On February 16, President Barack Obama announced loan guarantees totaling more than $8 billion for two new light-water reactors in Georgia, part of an initiative to restart the nuclear power industry in the U.S. Just three weeks earlier, Secretary of Energy Steven Chu had announced the formation of a Blue-Ribbon Commission on America's Nuclear Future to resolve what to do with the waste produced by those future reactors—as well as the 2,000 metric tons a year produced by the 104 reactors currently in operation in the U.S. After all, the Obama administration has halted plans to store spent nuclear fuel at Yucca Mountain in Nevada—a geologic repository that never opened.

Such struggles to find a permanent resting place for nuclear waste has prompted some to resurrect an idea that stretches back to the Manhattan Project: so-called fast-neutron reactors that can consume nuclear waste through fission. Whether it is billionaire philanthropist Bill Gates touting a new design for a traveling-wave reactor or the South Korean government promoting spent fuel reprocessing and fast breeder reactors, observers and governments seem to think it is time to reconsider fast reactors—despite the fact that the designs have a mixed track record. Since the 1950s, roughly $100 billion has been spent on the research and development of such reactors around the world, yet there is currently only one producing electricity—the BN-600 reactor in Russia, operational since 1980.

The U.S. "is at an impasse over disposing of nuclear waste," noted physicist Frank von Hippel of Princeton University and co-chair of the International Panel on Fissile Materials (IPFM), during a February 17 conference call with reporters that included several physicists, his co-authors on a new report on such fast-neutron reactors. "The interest in these reactors is that fast-neutron reactors are more efficient at fissioning long-lived isotopes…[and]...fissioning long-lived isotopes will minimize the waste problem."

Going fast with sodium
The most prevalent type of fast-neutron reactor, so-called because the neutrons used to initiate the fission chain reaction are traveling faster than neutrons moderated by water in conventional nuclear reactors, operate at temperatures as high as 550 degrees Celsius and use liquid sodium instead of water as a coolant. Sodium burns explosively when exposed to either air or water, necessitating elaborate safety controls. Nevertheless, as far back as 1951 at Idaho National Laboratory, such a sodium-cooled fast-neutron reactor produced electricity.

But attempts to make that technology commercial have largely failed, mostly because of difficulties with controlling sodium fires and the steam generators that transfer heat from the sodium to water. Japan's Monju sodium-cooled fast neutron reactor caught fire in 1995—and has just received permission to resume operation this month after years of technical difficulties in repairing it, along with legal challenges to its restart. The French Superphenix sodium-cooled fast-neutron reactor operated successfully for more than a decade—but only produced electricity 7 percent of the time, "one of the lowest load factors in nuclear history," said nuclear consultant Mycle Schneider, an IPFM member during the call. An accident at the plant cost one engineer his life and injured four other people when a leftover tank with roughly 100 kilograms of sodium residue exploded, according to Schneider.

Further, such reactors require that the spent nuclear fuel be reprocessed, a technical program that involves extracting plutonium and other fissile materials from the depleted uranium fuel rods. Such elements can then be used in the fast-neutron reactor or mixed with uranium to form so-called mixed oxide (MOX) fuel and deployed in a more traditional nuclear reactor. The U.S. had such a program until the 1970s that was briefly resuscitated by the second Bush administration; it was again shelved by the Obama administration in 2009.

Of course, such plutonium and highly enriched uranium are also exactly the isotopes used to fashion nuclear weapons, making the materials security threats. Already, the world has roughly 250 metric tons of such spare plutonium stockpiled, largely concentrated in the U.K. and France, that has been reprocessed but never used as nuclear reactor fuel. That's enough to make 30,000 "Nagasaki-size" nuclear bombs, according to von Hippel.

Bomb-proof reprocessing
The U.S. Department of Energy is spending $145 million to research a "proliferation-resistant" alternative to current reprocessing methods, and a House of Representatives hearing last June explored future needs for nuclear fuel recycling. Such reactors might also help address a potential deficit in uranium supplies caused by the generally low price of nuclear fuel over the past several decades. U.S. reactors consume some 25 million kilograms of uranium annually but only roughly 1.8 million kilograms of the nuclear fuel are produced in the country, says Amir Adnani, CEO of Uranium Energy Corp., a Texas-based uranium mining company; the remainder comes from mines abroad and other sources. In fact, one in 10 U.S. homes is powered by uranium derived from old Soviet nuclear warheads via the Megatons to Megawatts program, according to Paul Genoa, director of policy development at the Nuclear Energy Institute, but that agreement with Russia expires in 2013.

Fears of such a uranium shortage led India, which has limited natural supplies of the nuclear fuel, to explore another fissile element, thorium, as an alternative. Wrapping highly fissile plutonium in a thorium blanket could produce enough nuclear fuel indefinitely, according to the vision laid out by the architect of India's nuclear program, physicist Homi J. Bhabha, in 1954. The Indian government is currently building such a prototype fast breeder reactor, despite limited success with a precursor, said Princeton physicist M. V. Ramana during the IPFM call. "The cost of electricity is 80 percent higher than from heavy-water reactors," he added. Uranium prices would need to increase 15-fold from current levels of roughly $80 per kilogram to make it economically attractive.

Pricey power
Indeed, the cost problem plagues not just efforts to find a way to use nuclear waste, but also the nuclear industry in general—new conventional reactors such as the ones in Georgia that received the White House's initial loan guarantees could cost at least $7 billion per reactor. But the U.S. Nuclear Regulatory Commission may have just raised the price after it rejected the initial AP-1000 design for security and safety reasons, insisting that the power plant buildings need more structural strength. Yet the promise of a generator that continuously supplies electricity with low greenhouse gas emissions is driving a government-backed renaissance. Nuclear reactors "produce about 20 percent of our electricity but fully 70 percent of our carbon-free electricity," Chu noted during a conference call with reporters after the loan guarantee announcements.

Fast-neutron reactors would not improve the economics of nuclear power based on past experience, the IPFM members argued. Nevertheless, China has signed an agreement with Russia to design two 880-megawatt fast-neutron reactors based on the BN-600.

As far back as 1956, Adm. Hyman Rickover, who oversaw both the Navy's nuclear-propulsion efforts as well as the dawn of the civilian nuclear power industry, cited such sodium-cooled fast-neutron reactors as "expensive to build, complex to operate, susceptible to prolonged shutdown as a result of even minor malfunctions, and difficult and time-consuming to repair." That judgment remains despite six decades and $100 billion of global effort, according to physicist Michael Dittmar of the Swiss Federal Institute of Technology in Zurich who wrote, "ideas about near-future commercial fission breeder reactors are nothing but wishful thinking" in a November 2009 analysis.

"For that $100 billion we did learn some things," remarked physicist Thomas Cochran of the Natural Resources Defense Council, an environmental group, during the IPFM call. "We learned that fast reactors were going to cost substantially more than light-water reactors…[and]…that, relative to thermal reactors, they're not very reliable."

Traveling-wave reactor
New designs might help with that, such as the traveling-wave reactor from TerraPower touted by Bill Gates recently as part of an effort to get to zero carbon emissions from the energy sector. The proposed technology would employ cores that, starting with enriched uranium, fission over at least 30 years. The cores could theoretically also employ the depleted uranium from existing reactors, as well, thus consuming some of the nuclear waste problem, explains nuclear engineer John Gilleland, president of TerraPower, in a video demonstration

"The idea does have the advantage of being waste-eating. It wouldn't require reprocessing," von Hippel said.

But significant materials advances would be required to create a cladding, or cover, for the core that could contain a fission reaction for decades. "It will confront horrendous materials issues in achieving the long lifetime cores that are envisioned," Cochran argued. And, ultimately, some nuclear waste will remain. "The only thing breeders can do is change the volume of waste," Ramana insisted. "The issue of nuclear waste disposal is more of a social and political problem than a technical problem."

The disposal solution of the moment for nuclear waste will likely continue to be fuel rods cooling in water pools before being moved to dry casks sitting on the site of existing reactors—roughly 64,000 metric tons of spent fuel is stored precisely that way today. "There is no problem with that in the short-term. Dry cask storage is very safe," von Hippel said. "Over the longer term, you don't want spent fuel at 66 reactor sites indefinitely."

And even if a fleet of fast-neutron reactors were built, Cochran noted, "you're not going to eliminate the need for a geologic repository."