Dead and buried

2019-03-07 03:20:05

By Rob Edwards IF YOU bury it deep enough, high-level radioactive waste will seal itself into the rock and can be safely forgotten. So claims one geochemist, who believes he has the answer to a growing global problem. The world’s nuclear plants have accumulated vast stocks of highly radioactive waste. By 2010, Britain alone could have 2000 cubic metres of the waste emitting 100 million terabecquerels of radioactivity. Worldwide, high-level waste is currently stored above ground, and no government has a clear policy on its eventual disposal. While most experts believe that burying the waste is the safest bet in the long term, the problem is finding sites that everyone can agree are geologically stable. Decaying radioactive isotopes release heat. As a result, high-level waste must be constantly cooled otherwise it becomes dangerously hot. Many experts want to store waste above ground until it has decayed and is cool enough to be stored safely in sealed repositories several hundreds of metres below ground. Now Fergus Gibb, of the University of Sheffield says that instead waste should be lowered down boreholes drilled to 4 kilometres. The trick is to exploit heat generated by the waste to fuse the surrounding rock and contain any leaking radioactivity. Gibb says that containers of waste lowered into deep boreholes would heat up to between 800 and 900 °C, melting the surrounding rock. As the waste became less radioactive, it would slowly cool and the rock would solidify “into a sarcophagus of solid crystalline granite”, he says. Gibb also says that fluids moving through rocks 4 kilometres below ground don’t interact physically or chemically with groundwater in the top 700 metres—which means that any radioactivity that did leak shouldn’t make its way back to the surface. Britain’s high-level waste could be buried in just 20 boreholes costing around £90 million to build, according to some estimates. Designing containers for the waste would add to the cost, but Gibb says the sums are “peanuts” compared with what the nuclear industry could otherwise have to spend. Gibb’s idea receives support from a report on options for dealing with high-level waste commissioned by the British government. A leaked draft, written by the consultancy QuantiSci, based in Leicestershire, suggests that deep boreholes should be studied as a store for plutonium wastes. “It is a very promising approach,” agrees Stuart Haszeldine, a geologist at the University of Edinburgh. “But the difficulty will be to ensure that putting heat into the rock does not cause water to start circulating upward by convection.” British Nuclear Fuels, which funded Gibb’s work,