Nuclear waste to fuel voyages into dark space

BRITAIN'S burgeoning stockpile of nuclear waste may finally be put to good use - as fuel for Europe's future missions to the solar system's most distant and exotic planets such as Uranus and Neptune.

The European Space Agency (ESA) and Britain's National Nuclear Laboratory (NNL) want to use radioactive isotopes harvested from the waste to make the nuclear batteries essential to power such space probes.

Nuclear batteries have been used by the American and Russian space agencies since the 1960s, but Europe has not developed such technologies until now. This has limited it to exploring only those parts of the solar system that have enough sunlight to power solar panels.

"The ESA wants the ability to explore the most distant and darkest parts of the solar system," said Jean-Pierre Lebreton, a senior scientist with ESA for 32 years where he oversaw the Huygens mission to Titan, Saturn's largest moon.

"We are driven by science and the next big science challenges are to send orbiters to Uranus and Neptune which can drop probes into their atmosphere. Those planets are so far from the sun that solar panels would not work - so we need a nuclear battery instead."

Neptune is the eighth planet and lies 2.8 billion miles from the sun - roughly 30 times further than Earth. A Neptunian year, one orbit of the sun, lasts 165 Earth years. A gas giant, it has a rocky core surrounded by an extremely dense atmosphere that would instantly crush any human or spaceship. Scientists have been long fascinated by its powerful weather systems with winds up to 1,300mph.

Equally attractive for exploration is Uranus, on average 1.8 billion miles from the sun and unvisited by any orbiter, although Voyager 2 passed by them both on its way to interstellar space.

Under the scheme the NNL, which operates the £280m Central Laboratory facility at Sellafield, will exploit the 100-plus tons of plutonium waste stored on the site. That plutonium has been in storage for up to four decades and over that time some has radioactively decayed, producing an isotope called americium-241 which is ideal for nuclear power packs. The NNL has set up a trial production line to see if this can be extracted from the plutonium.

Tim Tinsley of NNL said there were about two tons of americium in the plutonium stored at Sellafield: "We estimate that we could build a plant, produce 10kg [22lb] of americium a year, and then decommission the plant for ESA at a lifetime cost of a few hundred million euros. Britain would gain investment and jobs and it would help us clean up our plutonium stocks."

ESA and NNL aim to create a prototype power pack within the next few years, but the first nuclear battery is unlikely to fly until the mid-2020s because of safety problems, especially the risk of a launch going explosively wrong. The extra time will be used to develop a containment system that can withstand explosions or the burning heat of a forced reentry.

Nasa's own Curiosity rover, now exploring Mars, is also nuclear-powered and there were fears that if its launch last year had gone wrong it could have released its 10.6lb of plutonium as deadly radioactive dust. In 1978 there was just such an accident when Cosmos 954, a Soviet satellite, fell to Earth over Canada, scattering radioactive waste across a 50,000 square mile area.

Richard Ambrosi, a reader in physics at Leicester University, which is working on the same project, said safety was vital. "We are looking at multiple layers of containment. A typical power pack might have 10kg of americium in pellets. Around that you would have multiple layers to contain the radioisotope. And around that you would have a heat shield."

For ESA the option of using nuclear power packs could be a boon. At the moment it is building the ExoMars rover, for launch in 2018, but this will be solar-powered, with its panels vulnerable to dust and other problems.

ESA is also due to launch the Jupiter Icy Moons Explorer (Juice) in 2022, which will explore Callisto, Europa and Ganymede, which are thought to have liquid oceans under their frozen exteriors and so could harbour life. Juice will be solar-powered, but its distance from the sun means it will need solar panels of 860 square feet.

Matthew Stuttard, national lead on future science programmes at Astrium UK, which builds many of ESA's satellites at its factory in Stevenage, said: "A nuclear power pack is like a kettle that will boil forever, producing heat and power. It would also mean we could go to lunar craters or the dark side of the moon where there is no sunlight."

From The Sunday Times