Rosatom has completed acceptance testing of the first three fuel assemblies (FAs) for the MBIR multipurpose research reactor, a fast-neutron research reactor being constructed in Dimitrovgrad, Russia. The tests were conducted at the Fuel Technologies Department of the Research Institute of Atomic Reactors (RIAR)—a part of the scientific complex of Rosatom. This milestone is notable in that the project has transitioned from individual fuel elements to entire fuel assemblies ready for placement in the reactor core.
From Single Fuel Elements to Complete Fuel Assemblies
Work on MBIR’s fuel began long before the recent tests. RIAR reported in August 2024 the manufacture of the first experimental batch of fuel elements using vibrationally compacted uranium-plutonium MOX fuel. The individual fuel elements were then subjected to preliminary and acceptance testing to ensure compliance with design and manufacturing documentation. The tests have been cleared for use in the fabrication of an experimental batch of fuel assemblies.
The technology chain has reached the next stage. The first 3 full fuel assemblies were tested by professionals in Dimitrovgrad. A commission verified the production process readiness and performed technical parameters of manufactured assemblies and control measurements. According to the published information, the test results confirmed that the assemblies met the established requirements.
This is especially true for MBIR, where the reactor will be not only a research facility but also a large experimental platform for the development of future nuclear technologies. Fuel is consequently a vital element of the entire program.
Fast Neutrons and MOX Fuel
MBIR is being designed as a rapid neutron sodium-cooled reactor with a thermal power of around 150 MW. It is designed to produce the high-intensity neutron field required for a wide variety of studies in reactor physics, materials research, and nuclear technologies.
The application of vibrationally compacted uranium-plutonium MOX fuel is associated with the development of fast-reactor technology and the closure of the nuclear fuel cycle. The new fuel-element design, developed in 2024, was designed to give the properties necessary for operating in the high-neutron-flux environment of MBIR, according to RIAR scientists.
So the current tests should not be seen as simply a quality check on three assemblies. This last one is an intermediate step between the technological development of the individual components and the fabrication of the fuel assemblies for the initial load of the future reactor.
The Reactor Is Being Built Alongside Fuel Preparation
The construction of the MBIR reactor is underway; installation and commissioning activities continue at the Dimitrovgrad site. Installation of components of the reactor’s primary loop and auxiliary systems is progressing while construction continues.
In 2025 cold filter traps were placed for the emergency heat-removal system, and work continued on pipes and industrial equipment. In January 2026, the equipment for handling used fuel assemblies and the systems for their steam-water cleaning were delivered to the site.
Against this background, the readiness of the first fuel assemblies represents another element of the preparation of MBIR’s overall infrastructure. Rosatom expects to finish deliveries of batches of components for fuel elements and the first batch of components for fuel assemblies by the end of 2026, Neftegaz reports. The company also intends to launch pumps by 2027.
A Reactor for Next-Generation Nuclear Technologies
The main distinction of MBIR is that it is not a conventional power reactor designed primarily for electricity generation. It is designed to supply an advanced experimental environment for a broad spectrum of nuclear research programs.
The reactor is expected to be used for research on new forms of nuclear fuel and structural materials, testing of equipment and technological systems, and generation of radioisotopes. Its capabilities are also aimed at contributing to the development of two-component nuclear energy systems and technologies for closing the nuclear fuel cycle.
An international research infrastructure is already being developed around the project. An International Research Centre has been established in the form of a consortium, allowing participating organisations to conduct experiments connected with their national peaceful nuclear-energy programmes.
MBIR Hits a New Milestone
“The first three fuel assemblies’ testing shows that MBIR preparations are being made on several fronts at the same time. The technological equipment is being installed, and the future fuel infrastructure is being designed in tandem with the construction of the reactor itself.
The next step will be to scale up production and supply the requisite batches of components once the first assemblies have been successfully tested. It is a major step from experimental fuel development to preparation for real reactor loading for a project meant to promote fast-reactor research and Generation IV nuclear technology development.
There is a long way to go before MBIR can begin operating at full scale. Its fuel program has already progressed from producing individual experimental fuel elements to testing whole fuel assemblies, an important step toward the functioning of Russia’s next-generation fast-reactor research platform.