The company, which has now been forced temporarily to stop production at a second station, is losing about £1m a day.
A spokesman for Nuclear Electric said: "It could make a big dent this year. No business can afford to lose that sort of money."
He said that both power stations, which have had problems related to cracks in welds, should be back on the system in a matter of weeks. The second faulty station, also an AGR, is at Heysham in the north-west of England. Nuclear Electric will have to convince the Government's safety inspectors that the power stations are fit to run before they can be reinstated.
Nuclear Electric's problems have been cited as the main cause of price volatility in the electricity trading pool.
However, the spokesman said: "Industrial users are the ones affected and they could get fixed-price contracts. Some chose to take their chance in the spot market."
Nuclear Electric accounts for almost a quarter of the electricity generated in England and Wales. The company, which has surprised the industry with its inroads into the marketplace, is keen to be privatised.
Problems with the AGRs will be seen as a blow to its aspirations. In the first half of this year, Nuclear Electric made pre-tax profit of £499m, but would have made a loss of £126m without a subsidy raised through a levy on electricity bills.
The company has been saying that it will be profitable without the levy within a few years, in a drive to convince the City that it will be viable as a private sector firm.Reuse content