Nuclear power firm British Energy has confirmed four of its reactors at two UK stations were likely to remain out of action until the end of the year.
British Energy has seen its share prices drop since the problems
Two reactors at Hartlepool and two at Heysham have been out of service after a routine inspection revealed problems with the boiler units last October.
British Energy said engineering work and inspections - costing up to £70m - should be completed by December 2008.
The two affected sites are capable of supplying electricity to 1.5m homes.
Both started power generation in 1983 and have estimated decommissioning dates of 2014.
Shares in British Energy, the UK's largest producer of electricity, have slid since the problems arose.
The company operates eight nuclear power stations and one coal-fired power station.