Al Fin spotted the news story at PhysOrg yesterday that describes a new method to recover the uranium in spent fuel enabling access to the nineteen times of the energy already produced to be used. The process also deeply concentrates the very nasty actinides the justifiably worry so many folks and even that is back to fuel in hundreds of years instead of hundreds of thousands of years of poisonous risk.
Today’s technology uses a bit less than 5% of the uranium in a fuel rod. After the fission the fuel rods are just replaced and stored in pools on the reactor site. It’s not much of a solution.
New techniques developed by scientists at the U.S. Department of Energy’s (DOE) Argonne National Laboratory have a new process that tackles the problems head on by using almost all of the uranium in a fuel rod. Recycling used nuclear fuel with the new Argonne process could produce hundreds to perhaps thousands of years of energy from just the uranium we’ve already mined, all of it carbon-free.
That’s news worth sitting up and noticing, as older technology put a halt to recycling used nuclear fuel in the United States leaving the 95% of the fuel sitting around doing nothing but frightening folks.
The first problem why so little uranium is used is that almost every commercial reactor today is a type called a light-water reactor, or LWR. LWRs are good at many things, they aren’t designed to wring every last watt of energy out of the fuel.
Another design called a fast reactor has the ability to “recycle” used fuel to get much more energy out of it.
The fundamental difference in the reactors is what cools the core. LWRs use ordinary water. Fast reactors use different coolants, such as sodium or lead. The metallic based coolants don’t slow the neutrons as much, so the reactor can fission most of the different isotopes in a reacting fuel. That means fast reactors designs can get electricity out of many more kinds of fuel, including all of that leftover used fuel from LWRs.
If the current LWRs were swapped out with fast reactors it would be possible and practical to use all of the used fuel we’ve generated over the past 60 years that’s currently stored at reactor sites, and feed it back into the fast reactors.
The down side to this is going from about 5% energy extraction so far to getting the remaining 95% extracted is going to take a long time.
Simply switching to a fast reactor presents the hard reality that about a fifth of the used fuel would still need to be permanently stored. Other countries have been doing this for decades using the old U.S. developed technique called PUREX that takes out the plutonium. The PUREX problem is the risk that the process could be used to extract
weapons-grade plutonium, a concern that prompted president Jimmy Carter to ban PUREX reprocessing in 1978.
After 34 years Argonne has a better process. Their innovation is a technique called “pyroprocessing”, which uses an electrical current to sift out the useful elements and does not separate pure plutonium.
Pyroprocessing starts when used fuel comes out of a light-water reactor in its hard ceramic form. Almost all of the “spent” fuel 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.
The next pyroprocessing step is chopping the ceramic fuel into little pieces and converting them back into metal. The newly made metal is submerged in a vat called an “electrorefiner”, of molten salts, where an electric current separates out uranium and other the reusable elements that can be shaped back into fuel rods.
The junk, the truly useless fission products stay in the vat to be removed from the electrorefiner by themselves and cast into stable glass discs. The junk leftovers do have to be put into permanent storage.
Here is where the anti nuke folks get their great improvement – the junk reverts 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.
Seemingly simple and vastly more appropriate for the energy value, the public safety, and the investment in a new reactor with what is essentially free fuel. So why not?
Uranium is fairly cheap, well dirt cheap on an energy content basis. So far it’s still cheaper to run the fuel through once and then store it. The driver for that situation is the new methods have to researched, tested and approved by the Nuclear Regulatory Commission (NRC), a very long tedious and expensive proposition. As it stands, the NRC is familiar with the LWR technology. Due to the process for approving a new reactor designs taking years, there’s not much incentive to build different types of reactors, including the fast reactors.
Then there is the public factor of nuclear opposition that can be counted on to oppose, even when what they want would be provided. Those fears are in part a worry that the spread of reprocessing technology will help terrorists gain access to plutonium and uranium for weapons.
The pyroprocessing concept addresses the fears 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. No transport is another benefit.
The Argonne team continues to work with the Engineering-Scale Electrorefiner, about the size of a large glovebox, testing pyroprocessing at a scale closer to what industry would use. They’ve also turned to computational modeling, which helps simulate the chemical processes down to molecules and up to whole facilities. Other scientists at Argonne research design and study small modular reactors and different types of fast reactors, including techniques to reduce the cost.
Neither the reports nor the Argonne article go into the details of the problems – but the incentives are very strong, the benefits very desirable and the productive potential astonishing. These kinds of ideas need speeding up, not slowed down by bureaucracies.