|
|
|
|
|
|
PROBLEM: Can science produce an energy source that is For approximately 50 years, domestic and international policymakers have been presented with periodic proposals for nuclear fusion, a technology that some advocates have claimed could be a "silver bullet" answer to the world's increasing demand for clean energy. Indeed, nuclear fusion has been touted by segments of the international scientific community as a genuine solution to a large portion of the world's increasing demand for energy. From their perspective, fusion energy is both safe and environmentally benign. Equally important, the fuel source used by fusion is virtually inexhaustible.
To skeptics, the promise of fusion energy represents a technology that for decades has always been "thirty years away" from deployment. For the first time, the thirty-year prediction may be realistic. Supported by an unprecedented international research effort, the first fusion reactor designed to produce more energy than it consumes is being constructed in Cadarache, France, by a coalition of nations that includes the European Union, Japan, China, India, South Korea, Russia and the United States. The experimental reactor, called ITER, is scheduled to go online in 2018. The American contribution to the multi-billion-dollar research and development effort is being spearheaded by the U.S. ITER Project Office at ORNL. "Oak Ridge was chosen to lead the ITER project largely for two reasons," says Deputy Project Manager, Carl Strawbridge. "ORNL has a depth of management expertise in distributed partnerships from our recent experience in designing and building the Spallation Neutron Source, In addition, at ORNL, Princeton Plasma Physics Laboratory, Savannah River National Laboratory and their associated research institutions, we have a collective wealth of technical expertise in the area of fusion energy—particularly in several specialized technologies where the U.S. is the world leader." Strawbridge notes that ITER is an enormous management challenge, not only because of the project's global scope but also because all of the member countries have major responsibilities to deliver complex components on time and within budget. "The failure by any country to deliver," he says, "has a ripple effect on the entire project. We are just now discovering how challenging it can be to put a system together with nations that have different cultures, different currencies, and different areas of technological capabilities." Strawbridge describes ITER as "an advanced prototype of a production fusion reactor that will test the feasibility of using this technology on a commercial scale." When completed, ITER is expected to produce 10 times more energy than it will use to maintain the thermonuclear reaction. The long-term benefits of commercializing fusion power could be worth the short-term frustration of building the reactor. Unlike oil, the fuel used by fusion is essentially unlimited. "Deuterium, a stable isotope of hydrogen found in water, is the primary fuel," ITER Chief Technologist Stan Milora says. The other essential fuel is tritium. Fusion reactor designers take advantage of the neutrons the reactor produces by lining its walls with components that contain a form of lithium. The lithium combined with a neutron makes tritium. "The production of tritium can be self-sustaining in that respect," Milora says "There is enough lithium to last for thousands of years." Compared with other large-scale power generation methods, fusion power has essentially no negative impact on the environment. Unlike both coal and nuclear, fusion power emits no greenhouse gas and leaves behind no long-term waste products. "The materials that we will use to build the reactors are called low-activation materials," Milora says. "When the materials need to be replaced, they will be much less radioactive than components from nuclear fission reactors. That means we can bypass the controversial issue of how to store highly radioactive reactor parts." Milora believes the absence of emissions and legacy wastes means that fusion reactors "could be built in any country, with the fuel available to all nations." The anticipated amount of power produced by ITER will be much greater than in previous experimental fusion machines," Milora says. "The Joint European Torus had fusion gains of about one half. ITER's gain is predicted to be about 20 times larger. The increased efficiency will come from making the plasma hotter and denser and maintaining it at a higher pressure. That will be accomplished by making ITER much bigger than its predecessors." Although ITER is strictly an experimental reactor, the project is being designed on a scale similar to a future commercial, power-producing fusion reactor. When fully functional, plans call for ITER to produce about 500MW of power. Milora expects that if ITER proves feasible, future production reactors of comparable size would produce as much as 2.5GW of power. To boost the power output by a factor of five in the same space, researchers will have to devise a way to increase the pressure of the plasma by a factor of about two. "That's a challenge on the physics side," Milora says, "because the plasma is essentially contained by magnets that balance the plasma pressure. As the pressure is increased, that delicate balance will be harder to maintain." Maintaining control of the plasma is one of the two big challenges confronting the ITER research staff. "The plasma has a very complex shape," Strawbridge says. "Controlling it is a very dynamic process. Monitoring the diagnostics associated with the plasma, understanding how it's behaving, and ensuring that it's stable are critical." The other challenge involves materials technology—developing components that can tolerate both the proximity to the intense heat of the fusion plasma and the huge temperature swings that occur as the ITER cycles on and off. The primary responsibilities of the U.S. contribution to ITER include providing the central solenoid magnets, which are the core of the ITER machine, and providing a sizable share of the plasma-facing components. "We are working with our partners at Savannah River National Laboratory on the tritium exhaust plant," Strawbridge says, "and with Princeton Plasma Physics Laboratory on developing diagnostics and providing steady-state electric power. ORNL's other major deliverable for ITER is the cooling water system for the tokamak—the part of the machine that contains the plasma."
Unlike a production reactor, ITER's initial objective is the generation of power in bursts that will enable researchers to understand how to control the energy-producing plasma. "There is a well-established mission for ITER," Milora says: "to generate 500MW of power for 500 seconds, wait 2000 seconds, then repeat continually the process of producing 500MW bursts for 500 seconds." The gaps between power bursts will be used to recharge the systems that produce and contain the plasma and to process data to prepare for the next pulse. Strawbridge anticipates that ITER will be able to produce and control plasma for up to four or five minutes. If attainable, the result would represent essentially a steady-state operation and a breakthrough in scale from previous fusion demonstrations measured in seconds. Once that capability is demonstrated, the subsequent goal would be a full steady-state operation of fusion power. A key principle of the ITER project is the sharing, not only of cost but also of the information and data generated by the experimental reactor. Once ITER is in operation, plans call for an exhaustive experimental regimen. "After about five years of experimentation," says Strawbridge, "any ITER partner should have access to enough information to begin designing a commercial fusion reactor. In theory, any country that has participated in the collaboration will know enough to build their own machine. Countries with huge energy demands may choose to head down that path quickly." Both Strawbridge and Milora are optimistic about the future of fusion energy, suggesting that if ITER proves successful, fusion might quickly become competitive with traditional energy sources. "We are convinced that when the demonstration reactors that follow ITER have completed the development cycle, the cost of building a production reactor will be competitive with that of other large fossil fuel or nuclear power plants," he says. "If we are able to generate fusion power on a commercial scale," Strawbridge says, "the hope is that it will be every bit as cost competitive as other major power sources—especially if we consider the substantial costs associated with the supply chain of other fuels." Perhaps even more important than cost and accessibility, ITER holds out the hope of abundant clean energy from a basically inexhaustible source—water. "The fusion process is entirely safe," Strawbridge says. "When the plasma's off, it's off." In effect, fusion power could be an energy option without dramatic accident scenarios and no long-lived waste products. Fusion is not a silver bullet for all of America's energy needs, but it could go a long way toward providing a part of an energy solution that is environmentally sustainable." |
 |
 |
 |
 |
 |
Web
site provided by Oak Ridge National Laboratory's Communications and
External Relations |
