THE end of reprocessing for managing the legacy of nuclear fuel from research
reactors could be in sight. The US government has just backed a new technique
for dealing with the spent fuel from research reactors. The “melt-and-dilute”
technique should cut pollution and be safer.
Until now, most of the fuel rods used in the world’s 170 research reactors
have been reprocessed to separate useful leftover uranium from waste. But the
process is the focus of mounting concern because the enriched uranium it
produces can be used for nuclear weapons. Reprocessing also causes pollution
because some of the less radioactive waste is discharged into the
environment.
In the technique developed by researchers at the Savannah River nuclear plant
in South Carolina, spent fuel is mixed with low-grade uranium and melted to make
ingots. The ingots will be difficult to make into bombs, because the uranium
would have to be enriched, increasing the proportion of uranium-235—the
isotope needed for making bombs.
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Last week, the US Department of Energy (DOE) backed the melt-and-dilute
technique as the best method of dealing with most of the 48 tonnes of
aluminium-clad fuel made in the US and used by research reactors in over 30
countries. Of this, 20 tonnes is already stored at Savannah River, while the
remaining 28 tonnes is due to be delivered there over the next 35 years.
In lab experiments at Savannah River, which is run by the power company
Westinghouse for the DOE, aluminium and low-grade uranium—uranium depleted
of the fissile isotope uranium-235—have already been melted together and
made into ingots. “You get a very nice homogeneous product,” says Natraj Iyer,
the spent-fuel technology manager at the site.
A pilot furnace, due to be completed in 2003, will heat spent fuel and
depleted uranium to 850 °C, about 200 °C above the melting point of
aluminium. This will reduce the volume of waste by up to 70 per cent by removing
all the pockets of air, while the proportion of uranium-235 will fall from as
high as 70 per cent to less than 20 per cent. The resulting ingots will still
have to be stored in an underground repository, says Iyer.
He says that the technology could be used for any aluminium-based fuel, which
may include that made by Russia for research reactors in eastern Europe. But he
thinks that there would be problems melting and diluting spent fuel from nuclear
power stations because most of it is clad with zirconium alloys with melting
points over 2000 °C.
The DOE’s support for the technology was welcomed by the Nuclear Control
Institute, a lobby group in Washington DC, which hopes it will discourage
reprocessing elsewhere. But in Britain the two state-owned nuclear companies,
British Nuclear Fuels and the UK Atomic Energy Authority, say it is too
expensive and impractical for their spent fuel.