Recycling nuclear fuel offers plentiful, clean energy

for decades in other countries using a technique called PUREX, which has its roots in 1940s U.S. research to separate plutonium out of used fuel. The problem with PUREX is the risk that the process could be diverted to extract weapons-grade plutonium, a concern that prompted president Jimmy Carter to ban PUREX reprocessing in 1978.

This spurred scientists at Argonne to search for a different, more efficient way to reprocess used fuel. Their brainchild is a technique called “pyroprocessing,” which uses an electrical current to sift out the useful elements and does not separate pure plutonium.

How it works
When used fuel comes out of a light-water reactor, it is in a hard ceramic form, and almost all of it is still just uranium — about 95 percent, along with one percent other long-lived radioactive elements, called actinides. Both of these can be recycled as fuel. The remaining four percent are fission products, which are truly unusable.

Pyroprocessing begins by chopping the ceramic fuel into little pieces and converting it into metal. Then it is submerged in a vat of molten salts, and an electric current separates out uranium and other reusable elements, which can be shaped back into fuel rods.

The truly useless fission products stay behind to be removed from the electrorefiner and cast into stable glass discs. These leftovers do have to be put into permanent storage, but they revert back to the radioactivity of naturally occurring uranium in a few hundred years — far less than the thousands of years that untreated used fuel needs to be stored.

Why don’t we use pyroprocessing already?

— Lack of financial incentive. Raw uranium is cheap. At the moment, it is cheapest to run the fuel through once and then store it, mostly because other methods would have to be researched and tested. Light-water reactors are cheaper to build, because both utilities and the U.S. Nuclear Regulatory Committee are familiar with the technology. Since the process for approving a new reactor design takes years, there is not much incentive to build different types of reactors, including fast reactors.

— Proliferation fears. Some worry that the spread of reprocessing technology will help terrorists gain access to plutonium and uranium for weapons. Pyroprocessing concepts address this fear in two ways. First, the technique itself laces the plutonium with uranium and highly radioactive actinides, making both stealing it and creating weapons with it more difficult. Second, pyroprocessing plants with fast reactors can be built directly on the site of a former light-water reactor to create an enclosed recycling facility. This approach reduces the security risk by eliminating the need to transport the used fuel from and new fuel to the fast reactors at the site.

Looking ahead
The Argonne release says that to date, nuclear energy remains the only stable, large-scale source of carbon-free electricity. Reactors are being built across Asia as its developing powers need more energy; China alone has quintupled its nuclear capacity in just the past decade.

Argonne scientists and engineers say they continue to work on ways to make fuel recycling safer, cheaper, and more efficient. In the Engineering-Scale Electrorefiner, a large glovebox, Argonne scientists test pyroprocessing at a scale closer to what industry would use. They have also turned to computational modeling, which helps simulate the chemical processes down to molecules and up to whole facilities.

Other Argonne research projects design and study small modular reactors and different types of fast reactors, including techniques to reduce the cost.