A new fuel may increase the time nuclear reactors can run between shutdowns. Longer runs mean cheaper electricity, which should help nuclear power plants compete with coal- and natural gas-powered plants.
Researchers from the Department of Energy's Idaho National Engineering and Environmental Laboratory lead an eight-institution collaboration to develop the fuel. The institutions have received a three-year, $3.3 million DOE Nuclear Energy Research Initiative grant for the research. INEEL will receive $660,000 to support its share of the work.
The other institutions working on the project are Argonne National Laboratory, the Massachusetts Institute of Technology, Purdue University, and the University of Florida. Nuclear-fuel manufacturers Framatome Technologies, Westinghouse Electric Corp., ABB Combustion Engineering Inc., and Siemens Power Corp. will also participate.
Researchers working on the project plan to add thorium dioxide to the uranium dioxide that powers commercial reactors. As the mixture undergoes a nuclear chain reaction, some of the thorium will turn into a type of uranium that can contribute to and sustain the reaction.
The researchers hope to double the time commercial reactors can run between refueling stops, which would allow nuclear power plants to produce five percent more electricity for the same cost and save the industry roughly a billion dollars each year. Most of the 104 nuclear power plants in the U.S. shut down at least once every 18 months to refuel. This research supports DOE's missions in energy and the environment by supporting a clean technology and reducing waste generation.
Work on the new fuel is in the early stages. "The three year NERI project is intended to convince ourselves and the fuel vendors that this will work," said INEEL nuclear engineer Philip MacDonald, principle investigator for the project.
Using a battery of sophisticated computer programs to simulate the workings of a nuclear reactor, the scientists and engineers will try to determine the optimal composition of the fuel. They will also study how the new fuel will behave in the core of a reactor.
The researchers will do laboratory experiments to find the best way to manufacture mixed-fuel pellets and to test the physical and chemical properties of the mixture. They will perform an economic study to determine whether the fuel can be made economically in current fuel production plants.
As the new fuel undergoes a nuclear reaction it produces one kind of uranium to replace another. Uranium comes in a variety of types called isotopes. Uranium-235 is the isotope that will undergo fission, the chain reaction in which a nucleus splits and spits out neutrons that crash into other nuclei and split them, too.
But 95 percent of the uranium in regular fuel is uranium-238, an isotope that will not sustain a chain reaction. With regular fuel, fission fizzles as the uranium-235 runs out.
Thorium nuclei rarely split when struck with neutrons. More often, a thorium nucleus absorbs a neutron and, through a process called beta decay, transforms itself into uranium-233, a type of uranium that will also undergo fission.
As a chain reaction begins in a fresh batch of thorium-uranium fuel, the neutrons will slowly turn the thorium into uranium-233. By the time the uranium-235 begins to run out, enough uranium-233 should have accumulated to keep the chain reaction going.
Using thorium to breed uranium-233 was tried briefly in three light water reactors more than 15 years ago. But in the earlier efforts, fuel runs were short, and the fuel was reprocessed. That is, at the end of a run, the remaining uranium-233 was extracted from the thorium, purified, and used to make a fresh batch of fuel.
The United States stopped reprocessing fuel from commercial reactors in the 1970s. Reprocessing allowed fuel to be recycled. Researchers working on the new fuel envision using it only once.
As well as allowing for longer runs, the new fuel should also generate less waste than all-uranium fuel. For example, if the fuel lasts twice as long as ordinary fuel, it will produce half the volume of spent fuel.
The mixed fuel should also improve resistance to the proliferation of nuclear weapons materials. The fuel will generate less plutonium than current all-uranium fuel. It will also produce a mixture of plutonium isotopes that would be extremely difficult to use in weapons -- the mixture generates a considerable amount of thermal heat, making it literally too hot to handle.
Interest in nuclear power is rising as the world looks for sources of energy that won't contribute to global warming. Given projections for population and economic growth, by 2030 humanity could be pumping 60 percent more carbon dioxide -- the gas most likely to cause global warming -- into the atmosphere.
"Each 1,000-megawatt coal plant burns enough coal each day to fill a train a mile long," says INEEL nuclear engineer Steve Herring. "A nuclear power plant prevents putting millions of tons of carbon dioxide into the air each year."
Nuclear reactors generate no carbon dioxide, but the nuclear power industry struggles because nuclear power plants are more expensive than coal- and natural gas-powered plants. The difference drives up rates for electricity from nuclear power plants.
"The fundamental problem is how can we make nuclear energy more efficient," MacDonald said.
The INEEL is managed and operated by Bechtel BWXT, Idaho, LLC (BBWI) for the U.S. Department of Energy.
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