For decades, nonproliferation scientists and engineers at the U.S. Department of Energy's Argonne National Laboratory have helped convert the fuel in dozens of research reactors around the world so that they operate safely and more securely. They find ways to change systems that rely on highly enriched uranium fuel, which can be used to make weapons, to systems that use low-enriched uranium fuel. With every fuel conversion, Argonne has gained experience, insight and a reputation for expertise solving some of the toughest reactor conversion problems.
Now, Argonne has helped researchers in Belgium achieve a significant technical milestone in what might be its most involved effort to date. Argonne scientists and engineers helped demonstrate safety metrics needed by Belgium's nuclear regulators in order to approve the fuel conversion in the BR2 research reactor at Belgium's nuclear research center, SCK CEN.
The BR2 research reactor is one of Europe's most complex, and it is also one of its most important, because it is a leading material testing reactor and producer of medical isotopes and semiconductor materials. By working together, the American and Belgian experts are helping to secure these capabilities at the same time that they are lowering the risk of anyone diverting the research reactor's fuel to make weapons.
"BR2 is an impressive reactor with a highly flexible core. … we need a design that reflects how the reactor is actually used, and then we have to show it can meet safety requirements across a wide range of uses." - Jeremy Licht, Argonne National Laboratory
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The BR2 reactor is responsible for producing about one-fourth of the world's supply of molybdenum-99, an isotope that decays into technetium-99m. Technetium-99m is widely used to diagnose a range of health conditions, including heart disease and cancer. BR2 also plays an important role in the production of therapeutic radioisotopes such as Lutetium-177 and Terbium-161; hospitals and communities depend on these medical isotopes to improve public health.
BR2 is also used for other valuable work, including a wide range of materials experiments and silicon doping. Doping is the process of intentionally adding impurities to a material to alter its properties. In silicon, this helps create semiconductors used in technologies such as electric vehicles, wind turbines and other high-power electronics.
Converting the fuel system in a nuclear reactor is always a challenge. Any proposed changes must be evaluated according to international standards to demonstrate continued safety, efficiency and functionality. However, BR2 is especially challenging because it is a high-performance research reactor with a wide range of specialized uses.
According to Jeremy Licht, a principal nuclear engineer who manages Argonne's Research Reactor Methods group, BR2 operates seven times a year in 30-day cycles. Its core can be reconfigured from one cycle to the next to support a wide range of user needs.
"BR2 is an impressive reactor with a highly flexible core," Licht said. "That creates a challenge during conversion because we need a design that reflects how the reactor is actually used, and then we have to show it can meet safety requirements across a wide range of uses."
Licht is among more than a dozen Argonne experts responsible for the technical support for Belgium's research reactor conversion. This work has already spanned a decade. The team's recent success reflects Argonne's expertise in research reactor analysis and the use of Argonne-developed codes trusted throughout the nuclear community to evaluate reactor safety and fuel performance.
"We're not done yet, but it is a major milestone to complete the fuel qualification and conversion safety analysis work so that SCK CEN could submit its conversion authorization request to their regulator," he said.
SCK CEN recently submitted the BR2 safety assessment report to its national regulator, the Federal Agency for Nuclear Control. They are working to obtain approval for the fuel conversion proposal in 2027 and to begin converting systems soon afterward.
Europe is home to three other high-performance research reactors of similar complexity. The SCK CEN milestone shows that these highly complex research reactors can also be converted to use more proliferation-resistant fuels. With each successful conversion, Argonne is improving nuclear security worldwide while sustaining reactors that provide a broad range of benefits to society.