LINDA WERTHEIMER, host:
As the people of Japan are finding out, you cannot just turn off a nuclear reactor and walk away. But what if you could? As NPR's Martin Kaste reports, some nuclear power advocates say new reactor designs are getting closer to the goal of so-called walk-away safety.
MARTIN KASTE: Nuclear reactors are like toddlers: as much as you'd like to, you can't leave them alone. But why can't we build a reactor that's a little more self-sufficient?
Mr. PER PETERSON (Chair of Department of Nuclear Engineering, Berkeley): Certainly it's technically possible to do that.
KASTE: Per Peterson is the chair of the department of nuclear engineering at Berkeley. He says, some newer designs use what's called passive safety features. For instance, the Westinghouse AP-1000. Like most reactors, it uses water to cool its fuel, but that cooling system doesn't require anybody at the controls.
Mr. PETERSON: You should be able to walk away for 72 hours with no intervention. And then at 72 hours the intervention is to come in and refill a pool of water, which would something you could do in many different ways, such as say just with a fire truck.
KASTE: But the promise of passive safety doesn't convince Edwin Lyman, a physicist at the Union of Concerned Scientists.
Mr. EDWIN LYMAN (Physicist, Union of Concerned Scientists): The idea is, you know, it's too good to be true.
KASTE: For instance, he says, the AP-1000 relies on gravity to move water through the core - and he's not sure that's good enough.
Mr. LYMAN: Gravity is just not as strong a driving force as you can achieve with a pump. And when you're dealing with an emergency situation that we're certainly seeing here at the Fukushima, it's not all that easy to be able to reliably inject water into a reactor vessel that's having a crisis.
KASTE: That's why some nuclear engineers say, forget the water. The better approach is to build a reactor that simply can't get hot enough to melt down. One such design is called the pebble bed reactor. Basically, the radioactive fuels are encased in balls of graphite. The graphite 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 un-dramatic.
Mr. DAVID PETTI (Idaho National Laboratory): 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 then starts to come down.
KASTE: The design seems immune to meltdown, but there's still some 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 to water-cooled reactors, the pebble-bed design is more forgiving.
Mr. PETTI: These accidents would take four days, five days to evolve. So it's a very slow, sluggish system, unlike some of the other reactor technologies where things happen more quickly.
KASTE: The biggest hurdle for the design seems to be start-up 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.
Martin Kaste, NPR News.