The head of Canada's Nuclear Safety Commission says two recent incidents at New Brunswick's Point Lepreau nuclear generating station are "unsettling."

On Dec. 13, there was a radioactive spill. Up to six litres of heavy water splashed to the floor, forcing an evacuation of the reactor building and halt of operations.

Then, on Dec. 14, NB Power issued a news release, admitting there had been another type of spill three weeks earlier. About 23 barrels of water laced with the toxic chemical hydrazine was released into the Bay of Fundy.

Both incidents occurred as part of preparations for restarting the plant, which has been undergoing refurbishments for nearly four years.

Michael Binder is president of the Canadian Nuclear Safety Commission. (Sean Kilpatrick/Canadian Press)

"Since this plant is almost finished refurbishing, it's a bit unsettling to hear about hydrazine and heavy water leak one after the other," safety commission president Michael Binder said during a regularly scheduled meeting in Ottawa on Dec. 15.

"So that is the discomfort level we all feel about this," he said.

Fellow commissioner Moyra McDill also expressed concerns that the heavy water leak appeared to originate from a piece of equipment meant to handle gases, not liquids.

"Since machines don't normally act on their own initiative … something must have been missed somewhere in the system if you have fluid entering a gas zone," she said. "I'm a little concerned that heavy water ended up in a pump for gas."

NB Power spokeswoman Kathleen Duguay said a faulty pump caused the heavy water leak.

The damaged pump diaphragm has been replaced and the utility plans to resume loading heavy water into the reactor within days, she said.

"The potential risk posed to the environment was negligible and there are no public health implications resulting from this event," Duguay has said.

The heavy water was released into a contained area in the reactor containment building, although NB Power officials told the safety commission that small vapourized particles of radioactive tritium did escape up the station’s ventilation stacks.

Still, station manager Wade Parker said the release was well below allowable levels.

In a further complication, safety doors that had closed to contain nuclear particles from further escaping ended up locking in two cleanup crew members for two hours after they had finished their work.

The workers, who wore special suits and breathing apparatus, were not in danger, according to NB Power.

Hydrazine concentration low

Meanwhile, Duguay also downplayed the hydrazine leak.

"It is believed that the discharge would have had a localized and minimal environmental impact, if any, when making contact with the Bay of Fundy," she stated in a news release.

Hydrazine is used to remove the oxygen from the water in the steam generators, protecting tubes from localized corrosion and maintaining the appropriate steam generator water chemistry, said Duguay.

This ensures that the steam generators continue to contribute to a high safety margin, that maintenance requirements are minimized and that workers are protected.

The leak was at low concentrations, said Duguay.

"Simply put, this concentration would be like having a single soft drink can of hydrazine in 4,500 litres of water."

A faulty valve in the steam generators was to blame in that case, said Duguay. It leaked light water onto the roof of the service building, which made its way to the roof drainage, which connects to a ditch that discharges into the bay, she said.

Point Lepreau, Atlantic Canada's only nuclear reactor, is undergoing a $1.4-billion refurbishment. It was originally expected to be back generating power by September 2009, but there have been problems, particularly with the calandria tubes.

The tubes, which are about six metres long and 13 centimetres in diameter, contain the reactor's fuel channels and fuel bundles.

Several of the 380 tubes that were installed were leaking and had to be replaced.

The next step will include the installation of pressure tubes, spacers, end fittings and positioning assemblies, as well as bellows welding.

It is estimated that NB Power spends $1 million a day to purchase replacement fuel while the reactor is offline.

The Canadian Nuclear Safety Commission is currently considering NB Power's application for a new five-year operating licence for Point Lepreau.