Medical isotopes, tiny radioactive particles injected into the human body to diagnose and treat a number of diseases, are the backbone of nuclear medicine.
When the world´s largest medical isotope producer, the National Research Universal (NRU) in Chalk River, Ontario, was shut down in May 2009, a global medical isotope shortage ensued, leaving hospitals with costlier and less effective procedures. The NRU facility supplies isotopes that typically result in the daily treatment of more than 76,000 people in over 80 countries. Faced with a sudden thirty percent supply shortfall in the wake of the reactor outage, doctors had no choice except to postpone vitally important diagnostic procedures. Similar supply issues arose in August 2008 when a temporary shutdown at the High Flux Reactor (HFR) in the Netherlands was unexpectedly extended.
Demand for medical procedures using isotopes is increasing, yet only five facilities ensure the vast majority of the world´s supply of the critical needed radioisotope, molybdenum-99 (99Mo). Worryingly, this isotope supply gap is only the tip of the iceberg of a much larger problem: global research reactor aging.
Over the past six decades, research reactors have served as an irreplaceable asset in developing nuclear science and technology, training nuclear personnel, enhancing operational expertise, and generating radioisotopes for various applications.
"The Massachusetts Institute of Technology (MIT) reactor currently supports research on advanced reactors, the University´s educational programs, and the development of experience-based nuclear resources and skills by training, licensing, and employing approximately 30 student operators," notes Ed Lau, engineering alumnus and current MIT Reactor Superintendant.
Nevertheless, more than half of the 250 research reactors operating worldwide started their work before 1970. For example, the Canadian NRU went online in November 1957. Many reactors worldwide have exceeded their originally planned design life or are subject to regulatory requirements that have evolved over the years of their operation. In addition, the market often demands products (or services) significantly different from those for which the reactor was conceived. Modernizing and refurbishing old reactors poses challenges. Over the years, research reactor operators and regulatory authorities have acquired significant expertise in dealing with problems arising from aging facilities. At a technical meeting, held from 5 to 9 October 2009 at the IAEA Headquarters in Vienna, relevant information was collected and shared with a broader community to provide a solid foundation for further endeavors.
"Ageing of facilities and staff was one of the concerns that called for the development of the IAEA Code of Conduct on the Safety of Research Reactors, and the Agency has continued to make intensive efforts for its effective application," said H. Abou Yehia, Head of the IAEA Research Reactor Safety Section, in his opening remarks to the meeting.
"This meeting has a very practical approach, it is all about lessons learned and examples, there is a large collection of experiences to learn from," said Jelmer Offerein, an engineering manager at the HFR in Petten, the Netherlands.
The IAEA is working systematically to collect existing knowledge and share it with operators and oversight authorities worldwide. This method has proven successful. For instance, the results of a 2006 meeting in the Netherlands, dealing with planning and conducting large refurbishment and modernization projects, were widely shared.
"Our aim was to make sure that practical advice is made available to operators," says Ed Bradley, a nuclear engineer from the IAEA Research Reactor Group.
"In practice, ageing management of research reactors is accomplished by coordinating existing programmes including maintenance, periodic testing, and inspection, and periodic safety reviews, as well as applying good operating practices. This meeting was a good occasion to disseminate the international good safety practices, which are established in the recently published IAEA Safety Standards, including the Safety Guide on research reactor ageing management which is in its final stage of development," noted Amgad Shokr from the IAEA´s Research Reactor Safety Section.
In its search for solutions, the IAEA is helping address aging issues by, for example, publishing a collection of recommended practices to optimize research reactor availability and reliability, collecting information on the development and implementation of large scale modernization and refurbishment projects, assessing plans for new reactors, and encouraging the use of low enriched uranium (LEU) as the target of choice for isotope production.
"This work is meant to assist operating organizations in their efforts to safely and securely operate their reactors through shared experiences and the implementation of sustainable management programs," said Bradley.
In the realm of medical isotopes, new, dedicated reactors are unfortunately years away from operation and face economic, political, and regulatory challenges. Amgad Shokr notes that "there is a need to establish criteria to achieve balanced considerations of all relevant impacts without compromising safety." Thus, today there is scant margin for any unplanned shutdowns or outage extensions given the limited number of suppliers.
"There are significant challenges for the medical isotopes market, if the Canadian research reactor does not go online as currently anticipated and our facility needs to start maintenance early next year," says Jelmer Offerein. The IAEA´s Ed Bradley notes, "The problem is now and a solution is needed."
Introducing isotopes into the body permits earlier and more comprehensive diagnoses by tracking the location and movement of the isotopes in the tissues affected by the illness. Radioisotopes can also be used to treat cancer by depositing radiation energy that destroys cancerous cells. The ageing of European and North American populations creates a rising demand for medical radioisotopes. Five government-owned reactors supply about 95 percent of the worldwide demand of the major product, molybdenum-99: Canada´s NRU, the Netherland´s HFR in Petten, Belgium´s BR2, France´s OSIRIS, and South Africa´s SAFARI-1. Several other smaller reactors make their products available to regional markets.
Molybdenum-99 is produced by irradiating target material (low or highly enriched uranium) with neutrons coming from a controlled fission in a research reactor and subsequently by extensive radiochemical processing (fission-produced Mo-99). For example, technetium 99m (99mTc) is the radioisotope used in 80 percent of all diagnostic nuclear medicine procedures in the world and a daughter product of molybdenum 99 (99Mo). Moly-99, as it is casually named, has a relatively short half-life of 66 hours. Consequently, regular weekly production is necessary to satisfy global demand.