Canadian agency pulls plug on molybdenum reactors

Atomic Energy Canada has halted development work on twin reactors at Chalk River, ON. They were the planned successors for an aging research nuclear reactor that is the source of molybdenum-99 isotope used in 19 million nuclear medicine imaging procedures annually.

Atomic Energy Canada (AECL) announced May 16 that work on the reactors would halt immediately, effectively killing the troubled project. The AECL decision was based on escalating development costs and the expected additional time and risks associated with eventually bringing the two reactors online, according to the company.

Construction of two Multipurpose Applied Physics Lattice Experiment (MAPLE) reactors was completed in 2000, but the AECL was still working as of April 2008 on modifications that had escalated their costs to $465 million, more than three times original estimates. Central to the problems at MAPLE are the reactors' inability to operate at a negative power coefficient reactivity value. Tests have repeatedly produced positive values, suggesting problems in the case of an accident. A new set of tests was performed this spring.

"We are making the right business decision given the circumstances," said AECL chief executive Hugh MacDiarmid in a release. "Our board of directors and senior management have concluded that it is no longer feasible to complete the commissioning and startup of the reactors.

Officials of MDS Nordion, a Canadian company that refines Mo-99 from the Chalk River facility, announced that AECL had not consulted with them before killing the project. Nordion distributes the isotope to North American customers, mainly through Lantheus Medical Imaging (formerly Bristol-Myers-Squibb Medical) in North Billerica, MA.

Nordion officials are encouraged that the Canadian government has asked AECL to pursue an extension of the National Research Universal operational license due to expire in 2011.

"The most important issue has always been the continuity of medical isotope supply for patients worldwide," said Nordion president and CEO Stephen P. DeFalco in a release.

The decision to halt development of MAPLE underscores nuclear medicine's ongoing reliance on the NRU reactor for Mo-99, the precursor for technetium-99m, a versatile isotope used in about 80% of nuclear imaging procedures. A 28-day shutdown of the NRU reactor from Nov. 18 to Dec. 14, 2007, triggered a moly shortage that forced many nuclear medicine departments in the U.S. and Canada to ration Tc-99m and delay procedures.

The shutdown stemmed from a dispute between the AECL and the Canadian Nuclear Safety Commission concerning the installation of backup safety equipment. The Canadian Parliament and Health Minister Tony Clement ordered the facility reopened, and it has since operated without incident.

U.S. providers have relied on foreign sources of Mo-99 since the last domestic source was shut down in 1989. Covidien in Hazelwood, MO, distributes Mo-99 to meet about 25% of the U.S. demand. Its isotope is produced at the High Reactor at Petten, the Netherlands.

At least three initiatives have been proposed to reestablish domestic sources of molybdenum. Planning is under way at the University of Missouri Research Reactor in Columbia, MO; Babcock & Wilcox Company, in Lynchburg, VA; and General Atomics in San Diego.

These efforts and details concerning the ongoing saga of the MAPLE reactors are the subject of the cover story in the June issue of Diagnostic Imaging magazine.