The first underground warren for disposing of spent nuclear fuel

a kilometre underground, in the Precambrian bedrock of Olkiluoto, an island off the south-western coast of Finland, a rough-hewn gallery a few metres wide and similarly high runs dead-straight through the granite. Underfoot, the floor is a bit muddy, though mostly rocky. Overhead, steel meshing stops any fragments that might have been loosened by the drilling falling onto people’s heads. Neither hard-hat-mounted torches nor the headlights of an electric van can reach far enough into the stygian darkness to pick out the gallery’s end, some 350 metres away in the distance.Within a few years, this gallery, part of the Onkalo spent nuclear fuel repository, should be a resting place for batches of waste from Finland’s two nuclear power stations to be sealed off permanently from the world. It was completed this month, the last of five almost identical tunnels that run parallel to each other, connected by a main access gallery (see diagram). If all goes well, a warren of roughly 100 more will be excavated as needed over the coming century. As new galleries open, old ones will be backfilled with clay and sealed with concrete, entombing their radioactive contents.