NB Power said a radiation alert at the Point Lepreau nuclear generating station in Canada's New Brunswick province on Tuesday was caused by a small spill in the reactor building.
The company said the event did not pose significant impact to the public or the environment.
In an email message last night, the province owned power company said it would continue to investigate the spill and the station remains safe and secure.
Officials at the company were not immediately available for comment Wednesday morning.
The 635-megawatt station has been shut since March 2008 for refurbishing. A spokeswoman told local papers the utility was refilling equipment with heavy water as it prepares to restart.