In a repository for spent nuclear fuel, gas generated by corrosion of the
iron in the canister may form small bubbles that will escape and rise to the
ground surface. Colloidal particles may attach to the surface of the bubbles
and be carried by them. If the colloids are supplied by the montmorillonite
clay of the buffer material surrounding the canister, the clay can be
carried away. Nuclides sorbed in the clay can be carried with the bubbles.
We have estimated the carrying capacity of the gas of the clay particles and
the escape rate of nuclides carried by the gas bubbles. The latter is also
compared to the escape rate by the conventional escape mechanisms from the
near field. We have further estimated the detachment of the nuclides from
the clay and their sorption onto the fracture surfaces of the rock as well
as their uptake by diffusion into the rock matrix along the bubble transport
paths.
The present paper is speculative and uses some hypothetical assumptions.
Although the processes that are modelled are known to exist there is not
enough known of several of them to quantify them accurately. The carrying
capacity of the gas used in the calculations is an upper bound and probably
very much exaggerated. Even so, the consequences are minor for the release
of radionuclides.