Countries using nuclear energy tend to favour disposal of Low-Level and Intermediate-Level radioactive waste in mined repositories consisting of series of tunnels or drifts connected to disposal tunnels at a few hundred meters depth. Abandoned mines can serve as repositories for such waste and the present study indicates that this would be possible also for High-Level Waste in the form of spent reactor fuel. The technique implies encapsulation of such waste in metal canisters surrounded by densely compacted smectite clay in relatively shallow mined repositories as well as in very deep bored holes. Intermediate-Level radioactive waste can be disposed of in caverns in the form of packages of metal containers cast in low-pH concrete and embedded in dense smectitic clay.