Thin uranium shields play a key role in the production of the valuable radiopharmaceutical molybdenum-99. A European patent, which has just been granted to a scientist at the National Center for Nuclear Research in Sverk, can optimize this production with 3D printed targets.
Modern methods of visualization of the structure and functions of the human body, necessary, for example, in the diagnosis of cancer, largely depend on radiopharmaceuticals, i.e. active substances containing appropriately selected radioactive isotopes. When a radiopharmaceutical is introduced into the patient’s body, its flows or accumulation sites can be controlled by recording photons emitted by the nuclei of the decaying radioisotope.
Why is molybdenum-99 so important?
Today, up to 80 per cent. diagnostic procedures using radiopharmaceuticals require the use of molybdenum-99. “In the future, the production efficiency of this valuable radioisotope can be improved, in particular, thanks to 3D printed uranium targets. A European patent for such a solution has just landed in the hands of scientists at the National Center for Nuclear Research (NCBJ) in Sverk.
“The global demand for molybdenum-99 is huge. This is a radioisotope that is usually produced in nuclear research reactors, i.e. in devices with limited production capacity. That is why it is so important to constantly improve the methods of its production,” says the co-author of the patent, prof. Pavel Sobkovich (NCBJ).
The half-life of molybdenum-99 is 67 hours. This is the time that allows the peaceful transportation of a radioisotope from the place of production to a medical institution.
What is molybdenum-99?
“Molybdenum-99 is most often obtained by neutron irradiation of small targets containing low-enriched uranium-235,” says the master of engineering. Maciej Lipka, one of the co-authors of the patent. “Reactor neutrons have a limited ability to penetrate the target material. To ensure the conversion of as many uranium-235 nuclei to molybdenum-99 as possible, targets are usually prepared in the form of thin plates from a dispersion of uranium or uranium oxide or silicide in aluminum. The tile production process does not leave much room for optimization. Therefore, we proposed another way to manufacture uranium targets: 3D printing by laser powder sintering.”
Laser sintering of metal powders is a type of 3D printing based on the use of a laser of appropriate power to selectively melt a thin layer of powder, previously evenly distributed inside a container on a working platform. After fixing the first layer, the platform is slightly lowered, the next layer of powder is applied and the whole cycle can be repeated as many times as necessary.
Uranium shields - how to print them?
“3D printing technologies have been known for a long time, but have not yet been used to manufacture uranium targets for neutron irradiation in reactors. However, we believe that this method of producing discs can have many advantages,” says Prof. Sobkovich.
In a target exposed to neutrons, nuclear reactions occur, the by-product of which is heat. According to NCBJ, the use of 3D printing makes it possible to optimize the shape of the targets so that heat is more efficiently dissipated into the environment. Thus, the targets themselves would heat up less, and this would increase the content of uranium-235 in them. As a result, more molybdenum-99 can be produced per exposure.
“When firing neutrons at a uranium target, not only molybdenum-99 is formed, but also many other isotopes. Therefore, after removal from the reactor, each screen must be subjected to an appropriate chemical treatment that serves to isolate molybdenum. Meanwhile, with the help of 3D printing, it is possible to produce, for example, openwork discs with a very large active surface that interact more effectively with chemical solvents,” says the master of engineering. Lipka.
Perhaps the most promising aspect of the patent, NCBJ officials comment, relates to the possibility of improving the efficiency of processing uranium-235 itself. In each irradiated target, some of the nuclei of this isotope do not undergo nuclear transformations. Thus, printed target shapes can be designed to increase the amount of recoverable uranium. Once extracted, it can be used to create additional shields.
“Currently, more than 10 per cent. The world demand for molybdenum-99 is covered by the Polish research nuclear reactor “Maria”, located in Swierka near Warsaw. NCBJ is also home to the POLATOM Radioisotope Centre, a manufacturer of technetium generators that are exported to over 70 countries.
Source: Wprost
