Geologic containment. The salt domes in the northern part of Germany where the tentative site for a waste repository is located are one example of a geologic containment under considera­tion. They are more than a hundred million years old. It was only after the formation of these salt domes that America and Europe began to separate, forming the Atlantic Ocean, and that the Alps came into being. The salt domes withstood numerous geologic catastrophes without changing their shape or location. The area was three times covered by ocean water and dried again, vulcanism developed all over Germany, and later several glaciers moved across the salt. Nothing, however, happened to the salt formations, thereby proving that they were in perfect equilibrium with the geologic environment. As long as this equilibrium is not disturbed by human activities, it is extremely unlikely that the salt domes will undergo any changes. The utilization as waste repository will influence this equilibrium mechanically by mining the salt and thermally by charging it with heat sources. Geologists and mining engineers, however, have no doubt that this can be done without serious disturbance of the equilibrium. This gives a very high degree of confidence in the long-term integrity of the salt formation.

Miration of radionuclides. Even in the event of intrusion of groundwater into the waste repository, the low solubility of the waste, the slow motion of water at depth, the sorptive capacity of the soil, and the distance from the repository to water used by people provide additional protection against contamination of the environment.

Burkholder [B8] and others [FI] have developed models for analyzing the consequences of accidental intrusion of underground water into a geologic repository for HLW. In an example calculation [B8] it is assumed that the geologic medium has sorptive properties typical of U. S. western desert subsoil, that the waste material dissolves at the slow rate of from 0.03 to 0.003 percent per year, that the solution percolates unidirectionally through 10 km of sorptive soil at rates of from 1 to 10 m/year, and that the underground water is discharged into a river used for drinking. The general result is that nuclides that are not sorbed by the soil, e. g., tritium, 14C, 1291, and possibly "Те, reach the river within a few thousand years. Other radionuclides that are sorbed by the soil are delayed for a much longer period, e. g., over a million years for plutonium, and are attenuated by radioactive decay and dispersion.

Procedures for evaluating the rate of migration in the event of intrusion of water into an underground repository are detailed in the foregoing references.