A disposal facility can be constructed in a stable geological formation to emplace packages containing radioactive waste. After closure of this 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 can be Paleogene clays due to their presence in its 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 becoming present in the biosphere. Non-radioactive counterparts of radionuclides in the waste and actinides are present as traces in Paleogene clays. Their concentrations can be similar to the concentrations of long-lived radionuclides in the waste forms. Their variation in concentration in the sediments is statistically highly correlated to the variation in the total clay content. Ion exchange has been hypothesized to be the main mechanism to chemically retain most of these traces for the following groups: alkali metals, rare-earth elements, some actinides, transition metals and perhaps even non-metals.
Neeft et al. (Thu,) studied this question.