Would encasing nuclear waste in concrete and then burying it in a tectonic subduction zone for Earth鈥檚 mantle to consume be an effective way of disposing of it? If not, why not?
鈥� Subduction zone insertion was 鈥� one idea proposed for the disposal of radioactive waste during the early history of atomic energy. Other ideas included a serious proposal to dump canisters of waste on the Antarctic snow and leave them to melt their way to the bottom of the ice sheet.
In fact, subduction zone insertion is perfectly sound in theory, but there are significant practical problems. The zones are inherently unstable and unpredictable, and the sediment on top of the subducting ocean crust plate tends to get scraped off rather than being carried into the mantle, to form what is known as an accretionary prism. This could lead to the waste being squeezed back to the seabed in the future. Drilling it deep into the basalt of the crust may solve this, but at the depths typically encountered in subduction zones, drilling is all but impossible.
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鈥淪ubduction zones are inherently unstable and unpredictable. This could lead to the nuclear waste being squeezed back to the seabed in the future鈥�
Some have proposed a more elegant seabed solution, which is to insert the waste into the deep clays that cover most of the shallower, geologically stable abyssal plains. This could be achieved either by drilling holes and slotting waste canisters into them, or by dropping waste through the ocean in rocket-shaped 鈥減enetrometers鈥�, which would use the kinetic energy of their descent to burrow many tens of metres into the soft clay. Though not without their problems, these methods have the advantage of inserting the waste into a stable, impermeable environment where any nasty leaks from the canister would be effectively absorbed by clay particles in the surrounding ooze.
However, none of the above are likely to be employed in the near future, because the disposal of radioactive waste at sea was banned under the London Dumping Convention of 1983, updated to include low-level waste in 1993.
Sam Little, Hale, Cheshire, UK