NARRATION 
We know the greenhouse gas message. More extreme weather, more acidic oceans, more flooded coastlines. There is a remedy - switch to more carbon-free nuclear power. 

Prof Per Peterson 
It's difficult for me to see how we can transition away from fossil fuels and not use significant amounts of nuclear energy. 

NARRATION 
Even environmentalists have put this energy option on the agenda. 

Prof Tim Flannery 
I can't see an alternative to nuclear power, at least as part of that generation of base load. 

Dr Graham Phillips 
But then came the Fukushima disaster in Japan, and that in turn reminded us of the Chernobyl accident a couple of decades earlier, and, in many people's eyes, nuclear was back off the agenda. It was just too dangerous. 

NARRATION 
We still don't know how many years it will take to decontaminate this area, and for the thousands of displaced people to be able to return home. 

Prof Derek Abbott 
My view is that nuclear power in any form is not sustainable on a global scale. 

NARRATION 
After Fukushima, Japan is now talking about phasing out its nuclear reactors. Germany too is moving away from nuclear in favour of renewables. 

Prof Barry Brook 
I think the consequences of ignoring nuclear energy or shutting it down worldwide would be severe from a climate-change perspective. 

NARRATION 
Should we embrace nuclear or not? Historically, our love hate relationship with the power of the atom goes back a long way. In the beginning, Marie Curie, who invented the word 'radioactivity', could see the great potential of nuclear for medicine. But in the 1940s, some big nuclear negatives exploded onto the scene. After the war came a push to love the atom again. Some peaceful uses never caught on, like using nukes for engineering. 

Man 
New harbours, big dams, canals, passes through rugged mountainous terrain. 

NARRATION 
Others - food irradiation - are used today, although in a limited way. 

Man 
The gamma rays are as fresh after 18 months as when they were dug. 

NARRATION 
But what did take hold was nuclear energy generation. The first commercial power plants appeared in the 1950s. These generation I reactors were pretty crude, but safety standards have been improving. 

Prof Per Peterson 
If you think about automobiles, a car that you would buy today is going to be intrinsically better designed and safer than one you would've bought 30 years ago. We're doing the same thing with nuclear plants. 

NARRATION 
And that's the Fukushima defence - these are older generation II reactors, built in the '60s and '70s, not the much safer generation III of today. 

Prof Per Peterson 
So what we need to do is to develop reactors that are increasingly safe, so that as we continue to use fission as an energy source, the safety level and therefore the risk of getting radioactive material into the environment is kept acceptable. 

NARRATION 
But can that be done? We went to California to get a glimpse of the next wave of reactors, generation IV. These are the nuclear engineering labs at the University of California, Berkeley, where they're developing a reactor they say is much safer. Its radioactive fuel is sealed and can't escape into the environment. 

Dr Graham Phillips 
In a conventional reactor, the fuel comes in the form of little cylinders, about that big. Now, they have no protective coating. But this reactor, however, has two layers of protection. One, the fuel pellets are housed inside spheres like this - spheres of graphite. There's thousands of them in there. In fact, we've got a simulation of them here. They're so tiny, you can barely see them. And for a second layer of protection, each one of those has a protective coating as well. So if there were an accident, it's very unlikely the fuel could escape into the environment. 

NARRATION 
Those spheres are simulated here by coloured balls. They're testing how they'll flow slowly but continuously through the reactor's reaction vessel. And made out of tough graphite, they're supposedly meltdown-proof.

Prof Per Peterson 
Once we go to reactor fuels that essentially are impossible to melt, then we've got reactors which have an even higher level of intrinsic safety.

NARRATION 
Already, a pebble reactor is operating in China. But the Berkeley design will step up the safety yet another notch, by using a new coolant. In a nuclear reactor, the coolant is the fluid that flows over and absorbs the heat from the hot radioactive fuel. The electricity's then generated from this heat. In this Chinese reactor, the coolant fluid is helium gas. In standard reactors, it's just water. But Berkeley's is very different. 

Dr Graham Phillips 
This reactor doesn't use water to flow through the fuel elements and extract the heat - it uses melted salt. Now not table salt, sodium chloride, but the related substances lithium and beryllium fluoride. Heat these guys to about 450 degrees Celsius and they turn into a clear liquid. 

Mike Laufer 
One of the big advantages of the salt is that it's very effective in moving heat around, but it's at low pressure. 

NARRATION 
Low pressure means a less accident-prone reactor. Today's generation IIIs run at a staggering 70 times atmospheric pressure. 

Prof Per Peterson 
If we switch to liquid coolants, like these fluoride salts that we're using, then we can build much more compact, high power density systems that operate at atmospheric pressure, and that gives us a system which is intrinsically safe, because there's no source of pressure to disperse radioactive material. 

NARRATION 
For another safety innovation, I went to the eclectic labs of General Atomics in San Diego. Here, they research everything from magnetically levitated trains to algae for car fuel. For nuclear reactors, they're planning to replace the fragile metal parts. 

Dr Graham Phillips 
One of the problems with high-temperature reactors is things can melt. For example, in today's reactors, the fuel is held in place by metal rods. Now, metal melts relatively easily. So the researchers have developed this amazing material, silicon carbide, that can withstand temperatures of up to 2,500 degrees Celsius. 

NARRATION 
At Fukushima, the metal rods did indeed break down. Silicon carbide would've prevented that. Could generation IV reactors be made fail-safe? 

Prof Barry Brook 
No-one can guarantee you 100% of the time, for a million years in the future, you'll never have another meltdown. But the probability of that type of accident that occurred at Chernobyl or Fukushima is virtually zero. 

Prof Derek Abbott 
Because a nuclear station is such a complex beast, there are always pathways to accidents, either through human incompetence, through human error, components rusting, corroding, or through natural disaster, as we well know. 

NARRATION 
And beside safety, Derek says there's another little mentioned problem with nuclear. Today's high-tech gadgets underline it. Building products like these requires increasing amounts of exotic metals, like hafnium and tantalum. The problem is these same metals are used in great quantities to build nuclear reactors, and they're lost to the world when the reactors are decommissioned and their waste buried. 

Prof Derek Abbott 
It's not that these metals can then be re-used and recycled - if they were recyclable, that would be different, but what happens is they become radioactive and you bury them for 100,000 years. So what we're essentially doing is making more and more elements extinct via nuclear power, and that's reducing elemental diversity. 

Prof Barry Brook 
I think he's making a mountain out of a molehill. The problem with Derek Abbott's viewpoint is he's trying to look a billion years into the future and say, 'What's the ultimate sustainability of different energy sources?' whereas I'm trying to think about how we solve a problem on the 100 to 1,000 year timescale. 

NARRATION 
Derek says we should skip nuclear and go straight to its great competitor. 

Prof Derek Abbott 
The amount of solar energy that hits the surface of the planet is 5,000 times the amount of energy we currently use. So we only have to tap solar energy at less than 1% of that and we've got our energy needs in the bag. 

NARRATION 
Like nuclear, big solar power stations could be built in the desert. 

Prof Derek Abbott 
If you add up all the solar energy that hits all the deserts of the world, that amount of solar energy over six hours is enough to power the whole world for a year. 

NARRATION 
The trouble is, unlike nuclear, sunshine is intermittent. It varies with the weather and seasons, and disappears completely at night. 

Prof Derek Abbott 
What is needed there are many solar farms all interconnected together on a grid and so you balance out that intermittency. 

NARRATION 
But nuclear's great attraction is it can slot straight in to today's grid. 

Prof Barry Brook 
It provides what I call a 'plug and play' alternative to coal. You can take out a coal-fired power station, you can put in a nuclear power station and you have something that has replaced coal. 

NARRATION 
Since we discovered the power of the atom, there's been great optimism for nuclear. We'll have to wait and see how this long-time love hate relationship works out.

STORY CONTACTS

Professor Per Peterson 
Nuclear Engineer
University of California, Berkeley

Professor Tim Flannery 
Environmental Scientist
Macquarie University

Professor Derek Abbott 
Biomedical Engineer
University of Adelaide

Professor Barry Brook 
Environmental Scientist
University of Adelaide

Mike Laufer 
Engineer 
University of California, Berkeley