AbstractRepositories for nuclear wastes. Repositories for nuclear waste are planned in many countries. The repositories will be located in deep geologic formations. In several countries crystalline bedrocks are studied for siting repositories. In Canada, Switzerland and Sweden there are large rock laboratories where various experiments are underway. In Sweden the first civilian repository for low and intermediate waste is in operation. The safety of a repository depends primarily on the hydrology, water chemistry, and the transport processes. The development of the chemistry and the transport processes are to a large part known from other areas of chemistry and chemical engineering. There are, however, differences which depend to a large part on the complex geometry of the flow paths. These differences call for new investigation and computing methods. Questions and problems relating to radionuclide transport from and safety of a repository for nuclear waste are described.