Pebbles

China is ramping up their research on Pebble Bed Reactors.

The idea is that each chunk of fuel is wrapped in a Silicon Carbide, ceramic and graphite shell. At the highest level of activity, the melting temperature of the SiC (2,700 Celsius) is far above the highest temperature the fuel can reach so there will be no leaks.

MS/NBC/Newsweek has the storyof one reactor in China:

China Leaps Forward
The people's republic is embarking on the world's biggest nuclear building spree.

American businessman Edwin deSteiguer Snead went to China seeking a future for nuclear energy. He's pretty sure he found it. On a recent bitterly cold day, Snead took a ride out to a military zone northwest of Beijing, not far from one of the most well-known sections of China's Great Wall. In the spartan lobby of an unassuming concrete office building that contains the control center of a nuclear reactor, Snead studied a model of the reactor, housed in a hillside at the site. Nuclear scientist Chang Wei pointed at the model, which looked like a basement furnace split down the middle, and explained how the design - including 27,000 balls of uranium wrapped in layers of super-strong silicon carbide, ceramic material and graphite - makes it physically impossible for the reactor to do anything but shut down if something goes wrong; the dangerous uranium would be trapped inside the spheres, which have a melting point much higher than the temperature inside the reactor could ever reach.

"So let me see if I can describe it in Texas English," said Snead, 76, an entrepreneur who hopes to build a nuclear power plant on 55 acres in Texas. "There's no way it can explode or melt?"

Chang nodded in the affirmative. She went on to explain how the design requires only a fraction of the control-room staff a more conventional reactor would need. Snead, apparently impressed, exclaimed that this newfangled Chinese technology may be the key to assuaging the nuclear fears of Americans. He wants to go back and sell the idea to Texas A&M University or another school willing to back a research center. "I think the Americans will be buying nuclear plants from China within five years," he said.

While experts in the United States and Europe talk about reviving plans for nuclear power, China, as in so many other fields, is racing ahead. The so-called pebble bed technology behind the Beijing test plant originated in Germany more than three decades ago, and the U.S. nuclear-power industry also pursued it. But when public opposition to nuclear energy forced those countries to curtail nuclear research in the 1980s, Beijing took over. China expects to complete a small commercial plant, which will produce 195 megawatts of electricity, within five years in the eastern province of Shandong. Huaneng Power, one of the country's largest electricity companies, is ponying up about half the $300 million price tag. What makes the pebble bed technology so important is its fail-safe design - it would not be possible for the reactor to melt down or explode like Chernobyl or Three Mile Island. The uranium in each sphere can't get hot enough to melt the casing and escape. Also, the main coolant for the system is inert helium, not water, as is used in other types of reactors (water, of course, contains oxygen, which is combustible). As global warming and politics render the world's reliance on fossil fuels problematic, China may in a few short years hold the key to a renaissance in nuclear power.

There are some disadvantages to Pebble Bed, the key one being that the core's power density is a lot less than a Pressurized Water Reactor so it takes a much larger reactor to generate the same amount of energy. The lower cost and simpler operation more than make up for this though.