Scientists including in China study thorium-fuelled nuclear power

In 1829, as Swedish chemist Jons Jakob Berzelius named a metallic element he had discovered after the Norse god of thunder and lightning, he surely had no inkling of its potential for unleashing enormous power. Yet today there's growing interest in thorium, which just might prove key to a new generation of nuclear reactors.

If so, it could slash our dependency on fossil fuels, greatly helping to limit global warming, as well as reducing air pollution. Both benefits could be significant for Hong Kong, which ranks among Asia's most vulnerable cities to climate change, and is frequently smothered in smog.

"I am told that thorium will be safer in reactors - and it is almost impossible to make a bomb out of thorium," Dr Hans Blix, formerly a United Nations weapons inspector and director general of the International Atomic Energy Agency, told the BBC. "These are very major factors as the world looks for future energy supplies."

Though thorium is radioactive, its naturally occurring isotope is stable, with a half-life of 14 billion years. This means that if you have a kilogram of it today, then although some will "decay" to other elements plus energy, after 14 billion years there would still be half a kilogram remaining. So thorium is in itself no use as nuclear fuel.

But, add a neutron to a thorium atom, and it will transmute, mainly becoming an unstable thorium isotope that swiftly decays to protactinium, which in turn decays to an isotope of uranium, U-233. This isotope is "fissile" - capable of sustaining a nuclear chain reaction, in which the nuclei absorb neutrons, decay, and emit sufficient neutrons to sustain the process plus carry additional energy.

Reading this, you might think, "Great - let's get started! We can solve the world's energy problems, stabilise the climate, and move on to eliminating poverty and finding a cure for cancer." But there are challenges to overcome, and no one yet knows if these will prove insurmountable.