Activities at the Nevada Test Site, including past testing of nuclear weapons and ongoing disposal of low-level radioactive wastes, could possibly result in radionuclide releases to the environment. The risks to health and safety after the repository is closed, are quite different in character than short-term or environmental risks. At some point, thousands or tens of thousands of years in the future, a portion of the radionuclides in the underground repository could escape from the waste packages. If this occurs, radionuclides could then be carried by groundwater to the human environment. 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.