Chalk River reactor shutdown halts Mo-99 production until late 2009

The nuclear reactor that serves as North America's primary source of molybdenum-99 will not return to service before late 2009.

Atomic Energy of Canada Limited, the reactor's operator, announced July 9 that it will need at least five more months to repair the National Research Universal (NRU) reactor. The 50-year-old reactor has been shut down since May 16, when a heavy water leak was discovered in the reactor facility at Chalk River, ON.

During normal operation, the NRU reactor produces enough Mo-99 to meet half the demand from the U.S. and Canada and 30% to 40% of the worldwide demand for the crucial medical isotope. Mo-99 is the precursor isotope for technetium-99m, a short-lived isotope used in about 70% of all nuclear medicine procedures.

The estimated duration of the shutdown was based on an analysis of the heavy water leak site, containment vessel condition, repair strategies, and critical path requirements for restart after an extended shutdown, according to AECL.

"We have identified three phases for our return-to-service plan," AECL president Hugh MacDiarmid said in a written statement. "Today, we are progressing toward the end of phase one, which involves a comprehensive condition assessment of the reactor, the development and testing of several repair options, and overall planning and critical path development."

During phase two, AECL will decide on a construction strategy to address the leak and deal with equipment corrosion problems that contributed to the shutdown.

The actual repair will take about two months, depending on the construction method, regulatory considerations, and more damage analysis, according to the AECL statement.

Phase three will take another two months. It involves restarting and testing the reactor.

The timetable was based on AECL's experience during a 1992 incident that involved refilling, refueling, and restarting the reactor.

The leak site itself is located at the reactor base, about nine meters from the closest access location. That area has been thoroughly analyzed, according to AECL. More than 60% of the reactor vessel's circumference has also been surveyed using remote, nondestructive methods. Wall thinning was noted at the leak site, and at least eight other areas of interest were identified.

Separately, Lantheus Medical Imaging, a maker and supplier of technetium-99 generators using Mo-99, announced that the FDA and Health Canada have granted regulatory approval for its Mo-99 supply relationship with the Australian Nuclear Science and Technology Organization (ANSTO).

ANSTO's Open Pool Australian Lightwater Reactor is nuclear medicine's newest source of Mo-99 and the first to manufacture the isotope using low-enriched uranium-235 as a production target and as the source of fuel for the reactor itself.

All other commercial Mo-99 facilities use highly enriched uranium as targets. Homeland Security concerns about the atomic bomb-grade material being applied in this way led the George W. Bush and now Obama administrations to push for worldwide conversion to LEU. A 2008 National Academies of Sciences report emphasized ANSTO's efforts in establishing the technical feasibility of LEU for Mo-99 production.