The plant was shut down after problems were found in a reactor
Electricity production has restarted at Wylfa nuclear power station after a shutdown of several weeks.
Both reactors at the ageing station on Anglesey had been out of action after potential problems were uncovered during a routine maintenance check last month.
Reactor one was recommissioned on 16 August and reactor two has been started up again in the last few days.
Opened in 1971, the station which at full capacity produces enough daily electricity for two cities the size of Manchester and Liverpool, is now moving back to full power.
Owners BNFL Magnox discovered problems among the welds and brackets inside reactor one during a regular two-yearly maintenance check last month.
"It was thought prudent to do work on the other reactor to make sure everything was OK there," said a spokesman.
The shutdown was another blow to the future of the power station as BNFL Magnox prepare a case for a bid to extend its licence which expires next year.
Generation of electricity at Wylfa is scheduled to end permanently in 2010.
The station also underwent a 15-month shutdown in 2001 but the latest difficulties are not related.
Opponents of nuclear power have said the latest setbacks should lead to the station's shutdown.