New technique promises non-U medical isotopes

16 September 2008

As the world shortage of medical isotopes continues, scientists at Delft University of Technology in the Netherlands say they have developed a new technology to produce molybdenum-99 which could help to avoid such shortages in future.


Molybdenum-99 (Mo-99) is used in hospitals to generate technetium-99m, a short-lived radioisotope which plays a key role in nuclear medicine in crucial diagnostic and imaging applications as well as in the medical care of patients suffering from cardiovascular diseases, tumours and various central nervous system.


Mo-99 is currently manufactured from the fission of uranium in a handful of specialist nuclear reactors around the world. However, a series of recent events culminated in five of those reactors being shut down for maintenance or refuelling outages of various lengths, plus the closure of another manufacturing site after an unexpected release of another isotope. The closures resulted in an acute shortage in the supply of medical isotopes, especially Mo-99.


Now, Bert Wolterbeek of Delft University of Technology's Reactor Institute Delft (RID) has developed a method of producing molybdenum-99 from naturally occurring molybdenum-98, the most common molybdenum isotope, without the need for a high neutron flux reactor. Most older research reactors were originally designed to use highly-enriched uranium, although many have been converted in recent years to use low enriched fuel instead. The newest models, such as Opal in Australia use only low enriched fuel.


Wolterbeek has developed a technique still works by bombarding the molybdenum atoms in the raw material with neutrons, producing Mo-99, but takes the neutrons from a different source. The energy transfer involved also separates the water-soluble Mo-99 from the surrounding atoms, meaning that the isotope can be produced in a highly concentrated form. Molybdenum is mined in Canada, Chile, China, Russia and the USA.


According to the university's weekly Delta magazine, because the new technique does not rely on the use of a research reactor its associated fuel, apparatus and safeguards, many more facilities could manufacture the isotope and this would in turn decrease the risk of supply shortages. According to Delta, Wolterbeek wishes to hold larger-scale tests in conjunction with uranium enrichment company Urenco which also uses its ultracentrifuge technology to produce stable isotopes for a range of medical, research and industrial uses.


Supply of technetium-99m in Europe is reported to be at about 50% of its usual level as isotope producing reactors in Canada and South Africa work to their maximum capacity to make up for the current unavailability of the European reactors. Shortages are expected to continue until at least the end of October.


The recent crisis in medical radioisotope production follows a worldwide shortage at the end of 2007, when Canada's National Research Universal (NRU) reactor at Chalk River was forced into an unscheduled outage. Now organizations such as the European Association of Nuclear Medicine are calling for long-term measures such as the construction of new reactors dedicated to the production of medicinal isotopes to prevent future crisis situations.


Earlier this year, Atomic Energy of Canada Ltd (AECL) cancelled the construction of the two MAPLE reactors which were to be the world's first reactors dedicated exclusively to medical isotope production. Both reactors had already gone critical but encountered problems in commissioning. Once completed, they could have supplied the entire global demand for Mo-99.