶解性与生物富集性（bioaccumulation）。未来的先进核燃料后处理策略，需将99Tc与129I固化于性能稳定的废物固化体（robust wasteform）中，并通过深部地质处置设施（deep geological disposal facility）使其与生物圈（bio-sphere）隔离10^6至10^7年。本研究致力于应对这一挑战，探索用于固化129I与99Tc的陶瓷材料的合成、结构与性能。本文拟采用中子粉末衍射（neutron powder diffraction）技术，对隶属于三大类别的共计七种此类陶瓷化合物的结构进行测定，实验将使用天然同位素丰度（natural isotopic abundance）的碘与99Tc样品。