There’s one thing every planned permanent repository for spent nuclear fuel has in common: They’re all underground mines.

Like any mine, a mined repository for nuclear waste is a complex feat of engineering. It must be excavated by blasting or a boring machine, it must keep the tunnels stable using rock supports, and it must have ventilation, seals, and pumps to handle groundwater and make it safe for people and machinery. Unlike a mine, however, a repository must also transport and entomb canisters of radioactive waste, and it must be engineered to exacting standards that ensure the tunnels will keep the canisters safe for many millennia.

There is an alternative idea that dispenses with most of those downsides: disposal in deep boreholes. But can they be both feasible and safe?