Chapter 10: Solid-solution formation and the long-term safety of nuclear waste disposal
Dirk Bosbach
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The disposal of nuclear waste in geological formations poses major scientific and social challenges to be met in the coming decades. One of the key issues is the long-term safety of a waste-repository system over extended periods of time (up to 106 years). Demonstrating the safety over geological time scales requires a sound understanding of the migration and retention of radionuclides in the geosphere. Predicting the geochemical evolution of a waste-repository system over such time scales cannot be based on ‘simple’ extrapolations of empirical phenomena, but requires molecular-level process understanding. In recent years it has been demonstrated that understanding fundamental reactions can improve the reliability of geochemically based long-term predictions. A sound understanding of radionuclide binding to minerals by sorption reactions is an important issue when discussing the long-term safety of nuclear disposal. The need of the radiogeochemistry community for molecular-level system understanding of structural incorporation of key radionuclides and subsequent solid-solution formation will be discussed on the basis of two prominent examples: (1) the (Ra,Ba)SO4 solid solution series; and (2) the uptake of trivalent actinides and lanthanides by calcite. The current status of our knowledge of these systems will be discussed critically and knowledge gaps for the long-term safety assessment will be identified.
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