Japan's nuclear crisis has raised fears about nuclear power around the world, including in the U.S. But advocates of nuclear power say new technology could allay many of those fears. It's possible to build reactors that are much less vulnerable to a meltdown — even if they're abandoned in an emergency.
Some newer designs use what's called "passive safety" features — like the Westinghouse AP1000, which uses water for cooling, like most reactors, but can operate with no one at the controls.
"You should be able to walk away for 72 hours with no intervention," says Per Peterson, chairman of the department of nuclear engineering at the University of California, Berkeley. "Then, at 72 hours, the intervention is to come in and refill a pool with water, which is something you could do in many different ways, such as, say, with a fire truck."
But the promise of "passive safety" doesn't convince Edwin Lyman, a physicist at the Union of Concerned Scientists.
"The idea is, you know, it's too good to be true," he says.
The AP1000, for example, relies on gravity to move water through the core, he says — and he's not sure that's good enough.
"Gravity is just not as strong a driving force as you can achieve with a pump," Lyman says. "And when you're dealing with an emergency situation that we're certainly seeing here at Fukushima, it's not all that easy to be able to reliably inject water into a reactor vessel that is having a crisis."
That's why some nuclear engineers say forget the water — a better approach is to build a reactor that simply can't get hot enough to melt down. One such design is the "pebble-bed" reactor. Basically, the radioactive fuel is encased in balls of graphite, which absorbs heat without melting.
At Idaho National Laboratory, David Petti directs research into this design. He says a loss of primary cooling in one of these reactors would be undramatic.
"The graphite just heats and heats, and then the vessel — the heat off the edge of the vessel starts to increase, and the fuel temperature peaks and starts to come down," Petti says.
The design seems immune to meltdown, but there are still doubts. Graphite doesn't melt, but some critics believe it might burn if exposed to oxygen. Also, researchers say a test pebble-bed reactor in Germany produced irradiated graphite dust, which could be dangerous if released.
Still, Petti says, compared with water-cooled systems, the pebble-bed design is more forgiving.
"These accidents would take four days, five days to evolve," he says. "So it's a very slow, sluggish system, unlike some of the other reactor technologies where things happen more quickly."
The biggest hurdle for the design seems to be startup costs; the government of South Africa recently cut off funding for a reactor there. But others are still interested: A trial pebble-bed reactor is now being built by the largest power company in China.