There are also pebble bed nuclear reactors, brief benefit of design... from the Wired Article,
Let a Thousand Reactors Bloom
The key trick is a phenomenon known as Doppler broadening - the hotter atoms get, the more they spread apart, making it harder for an incoming neutron to strike a nucleus. In the dense core of a conventional reactor, the effect is marginal. But HTR-10's carefully designed geometry, low fuel density, and small size make for a very different story. In the event of a catastrophic cooling-system failure, instead of skyrocketing into a bad movie plot, the core temperature climbs to only about 1,600 degrees Celsius - comfortably below the balls' 2,000-plus-degree melting point - and then falls. This temperature ceiling makes HTR-10 what engineers privately call walk-away safe. As in, you can walk away from any situation and go have a pizza.
"In a conventional reactor emergency, you have only seconds to make the right decision," Zhang notes. "With HTR-10, it's days, even weeks - as much time as we could ever need to fix a problem."
plus...
Coming to terms with nuclear energy is only a first step. To power a billion cars, there's no practical alternative to hydrogen. But it will take huge quantities of energy to extract hydrogen from water and hydrocarbons, and the best ways scientists have found to do that require high temperatures, up to 1,000 degrees Celsius. In other words, there's another way of looking at INET's high-temperature reactor and its potential offspring: They're hydrogen machines.
For exactly that reason, the DOE, along with similar agencies in Japan and Europe, is looking intently at high-temperature reactor designs. Tsinghua's researchers are in contact with the major players, but they're also starting their own project, focused on what many believe is the most promising means of generating hydrogen: thermochemical water splitting. Researchers at Sandia National Laboratories believe efficiency could top 60 percent - twice that of low-temperature methods. INET plans to begin researching hydrogen production by 2006.
In that way, China's nuclear renaissance could feed the hydrogen revolution, enabling the country to leapfrog the fossil-fueled West into a new age of clean energy. Why worry about foreign fuel supplies when you can have safe nukes rolling off your own assembly lines? Why invoke costly international antipollution protocols when you can have motor vehicles that spout only water vapor from their tail pipes? Why debate least-bad alternatives when you have the political and economic muscle to engineer the dream?
Wrathwilde