Manufacturing Molybdenum-99 for medicine at TUM’s Research Neutron Source

One cannot conceive of modern medicine without technetium-99m. It is ideally suited to making diseases visible, be it in the heart, the thyroid or the bones, and, moreover, minimising patient radiation exposure. It is used around 3 million times per year in Germany, and some 30 million times worldwide. However, fewer and fewer nuclear reactors are available for its production, leading to the risk of shortage. A new plant to produce isotopes is going to be established at the Research Neutron Source FRM II of the Technical University of Munich here in Garching. Dr. Heiko Gerstenberg is responsible for the irradiation facilities at the FRM II. “It was already clear since the design phase of FRM II, to use the reactor not only for basic research, but also for technical and medical applications. Since there is a permanent shortage with the isotope technetium-99m in nuclear medicine, it seems important to us, to provide a considerable contribution for the supply with this isotope.” At the moment, engineers and technicians are working on a 1:1 scale model in this hall. The construction reaches a height of two and a half meters. Philipp Jüttner is the engineer responsible for running the tests of the facility, supported by the technician Georg Haas. Slim fuel plates covered by an aluminum alloy are used in the facility. These targets hold 4 grams of uranium, the source material for the production of technetium-99m. At the moment, the two are still working with nuclear fuel free test plates. “This is a dummy of a target, that will be irradiated in our facility and this is the holder for the targets, which is built so that we can place eight targets together into our facility to irradiate them.” The holder with its eight targets is placed in a tubular container. Georg Haas currently handles this, but later on this task will be carried out remotely. The future irradiation position in the facility of the FRM II is difficult to reach. This is the main reason behind the construction. A grappler pulls the holder with the uranium-targets out of the container and moves it to a tube extending five meters deep into the reactor pool. “A big challenge for the construction of this facility was to place the irradiation position as close as possible to the fuel element to get as many neutrons as possible at the targets.” And there is another specialty: Philipp Jüttner chose gear rods for the insertion of the targets. The elements form a five-meter pole to push the targets down the long tube. And the gear rods can be folded up to save space. “I invented the gear rod assembly because the cooling water in our cooling channels is coming bottom up and the target holders are brought down. If there was no stiff rod the target holder would be blown out of the cooling channel.” The gear rod assembly is made of 23 singular elements. “Now we bring down the target holder to the fuel element, where the targets will be irradiated with neutrons. In this process we get molybdenum-99 which is the reason why we built this whole facility.” For six days the uranium targets are irradiated with neutrons, so that molybdenum-99 – in short “Mo-99” – is formed. Finally, the plates are transported to laboratories which chemically separate the resulting Mo-99 from the remaining material. Then it goes on to producers, who, with the aid of the gained isotopes, manufacture generators for use in medicine. Mo-99 decays with a half-life of only 66 hours to technetium-99m, the important radionuclide for the diagnosis of many diseases. Due to the short half-life of Mo99, as well as of Tc-99m, the generators must be delivered immediately to clinics and practices where technetium-99m is used for patients. Here in Garching the installation is still in progress. In addition to the development of the technical facility, a nuclear licensing procedure is under way. The engineer Mira Giourges is in close contact with the Bavarian State Ministry of the Environment and TÜV Bayern. “Our aim is to get an approval for installation and operation of the irradiation facility. That is why we submitted many documents to the nuclear experts. Based on these submitted documents the experts form an opinion, which builds the basis for our approval.” Meanwhile, in the test hall the irradiation system is placed in a large tank and flooded. In the research neutron source it will be operated in the reactor pool under five meters of water, which is why Philipp Jüttner and Georg Haas are testing the construction under water. “We want to make sure that the facility works properly. And if, for example, something is leaking, we will see the bubbles best under water.” Dr. Heiko Gerstenberg will be responsible for the operation of this irradiation facility in the future. It is important that the system works perfectly and can be installed into the tank of FRM II without a hitch. “One of the big advantages of this mockup is that we can check everything already here. That will help us to reduce the outage time of the neutron source during the installation phase of the facility within the pool of FRM II.” Ideally the test irradiations are scheduled for 2018. The start of routine production is foreseen for 2019 at the earliest.

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