If America’s nuclear waste could be turned into electricity, it could power the country for the next century. More than 77,000 tons of plutonium, americium, and other radioactive leftovers of uranium fission have piled up at America’s atomic power plants, turning them into radioactive waste warehouses. Known as transuranics, these materials remain radioactive for thousands of years, and are stored in above-ground, concrete-encased water pools and steel casks, fueling endless political battles about where they should be buried. In August 2013, the United States Court of Appeals for the District of Columbia Circuit ordered the government to resume planning for the Yucca Mountain dump site, but the Nuclear Regulatory Commission says it lacks the money.
But there is a better solution: Nuclear waste can be turned into electricity. A new generation of nuclear reactors, dubbed Gen-IV reactors, could do it with great efficiency. In the process, transuranics would be broken into elements that remain radioactive for a much shorter period of time, thus alleviating both our energy and our waste issues. As a country, we are sitting on a radioactive gold mine. But the economics of mining that gold are complicated. To make the new reactors work, new economic policies have to work first.
The existing U.S. nuclear reactors (and most other reactors in the world) use light-water technology in which uranium rods are dunked in water, which serves as a coolant. Uranium atoms release energy when they undergo fission: After capturing a moving neutron, they split into two new elements, releasing two or three neutrons as well as heat, which boils water into steam that spins a turbine to generate electricity.1 A series of subsequent atomic reactions creates plutonium and other elements.
For the fission reaction to continue, the released neutrons need to collide with uranium atoms. But the neutrons move too quickly to be captured. They need to be slowed down, which is done by using water that surrounds the rods. The water molecules slow down the neutrons to the speed needed for a sustained fission reaction.
As a country, we are sitting on a radioactive gold mine.
Only 5 percent of uranium atoms are used up by the time the rod becomes filled with fission products and is taken out of the reactor to be added to our stockpile of nuclear waste. The rod’s plutonium atoms, and its remaining uranium atoms, can undergo further fission in light-water reactors, but at low efficiency. Plutonium needs fast-moving neutrons to split its atoms. Reactors with fast neutrons are called fast reactors, and Gen-IV reactors are one example.
Running spent uranium rods through Gen-IV reactors would allow the energy in those rods to be extracted almost completely. “Instead of extracting 5 or 6 percent of the energy out of the fuel, you could get much closer to 95 percent or so,” says Paul Genoa, senior director of policy development at the Nuclear Energy Institute, a trade association for the nuclear energy industry. Furthermore, a Gen-IV reactor would produce elements that decay much quicker than the transuranics. “The transuranics have half-lives in the order of hundreds of thousands of years,” says GE Hitachi Nuclear Energy’s technology chief Eric Loewen. “But after we’ve broken them down into iodine and other elements they have half-lives in the order of 10 to 30 years.”
GE Hitachi has completed design work on a Gen-IV fast reactor called PRISM (Power Reactor Innovative Small Module), and is ready to offer it to power companies. In a PRISM reactor, plutonium fuel rods would be suspended in a mass of liquid sodium. The heat from nuclear reactions would boil the water on the outside of the reactor core’s casing; the steam would rise and spin turbines to produce electricity.
The fast reactor idea isn’t new. But not a single fast reactor has been built in six decades. The first reactor built in the U.S., which began operating in 1951, was a fast reactor. It was capable of using both uranium and the plutonium produced by uranium fission reactions. Back then uranium was thought to be a rare commodity, so it was important for reactors to extract the maximum out of the fuel. When geologists discovered that Earth had plenty of uranium, it became cheap and widely used, eliminating the need for more efficient reactors. Fast reactors that used sodium also raised safety concerns. Sodium is highly combustible and reacts violently with water. Fast reactors in Russia and India had fires because of sodium leaks.
But GE Hitachi says it designed PRISM to be leak-proof because the reactor would be contained inside a stainless steel case, which wouldn’t corrode. There is also a leak-detecting system. And, Loewen says that compared to light-water reactors, PRISM has safety advantages too, because the fuel, coolant, and cladding are all made of metal, which has a lower thermal resistance than water. In case of overheating it’s easier for heat to escape from the reactor vessel into the air without blowing up pumps and valves. (Lead or molten salt can also serve as coolant in fast reactors, but sodium has an important advantage—it doesn’t corrode stainless steel.)
Only 5 percent of uranium atoms are used up by the time the rod becomes filled with fission products and is taken out of the reactor to be added to our stockpile of nuclear waste.
The technical problems around fast reactors, then, have been significantly reduced. Now the main obstacle seems to lie in economics. Fast reactor technology is expensive and currently is “not economical,” says Per Peterson, a professor at the University of California at Berkeley’s Department of Nuclear Engineering. GE Hitachi’s typical water-based reactor produces 1,600 megawatts of electricity, while a PRISM unit would produce approximately 600. It’s cheaper for the nuclear industry to build light-water reactors that produce waste than to invest in fast reactors that eat it up. Raising the wholesale price of nuclear energy is not viable when fracked natural gas keeps electricity costs low. In fact, low electricity prices have contributed to the closures or pending closures of nuclear power plants in California, Wisconsin, Vermont, Florida, and New Jersey.
“The industry is in a fragile situation right now,” says Genoa of the Nuclear Energy Institute. “What we don’t want do to is be forced to bear the burden of developing this recycling technology before it’s economically feasible.”
Peterson thinks the technology will naturally find its path to market. “If fuel is easy to fabricate from recycled materials, then that will be the least expensive source,” he says. Yet, so far America is still pursuing a 31-year-old plan to bury nuclear waste instead of harnessing its energy for the next century. A shift from this plan requires new policies that would make fast reactor technology attractive to power companies, but the policymakers seem to have hit an impasse. “Our regulators are not ready to do it,” says Genoa. “There are commercial and marketing delays. It’s not clear how to finance those first few plants.”
U.K. politicians aim to bridge the financial gap with legislation. In 2004, they passed an energy act that provides subsidies to companies that turn nuclear waste into energy. That’s why, in 2011, GE Hitachi took PRISM across the pond. The company submitted their reactor design for the U.K. government’s consideration and expects to hear back by the end of this year. PRISM wouldn’t generate as much electricity as a comparable conventional reactor, but its owner would have two revenue streams: one from the sale of electricity and another one from government subsidies. “From a business standpoint, the near-term opportunities seem to be more aligned in the U.K. than they do in our own country,” Loewen says.
Others agree. Two years ago, Mujid S. Kazimi and Ernest Moniz, both nuclear experts then at MIT, coauthored a paper that concluded that uranium will remain so inexpensive and accessible that conventional reactors will remain the preferred nuclear option for the U.S for “the next several decades.”
Kazimi also cites other concerns, including fear that the technology of refining nuclear waste into fuel can be stolen and used to produce nuclear weapons. There are also concerns that transuranics may be hijacked en route to the new reactors (although the same risk applies to transportation to burial sites.) And that means that reactors capable of processing our radioactive goldmine are off the radar for now. At least for the next few decades, we’ll continue wasting our nuclear waste.
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