Wylfa Power Station will now continue to generate energy until 2014, after plans to transfer fuel from one reactor to another were approved.
The Anglesey site's Reactor 2 shut down in April. Owner Magnox will now use its remaining fuel to power the remaining Reactor 1.
The process - known as Inter-Reactor Fuel Transfer (IRX) - has already been used at Oldbury Power Station and has now been successfully trialled at Wylfa.
It follows several independent reviews, and approval from the Office for Nuclear Regulation and y the Department for Energy and Climate Change (DECC).