President Obama promised to eliminate 34 tons of plutonium from the U.S. nuclear weapons program as part of this week's nuclear security summit. But how does one actually get rid of bomb-making material that has a half-life of more than 20,000 years?

One way is to burn it in nuclear reactors. Already, roughly half of the electricity generated from nuclear power plants in the U.S. comes from the fissile materials out of Russian warheads, albeit highly enriched uranium, the other fissile material used in bombs. Such reprocessing might also help cope with nuclear waste.

In fact, Obama's recently appointed Blue Ribbon Commission on America's Nuclear Future has specifically chosen to investigate the possibility of reprocessing spent nuclear fuel rods. After all, the French, Japanese and others routinely do so—and the South Koreans and Indians would like to do so.

"[Reprocessing] displaces the need for 25 percent of the uranium, it displaces some enrichment," says nuclear engineer Alan Hanson, executive vice president of technologies and used-fuel management at Areva, a French nuclear power company that conducts that country's reprocessing. "We need to destroy this material. If you think this stuff [plutonium] is so bad, what's so bad about burning it up?"

In essence, reprocessing involves taking the spent nuclear fuel from reactors and separating out the plutonium and other fission byproducts. Chemicals, such as nitric acid, are applied to the spent fuel, and solvents then separate out the fission byproducts, including uranium and plutonium. The separated byproducts (or downblended fissile materials from nuclear weapons) are then combined with fresh uranium to create a new fuel—so-called mixed oxide (MOX) fuel—that can be used in modified existing reactors. In that subsequent use, some of the plutonium is destroyed via fission.

Reprocessing may reduce the demand for fresh uranium fuel. Although various estimates catalog known uranium reserves capable of fueling the existing global fleet of 440 reactors for at least 100 years, the growth in demand for new reactors in China, the U.S. and elsewhere might change that equation. "If we build 200 to 400 more reactors, then it's definitely only 100 years of supply," argues Hanson, whose company is the largest supplier of uranium fuel in the world. "Would you build a nuclear power plant with a 60-year lifetime with only 100 years of supply? I wouldn't if I was an investor."

Nevertheless, Areva has also sold all its mining operations in the U.S. "The U.S. is the most unfriendly place on Earth for mining," Hanson says. "The grades [of uranium] are not high enough to make it worthwhile."

But even low-grade uranium is cheaper to work with than reprocessing, according to critics such as physicist Frank von Hippel of Princeton University. "Recycling and reprocessing don't buy you much in terms of uranium resource savings unless you go to breeders, which have not succeeded commercially."

As von Hippel notes, to really take advantage of reprocessed fuel requires a new type of nuclear reactor: so-called fast breeder reactors that essentially create, or breed, their own fuel. There is only one problem: commercial versions of such reactors have not worked despite efforts for at least 60 years to improve them. "We have spent $100 billion trying to make them commercial and they still have safety, proliferation and cost issues," says physicist Arjun Makhijani, president of the Institute for Energy and Environmental Research. And Hanson agrees: "Fast reactors are not ready for prime time."

Even without fast-neutron reactors, however, some, such as new Nuclear Regulatory Commission commissioner William Magwood, have argued that reprocessing makes sense to deal with nuclear waste in the absence of a geologic repository like the one proposed for Yucca Mountain in Nevada. All told, the U.S. fleet of 104 nuclear reactors produces roughly 2,000 metric tons of waste per year, according to the Department of Energy (DOE). That adds up to roughly 70,000 metric tons at various places throughout the country—and reprocessing could reduce the radioactive half-life of much of this waste.

Hanson also argues that reprocessing turns spent fuel rods—rods of lightly enriched uranium fuel clad in zirconium—into a form more suitable for long-term storage: glass logs of vitrified nuclear waste. "Used fuel is hotter than hell. And nobody designed it to be thrown away," he says. "Glass has durability."

But reprocessing can end up producing more waste. According to the DOE, reprocessing spent fuel ends up increasing the total cumulative volume of nuclear waste by more than six times—thanks to more materials being contaminated with plutonium—from a little less than 74,000 cubic meters destined for some form of repository to nearly 460,000 cubic meters. Reprocessing also results in radioactive liquid waste: the French reprocessing plant in La Hague discharges 100 million liters of liquid waste (pdf) into the English Channel each year. "They have polluted the ocean all the way to the Arctic," Makhijani says. "Eleven western European countries have asked them to stop reprocessing."

And separating plutonium and highly enriched uranium is exactly how governments go about building nuclear weapons, so reprocessing can raise the risk of proliferation or theft of fissile materials. Already, at least 250 metric tons of plutonium sits waiting at various sites around the world—enough to make 30,000 nuclear weapons equivalent to the bomb dropped on Nagasaki, according to von Hippel.

Reprocessing is also expensive. The French spend roughly an extra 800 million euros ($1.1 billion) per year for reprocessed fuel compared to conventional uranium fuel rods and the National Research Council estimated in 1996 that reprocessing existing U.S. spent nuclear fuel would cost at least $100 billion. "The power produced from MOX fuel costs 2 cents more than that produced from uranium fuel," Makhijani says. "It is tenfold higher than the underlying resource cost."

Hanson disagrees. "There's plenty of money for recycling…. A light water [nuclear] reactor is a machine that turns foreign uranium into domestic plutonium."

The mixed oxide fuel rods that result from reprocessing have a mixed track record for performance. Although not a single such MOX fuel rod has failed, according to Hanson, they have not lasted as long as fuel rods from fresh uranium. "It was supposed to go around for three refueling cycles," or roughly 4.5 years, von Hippel notes of U.S. excess weapons plutonium turned into MOX fuel. "They had to pull it out after two [refueling cycles of 18 months each] because the fuel had expanded so much. It isn't fully equivalent to low-enriched uranium fuel."

As a result, some have proposed moving toward smaller reactors that could use spent fuel directly, such as contained nuclear reactor modules that would consume nuclear waste over a 30-year lifespan. "We were driven to large reactors by the need for economies of scale," Hanson says. "It's hard to see how you go back down in size."

In the end, the solution—at least in the next few decades—will continue to be the same solution in use today: moving spent fuel rods from cooling pools to dry casks that sit on the grounds of a nuclear power plant. "Dry cask storage is going to go on forever," Hanson says.

And, whether there is reprocessing or not, a repository for nuclear waste would still be required. "Recycling doesn't eliminate the need for a repository, just changes it," Hanson adds. As it stands, the waste plutonium from the U.S. nuclear weapons program goes into a salt cavern in New Mexico. More such sites may be needed to secure the fissile materials that result from civilian nuclear power.