Artisanal cobalt miners in the Democratic Republic of Congo risk exposure to uranium while working. Wikimedia CommonsThe southern region of the Democratic Republic of Congo (DRC) is known as the Copperbelt because of its rich deposits of copper and other minerals. The area was the original source of uranium ore for the first nuclear weapons built by the US’s Manhattan Project (1942 and 1947). Two atomic bombs were then dropped on the Japanese cities of Hiroshima and Nagasaki in 1945.The Manhattan Project’s main source of uranium was the Cobberbelt’s Shinkolobwe mine in south-east DRC. It has been officially closed to excavation since 2004. The DRC hasn’t officially reported any uranium exports in decades.However, our recent research shows that substantial unreported quantities of uranium are likely to be leaving the country today. I am a geologist with expertise in analysing data concerning the chemical and mineral contents of rocks. I do most of my work in map-view, taking in spatial data points – like regional cobalt statistics – and drawing conclusions.Our research is the first to systematically take two crucial factors into account:the natural geologic co-occurence of uranium and cobalttheir similar behaviour in processing chemistry. Uranium and cobalt occur together in rock and respond the same way to chemical processing, so they are hard to separate.From this we were able to come up with a single estimate of how much uranium is at stake when cobalt is mined and exported.Very few data points about uranium concentrations in ores or the chemical steps that prepare cobalt for shipment are publicly available. We reached our estimates by using geologic maps to model the likely uranium grades in cobalt ores. We combined these grades with the amount of ore being processed at each facility in the Copperbelt, and a model of uranium behaviour during the processing chemistry prior to shipment.The end result links cobalt production to likely uranium export. Our calculations show that, in the most likely scenarios, 2,000-5,000 tonnes of natural uranium were exported from the DRC in cobalt-hydroxide shipments between 2000 and 2024. Read more: How a rich uranium mine thrust the Congo into the centre of the Cold War Less than 10% of this material appears to have been publicly declared to the International Atomic Energy Agency. The agency is responsible for uranium accountancy and safeguards. Most of the material was exported to China, which dominates the global cobalt market. This quantity of uranium could be processed into enough material for roughly 600-1,500 nuclear weapons, by our calculations. Or fuel a standard light-water nuclear reactor for 10-25 years.Our findings identify a substantial gap in nuclear accountancy and environmental oversight within a critical mineral supply chain. In the weeks following our study’s publication in July 2026, the DRC launched a probe to test outgoing cobalt shipments for uranium content. It will also consult with the International Atomic Energy Agency. But more needs to be done.Putting pieces of the puzzle togetherThe specific risk of uranium exports as a byproduct of cobalt is not a story of covert access to deposits and smuggling. It stems from a geologic coincidence.Cobalt is key to many modern conveniences and technologies, such as smartphones and laptops. Southern DRC is the source of 70% of the world’s cobalt. The ores that supply this cobalt sit in close proximity to the several concentrated uranium deposits, like Shinkolobwe, that dot the region. Over the past few million years, uranium has spread throughout the Copperbelt as rainwater has gradually carried it away from the concentrated deposits that formed roughly 600 million years ago, before the first animals even walked on land. Heterogenite, the main mineral that supplies cobalt, can adsorb – or grab hold of – this uranium as it passes by.The result is that the same minerals that form the world’s majority supply of cobalt are known to have elevated uranium content. We reviewed several pieces of prior research that noted that uranium and cobalt have similar chemical behaviours in the crude refining that takes place in the DRC. So nearly all the uranium that comes out of the ground when extracting cobalt minerals will remain in the final product that’s ready for export. Refineries can follow explicit processes to remove uranium from cobalt. Discussions about these techniques have only begun to happen in recent years, starting roughly in 2020. They are not common. We compiled DRC import records of the chemicals required to remove uranium and found only three of the 31 operations we investigated appeared to be consistently implementing uranium removal measures. We built a model that took the uranium and cobalt’s geologic co-occurrence and similar behaviours in processing chemistry to form a single estimate of how much uranium is involved. The end result linked cobalt production to likely uranium export.The risksThe sheer size of the DRC cobalt industry poses a uranium accountancy problem, regardless of uranium grades in ores or removal strategies. The country exported over 200,000 tonnes of cobalt in 2024. Each shipment should be checked for radioactivity when entering ports or crossing borders. It should be flagged if a geiger counter – which detects and measures radioactive energy – returns too high a reading. However, this system requires consistent applications of sensitive instruments, and high-uranium shipments are known to escape regulatory control.Even if mines in the DRC were systematically implementing uranium removal strategies to keep cobalt products within international shipping limits for radioactivity, enough uranium would be reaching China to make approximately 12 nuclear weapons per year. This is based on our calculations and the size of the DRC’s cobalt industry. Read more: What is uranium enrichment and how is it used for nuclear bombs? A scientist explains Beyond the clear global security risk that comes from the undocumented flow of uranium, our results demonstrate a widespread risk to the people and environments near these mines. People are exposed to this uranium when working in the mines. We estimate 1,000-4,000 tonnes of uranium have been discarded in highly mobile forms in tailings areas – sites used to hold material left over after mining. This poses an environmental health and safety risk to the surrounding communities.Prior research has shown that some populations of miners and communities near mines in the DRC show signs of uranium exposure, based on sampling of their blood and urine. Our research shows that this risk must be considered across the entire Copperbelt.What nextSystematic assay measurement of cobalt products is a crucial first step in bringing transparency to this issue. This would involve an independent agency taking representative samples of cobalt shipments and measuring the precise amount of uranium present to produce a shared record.In addition to testing the outgoing shipments, we would also recommend monitoring workers in the DRC cobalt industry for radiation exposure. Our results indicate that even ores that have modest uranium grades present a potential exposure risk as they can eventually achieve high concentrations through processing.And policies are needed that mandate the treatment of cobalt products to remove uranium and dispose of it in stable forms in tailings areas that are isolated from public water supplies.Ryan A. Manzuk does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.