Nuclear waste plan in trouble?
17 January 2007
Plans for storing part of the UK's nuclear waste could need a rethink. Scientists thought a group of minerals called zircons could contain the waste safely. But new research reveals the material isn't as durable as hoped. Antenna investigates...
This research was published in the journal Nature on 11 January 2007.
The UK's first generation of nuclear power stations is being closed down, leaving a legacy of radioactive waste. The waste stockpile includes large amounts of potentially dangerous plutonium - a by-product of uranium-fuelled nuclear reactors and the weapons industry.
Calder Hall in Cumbria was the world's first industrial-scale nuclear power station. It was shut down in 2003 after 47 years of generating electricity.
Image: British Nuclear Group Ltd/Keith Beardmore
In July 2006 the Committee on Radioactive Waste Management said this radioactive waste should be disposed of by burying it deep underground.
But before waste can be locked away like this it has to be mixed with safe, solid materials that make it less mobile. In recent years scientists have been investigating minerals called zircons that looked like they'd be up to the job.
In Finland construction of deep underground vaults for storing nuclear waste is already underway.
Image: Posiva
Naturally occurring zircons have contained radioactive uranium and thorium for billions of years without leaking, even through earthquakes and volcanic eruptions.
Scientists hoped man-made versions of the mineral would be able to do the same for nuclear waste. But new investigations by researchers from the University of Cambridge and the Pacific Northwest National Laboratory in America suggest synthetic zircons might not be as radiation resistant as previously thought.
This is a crystal of synthetic zircon: in daylight (left) and in the dark (right). Radiation damage caused by plutonium decay makes the crystal glow in the dark.
Image: B Burakov, V G Khlopin Radium Institute, Russia
The scientists used a technique called nuclear magnetic resonance (NMR) to see how plutonium affected synthetic zircons.
'It works a little bit like clinical MRI scans,' says Ian Farnan from the University of Cambridge. 'Like doctors use nuclear magnetic resonance to tell healthy from cancerous tissue, we can use it to spot areas of mineral that are damaged by radiation.'
Ian Farnan, materials expert, University of Cambridge
Image: Tom Farnan
'As materials like plutonium decay, they emit a type of radiation called alpha particles. If plutonium is contained in a mineral like zircon, the decay process can knock atoms of the mineral out of position. Eventually this makes the mineral break down and the radiation can escape,' Ian explains.
Using NMR, the scientists were able to count the number of mineral atoms knocked out of position. From this they could work out how zircon would behave over millions of years. 'This technique is far more sensitive than the ways we've used to calculate radiation damage before,' says Ian.
When an atom of plutonium (large blue dot) decays it can knock between 5000 and 6000 surrounding atoms out of place, as this computer simulation shows.
Video: Kostya Trachencko, University of Cambridge
What were the results?
The researchers found that plutonium damaged zircons between 3 and 4 times more than previous estimates - enough for the mineral's crystal structure to be destroyed and be prone to corrosion in as little as 1400 years. This is a short amount of time considering plutonium takes 241,000 years to decay to the point of being safe.
So what does this mean for the UK's nuclear waste plans?
'Far from being bad news, being able to predict radiation damage accurately into the future is good news,' says Ian. 'It will allow us to increase our understanding of the long-term behaviour of materials used for storing waste and let us be confident that the risk we are passing on to future generations is no greater than our risk today.'
Image: British Nuclear Group/Brian Granger
Jane Insley, curator of the Environment and Energy Collections at the Science Museum agrees. 'This research gives us clear guidance for the future,' she says. 'Waste is a major factor in the nuclear debate. Knowing how we can expect it to decay will inform our decisions and could mean the nuclear option remains available to us for years to come.'