All Mo-99 made for global distribution is produced from uranium-235 fission at just five nuclear reactors, all of which are over forty years old. A sixth, much newer nuclear reactor in Australia is due to start feeding the US and Canadian market shortly, though the amount of Mo-99 exported to North America has yet to be confirmed.
The robustness of the Mo-99 supply chain has been called into question many times over the past 18 months, following technical problems and extended maintenance stoppages at different reactor sites. Most recently, the National Research Universal (NRU) reactor at Chalk River in Canada has been forced to close whilst a heavy water leak is sealed. The High Flux Reactor (HFR) in Petten, the Netherlands will also be shut for up to six months in early 2010 so that pipes in its primary cooling system can be repaired.
Given the widespread use of Tc-99m for diagnostic imaging, and the recurring problems with the existing, middle-aged infrastructure, new sources of Mo-99 are being sought urgently. Upgrading the four-year-old FRM II is an obvious solution, according to Winfried Petry, scientific director of the FRM II, not least because this strategy would be far cheaper and quicker than building a new facility from scratch. "To build a new reactor in Europe would cost €300 million and take 12-15 years if you started the project now," he said.
Germany is currently the biggest consumer of Tc-99m in Europe. Approximately three million diagnostic tests involving Tc-99m, for example, to locate cancer metastases or sources of infection, are carried out in Germany each year.
The total cost of the FRM II upgrade has been put at €5.4 million, with a view to beginning Mo-99 production in five years. The main changes include altering a thimble near the fuel element to fit the U-235 targets, installing an effective cooling mechanism to deal with heat generated by the fission process, and setting up a safe internal transport system for the irradiated targets.
The FRM II generates a high flux of neutrons so would be well-suited to making commercially-viable quantities of Mo-99, Petry told medicalphysicsweb. A feasibility study has shown that assuming a mean annual uptime of 240 days, the reactor would produce approximately 65% of annual European requirements for Mo-99, or just over one-eighth of the current global demand.
These forecast yields are based on the use of highly-enriched U-235 targets. Switching to low-enriched targets would reduce the amount of Mo-99 produced by a factor of four. "Technically, we could use low-enriched uranium targets immediately, but worldwide we wouldn't get enough Tc-99m at the moment," Petry said.
Time and space for scientific research at the FRM II will not be affected by the decision to move into Mo-99 production. "Our source throws away most of its neutrons, they are diffused in all directions," Petry said. "I can take a few more out without disturbing what is going to any of the other thimbles or beam-holes."
The state government of Bavaria has committed to contributing €1.2 million towards the upgrade. Additional funding is now being sought from the German national government.