ANSTO-designed target increases Mo-99 yield

ANSTO said that porous, cylindrical, reusable targets are being tested in its Open Pool Australian Lightwater (OPAL) reactor by nuclear materials research and technology group scientists, working with teams across the organization.

According to the National Center for Biotechnology Information, the 20-MWt OPAL research reactor produces 1,750 6-day curies of Mo-99 per week and currently accounts for about 8 percent of globally available production capacity.

Mo-99 is the precursor of technetium-99m, which is one of the most commonly used nuclear diagnostic imaging agents for the diagnosis of cancer, heart disease, and organ structure and function. It also supports other medical applications.

The work: According to ANSTO, research work has focused mainly on the modeling of neutron yields from a porous, reusable target containing U-235. Computer simulations compared three target shapes: flat (rectangular), spherical, and cylindrical.

Targets of different sizes were tested, all made with the same uranium material and density. Each target was simulated under typical operating conditions for several days to see how shape and size affected Mo-99 production, heat buildup, long‑term usability, and the creation of unwanted byproducts.

The cylindrical target performed best overall, as it produced the most Mo-99, had good long‑term performance, and resulted in the lowest amount of undesirable byproducts, ANSTO said. Heat levels were low for all target shapes and sizes, suggesting that overheating was unlikely to be a problem.

The research exploring the different target shapes was published was published in Frontiers in Nuclear Engineering.

Validation: Following successful modeling, proof-of-concept experiments followed using simulated targets to confirm predicted yields and stability. The targets were irradiated using neutron activation analysis in the OPAL multipurpose reactor.

According to ANSTO, the prototype spherical target that was developed enables fission recoil to eject the Mo-99 from the matrix into the pores, where it can be removed using a liquid compatible with the current molybdenum extraction processing system at ANSTO.

“Once the uranium-235 is exhausted, it can be disposed of using ANSTO’s Synroc waste encapsulation technology,” said Gordon Thorogood, an ANSTO senior principal research scientist.

“We now have a much greater understanding of the entire process of Mo-99 production, which provided unique training opportunities in nuclear materials research as well,” Thorogood added.