In both cases, the issues are how long it would take radionuclides to reach the environment, whether humans would be exposed to such releases, and whether those exposures would be harmful. Several factors contribute to the ability of the repository to contain radionuclides. A key factor is that waste packages will generate a great deal of heat. Characteristics of backfill materials and the design of repository tunnels will determine movement of radionuclides in the immediate vicinity of the waste packages. The geologic setting of the repository must provide the ultimate containment for the waste.
Zeolites help to slow movement of radionuclides from the repository to the human environment.
The repository block is located several hundred feet above the water table. This means there should be minimal or no contact between waste containers in the repository and the water table. However, some water is present in the repository block. One of the major questions is how the heat generated by the waste will affect the water. Although the site receives only four inches of rain a year, and much of that evaporates before it soaks into the ground, the possibility that surface water could reach the repository through these fast pathways must be considered.