London, April 15 (IANS): Scientists have suggested a new way of safely disposing high-emission nuclear waste -- burying it deep down into the earth. The concept, called deep borehole disposal, has been developed primarily in England but is likely to see its first field trials in the United States next year.

"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 from University of Sheffield.

"Much of the drilling expertise and equipment to create the boreholes already exists in the oil and gas and geothermal industries," he added.

All of England's nuclear waste from spent fuel reprocessing could be disposed of in just six boreholes five km deep, fitting within a site no larger than a football pitch, scientists suggest.

If the trials are successful, the US hopes to dispose of its 'hottest' and most radioactive waste -- leftover from plutonium production and currently stored at Hanford in Washington State -- in a deep borehole.

Gibb and co-researcher Karl Travis said that around 40 per cent of the waste 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 -- to melt a layer of granite over the waste, which will re-solidify to have the same properties as natural rock.

The waste within the borehole must be surrounded with specialist cements able to handle the temperatures and pressures at that depth, the researchers said.

DBD has limited environmental impact and does not require a huge site: the holes are a maximum 0.6m in diameter and can be positioned just a few tens of metres apart, the scientists said.