The repository's location has not been selected yet, but several sites have been studied extensively for several years. All of the sites are compatible with copper. Spent fuel contains a number of mineral-like compounds, some of which are only sparingly soluble in groundwater. A corrosion-resistant copper canister . The outer shell of the canister consists of a thick layer of pure copper.
Copper is the primary barrier between the fuel and the environment.
It alone will retard release of radionuclides for at least 100,000 years. A bentonite clay buffer , which completely surrounds the copper canister. Ben-tonite is a clay mineral found in Wyoming. It swells when soaked with water, causing it to squeeze into and seal crevices in the rock surrounding the canisters. Any radionuclides that leak from a canister would have to diffuse through the bentonite, a process that could take more than 10,000 years.