A planned 33-day shutdown of the NRU isotope reactor at Chalk River is underway to allow the first major inspection since emergency repairs ended last August.

The outage began Sunday, part of a commitment by operator Atomic Energy of Canada Ltd. (AECL) to inspect the reactor’s repaired containment vessel within nine months of returning to service after a 15-month, $70-million breakdown. That crisis forced hospitals and doctors worldwide to scramble for scarce alternate medical isotope supplies.

It followed another emergency safety shutdown in 2007 that ended when Parliament legislated the reactor to resume operation. The move overruled a refusal by the Canadian Nuclear Safety Commission (CNSC) to allow a restart until a backup safety system was installed to prevent the remote risk of a core meltdown during a disaster.

In a statement Thursday, AECL said the isotope community was informed “well in advance of this outage and have taken steps to adjust their activities.”

The key task will be to inspect repairs to the reactor’s 65,000-litre heavy-water containment vessel, which sprang a pinprick leak in May 2009.

Since then, NRU has been operating on a 28-day cycle, including regularly scheduled five-day outages for maintenance. The scope of the current planned inspection requires far more down time.

The reactor is scheduled to return to service June 17.