More problems at the Point Lepreau nuclear generating station have had the plant operating at less than one per cent power since Wednesday night, NB Power acknowledged late Friday.
"We were at less than zero (per cent) late Wednesday night and early Thursday morning," utility spokesperson Kathleen Duguay stated in an email to CBC News.
"We have been evaluating the benefit of going to zero since early last week."
NB Power says it continues to have problems with the chemistry of the water in Lepreau's non-nuclear boilers, an issue that caused the reactor to be turned off once already in December.
Duguay says that, in combination with ongoing problems refuelling the reactor, led to a decision to power Lepreau down almost completely to allow both issues to be tackled at once.
She said it won't be known until next week when the reactor will be able to be powered back up.
Refuelling will resume when the reactor is back online.
Lepreau has operated at less than full capacity since coming back online last November, following a four-and-a-half year refurbishment.
Last month, it was down to 35 per cent capacity, despite an operational plan filed with the Energy and Utilities Board calling for performance of 93 per cent during its first six months.
The problems have cost the utility more than $30 million in lost production. Most payments on the $2.4 billion reactor started to come due as soon as it came online.
In a news release put out Friday afternoon, NB Power said it expects Lepreau's poor early performance to be made up with better performance later.
"These hours of forgone operation do not come off the expected full-time life of the reactor," said the press release.
"They will be made up later as part of the full-time life expectancy of the plant."
The refurbishment cost $2.4 billion, more than $1 billion more than the original estimates. The New Brunswick government is attempting to get the federal government to cover the cost overruns.
The Point Lepreau project was the first time Atomic Energy of Canada Ltd. (AECL) had refurbished a Candu-6 reactor.
Point Lepreau is Atlantic Canada's only nuclear reactor.