Car that needs refueling only every 100 years

The density means it's highly efficient in producing huge amounts of heat. One gram of the thorium delivers more energy than 28,000 litres of petrol, and about eight grams could power the car's engine for 100 years.

And the research and development isn't just aimed at resulting in some sort of sci-fi one-off concept car. Laser Power Systems intends to put the engine into mass-production, and sees a future in which the thorium turbine could power a huge number of the one billion cars on the world's roads -- massively reducing emissions.

The latest version of the engine weighs around 250kg -- about the weight of an old-school iron block V8 -- and is small enough to fit under the bonnet of most cars.

This isn't the first time thorium has been touted as a car fuel, with the Cadillac World Thorium Fuel concept -- or Cadillac WTF, as it quickly became known -- unveiled by General Motors at the 2009 Detroit motor show to promote Caddy's centenary.

To celebrate the landmark, the WTF also boasted a 100-year refill span and the same period of time maintenance-free on all its systems, although the 'tyres' (actually six integrated wheels at each corner) were said to need adjustment every five years or so. However the claims were theoretical, and the concept never reached the working prototype stage.