Despite negative perceptions generated by failures at Three Mile Island and Chernobyl, nuclear reactors remain workhorses in today’s energy mix. Running almost nonstop, about 100 plants across the U.S. produce 20 percent of the nation’s electricity. But these plants, most of which were designed 30 to 50 years ago, are due to be updated and replaced.

NC State nuclear engineering professors Ayman Hawari and Mohamed Bourham are working with the U.S. Department of Energy’s (DOE) Idaho National Laboratory (INL) on the so-called Generation IV reactor, a long-range project that officials don’t expect to be operational for about 30 years. “Nuclear has to be part of the energy equation in the future because it produces so much so reliably,” Bourham says. “Gen IV looks beyond solving the problems of today to what the needs will be down the road.”

Gen IV’s drastically different design would provide improved efficiency and safety, reduce radioactive waste, and limit the proliferation of weapons-grade nuclear materials. The system would operate at about 1,000 degrees Celsius—several times the temperatures of existing reactors—and the excess heat could be piped to a nearby plant to power hydrogen production. “That’s the main benefit of the Gen IV design,” Hawari says. “We can produce fuel and electricity at the same time.”

The high-temperature reactor would replace long fuel rods with pellets of coated uranium smaller than grains of sand. Under a three-year DOE contract, Hawari and Bourham are testing the failure rate of the fuel to help come up with the optimal design of the pellets and coatings. After using theoretical computations to simulate a failure, they built a monitor to study gamma rays in the flowing helium gas that will be used to cool the prototype reactor. The gamma rays reflect which radioactive isotopes are being released, which in turn tell the researchers when the pellets failed. They can use that information to refine both the accuracy of their calculations and the design of the fuel.

In addition to replacing water with helium for cooling, the Gen IV reactor would use graphite instead of water to control the neutrons whizzing about in the chain reaction of fissioning uranium atoms. But since no one has yet even predicted how neutrons may affect the graphite, Hawari has a contract with INL to study the impact of radiation. “If the chain reaction is affected, it influences the fuel efficiency of the reactor,” he says. “We need to determine all these factors before Gen IV can become a reality.”


For more information, please visit www.ne.ncsu.edu