Could deep drilling solve our nuclear waste problem?

Enlarge / Artist's impression of a deep borehole for nuclear waste disposal by Sandia National Laboratories in 2012. The red lines indicate the depth of mining repositories: Onkalo is the Finnish repository and WIPP is the US DOE repository for defense waste in New Mexico. Sandia National Laboratories

There is one thing that all planned permanent repositories for spent nuclear fuel have in common: they are all underground mines.

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

There is an alternative idea that eliminates most of these disadvantages: disposal in deep boreholes. But can they be both feasible and safe?

Go deeper underground

At first glance, disposal by deep drilling seems quite feasible.

The U.S. Department of Energy planned to drill a 4-5 kilometer (2.5-3 mile) vertical borehole to gain experience with the process, but the project was canceled in 2017. This borehole would have been about 10 times deeper than a mined deposit, but such depths are not unusual for oil and gas drilling.

Governments are not the only ones interested in this approach. Deep Isolation, a California-based company founded in 2016, aims to offer nuclear waste disposal in deep boreholes as a commercial service anywhere in the world. "Depending on your geology, we can design a borehole for this," said John Midgley, geologist at Deep Isolation. The company's designs could be anything from deep vertical boreholes to shallower J-shaped holes with horizontal disposal sections. Again, the oil and gas industry came first, drilling an estimated 160,000 boreholes with horizontal sections in the United States alone.

Illustration of a J-shaped deep horizontal borehole storage for nuclear waste (not to scale). Deep isolation

"There are a lot of oil and gas wells that deep, so the issue is going to be the hardness of the rocks and how often your drill bits wear out, things like that, but in general ... I don't think [the depth] presents additional problems,” said Sherilyn Williams-Stroud of the University of Illinois, an expert in the geological storage of nuclear waste and CO2.

Since multiple escape holes can be drilled and flared underground from one point on the surface, costs and environmental impact can be minimized, and there would be far fewer rocks to remove and to dump than with a mine. In theory, each nuclear power plant could therefore have its own storage borehole, eliminating the need to transport spent fuel across the country.

Deep boreholes should also be able to receive hotter waste than mining repositories, as the containers would be placed end to end and cooled by the surrounding rock. This means that spent fuel would not need to spend as long as it currently does in power plant cooling pools. Proponents also claim that because deep boreholes would take up less space, be much deeper, and be unoccupied, they would require much less and much simpler investigation of the site geology, saving even more money. time and money.

Boreholes should also be able to...