It's a word that's been generating a steady, background hum in the scientific community for decades now. And the glow of hope emanating from the word "thorium" is now burning brighter than ever. Is this element really the nuclear fuel of the future? Is it really - as some are claiming - cleaner, greener and safer than its scarcer cousin uranium? One thing's for sure: there are massive reserves of thorium throughout the world, and if the power that represents could be harnessed, it could keep us in energy-saving light bulbs for thousands of years to come. So why aren't governments investing in the technology needed to make that potential a reality?
Over the past year, Professor Egil Lillestol of the Institute of Physics and Technology at the University of Bergen, has been attempting to convince the world that nuclear reactors fuelled by thorium could be the answer to the world's energy problems. If we accept that we need alternatives to the CO2-belching fossil fuels, then, Lillestol says: "We all have to do whatever we can to reduce the consumption of energy and to develop solar and wind energy. These are, currently, the only two sources that can give us substantial amounts of renewable energy, but unfortunately far from enough."
Lillestol believes that nuclear power is the only solution. But nuclear power has a bad reputation. The public remembers the disasters all too well, from the Sellafield fire of 1957 to Chernobyl's meltdown in 1986. We are frightened, too, by the prospect of waste from spent fuel rods that remain lethally radioactive for many thousands of years. If that's not nasty enough, some nuclear waste can also be reprocessed into weapons-grade plutonium. The processing of plutonium for re-use as fuel for reactors is difficult and consequently much of the waste is left to build in weapons-grade stockpiles that could pose a serious security threat were some to fall into the wrong hands.
But according to some, including Lillestol, thorium - a silvery white metal discovered in 1828 by the Swedish chemist Jons Jakob Berzelius, who named it after Thor, the Norse god of thunder - could solve all these problems. As Lillestol points out, thorium is "three times more abundant than uranium in the earth's crust, and produces 250 times more energy per unit of weight than uranium in the present reactors". Unlike a uranium reactor, a thorium power station would produce no plutonium. Consequently, the waste produced from burning thorium in a reactor would not be such a security risk if it fell into the wrong hands, and the spent fuel rods are dramatically less radioactive than conventional nuclear waste. Dr Paul Norman of the University of Birmingham's Physics department talks in terms of "hundreds of years of radioactivity as opposed to thousands".
Furthermore, thorium requires an accelerator-driven system (or ADS) reactor, and these have significant differences from reactors commonly used for uranium. When a uranium-235 atom splits, it releases a wave of high-energy neutrons which can then collide with other U-235 atoms, releasing more neutrons. This is the chain reaction responsible for the explosive power of an atom bomb, and when out of control, it is also the force that can drive a disastrous meltown in a reactor's core.
But in an ADS reactor, that chain reaction cannot get out of control. "The technology for building such a reactor became ripe some 10 years ago. It uses an external beam of protons to kick-start the reactions," says Lillestol. The thorium does not then continue the reaction on its own - it needs the external beam of protons to keep it running. To stop the reaction, and close down a power station, all that would be needed to be done would be to pull the plug on that external beam of protons.
"In the first step, the protons enter into molten lead where a large number of neutrons are produced," continues Lillestol. "These neutrons enter into the thorium blanket. In fact the proton accelerator has to have a rather intense proton beam, and such accelerators could not be built 10 years ago. This is no longer considered to be a major obstacle."
Lillestol says that the problem is political will - and money. "Nobel laureate Carlo Rubbia began work on the ADS while he was director-general at CERN [the European Organisation for Nuclear Research]. He and his group made so much progress that we all believed that a prototype would be built within a decade. However, when the EU turned down the application for $500m first in 1999 and then in 2000, Rubbia gave up pushing and concentrated on solar energy which he then was also heavily engaged in."
Lillestol - whom Rubbia appointed as deputy division leader of CERN's Physics Division back in 1989 - has continued to fight for the thorium cause. He estimates the cost of a prototype reactor at 550m euros and believes it will take around 15 years to develop: "Molten lead becomes highly corrosive - and the problem is, how do we contain that lead? But the greatest difficulty is getting the world's experts to work together in one place and on one prototype. This, I believe, can only be achieved if all the participating countries have equal rights to all the results." Of course, the supply network for uranium has already been established, and is an important issue for governments all over the world. Switching to thorium would move the goalposts and put new power in the hands of the countries that have the thorium. And on such massive issues, it seems that no one likes change.
India, which has about a quarter of the world's total reserves, has already planned its nuclear power program eventually to use thorium, phasing out uranium. But Greenpeace thinks this is a bad idea. The organisation's senior adviser on nuclear energy, Jean McSorley, says: "Operating thorium reactors would mean taking an enormous risk with untried and untested reactors. We shouldn't forget that we need to reduce energy demand, and fully embrace clean, safe and secure alternatives such as renewable energy systems."
But Dr Norman says that new nuclear technology, of some description, is the future. "If you want evidence that nuclear power is back on the agenda, then take a look at what's happening at universities. Our Masters course on the Physics and Technology of Nuclear Reactors was launched 50 years ago, and this year we've got 36 students - the most we've ever had, almost double the previous highest number which was 19 students back in 1957. Global warming is proving far more deadly than Chernobyl. We could try and keep running with the current reactors, which will run as long as uranium-235 lasts. Or we could try something new." He agrees the something new could well be thorium. Or nuclear fusion, which, he admits, "is technically harder to achieve". Perhaps a thorium reactor is not so far-fetched.