NB Power says there has been another heavy water spill in the reactor building at the Point Lepreau Nuclear Generating Station.
Officials say about 300 litres of tritiated heavy water spilled when a valve opened too soon during pressure testing at the plant on Monday.
NB Power says the water was not released to the environment and staff at the plant were not exposed.
Officials at the nuclear facility informed the Canadian Nuclear Safety Commission about the spill and recovered the water for reuse.
"In the nuclear industry, plants such as the Point Lepreau Generating Station are required to prepare for a wide range of contingencies and to have appropriate plans in place to address them efficiently and effectively." said Rod Eagles, director of the Lepreau refurbishment project, in a statement on NB Power's website.
"Highly trained and qualified staff are in place at all times to respond to an event such as this one. All alarms sounded as per design and heavy water was collected safely and in a timely manner."
This is not the first time that NB Power has had to report a heavy water spill during the refurbishment.
On Dec. 13, less than six litres of heavy water splashed to the floor, forcing an evacuation of the building.
The following day, NB Power issued a statement that three weeks earlier another spill had occurred. 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.
At hearings in Ottawa in December, the head of Canada's Nuclear Safety Commission said the body was concerned by the mistake.
"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.
NB Power said in a statement the latest heavy water spill is "fundamentally different" than the December spill.
There were no requirements to evacuate the reactor building because the room where the spill happened was designed to contain and collect heavy water.
Point Lepreau is Atlantic Canada’s only nuclear reactor. It is located west of Saint John.