Superior techniques for disposal of highly radioactive waste (HLW)

The Swedish Nuclear Fuel and Waste Company (SKB) has recently worked out a concept, KBS-3V, for disposal of highly radioactive waste in the form of spent reactor fuel, and asked for the Government’s approval and licensing. It implies blasting of tunnels at about 400 m depth and boring of large-diameter canister deposition holes extending vertically from the tunnel floor. The rock stresses will be critically high in the construction phase and lead to failure by spalling when the heat pulse from the canisters evolves. The canisters will be surrounded by dense expansive “buffer” clay for minimizing groundwater flow around and along them but the long-term performance of either of them is not adequately proven and the placement is impractical and risky. Four major changes of the concept would make it satisfactory. One involves reorientation of the deposition holes from vertical to 45° inclination in two directions for reducing the risk of rock failure. A second is to prepare ready-made stiff units of “supercontainers” with highly compacted blocks of clay tightly surrounding the canisters for simpler and safer installation of clay blocks and canisters. A third is to surround the supercontainers by clay mud that provides the dense buffer with water from start and supports the surrounding rock when the thermal pulse begins to raise the rock stresses. A fourth is to replace the proposed smectite-rich buffer by clay with higher chemical stability and lower but sufficient expandability. A possible fifth change can be to manufacture homogeneous copper canisters of HIPOW type, which would radically reduce the risk of contamination of groundwater by released radionuclides.

► Containers with clay-lined waste. ► Mud in holes matures clay. ► Leaning holes give stable rock.