The Point Lepreau nuclear generating station is back online, operating at 35 per cent capacity, NB Power announced on Tuesday.
Earlier this month, the plant had been down to less than one per cent power, due to refuelling problems and issues with the chemistry of the water in the non-nuclear boilers.
It began sending energy to the provincial electricity grid on Monday, officials said.
Refuelling will resume in the coming week, they said.
"The issues that we have been managing in our first five months of operation are normal issues one can expect in restarting a plant that has recently been refurbished," NB Power president and CEO Gaëtan Thomas stressed in a statement.
"We want New Brunswickers to understand that their investment in this facility is safe and sound, there will be no rate impacts now or in the future due to any issues we have experienced to date and we fully expect to produce clean, low-cost energy here at this location for the next 25 to 30 years," he said.
Canadian Nuclear Safety Commission staff continue to monitor operations, Thomas said.
Lepreau has operated at less than full capacity since coming back online last November, following a four-and-a-half year refurbishment.
An operational plan filed with the Energy and Utilities Board had called for performance of 93 per cent during its first six months.
The problems have cost the utility more than $30 million in lost production.
Lepreau is the source of electricity for more than one-third of New Brunswick's in-province energy requirements, on average, according to the utility.
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.