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Millions of years ago a volcanic eruption deposited ash that became bentonite clay.

Collins, over at Washington State University, has been experimenting with spraying fine-powdered kaolin or bentonite, which are clays, mixed with water onto wine grapes so it absorbs materials that are in smoke.

Layers of clay — bentonite and montmorillonite, to be specific — are found beneath the ground, interspersed between layers of bedrock.

A series of barriers—giant copper casks, water-absorbing bentonite clay, and water-resistant crystalline rock—are expected to protect harmful radionuclides from seeping out of the site and into the local ecosystem.

If water were somehow able to seep into the repository, it would still have to get past the bentonite and copper to reach the spent fuel.