Deep geological repository means that radioactive waste and spent nuclear fuel, after period of temporary storage, is placed in a big depth (300–1,000 meters) in geological environment, which is very stable from long-term point of view. Insulation of radioactive waste from the biosphere for a very long time is achieved by system of manifold insulation barriers. The radioactive waste is insulated from the biosphere by appropriate option of waste treatment, engineering barriers and geological environment for several tens of thousands years as minimum.

With geological storage of radioactive waste two basic approaches are applied. The first consists in insulation of waste on the spot, to prevent release of radionuclides to environment. The second approach consists in controlled release and scattering of radionuclides in environment with a very well-known properties (dilution). Most of proposals of storages use both the above mentioned principles in an appropriate way, i.e., after phase of insulation follows the phase of controlled dilution and scattering. Effective immobilization and scattering will decrease concentration of radionuclides on levels that do not represent, neither in a very remote future, any risk for environment and population.

Deep geological repository is passive and long-term, with no requirements for further activity or institutional inspection. The risk of unintentional violation of the storage by human activity in the future is very low due to careful selection of locality. If society develops steadily in the future, then records about the locality and social control will retain a very long time after enclosure of the storage, by which risk of violence becomes even lower.