The test reactor, part of the Department of Energy's (DOE) Idaho National Laboratory (INL), sits on an 890-square-mile tract of land known simply as "The Site." Located 45 minutes from Idaho Falls in the southeastern corner of the state, this swath of windswept desert is the epicenter of American nuclear energy research. Over the past half century, 51 reactors have been built here, including first-generation prototypes of the 1950s; only three still operate. But it is among the relics of these early experiments that the country's energy future is taking shape.
In recent years, the debate over nuclear power has moved to the front burner, spurred by concerns about foreign oil and the specter of global warming. But what many on both sides of the issue often fail to note is that America's 103 existing nuclear reactors are aging. Over the next few decades, they will have to be decommissionedtaking 20 percent of the country's electrical supply with them.
In the Energy Policy Act of 2005, Congress approved up to $2.95 billion in incentives for new nuclear plants, and set aside another $1.25 billion for an experimental reactor to be built here in the Idaho desert. The reactor will be the centerpiece of a modern-day Manhattan Project, with scientists from around the world working together to revolutionize the production of nuclear power.
At the heart of every reactor is fuelusually uraniumundergoing a chain reaction that generates heat and fast-moving neutrons. A coolant draws away the heat and uses it to spin a turbine to generate electricity, and a moderator slows the neutrons to keep the reaction under control. Any material used in building a reactor has to withstand the heatas well as intense pressure and a constant barrage of neutronsfor the reactor's projected lifetime. To prove that a new alloy can last 25 years, you could put it in a furnace for 25 years and bombard it with neutronsor, if you don't want to wait that long, you can use the ATR.
"It is like a time machine," says Duling, the facility's former deputy director. The reactor uses uranium enriched to 92 percent (anything more than 20 percent is considered weapons-grade) to generate a quadrillion neutrons per square centimeter per second100 to 1000 times greater than commercial reactors. By cranking up the neutron dose, the ATR can simulate as much as 40 years of wear and tear on a new fuel or alloy in a single year.
The test reactor is a simple water-cooled model built in 1967. But by tuning the pressure, temperature and chemistry inside its core, scientists can use it to reproduce the conditions in just about any other type of reactor. Recently, they tested chunks of graphite to see whether it's safe to extend the life of Britain's antiquated Magnox reactors. INL staff are now gearing up for an even bigger challenge: testing parts for proposed Generation IV reactors, which would leap technologically two steps ahead of the Gen II designs operating commercially in the United States today.
Despite concerns about catastrophic accidents and radioactive waste disposal, Gen II plants "are cost-effective and working well, and safety continues to improve," says James Lake, INL's associate director. Yet, no new reactors have been ordered in the States since the industry's peak sales year of 1973. Simple economics quashed further growth.
Thanks to the 2005 congressional incentives, a dozen utilities around the country have once again started the lengthy process of applying to build nuclear plants. If all goes smoothly, they could produce power by the middle of the next decade. These reactors would be Generation III and III+ designsevolutionary improvements on today's Generation II reactors, which use water in some form as both a coolant and a moderator.
But, according to the DOE, what is really needed are even safer, cheaper reactors that produce less waste and use fuel that's not easily adapted for weapons production. To develop this kind of reactor, 10 countries, including the United States, joined forces in 2000 to launch the Generation IV International Forum. A committee of 100-plus scientists from participating countries evaluated more than 100 designs; after two years, they picked the six best. All of the final Gen IV concepts make a clean break from past designs. Some don't use a moderator, for instance. Others call for helium or molten lead to be used as coolants.
How It Works: Generation II and III Reactors:
All 103 nuclear power plants now operating in the United States employ light-water reactors, which use ordinary water as both a moderator and a coolant. The next wave of nuclear plants has taken these Generation II concepts to the next level, improving both safety and efficiency. Utilities plan to begin building Generation III reactors by the end of the decade.
In a Gen II Pressurized Water Reactor, water circulates through the core  where it is heated by the fuel's chain reaction. The hot water is then piped to a steam generator, and the steam spins a turbine  that produces electricity. The Gen III Evolutionary Pressurized Reactor improves upon this design primarily by enhancing safety features. Two separate 51-in.-thick concrete walls , the inner one lined with metal, are each strong enough to withstand the impact of a heavy commercial airplane. The reactor vessel sits on a 20-ft. slab of concrete with a leaktight "core catcher,"  where the molten core would collect and cool in the event of a meltdown. There are also four safeguard buildings  with independent pressurizers and steam generators, each capable of providing emergency cooling of the reactor core.