Performance assessment of salt isolation system for CANDU and LWR spent nuclear fuel

A long-term safety assessment of a repository for either spent CANDU or LWR fuel elements in a salt formation has been performed. A hypothetical repository site has been considered, using data of the European Community project PAGIS for all parts of the system: near field, overburden, and biosphere. Three scenarios have been taken into account: subrosion as the normal evolution of the salt dome, a combined scenario with brine intrusion from the overburden and from undetected brine pockets, and a cavern scenario representing future human actions. Spent fuel elements have been assumed to be disposed of in big storage casks in drifts. For reason of comparability, the same source term model has been applied for both waste types, but different inventories of radionuclides and different heat productions have been taken into account. The key parameter for assessing long-term safety was the radiation exposure in the biosphere. The results of the calculations demonstrate that both types of waste can be disposed of safely. For the combined brine intrusion scenario and for the human intrusion scenario, the radiation exposures are below the limit of the German radiation protection law. In the subrosion scenario, however, for conservative values of the input parameters the limit is exceeded in some calculations. (orig.)