France’s Framatome has announced a key advance in development of monolithic molybdenum-uranium (U-Mo) fuel for Germany’s Forschungsreaktor München II (FRM II) research reactor, operated by the Technical University of Munich (TUM).

Framatome’s CERCA Research & Innovation Laboratory (CRIL) and TUM developed the main component of a high-quality U-Mo fuel in record time and within budget. They also manufactured the prototype, established a qualification procedure, and installed a pilot line for the fuel. Framatome said this is “Europe’s low-enriched fuel with the highest density ever realised for research reactor operations”. It represents a key contribution to the continued operation of FRM II which provides neutrons to industry and the scientific community.

“Producing innovations for safe and reliable operations of research reactors is at the heart of what we do every day,” said CERCA vice president François Gauché. “Developing this sophisticated fuel while creating knowledge useful for future manufacturing was a significant challenge. We are proud of our CERCA team for providing a solution that meets the customer’s objectives and will ensure the continuation of its scientific activities.”

FRM II currently uses highly enriched uranium (HEU) fuel to generate a dense neutron flux for scientific experiments and the production of medical radioisotopes. Several years ago, TUM launched a programme to explore the feasibility of a fuel based on low-enriched uranium (LEU) while maintaining good performance of the reactor. In 2019, the university contracted Framatome to develop the U-Mo foils manufacturing technique to support the existing technology of embedded foils in a cladding of aluminium.

Framatome’s U-Mo fuel allows the reactor to maintain its high level of performance with LEU as a result of its high uranium density. The first U-Mo foils were recently manufactured at CERCA using high quality uranium material. Irradiation of the first monolithic U-Mo fuel plate prototype is scheduled for September 2023.

FRM II is a world leading research reactor and neutron source. It is optimised for neutron scattering experiments at beam tubes and neutron guides. It has irradiation facilities that produce homogenously doped silicon for the renewable energy transition, and radioisotopes needed for medical diagnostics and cancer treatments.

However, the reactor is currently not in service operation. After a micro-leakage in the central channel the production of a replacement part is ongoing. “The procurement of a highly complex individual piece of the highest nuclear requirements requires special care and is being carried out with intensive assessment by the expert appointed by the nuclear regulatory authority,” said FRM II Technical Director Dr Axel Pichlmaier. He added that operation is expected to resume in 2024.

Meanwhile, TUM said German politicians support the conversion to LEU fuel. “The responsible Bavarian State Ministry for Science & Art gave its approval to this plan,” TUM said. “This was preceded by successful research at TUM on the theoretical possibility of retrofitting. Preparations for the approval process for the new fuel can now begin.”

Science Minister Markus Blume said: “We want to operate Germany's most powerful research reactor in the future with the most advanced low-enriched fuel – with the same performance as before. In this way, we will secure neutron research at the Bavarian science site, which is elementary for so many future fields, and invest in the further development of fuels. It is clear to us that research strength and open technology without ideological blinkers are prerequisites for a good and secure future.”

TUM President Professor Thomas F Hofmann welcomed the positive reaction from politicians. “The research reactor is an alternative tool for science. With the neutrons generated there, for example, batteries or the materials for high-performance gas turbines can be examined without destruction. The system is also used for the production of cancer drugs and was even involved in the research of mRNA vaccines.”

Plans have been approved for fuel with a maximum of 50% uranium-235 enrichment “as soon as the new fuel is developed, is qualified and industrially available”. However, complex computer simulations and calculations have shown that uranium-235 can be enriched by less than 20% if monolithic uranium-molybdenum is used as fuel.

TUM says the task now is to put the theory, which has been confirmed by independent teams of experts, into practice. For this purpose, a cross-departmental project team at FRM II will carry out further optimisations in the fuel element design in the next few years and prepare the initiation of the approval process and the procurement of new fuel elements

The calculations were carried out by researchers from TUM and the US Argonne National Laboratory while Framatome is developing fuel production. Research at the TUM Centre for Nuclear Safety & Innovation was funded by the Federal Ministry of Education & Research (BMBF) and the Bavarian State Ministry for Science & the Arts (StMWK).

Image: A Framatome operator fabricates UMO foils at CERCA (courtesy of Framatome)