Friday, May 23, 2008

Should We Have a Molybdenum-99 Source in the United States?

In the December 14, 2007 entry to this blog, I discussed how the shutdown of a nuclear reactor at Chalk River, Ontario caused a shortage of an isotope of technetium (Tc-99m) used for medical imaging. Tc-99m is obtained from an isotope of molybdenum, Mo-99, that is produced at a handful of international facilities, including the Canadian reactor. The production and use of Tc-99m in nuclear medicine is discussed in chapter 17 of the fourth edition of Intermediate Physics for Medicine and Biology.

The most recent (May 2008) issue of Physics Today contains an article by science writer Toni Feder that explores this topic further. Feder writes:

"The disruption late last year of Mo-99 production in Canada threw the nuclear medicine community into a panic. With a half-life of 66 hours, Mo-99 can't be stockpiled. The Canadian reactor was down for maintenance, and its startup was delayed because of safety violations. Such was the upset in the nuclear medicine community that the Canadian government stepped in and ordered the reactor to start up despite some remaining safety concerns--and demoted the head of Canada's nuclear regulatory agency."

The article also discusses plans for the production of Mo-99 in the United States. The US producers will use "low-enriched uranium" (LEU) rather than the "highly enriched uranium" (HEU) used at other facilities, including the Chalk River plant. This would have advantages for nonproliferation, and could reduce the amount of HEU available for production of weapons of mass destruction by terrorist groups. Feder continues:

" 'Our program is to minimize civilian use of HEU,' says Parrish Staples, manager of the National Nuclear Security Administration's program to convert reactors from HEU to LEU fuel. 'The only HEU the US is currently exporting is for production of Mo-99 in foreign production facilities.' The US exports about 25 kg of HEU each year, or about half the total used for making Mo-99, he says. If the US stops exporting HEU, he adds, according to the IAEA [International Atomic Energy Agency] definition 'a weapon's worth of material would be removed [from circulation each year]'

'At some point there will be an incident somewhere in the world that will cause the US to close its borders to radioactive materials for a day, a week, two or three weeks, whatever,' says MURR [The University of Missouri-Columbia Research Reactor] director Ralph Butler. 'And when you think that there are tens of thousands of patients per day [in the US] utilizing this diagnostic tool [radioactive isotopes], that's a huge impact.' The US does not have a Mo-99 source, he adds. 'There is a national need, and it's an opportunity we [at MURR] can meet.' "

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