The half-century-old National Research Universal reactor in Chalk River, Ontario has shut down for a planned, 33-day period of inspection and routine maintenance.

The outage began Sunday and will last until June 17, according to Atomic Energy of Canada Ltd, which runs the site.

The NRU restarted last August after a nearly 15-month shutdown to fix leaky reactor vessels. The extended shutdown created havoc in the nuclear medicine community, as the NRU had supplied 30 to 40 percent of the world's molybdenum-99, the parent isotope of technetium-99m, widely used in SPECT imaging.
The inspection follows a promise by the AECL to inspect the repaired vessels within nine months of resuming operations.

“This is a planned outage,” Ernest Drumhiller, vice-president operations and chief nuclear officer, said in a video on AECL’s website. “And a comparison to the previous outage, the vessel leak repair, which was a forced outage – it’s totally different.”

The AECL said it had coordinated with the "international isotope community" to prevent disruptions.

Since re-starting last year, the NRU runs in cycles, with a five-day outage once a month, the AECL said.

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