Plans to test a new disposal method of the world’s most highly radioactive nuclear waste will go ahead next year, in the US.
The technique, developed in the UK by researchers at the University of Sheffield, involves drilling a borehole around sixty centimetres wide and five kilometres deep, and lowering the waste into it, hence the term Deep-Hole.
The approach, known as deep borehole disposal (DBD), is much cheaper than the mined repository proposed by the UK government for burying the country’s nuclear waste, according to its pioneer, Fergus Gibb, emeritus professor of petrology and geochemistry at the University of Sheffield.
Each borehole would represent a significant saving to the taxpayer, costing just tens of millions each rather than ranging from hundreds of millions, up to the billions for a mined repository. As few as six boreholes would be enough to store all of the UK’s existing high level waste. Due to significant advances in drilling made by the oil & gas industry, each borehole could be drilled, filled and sealed in less than five years.
Deep borehole disposal is believed to be far safer than conventional disposal which only deposits material five hundred metres below the surface, which is within the zone of circulating ground water. Any leakage caused by an earthquake, for example, could potentially return to the surface and contaminate water sources and soil.
‘By going down several kilometres, it means the disposal zone at the bottom of the borehole is in a geology which is below, and isolated from, the normal ground water,' Said Gibb. 'So even if the waste eventually leaks out of the containers into the surrounding rock and water, it will never come back to the surface. Instead it will leak into waters in the deep rocks that have been isolated from the surface waters for millions of years.
‘This should make it easier to gain public acceptance for a burial site.’ He said.
Concerns remain over leakage, corrosion, or theft after the waste has been buried so researchers have developed two distinct sealing techniques that were presented to the American Nuclear Society. The first is a specially developed sealing and support matrix that would be poured in with the containers as they were lowered. The second is metal ‘shots’ would be placed in with ‘hot’ radioactive waste. These shots would melt to solder and seal the waste inside a metal casing.
For the waste that does not give off as high a level of radiation Gibb’s colleague, Doctor Nick Collier, is developing a special type of cement that can be poured down the hole, which will not set until it reaches the bottom, up to five hours later.
The next step would be to use crushed granite and rock welding to completely seal the nuclear waste in. 'So we create a weld that is both continuous with, and identical to, the host rock around the borehole,' Said Gibb. 'This completely seals the hole, just as if you’ve never drilled through it.'
The US trial, which is being run by Sandia National Laboratories for the Department of Energy (DoE), will take place at a yet to be determined site in late 2016. If all goes to plan the DoE will begin work on narrower, twenty-two centimetre-wide, boreholes to dispose of radioactive caesium and strontium currently housed in a facility in Washington State.
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