OTTAWA - There's been another small leak of heavy water from the nuclear research reactor at Chalk River, Ont.

It is the third such leak since December at the aging facility that currently provides about half the global supply of isotopes used in medical imaging.

The reactor remains online and the leak did not cause any disruption in the isotope supply.

News of the latest leak came as top officials from both the Canadian Nuclear Safety Commission and Atomic Energy Canada Ltd., were appearing Tuesday at the Commons committee on natural resources.

An AECL official told the committee that 11 kg of heavy water was ventilated from the reactor after two tiny pin holes were found in a pipe Sunday morning.

The pipe has been patched and will be replaced at a later date.

A larger leak at the 50-year-old reactor in December was not reported to the public for weeks, prompting allegations of coverup and suggestions the public had been endangered.

However the head of the nuclear regulator, Michael Binder, told the committee the December leak wasn't reported because it was so small as to be an "almost routine operational issue."

There was never any danger to the public or the environment, said Binder, the CEO of the CNSC.

Binder acknowledged being surprised by the public uproar that followed the revelation of the December leak, and that is why the reporting mechanism has been changed so that even minor events such as Sunday's leak are quickly publicized.

Binder said there is about 65 tonnes of heavy water at Chalk River and he likened the 47 kg December leak to faucet trouble in your home.

"You know: drip, drip, drip. It's of the same order of magnitude."

But NDP MP Nathan Cullen said public confidence in the NRU reactor at Chalk River is being damaged.

"The cumulative effect of all these leaks, can this not be a death by a thousand cuts?" asked Cullen.

"That small leak after small leak after small leak speaks to the public as there being a significant problem."

The reactor's current licence expires in 2011 and AECL and the nuclear regulator said they are in formal communication on exactly what will be required to get an extension.

"We are looking to ensure that the NRU reactor is fully capable of producing isotopes beyond its licence renewal date of October 2011," said Hugh MacDiarmid, president and CEO of AECL.

"We have done a very significant amount of detailed evaluation to understand what is necessary for us to achieve that."

Out of $351 million provided to the Crown corporation in the 2009-10 federal budget, MacDiarmid said $47 million will go towards the licence renewal project for the Chalk River reactor.

Another $25 million is earmarked for the longterm issue of decommissioning the MAPLE reactors that were supposed to replace the NRU but were scrapped because of design problems.