The NRU entered a regularly scheduled maintenance shutdown on November 18 (see A break in the supply chain on medicalphysicsweb). That shutdown resulted in an interruption in the supply of molybdenum-99 (Mo-99), a fission by-product that's used to make technetium-99m (Tc-99m) and iodine-131 (I-131). Tc-99m and I-131 are the predominant radionuclides used in diagnostic and therapeutic nuclear-medicine studies.

In early December, however, things started to get messy. Atomic Energy of Canada Limited (AECL), the government-owned company which runs the NRU reactor, announced an extension of the outage till early/mid-January to allow "modifications required for the installation of two new motor starters for the reactor cooling pump, and to connect the motors to an additional back-up power supply".

That announcement came against an already grim clinical backdrop, with thousands of seriously ill patients in North America facing delays to diagnostic procedures as a result of the disruption to isotope supply lines.

On December 11, in response to concerns from the medical community, the Canadian parliament agreed a bill that temporarily suspended (for 120 days) the CNSC's oversight role, thus allowing the NRU to start up again even though it still did not fully meet safety standards.

The reactor was safely returned to service on December 16, which means that medical isotopes will by now be ready for removal, processing and distribution. In the coming weeks, AECL will complete the maintenance work during normal reactor operations.

The next time the NRU needs to be shut down for maintenance the AECL is likely to be better prepared. The agency has built two new reactors, MAPLE 1 and MAPLE 2, for exclusive production of medical isotopes. Originally scheduled to go online in 2004, they are now due to start up in October 2008 and October 2009, respectively.

• MDS Nordion (Ottawa, Canada), a leading supplier of medical isotopes, had reckoned it would take an $8-9 million earnings hit in its current quarter as a result of the NRU outage. With the reactor back online, however, the company anticipates less of a financial impact than previously estimated.