FREDERICTON -- Atlantic Canada's only nuclear power plant returned to commercial operation Friday for the first time since March 2008, when it began a major refurbishment that was plagued by repeated delays and massive cost overruns.

The Point Lepreau reactor in New Brunswick resumed generating power following an overhaul that was scheduled to last 18 months and cost $1.4 billion. Instead, the project took three years longer than expected and cost the province's Crown-owned utility an extra $1 billion.

NB Power president Gaetan Thomas said he could hardly contain his enthusiasm as he announced that the power plant was operating at 98 per cent capacity on Friday.

"This is a great day for our customers and our employees," he said.

Thomas said the reactor is expected to last another 27 years after the work that was done.

"It's a foundational piece of our domestic energy supply and our export sales, and provides rate stability and the financial flexibility to now begin reducing debt," Thomas said.

Ed Barrett, chairman of NB Power's board of directors, said he hopes to pay down the company's $4.6-billion debt by $1 billion over the next decade.

"The completion of this project allows us to begin this pursuit in earnest," he said in a statement.

Thomas said Point Lepreau is now generating revenue by putting the province back in the power export market.

The province has tried in vain to persuade Ottawa to shoulder the extra costs of the Point Lepreau overhaul, arguing the province should not be on the hook for delays that were the result of Atomic Energy of Canada Ltd. learning how to fix up a Candu-6 reactor for the first time.

But Prime Minister Stephen Harper has not budged, saying only that his government will abide by the terms of the contract for the federal Crown corporation to refurbish the reactor.

On Friday, Thomas said he believed the company has a good case to recoup at least some of the cost overrun.

"We are in the process with insurers, and we have some protection guarantees, warranties and insurance," he said. "We are going through all these various steps and processes to ensure we recoup as much of the overrun as possible."

Energy Minister Craig Leonard wasn't available Friday to comment on the province's negotiations to recover the cost overruns from Ottawa.

In a statement, he said Point Lepreau is critical to the province's goal of generating 75 per cent of its electricity from clean, renewable or non-emitting sources by 2020.

The power plant was commissioned in 1983 and was the world's first Candu-6 reactor to begin commercial production of electricity.

One of the biggest lessons learned from the overhaul of the reactor involved replacing its 380 calandria tubes, which house fuel channels and uranium fuel bundles that power the reactor.

The first effort by AECL to install the tubes failed when tiny scratches caused by wire brushes raised concerns that joints might not be reliable for 25 years. The tubes had to be removed and reinstalled.

Thomas has said AECL benefited from that lesson when they began a similar refurbishment of the Wolsong-1 reactor in South Korea. The refurbishment of the Candu-6 at Wolsong began in April 2009 -- a year after the start of the Lepreau project -- and ended in July 2011.

By spreading the refurbishment costs over the life of the reactor in New Brunswick, Thomas said the utility will be able to keep power rate increase at an average of two per cent per year for the next 10 years.

The next major power project in the province is expected to be the overhaul or replacement of the Mactaquac hydro-electric dam near Fredericton about 15 years from now.