How sustainable is nuclear fusion?

With a growing global population, increasing power consumption, and an urgent need to reduce fossil fuel usage, where will we get sustainable energy sources from, in quantities that meet our needs? One option is nuclear - we already have nuclear fission plants in the UK and around the world. But fusion - the other side of the nuclear coin - isn’t yet a feasible way to power your tele, or the kettle to make your morning cuppa. So how sustainable is nuclear fusion as a source of electricity? When will we get it? And how does it work? Physicist Nick Walkden is a fusion expert from the UK Atomic Energy Authority, based at the Culham Centre for Fusion Energy in Oxfordshire, and he spoke with Adam Murphy...

Nick - Fission and fusion are two sides of the same coin. In fission, we're taking very big elements and we're splitting them apart. It turns out that when they get split apart, they weigh a little bit less than when they're together and that difference in their weight turns into energy so we can extract energy from them. In fusion, we're doing the exact opposite, so we're taking two very light elements, and we're pushing them very very close to one another, and when they pretty much touch each other they cling together and they form a new element. And it turns out that when they cling together, they're a little bit lighter than when they're separate and we can extract that change in weight as well, as energy. But to get fusion to work we have to get these things very close to one another and they really do not want to be close to each other, so we have to get them to very, very high temperatures so that they're whizzing around, colliding with one another, and that's what we’re trying to do in our lab down in Culham.

Adam - How safe is fusion compared to fission?

Nick - It's inherently safe. In fission, you get fission to work basically by taking a lot of fuel and putting it next to each other, and the fuel produces neutrons, neutrons creates more fission, that fission creates more neutrons and you have the chance of having these meltdown effects. We don't have that in fusion, we have to supply the thing with heat for it to work and we only have a limited amount of fuel. So we put a certain amount of fuel into the machine, if all of that fuel fuses then we have no more fuel to create any more fusion, and it doesn't matter how hot the thing is it's not going to create any more fusion, so we have to continuously refuel the machine.

There is a study that was done by the ITER organisation about this and they found that a fusion power plant would have an effective radiation outside it, that was a thousand times less than the ambient radiation that you'd see. And if the worst possible containment breach of a fusion power plant actually happened, and someone happened to be standing exactly at the location of that containment breach, they'd receive a radioactive dose about the same as eating a few bananas a day for a year or living in Cornwall for a year. So it's an inherently safe fuelling option.

Adam - So the tricky bit is keeping it going as opposed to it running away from you?

Nick - Exactly. Fusion is kind of funny because we can do the two ends of the things. So we can get things to fuse and we can extract energy from it, but keeping that process going is extremely tricky, and that's really been the challenge over the many years that people like myself have been working on this.

Adam - How do make it do this consistently?

Nick - We puff a load of gas into the chamber of one of our devices. Once we start pumping heat into it we develop this thing called a plasma which is a soup of electrons and ions whizzing around the place, and we use very, very, very high magnetic fields to keep everything in place. We heat this thing up, we continue fuelling, and eventually we get to the kind of fusion relevant temperatures and these things start to collide. And once they start to collide, we start to get fusion going so we can keep it going as long as we can fuel the machine.

Adam - What kind of temperatures are we talking?

Nick - Sort of 100 million degrees Kelvin. We're talking ten times hotter than the Sun. When Jet is running one of our machines, it's the hottest place in the solar system.

Adam - Wow. Now how sustainable are the ingredients needed for fusion and what are those ingredients?

Nick - The ingredients that we use or we will be using in the reactors of the future are deuterium and tritium. They're both like hydrogen but we've added extra neutrons. So in deuterium we add one extra neutron, and you can find deuterium in seawater - something like one in every 6000 atoms of hydrogen in seawater is actually deuterium.

Tritium is not natural, it doesn't come through natural processes on Earth but it turns out we can get tritium from lithium just by bombarding lithium with neutrons. If you take all of the lithium in a laptop battery for example, and a bath full of seawater you've got enough potential fuel there to power your home for about 20 years.

Adam - That'll do me - one bath. When this comes around, will people actually be able to afford it?

Nick - Current projections are that when fusion becomes a reality it should be about as affordable as nuclear fission is now. But, of course, this is an emerging technology so we're still a couple of decades away from seeing fusion electricity on the grid and there's decades of innovation still in line to start bringing that cost down. But once we build the first fusion reactor, the 10th becomes a lot cheaper and the 100th certainly becomes a lot cheaper than that.

Adam - The big question of course is how green will this be? We don't want another kind of fossil fuel type energy coming around.

尼克- Absolutely. And this is really, really one of the big gains from nuclear fusion. The fuel sources themselves, or the reaction itself has no carbon in it so the product we get back out at the end is helium. Helium is currently quite scarce around the globe so this is probably a good thing. The only carbon we'll spend in the nuclear fusion is building the machine itself.

Adam - What kind of timescale are we looking at before we have fusion powered televisions in our house?

Nick - There's this old anecdote that fusion is 20 years away, and it's been 20 years away for 50 years. It's nice to be able to say fusion genuinely is around 20/30 years away. There's this machine being built in the South of France called ITER at the moment, and when ITER comes online and starts running it will be the proof of principle. And once we've proven the principle and we proven that fusion can produce electricity, then we can start building reactors and start seeing it really impact our day-to-day lives.