Completed uranium-silicide mixed fuel assembly.
Fuelling the future of medical radioisotope production Radioisotopes are typically produced in research reactors, which require a regular supply of nuclear fuel. Researchers in the EU-QUALIFY project are working to qualify low-enriched uranium nuclear fuels for use in European research reactors, helping maintain Europe’s capability to produce medical radioisotopes for both diagnostic and imaging purposes, as Jared Wight explains. A large proportion of the medical radioisotopes used around the world are produced in European facilities, including about 80 percent of molybdenum-99 (Mo99), which is widely used to identify and locate tumours. This particular radioisotope can only be produced at commercial scale in research reactors, the operation of which requires a regular supply of nuclear fuel, now Jared Wight and his colleagues in the EU-QUALIFY project aim to help keep these high performance research reactors (HPRRs) operating. “We need to sustain our capability to produce these radioisotopes – particularly Mo-99 – and also some upcoming drugs, like lutetium-177 PSMA. To achieve this, we need to ensure that these reactors can continue to run,” he outlines. This involves converting the reactors from using highly-enriched uranium-based fuels to low-enriched uranium (LEU), which has a concentration of below 20 percent of the 235U isotope. “This is an internationally agreed upon level that ensures the material is proliferation resistant,” says Wight.
EU-QUALIFY project
focused on developing and demonstrating novel, LEU-based fuels with a higher density of uranium. Three types of LEU-based fuels have now been identified; dispersed Uranium Molybdenum (U-Mo), monolithic U-Mo and Uranium Silicide (U3Si2) dispersion fuels. “In the EU-QUALIFY project we’re looking to qualify these fuels further. We are gathering data to be able to qualify these fuels in a
systems to a higher density in fabrication and higher power under irradiation than before,” he continues. “For example, the U3Si2 fuel is a metal-based powder, homogeneously dispersed in an aluminium-metal matrix. This fuel ‘meat’ is being optimized to increase the fuel to matrix loading ratio to increase the resulting fuel plate to a higher density, thus enabling LEU conversion of HPRRs which
“A further project has been granted by the European Commission, EU-CONVERSION, building on the work in the earlier EUQUALIFY, LEU-FOREvER, and HERACLES-CP initiatives.” generic sense, so that they can then be used in different reactors,” explains Wight. Each of these fuels have been rigorously analysed, with Wight and his colleagues looking to ensure that they are acceptable, safe and affordable. “In previous research, dispersion U-Mo was found to be the best candidate to substantially increase the fuel loading, but now, monolithic U-Mo and high density uranium silicide fuels have also been identified to meet the requirements for some reactors. We’re now pushing the candidate fuel
are the backbone of producing medical radioisotopes.” The project team now aims to take these three fuels through a generic fuel qualification process, which is crucial to understanding how they will behave in a variety of different conditions. First there is a fabrication and development stage, followed by a numerical neutronics analysis stage verifying that the irradiation targets can be met. Then the fuel is irradiated and tested, after which post-
This research builds on two previous projects, HERACLES-CP and LEU-FOREvER, that were
RHF reactor at ILL.
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BR2 reactor at SCK CEN.
FRM-II reactor at TUM.
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irradiation examinations (PIE) are conducted. “We take the data from all the different design and assessment steps into account for the fuel qualification and further process the results to improve fuel performance models. We want to be able to predict what might occur in certain scenarios,” outlines Wight. Safety is a paramount consideration in this respect, says Wight. “Whenever a new reactor enters operation, or a reactor is changed in some way, this is accompanied by a very significant amount of safety analysis,” he stresses. “We have to consider a variety of different scenarios, including some seemingly unlikely ones. We need to be able to demonstrate that there will not be a significant release of radioactivity to the workers, the public, or the environment under even these very unlikely scenarios.” This research is continuing apace, and significant progress has been made over the course of the project. There are four experiments within EU-QUALIFY, two of which have been successfully performed. “We’ve made some great progress on the tests for U3Si2, although we still need to finalize the PIE work. There have been some delays with the U-Mo dispersion and the U-Mo monolithic, but we’re making some progress now,” says Wight. The backdrop to this research is severe constraints on the supply of HEU on which Europe’s HPRRs previously depended. “There are really only two sources of HEU in the world, the US government and Russia. It is nearly impossible for reactors in Europe to get fuel from Russia with the sanctions that are currently in place, while the US government will only provide it if you can demonstrate that there is a real need,” explains Wight. “Under the Schumer amendment, they will also only continue to export HEU if that reactor is actively pursuing LEU conversion.”
Irradiated silicide fuel plate from HiPROSIT experiment. Above right image: Irradiated uranium-silicide mixed fuel assembly.
the production of radioisotopes, so they have very different fuel performance requirements. “These reactors are all very different, with their own particular engine specifications,” says Wight. There are also other facilities which can produce Mo-99, notably the HFR reactor in Holland which has been converted to LEU, while new facilities are at different stages of
development. The Jules Horowitz reactor in France is currently under construction, while the proposed replacement of the HFR reactor – PALLAS – will use the same fuel as HFR, further underlining the wider importance of the project’s work . “The authorities in the Netherlands are looking to increase their ability to produce Mo-99, or at least reduce their fuel costs by using these upgraded fuels
JHR fuel assembly design (CEA).
Refuelling reactors The partners in the EU-QUALIFY consortium are now working towards this goal, so that these reactors can be essentially refuelled on an ongoing basis, and continue producing valuable medical radioisotopes. There are three main HPRRs currently in operation in Europe that need to be converted to LEU. “These are the BR2 reactor, which is located at SCK CEN in Belgium. Then there’s the RHF reactor, which is in Grenoble, and the FRM II reactor, which is at the technical university in Munich,” outlines Wight. The intended purpose of these reactors at the time they were built was to test new materials and conduct basic research, but over time their usage has evolved to increasingly focus on
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SCK CEN hot cell operation.
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