A new study has found that large amounts of uranium have been leaving the Democratic Republic of the Congo (DRC) for more than 20 years without being officially reported.
The uranium was not shipped as a separate product. Instead, it traveled mixed with cobalt, a metal widely used to make rechargeable batteries for electric vehicles and other electronics.
The research, led by scientists from the University of Wisconsin–Madison and Princeton University, was published in Nature Communications.
The researchers say this discovery reveals an important gap in the way nuclear materials are tracked around the world. It also raises concerns about possible environmental pollution and health risks for people living and working near mining sites.
The DRC is the world’s largest producer of cobalt, and demand for the metal has increased rapidly as countries expand the use of electric vehicles and renewable energy technologies.
However, the rocks that contain cobalt in the DRC often also contain naturally occurring uranium.
The researchers found that when cobalt ore is mined and processed into cobalt hydroxide, much of the uranium remains mixed with the product unless it is deliberately removed. As a result, uranium has been exported alongside cobalt without being separately recorded.
By combining geological information, mining records and computer models of cobalt processing, the team estimated that between 2,000 and 5,000 metric tons of natural uranium were exported in cobalt shipments between 2000 and 2024. During the same period, the DRC officially reported no uranium production.
According to the study, less than 10% of this uranium appears to have been publicly declared and placed under the international safeguards overseen by the International Atomic Energy Agency (IAEA). The researchers say this lack of reporting means it is difficult to know exactly where the uranium eventually ends up or how it is used.
Most of the cobalt shipments were sent to China, where the vast majority of the world’s cobalt refining takes place. During refining, uranium must be separated from the cobalt because it is an unwanted impurity in the final metal. Once removed, however, the uranium itself becomes a valuable material.
The researchers stress that their study does not show that anyone intentionally mined cobalt to secretly obtain uranium. Instead, they argue that the current supply chain allows significant amounts of uranium to move through international trade without being properly documented.
The study also highlights possible environmental problems. The team estimates that another 1,000 to 4,000 metric tons of uranium may have been discarded into mining waste, known as tailings. Because some of this uranium may be in forms that can move through soil and water, it could create long-term environmental contamination and increase health risks for miners and nearby communities.
To reduce these risks, the researchers recommend better tracking of uranium that is extracted alongside cobalt, regular testing of cobalt shipments for uranium content and improved radiation monitoring for mine workers. They also suggest stronger environmental oversight of mining waste to help protect local communities.
In the longer term, the researchers believe refining cobalt into metal within the DRC could make it easier to separate and properly account for uranium before it enters international trade.
The study combined scientific research with investigative journalism through a collaboration involving Lighthouse Reports and the Financial Times.
The researchers hope their findings will encourage governments and industry to improve oversight of the cobalt supply chain, strengthening both global nuclear security and environmental protection.
