Unit 2 of the Bruce A nuclear generating station in Canada was given permission to restart, 16 March, after being offline for almost two decades. However, a moderator leak during start up means that the unit now remains shut down while an investigation is carried out and steps are taken to prevent recurrence. Repairing the leak will take a few days, after which restart activities will resume, according to the operator.

Bruce Power, which operates the eight-unit Bruce plant in Ontario, said in a statement that permission from the Canadian Nuclear Safety Commission to remove reactor shutdown guarantees from 750 MW unit 2 meant that it could complete final safety checks in preparation for connection to the grid.

Hawthorne added that that Bruce A unit 1 is following behind unit 2 and should achieve a similar milestone in a ‘few short months.’

Bruce A unit 2 was laid up in 1995 due to a maintenance accident in which lead contaminated the core. Unit 1 was laid up at the end of 1997. Both units have been undergoing refurbishment since mid-2006. Work has involved replacing their fuel channels and steam generators plus upgrade to ancillary systems, which should enable them to operate for a further 25 years.

CNSC said that it had a ‘high degree of confidence’ in authorizing the restart for Bruce A unit 2 and that its assessments had given assurances that the operator had taken all necessary measures to protect workers, the public and the environment.

At around 7:10am on Saturday 17 March, CNSC was informed of a moderator leak on Bruce A Unit 2 as it was being re-started following refurbishment. The unit was returned to shut down state while the cause was investigated.

“The leak was determined to be inside confinement and has been isolated,” CNSC said, adding that “there was no release to the environment and no plant worker received any dose.”

Bruce Power said in a statement, 19 March, that repairs are in progress and will take a few days to complete. Once the final repairs are completed it will continue with unit 2 restart activities.