When the old is the new

Sir Ernest Rutherford, winner of the 1908 Nobel Prize for chemistry, is considered the father of nuclear physics.

With the UAE's population growth prompting energy consumption to jump by about 10 per cent per year, the authorities are exploring the creation of a nuclear power programme. The novelty, however, is that reactors located here could well be fuelled by thorium instead of uranium. Thorium, the radioactive element first named for the Scandinavian site of its discovery, and experimented with by Ernest Rutherford, one of the founding lights of nuclear physics, has become an increasingly attractive energy option.

Rutherford and fellow physicist Frederick Soddy showed how thorium decayed at a fixed rate over time into a series of other elements. This observation led to the identification of half-life as one of the outcomes of alpha particle experiments that led to their disintegration theory of radioactivity. Earlier this year the UAE Government signed two consulting agreements with Thorium Power, a US company, to explore the possibilities of creating a thorium-based nuclear energy programme.

India and Norway, which both have significant natural reserves of thorium, are among numerous other countries looking into the possibility of building thorium-based reactors. As reserves of uranium decline - they are expected be depleted within the next 70 years - and as prices of the element increase, other countries could jump on the bandwagon, particularly since worldwide energy consumption is predicted to double by 2050.

Thorium, whose chemical symbol is Th, has several advantages over uranium, among them the fact that it is five times more abundant on the planet. In pure form thorium is a silvery-white metal, but when bombarded with neutrons, it converts into an unstable form of uranium than can be used as nuclear fuel. Dr Frodo Klaassen, a nuclear power researcher at the Nuclear Research and Consultancy Group (NRG) in The Netherlands, says thorium is one of a very limited number of alternatives available to uranium. Few elements, he says, "behave" properly in a reactor and can withstand temperatures as high as 1,500C while generating nuclear fission products.

"There are a number of aspects linked to the behaviour of fuels; that's why it's difficult to find alternatives," he explains. Thorium does behave well, Dr Klaassen says, elaborating that this has been demonstrated at a thorium test reactor operated by NRG at Pletten in North Holland and at a nuclear power plant in Obrigheim in Germany. At each location, reactors fuelled by thorium were operational between 2001 and 2005. A reactor contains rods that contain the nuclear fuel in pellet form. If something goes wrong - not impossible in such a hot and highly pressurised environment - the fuel rods could rupture, leaving nuclear material to come into contact with the cooling water that surrounds the rods.

"The most important thing is that there has to be compatibility between your fuel and the coolant water. For both uranium and thorium, this is good. Thorium is neither better nor worse," Dr Klaassen says. "What's important is that there's no melting of your fuel. Some of the biggest accidents happen when the core melts." Fortunately, with thorium such melting is highly unlikely as thorium dioxide has a melting point of 3,300C - the highest for any oxide.

"Also, when the temperature rises, you want your nuclear chain reaction to go down and to produce less energy. This so-called 'Doppler' feedback mechanism is very important and it is there for thorium and uranium," says Dr Klaaffen. Another advantage to thorium is that it produces waste that is less problematic than other fuels. It takes 130,000 years for the waste from a uranium plant to return to the radioactivity level of the original raw material, while for a thorium power plant, because less plutonium is generated, the time is reduced to several thousand years.

There are disadvantages to thorium, however, most of them stemming from the fact that it is not currently used for any commercial power generation. In contrast to the case with using uranium in reactors, the technology is at an earlier stage and therefore it would take "decades" to have a reactor fully up and running. Setting up a uranium nuclear energy generating process involves mining the raw material, enrichment, fabrication of the nuclear fuel, power generation in the reactor and reprocessing of spent fuel. But for thorium creating such a cycle is a long way off.

For the time being, however, organisations creating a nuclear power plant can buy uranium fuel rods from commercial companies based in countries such as France or Japan. Although enrichment is not needed with thorium (neutron bombardment to create the fissile isotope is necessary, however), thorium fuel rods are not available commercially. According to Dr Klaassen, a fuel fabrication plant would have to be built specially to supply a reactor.

The reactors are the same whether fuelled by thorium or uranium, so the design and construction of a facility should not pose any serious obstacles. However, reprocessing the spent material differs from reprocessing that from uranium reactors, and the procedures are not well developed on an industrial scale. "If you want to reuse the uranium that you've used in the thorium cycle, you have to take it out and do a number of recycling steps. There is some technological development to be done," said Dr Klaaffen.

"At the moment we're not mining and fabricating thorium fuels. That's something we need for sure. For a more advanced cycle, you need reprocessing in place as well." Given these uncertainties, Dr Klaassen is cautious about making predictions regarding the future of thorium-powered nuclear power stations. Thorium nuclear energy is only something that governments taking the long-term view will consider, he says, because there are so many expensive hurdles to overcome.

"Using thorium is not going to be a commercial decision," Dr Klaassen says. "It will be a strategic decision by a country to secure their energy supply for when uranium becomes less abundant or very expensive. It's a decision for the future." Although thorium is certainly not the easiest option, as uranium prices continue to increase, the balance could swing in its favour. "The higher the price of uranium, the more interesting thorium will become," Dr Klaassen says. "From a technical point of view, it wouldn't be the holy grail of nuclear energy, but technically and economically it would be a very nice system.

"We have to fight climate change and create energy in an environmentally friendly way and thorium is opening new resources for energy because it's abundant and it produces less-dangerous nuclear waste." @Email:[e-mail]