PROBLEM: Can new technologies deliver a nuclear future
Alarmed by the prospect of global warming and impatient with the economic disruption and unpredictability of global energy markets, polls have revealed a gradual increase in support among the American public for nuclear power. Although recent surveys suggest that as many as two-thirds of Americans favor expanding the nation's nuclear power base, much of the support remains tentative. Despite their desire for a carbon-free source of energy, for many, their comfort level with nuclear power rests with concerns about whether advances in nuclear technology have successfully addressed the issues of safety and affordability.
Sherrell Greene, Director of ORNL's Nuclear Technology Programs, sees nuclear power as one of the few near-term options for generating the volume of low-carbon power required for the world's largest economy. In fact, Greene views nuclear power as the bridge to a low-carbon future. "Today we have 104 nuclear power plants operating in the United States," says Greene. "These plants are responsible for 70% of the low-carbon electricity we produce and are operating efficiently and safely."
"A little known fact is that we are getting more energy out of these plants than we would have thought possible three decades ago," adds Kelly Beierschmitt, Executive Director of the lab's High Flux Isotope Reactor. "That increased volume of energy is not a result of building more plants. The increase comes from making nuclear power plants more efficient and reliable."
Reliability, to the surprise of skeptics, is one of nuclear power's major selling points. Greene notes that the availability of nuclear plants in recent years has been more than 90 percent. That performance compares favorably with other carbon-free energy options, such as solar panels and wind turbines that generate far less power and often do not exceed 30 percent availability.
Reliability aside, no one should mistake Greene's enthusiasm for nuclear energy with disdain for other sustainable energy sources. "We will need a broad variety of energy options to reduce consumption and increase our production of clean energy," Greene says. "When I look at the scenarios for economic growth in the United States, I conclude that every viable solution includes a substantial contribution of nuclear power. Although other energy options may lie over the horizon, nuclear power is the only large-scale, low-carbon energy source deployable right now."
Greene sees four major challenges along the road to an expanded nuclear power infrastructure:
(1) Maintaining the integrity and extending the life of existing commercial reactors
Greene maintains that ORNL is well positioned to provide leadership in maintaining the health and extending the life of our existing nuclear reactors as long as possible. "Nuclear materials research is one of the signature capabilities of this laboratory. It is an important capability to have when it comes to extending the life of existing reactors."
Nuclear plants that were originally licensed for 40 years are now being considered for 20-year extensions. Currently, 52 of the 104 nuclear reactors in the United States have been granted 20-year extensions to their operating licenses. It is assumed that all but a few of the remaining plants will eventually apply for extensions as well.
The key to extending the life of nuclear reactors is monitoring and maintaining the integrity of the materials used in their construction. To help accomplish this, ORNL materials researchers have developed techniques for testing materials in the field using very small samples. For example, a sample of base metal from a reactor vessel can be used to help determine its condition and integrity.
Other lab-developed monitoring techniques include "health monitoring" instrumentation and sensors that provide an overall picture of the health of reactors as they operate.
2) Developing a range of nuclear power plants in terms of size
Greene contends that in addition to more nuclear plants, America needs a greater variety of plants to suit economic and geographical realities. "Henry Ford used to say you can have any color Model T as long as it's black. Well, today you can have any size nuclear power plant you want as long as it's over a gigawatt in size."
Greene notes that the country will need a small- to medium-sized nuclear power plant option—one that provides 300MW of power or less—for a variety of reasons. "One is the large capital cost," he says. "All gigawatt-class plants—coal or nuclear—are getting prohibitively expensive—from $4000-$8000 per kilowatt. That's a massive lift in a market where most power generators are capitalized below $20-$25 billion. Asking a company that has an asset value of $20 billion to go out and purchase a $6-$8 billion power plant is unreasonable.
"We also need small- to medium-sized plant options so we can put plants in locations that are near the demand for power but may not be suitable for larger plants because of the capacity of the electrical grid or limited availability of water,"
(3) Developing non-electrical applications
Just as a range of power plant sizes would broaden the applicability of nuclear power, so would the development of nuclear plants dedicated to non-electrical applications, such as providing high-temperature process heat for industrial applications.
"Most power plants that use a steam cooling system—nuclear, coal, or otherwise—lose approximately two-thirds of their energy as waste heat," says Greene. One of the scientific challenges is that the current generation of reactors operates at relatively low temperatures—not high enough to support petrochemical processing and similar industrial applications. Our goal is to build higher temperature reactors to support industrial applications."
The laboratory's advanced materials expertise could also be applied to the development of other power plant components, such as the heat exchangers needed to transfer thermal energy from nuclear plants to nearby industry. To further explore the potential for non-electrical applications of nuclear power, the lab recently completed a study of the feasibility of coupling a small nuclear power plant to a biofuels production plant.
(4) Designing advanced reactors and closing the fuel cycle
A new generation of nuclear plants that incorporates advanced designs and fuel cycles that reduce the production of long-lived radionuclide waste elements in the spent fuel is needed.
Current practice at nuclear power plants is to use fuel assemblies for four to six years and then remove them and store them. "When we do that," says Greene, "we throw away more than 90 percent of the fuel's original energy value."
Greene outlines three main goals in recycling nuclear fuel. "We would like to recover and reuse the uranium, potentially recover the plutonium for use as mixed oxide fuel, store the short-lived fission products, and mix the long-lived waste products back into reactor fuel to transmute them into shorter-lived radionuclides."
"The ultimate goal would be to achieve an economical, environmentally sustainable fuel cycle that achieves as close to 100 percent recycling of nuclear fuel as possible," Greene says.
Beierschmitt notes that, "The nation no longer has a dedicated experimental fast reactor, but our High Flux Isotope Reactor can produce fast neutron fluxes in the core that are approximately equal to those produced at the last operating fast reactor."
A large part of the research done at ORNL's nuclear facilities focuses on the fast reactor technology needed to close the fuel cycle by reprocessing spent fuel in ways that would minimize waste and eventually allow the industry to "burn-up" the heavy actinides that pose long-term storage problems.
"That's a big part of our program here," Beierschmitt says, "doing that design work for the next generation of fast reactors. There are a lot of players involved in this effort—from engineers developing the processing equipment to materials researchers fabricating targets for burn-up. Computational researchers are also involved—creating simulations to help us understand the physics behind how fuel is burned in current reactors and to validate models that will help us design the next generation of reactors."
Beierschmitt sums up a complex issue succinctly. "Nuclear power is the simplest path to getting carbon-free megawatts on the grid." Less simple is how fast the American public can get comfortable with the idea that nuclear power will be an increasing part of their energy future.
Web site provided by Oak Ridge National Laboratory's Communications and External Relations