From Recycling to New Nuclear Fuel
As countries move toward low-carbon energy, nuclear power still matters. It delivers large amounts of steady electricity with very low operational emissions. In Sweden, nuclear energy produced about 30 percent of total electricity in 2024. Globally, the share was close to 9 percent.
At the same time, attention is shifting toward how nuclear fuel is managed after use. One option is the closed nuclear fuel cycle. Instead of treating used fuel as waste, it treats it as a resource.
At Chalmers University of Technology, researchers are studying this approach in detail. Their work also supports ANItA, a Swedish initiative focused on small modular reactors and long-term nuclear strategy.
What Is Spent Nuclear Fuel
Fuel inside a reactor produces heat by splitting atoms. Over time, this process creates new elements and radioactive byproducts. Fuel usually stays in the reactor for three to five years.
Once removed, the fuel is very hot and highly radioactive. Because of this, it must cool underwater in spent fuel pools for several years. After cooling, the fuel can be prepared for recycling by cutting it into pieces and dissolving it in nitric acid.
Even after use, most of the fuel remains usable material. A typical uranium oxide fuel contains about 94 percent uranium, mostly U 238. Around 1 percent of plutonium is formed during operation. Minor actinides such as neptunium, americium, and curium make up roughly 0.2 to 0.3 percent. The remaining 4 to 5 percent consists of fission products.
What a Closed Fuel Cycle Means
In an open fuel cycle, used fuel is cooled, stored, and then placed in a deep geological repository. It must remain isolated for hundreds of thousands of years.
A closed fuel cycle works differently. It recovers uranium and actinides from spent fuel and reuses them to make new fuel. This reduces the need for fresh uranium mining. It also changes the nature of nuclear waste.
When long-lived actinides are recycled, the remaining waste mainly contains fission products. These decay much faster. As a result, the waste stays radioactive for a far shorter time and produces less heat.
How Reprocessing Works
To close the fuel cycle, reprocessing is essential. The most common method today uses liquid-liquid solvent extraction.
First, the fuel dissolves in nitric acid. Then, specific chemicals pull selected metals into an organic liquid. Later, those metals move back into a clean water-based solution for further use.
This process depends on chemistry, temperature, acidity, and careful control of mixing. While the idea is simple, operating it safely under high radiation is complex.
The only industrial process used today is PUREX. It separates uranium and plutonium and allows the production of MOX fuel, which mixes plutonium and uranium oxides.
The CHALMEX Approach at Chalmers
Chalmers University has developed a different concept called CHALMEX, short for Chalmers Grouped Actinide Extraction.
Instead of separating pure plutonium, CHALMEX extracts all actinides together after removing most of the uranium. This reduces process steps and improves safeguards by avoiding isolated plutonium streams.
The system uses a fluorinated sulfone diluent and two extractants. One targets nitrogen-binding metals. The other handles broader actinide chemistry.
The process has three main stages. First, actinides move from the water phase into the organic phase. Next, a scrubbing step removes unwanted metals and excess acid. Finally, stripping transfers the actinides back into a clean water solution for fuel production.
Turning Recycled Material into Fuel
Reprocessing alone is not enough. The recovered materials must become usable fuel.
One promising method is sol-gel fuel fabrication. Unlike traditional powder-based techniques, sol-gel starts with liquid solutions. This reduces dust and improves safety.
In this process, metal nitrate solutions form tiny droplets. Heat then triggers a chemical reaction inside each droplet. This creates solid microspheres. After heat treatment and sintering, these particles become dense ceramic fuel.
This route is especially suitable for nitride fuels. In these fuels, nitrogen replaces oxygen. Uranium nitride and plutonium nitride have higher density and much better thermal conductivity than oxide fuels. Their melting temperatures remain very high.
Because of these properties, nitride fuels suit advanced reactors that use recycled actinides.
Why Fast Reactors Matter
Today, recycled fuel is mainly used as MOX in light water reactors. However, MOX fuel has limits. It struggles with repeated recycling and minor actinides.
Fast reactors solve this problem. They operate with high-energy neutrons rather than slowed ones. This allows them to fission a wider range of isotopes, including minor actinides.
If a country wants to recycle neptunium, americium, and curium, it needs reactors that can use them. Fast reactors are one of the most realistic options. For this reason, many long-term nuclear strategies pair fast reactors with grouped actinide recycling.
Challenges Beyond Research
Closing the fuel cycle is not only a technical task.
Scaling up reprocessing requires new facilities, heavy shielding, and strict criticality control. The costs are high, and economic viability depends on uranium prices and future reactor deployment.
There are also safeguards and non-proliferation requirements. Any system handling plutonium must meet international rules. Processes like CHALMEX help by avoiding pure plutonium separation.
Public acceptance is another major factor. Transport, recycling, and storage of nuclear materials require trust, transparency, and strong regulation. Technical performance alone is not enough.
A Broader Energy Perspective
A closed nuclear fuel cycle treats used fuel as a resource rather than a burden. It improves uranium use, reduces long-term waste, and supports advanced reactors.
Still, it only works as part of a complete system. Reprocessing, fuel fabrication, reactor design, regulation, and public trust must move together.
In Sweden, initiatives like ANItA help build this full chain. As the country considers small modular reactors and future nuclear capacity, the back end of the fuel cycle deserves as much attention as the front end. Recycling is complex, but it may be essential for a sustainable nuclear future.
