Two minor earthquakes were felt in late December near the Ontario nuclear plant that supplies much of the world's medical isotopes, but neither was strong enough to be a safety concern, the Crown corporation that operates the plant said Wednesday.

On Dec. 20, a 3.0-magnitude tremor, centred 13 kilometres east of Pembroke, was felt. Two days later, a 3.6-magnitude quake struck 22 kilometres northeast of Deep River.

Both communities are close to the village of Chalk River, which houses the 50-year-old reactor that was shut down last November amid safety concerns.

"Neither had any impact on [the Chalk River facility]," Brian McGee, senior vice-president of Atomic Energy Canada Ltd., which runs the reactor, told a regular meeting of the Canadian Nuclear Safety Commission (CNSC).

Those on duty at the nuclear plant said they did not feel the seismic activity, said McGee.

The closure of the facility, which produces two-thirds of the radioisotopes used around the world in medical procedures, resulted in a worldwide shortage.

CNSC, the nuclear safety watchdog, ordered the facility shut because a cooling pump was not hooked up to the back-up power supply, as required to prevent the risk of meltdown during an earthquake or other disaster.

But the federal government overturned the decision, restarting the facility and giving the corporation 120 days to repair the problems.

McGee also reassured the CNSC that the upgraded pumps at the reactor can withstand tremors of up to a magnitude of 6 on the Richter scale.

Though, with the Ottawa Valley on a fault line, the area is historically a seismically active one, there's no indication an earthquake of that size has occurred since record-keeping began 150 years ago, CNSC director general Barclay Howden said at the meeting.

McGee also noted that the facility is ahead of schedule on installing the last cooling pump to its back-up power supply and expects the work to be completed by mid-March.

Between now and the final completion, McGee says there will be five scheduled outages, each lasting four to five days, during which the cooling pump will be installed.

The outages are spaced out to prevent another critical shortage of the isotopes, used for medical tests for cancer and other imaging tests, he said.

Also Wednesday, federal Liberal and Green parties called for the resignation of Natural Resources Minister Gary Lunn for what they call his interference in the work of the country's nuclear watchdog.

A letter from Lunn to CNSC president Linda Keen on Dec. 27 in which he threatened to fire her was recently leaked to the press.

Keen responded on Tuesday with a letter accusing Lunn of improper interference and threatening to fight in court any attempt to remove her from her job.