Radiation-Stability of Smectite

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• 作者：Sté ; phanie Sorieul ; Thierry Allard ; Lumin M. Wang ; Caroline Grambin-Lapeyre ; Jie Lian ; Georges Calas ; Rodney C. Ewing
• 刊名：Environmental Science & Technology
• 出版年：2008
• 出版时间：November 15, 2008
• 年：2008
• 卷：42
• 期：22
• 页码：8407-8411
• 全文大小：188K
• 年卷期：v.42,no.22(November 15, 2008)
• ISSN：1520-5851

文摘

The safety assessment of geological repositories for high-level nuclear waste and spent nuclear fuel requires an understanding of the response of materials to high temperatures and intense radiation fields. Clays, such as smectite, have been proposed as backfill material around waste packages, but their response to intense radiation from short-lived fission products and alpha decay of sorbed actinides remains poorly understood. Cumulative doses may amorphize clays and may alter their properties of sorption, swelling, or water retention. We describe the amorphization of smectites induced by electron and heavy ion irradiations to simulate ionizing radiation and alpha recoil nuclei, respectively. A new “bell-shaped” evolution of the amorphization dose with temperature has been determined. The maximum dose for amorphization occurs at about 300−400 °C, showing that temperature-induced dehydroxylation enhances amorphization. The exact shape of the bell-shaped curves depends on the interlayer cation. At ambient temperature, ionizing radiation and alpha-decay events do not show the same efficiency. The former results in amorphization at doses between 10¹⁰−10¹¹ Gy which are greater than the total radiation dose expected for radioactive waste over 10⁶ years. In contrast, alpha-decay events amorphize clays at doses as low as 0.13−0.16 displacements per atom, i.e. doses consistent with nuclear waste accumulated over approximately 1000 yrs. However, the limited penetration of alpha particles and recoil nuclei, in the 100 nm - 20 μm range, will minimize damage. Clays will not be amorphized unless the waste package is breached and released actinides are heavily sorbed onto the clay overpack.