The Point Lepreau Nuclear Generating Station operated at 43 per cent power in May new figures show, losing millions of dollars for the month and dragging its overall performance numbers to a new low, six months after coming back online.

"It's exactly what the Public Utilities Board warned against back in 2002 when it rejected the refurbishment as too risky," said Green Party Leader David Coon.

"The costs are higher than expected, the performance is poorer than expected, expensive repairs crop up that were not expected. That's the story of nuclear power in Canada."

The nuclear reactor was hit with boiler and then refueling problems shortly after coming back online in November, operating at an average of 54 per cent power during the first six months of its new life following May's poor performance.

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The Point Lepreau Nuclear Generating Station was operating at less than one per cent capacity in April. (CBC)

That's well below the 93 per cent NB Power projected and budgeted for in its regulatory filings.

The reactor was operating at less than one per cent capacity in mid April and was brought up to 35 per cent capacity in late April.

The difference represents more than $70 million in lost production, money the plant was expected to generate to pay for its significant operating and financing costs.

NB Power has to make $13 million a month in interest and principal payments to finance Point Lepreau's $2.4-billion refurbishment on top of several million more needed to operate and fuel the plant.

The utility requires a high level of production over a long period of time that so far Point Lepreau has not been able to meet.

In filings with the New Brunswick Energy and Utilities Board last winter NB Power said it was anticipating 13 lost days of production in the first six months of operation for various startup issues. Instead it lost 83 days.

On Thursday, Kathleen Duguay, a NB Power spokesperson, said Point Lepreau has improved its output to 82 per cent as the refuelling problems get resolved. 

That's still below what's needed for the plant to be self financing but Duguay said that will come. 

"Of course our plan is to raise to higher power," said Duguay in an email to CBC News.

"We will raise power as conditions permit."