deep-borehole

UK's total nuclear waste could fit in to one football pitch-sized site

All of the UK’s high-level nuclear waste from used fuel reprocessing could be buried in just six boreholes fitting within a site no larger than a football pitch, new figures have revealed.

Scientists at the University of Sheffield calculated the disposal of nuclear waste and came up with new ways for sealing waste into boreholes, which could see its first field trials in the US next year after being primarily developed in the UK.

A borehole could be drilled, filled and sealed in less than five years, compared with the current timescale for a UK mined repository yet to be approved but due to open in 2040 and take its first waste by 2075.

Professor Fergus Gibb, of the University of Sheffield's Faculty of Engineering, said: “Deep borehole disposal (DBD) is particularly suitable for high-level nuclear waste, such as spent fuel, where high levels of radioactivity and heat make other alternatives very difficult.”

He said that much of the drilling expertise and equipment to create boreholes already exists in the oil and gas and geothermal industries.

“A demonstration borehole - such as is planned in the US - is what is now needed to move this technology forward,” Gibb said.

Researchers estimated the nuclear waste in the UK could be buried in six 5km deep holes and also confirmed that around 40 per cent of the waste, in terms of radioactivity, currently stored at the US site could be disposed of in a single borehole.

If the trials go well, the US could be rid of its most radioactive waste, left over from plutonium production and currently stored at a site in Washington, in one deep borehole.

The trial in the US will drill a borehole just under half a metre in diameter to assess whether waste packages can be inserted into the borehole and retrieved if necessary, with initial results expected in 2016.

Sealing the hole completely to prevent radionuclides getting back up to the surface is essential in DBD and Gibb devised a method to ensure its success. It involves melting a layer of granite over the waste, which will re-solidify to have the same properties as natural rock.

Researchers also devised a method of fixing and surrounding the waste within the borehole with specialist cements that can handle the temperature and pressure at that depth.

Cost considerations could also play a part in switching from mined repositories to boreholes as it would be cheaper to build one.

Another plus is there are more geological sites suitable for DBD as the granite layer that is required can be found at appropriate depths under most of the continent crust.

Researchers have noted that because DBD disposes of nuclear waste at greater depths and there are more potential sites available, it should be easier to obtain public consent for the technology.

The holes are usually a maximum 0.6m in diameter and can be positioned just a few tens of metres apart. Once a borehole is complete, all physical infrastructures on the surface can be removed.

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