UK scientists have calculated that all of the country's high level nuclear waste from spent fuel reprocessing could be disposed of in just six boreholes 5 km deep, fitting within a site no larger than a football pitch.
The concept - called deep borehole disposal - has been developed primarily in the UK but is likely to see its first field trials in the US next year.
If the trials are successful, the US hopes to dispose of its 'hottest' and most radioactive waste - left over from plutonium production and currently stored at the Hanford site in Washington State - in a deep borehole.
University of Sheffield researchers are presenting the latest findings relating to these trials and new concepts for sealing the waste into the boreholes at the American Nuclear Society (ANS) conference in Charleston this week.
"Deep borehole disposal is particularly suitable for high level nuclear waste, such as spent fuel, where high levels of radioactivity and heat make other alternatives very difficult," said Professor Fergus Gibb, of the University of Sheffield's Faculty of Engineering.
"Much of the drilling expertise and equipment to create the 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.
Modelling work carried out by the University of Sheffield team on the Hanford waste, confirms 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.
Fundamental to the success of deep borehole disposal is the ability to seal the hole completely to prevent radionuclides getting back up to the surface.
Gibb has designed a method to do this which includes melting a layer of granite over the waste, which will re-solidify to have the same properties as natural rock.
Gibb's colleague at the University of Sheffield, Dr Nick Collier, has proposed a method of fixing and surrounding the waste within the borehole using specialist cements able to handle the temperatures and pressures at that depth.
Deep borehole disposal (DBD) has a number of advantages over the current solution envisaged for all UK nuclear waste, which is in a mined repository at 500 m depth.
A mined repository can cost from hundreds of millions to tens of billions of dollars to construct before any waste can be disposed of; DBD costs a few tens of millions of dollars per borehole.
Researchers said a borehole could be drilled, filled and sealed in less than five years, compared to the current timescale for a UK mined repository, which is to open in 2040 and take its first waste by 2075 (although a site has not yet been agreed).
The demonstration borehole in the US will be drilled just under half a metre in diameter and trials will be conducted to ensure waste packages can be inserted into the borehole and recovered if required.
