A commission appointed by the US Department of Energy is studying different options for dealing with spent fuel from nuclear power plants. New Scientist weighs the pros and cons of each.
Room-temperature radioactive waste from the production of nuclear weapons has already been stored in one salt deposit – in the Waste Isolation Pilot Plant near Carlsbad, New Mexico, since 1999. Now the US and Germany are considering salt for future waste repositories.
Pros: Salt can flow like slow-moving Silly Putty – so any fissures seal themselves. Buried waste would relatively quickly become encapsulated by the salt, which would close in around it due to pressure from surrounding rock.
Cons: The still-hot waste could cause small amounts of water trapped in the salt around it to move, carrying with it radioactive materials.
(Image: New Scientist)
France plans to open the first underground nuclear waste repository in shale in 2025.
Pros: Shale’s properties mean it could trap radioactive material that passes through the rock. Soft shale is unlikely to fracture and is self-sealing, like salt. Shale deposits are found throughout much of the US, including areas of low seismic activity.
Cons: Hard, compacted shale is prone to fracturing and doesn’t self-seal. Shale deposits in the US have not been studied in enough detail to determine their suitability for storing nuclear waste.
(Image: S Gonzales and KS Johnson, 1984, Shale and other argillaceous strata in the United States/Oak Ridge National Laboratory)
In the 1980s, the US temporarily stored spent nuclear fuel in an underground research laboratory surrounded by granite in Nevada. Finland and Sweden are pursuing nuclear waste repositories in granite, the first of which is scheduled to open in Finland in 2020. China, Japan, Switzerland, and the UK are also giving the hard rock a closer look.
Pros: Strong, stable rock that has a long history of being mined.
Cons: Granite is brittle and fractures easily, creating fissures through which nuclear waste could migrate into surrounding environments and possibly freshwater aquifers. Safe storage would require man-made barriers made of metals such as copper or stainless steel, but these could potentially fail while the waste was still radioactive.
(Image: JB Bush, 1976, Economic and Technical Feasibility Study of Compressed Air Storage, ERDA 76-76 report prepared by General Electric Company)
Deep borehole disposal
Pros: Deep boreholes offer all the strengths of granite, plus they are far below any freshwater aquifers. If any radioactive material seeped into the surrounding environment, it would remain trapped in dense, highly saline water.
Cons: The concept is untested.
(Image: New Scientist)
Pros: Reprocessing recovers unused uranium and plutonium from spent fuel for reuse, thereby increasing the energy output from the original fuel by approximately 25 per cent. The process also reduces the volume of material to be disposed of as high-level waste to about 20 per cent of what it would otherwise be, according to the World Nuclear Association.
Cons:Plutonium that has been separated from used fuel can be used to make nuclear weapons, raising fears that it could be stolen.
(Image: Steve Allen/Brand X/Getty)