Solubility equilibrium and surface reactivity at solid/liquid interfaces of relevance to disposal of nuclear waste

- Solubility of solids in water is often a surface and not a bulk phase phenomena.
- This indicates that bulk phase thermodynamic data cannot always be derived from solubility data.
- Sorption/desorption equilibria and solubility equilibria have been linked.
- New interpretation of solubility control of radionuclide release from spent nuclear fuel.

Solubility equilibria of solids in water are an integral part of the thermodynamic assessment of the long term behavior of nuclear waste in geological formations. In this paper, we do not provide new thermodynamic data on solubility of relevant solids but we show, under which conditions meaningful thermodynamic data can be derived from solubility data and under which conditions this is not the case. Application of isotopic exchange techniques shows that sometimes equilibrium is only established between the surface and the solution, in other cases equilibrium involves the overall solid/liquid phase system. In case of slow reaction rates of oxides of tetravalent radionuclides, bulk phase thermodynamic data cannot be obtained from such systems.