Alternative Energy

[Ed Monton]

Crystal options for nuclear waste

By Jo Twist

BBC News Online science and technology staff


http://news.bbc.co.uk/2/hi/science/nature/3896463.stm

Storing radioactive waste in a safe form is one of the biggest problems facing the nuclear industry.
The UK's Prime Minister, Tony Blair, has talked about a possible renaissance of nuclear power generation as a means to combat global warming.

Many greens are even thinking the unthinkable for the same reason - the evils of climate change could weigh more heavily on the planet than the nuclear dangers they have traditionally warned about.

But any resurgence would also have to include a long-term solution to that waste issue - not just for newly created radioactive products but for all the spent fuel rods and associated materials that have been kept in storage, in various forms, since Britain's Magnox reactor programme began in the 1950s.

People won't accept nuclear power until you deal with waste... It is a problem that lasts for so long, it becomes a moral issue


Science believes it is moving towards that goal - by finding new containment technologies that could lock away even high-level radioactive waste for thousands of years.

Currently, after a period of temporary storage, when the most radioactive products have had a chance to decay, high-level waste from spent nuclear fuel is encased in a borosilicate glass and sealed in stainless steel drums.

But this is really only a short-term solution because the radiation emitted by the waste will slowly attack the integrity of the containers.


The emissions jostle the atoms out of their carefully ordered arrangement within the storage materials. Eventually, this can make the materials swell and crack, allowing highly toxic substances to leak out.

Various research groups are now looking to alternative, ceramic materials that can withstand the bombardment much better.

At the Cambridge-MIT Institute (CMI) in the UK, scientists are seeking guidance from the natural world. They have been examining how the mineral zircon (ZrSiO4) has managed to contain radioactive elements.



"If nature has shown it can store radioactive atoms and that they remain intact, then we should be looking at that," the CMI's Professor Martin Dove told BBC News Online.

Zircon is the ore for cubic zirconium, which can be cut and polished to make gemstones, like artificial diamonds.

Professor Dove, an earth scientist at CMI, said his team had developed computer simulations to show how the atoms in zircon rearranged themselves when they were damaged by radioactive emissions.

They have also done some experimentation to support this - although they have been limited because of strict controls on the testing of radioactive materials.

"The simulations suggest that when zircon gets heavily damaged, inside it there is crystalline damage, but on the outside it looks intact," Professor Dove explained.

Scaling up

The simulations track damage over time. The way the atoms sort themselves looks rather like ants scattering to form a protective ring against an intruder.

This means that radioactive materials should find it much more difficult to escape the crystalline structure than if incorporated into a glass.


There are many who believe nuclear has an important future
The atoms in zircon will actually spontaneously arrange themselves within the damaged area to form a protective shell.

Using magnetic resonance, the atoms that have moved in response to a single radioactive decay can be counted; and X-ray diffraction techniques can show the extent of the damage.

The computer simulations, said Professor Dove, had been made possible because of coding work within the project team that allowed for the modelling of millions of atoms instead of just a few thousand.

The challenge Professor Dove and his team now face is to prove their principle - to fully understand what is going on at the atomic level; and then explore similar materials that could be produced on a much larger industrial scale.

For that, they will need to be permitted to do more "real-world" experiments.

"People won't accept nuclear power until you deal with waste," said Professor Dove. "It is a problem that lasts for so long; it becomes a moral issue. But what we are doing now is setting the agenda for the future."

Maintained access

The Department of Trade and Industry recently said managing the UK's nuclear waste would cost over £47bn in the coming years, and the waste has to be held safely for centuries.

The official regulatory requirement is that any method to house waste must withstand environmental changes, even ice ages.

There are currently over 30 locations holding waste across the UK, with Sellafield storing 98% of the country's most hazardous materials.

It currently houses over 60 tonnes of plutonium in a powder form.

The government's Committee on Radioactive Waste Management (CORWM) has been charged with finding a publicly acceptable option for storing radioactive by-products, and is set to report its recommendations to the government by 2006.

One of the issues it will have to consider is how recoverable plutonium should be in any storage solution, either to prevent it from falling into the "wrong hands", or to retrieve it to be used again.

Currently, plutonium is not officially classified as a "waste" material, according to Nirex, the UK's nuclear waste agency.

"Plutonium was going to be used as fuel, but because the government has made no decision on that yet, it is being stored for potential future use," explained Samantha King, waste management research scientist at Nirex.

"[CORWM] will have to determine what proportion of materials, including plutonium, should be managed as waste."