RENEWABLE ENERGY

Chemical Engineering Progress, Nov 2006 by Eymard, Frank C

Testing the Mettle of a Fusion Reactor

China has conducted its first successful test of an experimental fusion reactor, powered by the process that fuels the sun. The government's Institute of Plasma Physics carried out the test on a Tokamak fusion device, which uses a dough nut-shaped magnetic field to contain the hot gas. The test, concluded in the eastern city of Hefei, was considered a success because the reactor produced plasma, a hot cloud of supercharged panicles. "China is speeding up with the development of nuclear fusion and I think at the moment they are making considerable progress." says Karl Heinz Finken, a senior scientist at the Institute for Plasma Physics in Juelich, Germany.

The Chinese facility is similar to the International Thermonuclear Experimental Reactor, or ITER, being built by a seven-nation consortium in Cadarache in southern France. That reactor is due to be completed in 2015. China is a partner in the ITER reactor, along with the EU, the U.S., Japan, Russia, India and South Korea.

Several countries have produced plasma using a Tokamak or similar device, reports Gabriel Marbach, deputy head of fusion research at the ITER facility. He notes, however, that producing plasma is only one step toward the fusion that ITER aims to perform. This effort could be helped by the Chinese experiments

Pressurize Water Reactors - Safely

In a nuclear reucior, the fission of uranium atoms provides heat used to produce steam for generating electricity. "Already, one pickup truck full of uranium fuel in a nuclear reactor can supply a city with enough electricity for a year," says Pavel Hejzlar, a principal research scientist in Massachusetts Institute of Technology's (MIT; www.mit.edu) Dept. of Nuclear Science and Engineering.

Together with fellow MIT researcher Mujid Kazimi and scientists from Westinghouse, Hejzlar has found a way to increase the energy efficiency of pressurized water reactors by 50%, while maintaining safety margins. "This is significant, given that about two-thirds of the 103 reactors operating in the U.S use high pressure to prevent the water from boiling," says Hejzlar.

Typically, uranium fuel is formed into cylindrical ceramic pellets about a half-inch (1 cm) in diameter. The scientists changed the shape of the fuel from solid cylinders to hollow tubes, which increased heat transfer by allowing water to flow inside and outside the pellets. "In the boiling-water reactor, where water is used as both coolant and moderator, water boils in the radioactive core," explains Hejzlar. The steam can he used to drive a turbine and an electrical generator, which produces electricity.

Water is kept under high pressure and at a high temperature in the pritnan system, while the heat is transferred from the core to an exchanger by the water. Steam is produced in a different circuit. "The new fuel design also is much safer because it reaches an operating temperature of about 1.300°F (700°C) - much lower than 3,270°F (1,800°C), for the conventional fuel, and further from the fuel's melting point of 5,144°F (2,840°C)," he says. The scientists estimate that commercialization of the new fuel concept, will take 10 years.