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Sheffield 99 Wednesday, 15 September, 1999, 15:58 GMT 16:58 UK
Self-sealing nuclear waste disposal plan
rock
High level waste is locked into rock
by BBC News Online's Damian Carrington

Burying high level nuclear waste nearly five kilometres down and letting its own heat seal a cocoon could be the safest and cheapest disposal option, says a British geologist.

Festival of Science
Dr Fergus Gibb, a geologist at the University of Sheffield, has built a laboratory and shown that, in principle, high level waste could be safely locked away until it had decayed to safe levels.

"Radioactive waste is a dreadful problem, one of the worst we face as a technological society," said Dr Gibb. "But, with funding, I see no reason why this scheme could not be in operation in 10 or 20 years."

Melting rock

design
Design of self-sealing system
The experiments revealed for the first time that waste at 900 degC heat could partially melt the surrounding rock in a few days, then cool and recrystallise to lock it in, over a few months.

"That's quite quick for a scheme which will run for thousands, perhaps tens of thousand of years," said Dr Gibb. "The complete recrystallisation of the melt, vital for sealing in, was a real surprise to us. It happened ten times faster than we expected."

Better still, he says, is that even if the container did leak, there is no water circulation 4.5 kilometres down which could bring any waste back up, providing the borehole is sealed probably.

Marking the spot

melted rock slide
Slide showing melted rock from the experiments
Site selection for nuclear waste disposal is always hugely controversial and largely a political, economic and logistical issue said Dr Gibb.

"But my very deep disposal scheme gives a far wider choice than other ideas, because there are vast areas of the world with granitic rocks down at this level."

In the scheme, each container would be about four metres long, but up to 50 could be put down each hole, disposing of about 50 cubic metres of high level waste. The diameter of the hole depends on the size that can be drilled, but would probably be about 40cm.

There is expected to be 2,000 cubic metres of high level waste in the UK by 2020, so 400 boreholes would be needed.

No maintenance

The cost saving Dr Gibb predicts result from the fact that there is no maintenance: "Once it has gone, it's gone forever. I think that retrievability is wishful thinking - wait long enough and someone will come up with a solution. We should be doing something about this now."

British Nuclear Fuels have funded Dr Gibb and his colleague Phillip Attrill and when more money is available work will focus on the container material.

"Environmentally, putting high level nuclear waste back into the crust - even deeper than where it came from - is probably the next best thing to never having dug it up."

Links to more Sheffield 99 stories are at the foot of the page.


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