Fear of nuclear terrorism lurks behind molybdenum supply debate

June 3, 2008

The crash of the radioisotope supply last winter gets a close look in this month's cover story. It details the politics and policy issues that closed down the Chalk River reactor in Ontario for nearly a month, leaving North American nuclear medicine physicians without a reliable supply of technetium-99.

The crash of the radioisotope supply last winter gets a close look in this month's cover story. It details the politics and policy issues that closed down the Chalk River reactor in Ontario for nearly a month, leaving North American nuclear medicine physicians without a reliable supply of technetium-99.

There's an interesting back story as well: Continued access to medical isotopes is increasingly tied into a hot political battle over how to make these isotopes without exposing all of us to the threat of nuclear terrorism.Most of the medical isotopes made today rely on weapons-grade uranium to produce the molybdenum (Mo-99) that decays into theTc-99m used in radioisotopes for medical imaging. There are four major sources: The reactor in Chalk River receives its U-235 from the U.S. Facilities in Europe-one in the Netherlands and one in Belgiumget theirs from European nuclear powers (France, the U.K., and Russia). And a reactor in South Africa gets U-235 from supplies accumulated before the country renounced its nuclear weapons program.

The legitimate fear is that the shipping and storage of this highly enriched uranium risks the loss of weapons-grade material to terrorists who could use it to assemble a crude nuclear bomb. By some accounts, the waste material from the process poses an even greater risk, because it can be handled after three years of storage.

Although other sources exist of highly enriched uranium that could be obtained by terrorists, the growing use of radioisotopes for medical imaging is perceived as boosting the risk.

It is possible to substitute low-enriched uranium, which can't be used to make nuclear weapons, in the medical isotope production process. The question, and a source of dispute, is just how feasible this approach is in a global market. The battle generally divides people into two camps: nuclear nonproliferation advocates who say it can be done versus major suppliers of Mo-99 who say the transition is costly and not feasible.

A long-standing global movement supports converting nuclear reactors so that they are powered by low-enriched uranium. Legislation approved by the U.S. Congress in 1992 gave some teeth to this movement by requiring that plants that make Mo-99 for medical isotopes can continue to receive high-enriched uranium shipments so long as they show progress in shifting their processes to low-enriched uranium. The bill was modified in Congress in 2005 to allow high-enriched uranium shipments to the Cana­dian and European reactors.

Progress toward a low-enriched system has been slow. Today, about 95% of all Mo-99 for medical isotopes involves the use of weapons-grade uranium, according to the Argonne National Laboratory, which has a program to encourage conversions.

Almost five times more low-enriched than high-enriched uranium is required to produce the same amount of medical isotopes, entailing a major overhaul of facilities and huge potential costs. A 2004 report from the General Accounting Office states that medical isotope producers operate on thin margins and that the U.S. has no power to compel such conversions by the European reactors because, unlike the Canadian reactor, they don't get their high-enriched uranium from the U.S. Other commentators have noted that a shift to low-enriched uranium by one Mo-99 supplier, but not the others, would give the others an economic advantage.

So where does that leave U.S. practitioners? At least two low-enriched facilities are in development, each capable of supplying 30% to 50% of the U.S. demand, according to a 2007 report from the Argonne lab. One could be in operation by 2012. In addition, the 2005 modification of the high-enriched export restrictions by Congress required a study by the National Academies of Science that will evaluate whether the low-enriched approach for medical isotopes is feasible. That report is due out this year.

For now, nuclear medicine remains on the horns of a dilemma, balancing access to medical isotopes against the risk of a nuclear terrorism attack.