In late December, uranium producer Cameco resumed work to try to reclaim the flooded Cigar Lake mine in Saskatchewan. For the company, the Oct. 23 flood was a huge blow, delaying the opening of the mine by at least a year. But it was also a blow to the world's uranium supply — the Cigar Lake deposit contains reserves of more than 100,000 tonnes of uranium with a gross market value of $16.7 billion.

Potential thorium reserves

Country	Thorium reserves (in tonnes)
Australia	300,000
India	290,000
Norway	170,000
United States	160,000
Canada	100,000
South Africa	35,000
(Source: 1999 U.S. Geological Survey)

Even before the Cigar Lake flood, uranium prices had been skyrocketing. Already up more than 800 per cent this decade, they jumped another seven dollars to over $70 US a pound following an auction in December.

As these prices rise, nuclear energy providers have begun to search for innovative ways to power reactors without relying on uranium. And increasingly, they are turning their attention to a lesser-known radioactive element on the periodic table called thorium.

A shiny silvery-white metal, thorium is being trumpeted as uranium's cleaner cousin. Its boosters say thorium produces less radioactive waste and no plutonium that can be used for nuclear weapons. It's also three times more common than uranium, making it a potentially cheaper option as uranium prices climb.

Discovered in 1828 and named after the Norse god of thunder Thor by Swedish chemist Jons Jakob Berzelius, the unique metal with an atomic weight of 232 has been used to coat tungsten wires and added to magnesium to impart strength. Canada also has the fifth-largest reserves of thorium in the world, with an estimated 100,000 tonnes.

Thorium in reactors

The problem with using thorium in reactors is that the element is only mildly radioactive, requiring an extra step in the nuclear fuel cycle to produce the more reactive uranium-233.

In a nuclear fission reaction typical of a reactor, bars of a radioactive substance like uranium-235 are used. When a neutron hits a uranium-235 atom it can join the nucleus, creating uranium-236. Uranium-236 is unstable and has a high probability of falling apart, and when it does, it releases massive energy and radiation and two or three more neutrons.

Normally these neutrons are too fast to be captured by other uranium atoms. But in a typical thermal reactor, the uranium is stored in water — or in the case of CANDU reactors, deuterium — which helps to slow the neutrons enough to react with other uranium atoms. The resulting chain reactions help a nuclear reactor generate energy.

Thorium reactors typically have a bar of uranium-235 surrounded by thorium. The uranium keeps the process of releasing neutrons while converting the thorium into uranium-233. The uranium-233 can then be recycled and used, like uranium-235, to generate further reactions.

One of the problems with uranium-235 is that it is rare and most often found in its heavier and more common isotope, uranium-238. Like thorium, uranium-238 is not itself fissile. But it can be enriched to contain more uranium-235 and be used in reactors.

A plutonium-free process

The difficulty with using uranium-238 in a reactor is the byproduct it creates: when a neutron is added to uranium-238 it becomes uranium-239 and - after two beta decays - turns into plutonium, which can be used for nuclear warheads and other weapons.

Thorium reactors, on the other hand, are seen as a safer nuclear fuel technology, in that they don't create any byproducts usable in nuclear weaponry.

"Thorium reactors produce a pretty broad spectrum of garbage, just about every kind of isotope," said McMaster nuclear engineering professor Bill Garland. "But you are less likely to have plutonium than with a uranium reactor."

Most nuclear reactors recycle their waste back into the fuel cycle, however.

As a result of the extra step required to create the uranium-233, the thorium process is less cost-effective. But that could change as uranium prices continue to rise.

Turning off the reactor

Another innovation in reactor technology, called accelerator-driven reactors, could make the potential danger of a nuclear meltdown less likely.

With an accelerator-driven reactor, a proton accelerator aimed at a rod of lead is used to start the nuclear reaction. The protons hit the lead, which releases the neutrons.

While thermal reactors rely on temperature monitors to keep a chain reaction started by uranium-235 in check, a thorium reactor using the beam could simply stop the chain reaction from continuing by turning the beam off.

"Now you can control the reaction," said Garland. "It would no longer be self-sustaining."

The problem with the use of an accelerator is the energy required to power the beam, said Garland. As a result, most accelerator-driven reactors are used only for experiments.

Prof. Egil Lillestol at the University of Bergen's Institute of Physics and Technology in Norway is one of the leading proponents of accelerator-driven thorium reactors and is leading the cause in his country, which has the third-largest reserve of thorium.

He told the Independent in the U.K. the greatest difficulty in developing the technology is settling on one prototype.

Research in thorium reactors has become big business, especially in Australia and India, the two countries with the largest reserves of the element. India in particular has made thorium reactor technology a priority, because it has difficulties importing uranium that might be used in nuclear weapons. India is outside the Non-Nuclear Proliferation Treaty after developing weapons of its own.

In 2003 India's regulatory authority approved construction of a thorium prototype reactor, set to begin operating in 2010. If the prototype is successful, it could pave the way for an ambitious thorium-based reactor program India hopes to have running by 2020.

By the time the prototype begins operating in India, the Cigar Lake mine in Saskatchewan should have opened, and thorium may once again take a back seat to uranium as nuclear energy's prime material. But if the current cost of uranium is any indication, nuclear energy may have room for both fuel options.

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