Isolation is achieved through the presence of barriers around the radioactive waste which can be either natural or engineered. A system of multiple barriers helps to ensure that any release of radionuclides to the environment will occur at an acceptably low rate. Barriers can either provide absolute containment for a period of time, such as the metal wall of a container, or may retard the release of radioactive materials to the environment, such as a host rock or a backfill material through sorption of radionuclides. During the period when the radioactive waste is contained by the system of barriers, the radionuclides in the waste will decay. The barrier system is designed according to the disposal option chosen and the radioactive waste forms involved.
Geological disposal is appropriate for high level and other long lived radioactive waste.
Many countries are in the process of developing or licensing such repositories. Experience shows that an iterative systems approach is very important in assuring that interdependencies between the different activities of site characterization, safety assessment, design, construction, waste package development, operation and closure are sufficiently considered and well integrated. The key feature of this concept is to ensure, after closure of the repository, a safe and passive solution which depends neither on the stability of institutions nor on the future level of development of society. This approach is of particular importance in developing geological disposal facilities. Although disposal of radioactive waste is normally carried out without the intention to retrieve the waste there is a discussion under way on retrievability, for a certain period of time, of radioactive waste from a repository.