Erika A. C. Neeft, Alwina Hoving, Jasper Griffioen, Thilo Behrends, Marja R. Vuorio, Mingkai Ma
A disposal facility can be constructed in a stable geological formation to emplace packages containing radioactive waste. After closure of such a facility, the waste is isolated and the radionuclides are contained for the far future by a multibarrier system composed of engineered and natural barriers. Favourable Dutch geological formations may include Paleogene clays due to their presence in the subsurface. Radionuclides from the waste may enter the clay host rock if they have not decayed and are released from the engineered barriers. The low permeability physically retains them but there are also chemical retainment processes in the clay host rock that prevent radionuclides from entering the biosphere. Non-radioactive counterparts of radionuclides in the waste and actinides are present in trace amounts in Paleogene clays. Their concentrations can be similar to those of long-lived radionuclides in the waste forms. Their variation in concentration in the sediments is statistically highly correlated with the variation in total clay content. Ion exchange has been hypothesized to be the main mechanism to chemically retain most of these trace concentrations for the following groups: alkali metals, rare-earth elements, some actinides, transition metals and perhaps even non-metals.