A nuclear power station will stop generating electricity next February after 44 years because it would not be economically viable to continue after that time, it has been announced.
The reactor at Oldbury in Gloucestershire is the oldest civilian nuclear reactor in the world and has been generating power safely since 1967.
Operators Magnox and site owners the Nuclear Decommissioning Authority (NDA) said Oldbury will move through a transition period before decommissioning begins.
Phil Sprague, Oldbury site director, said: "Oldbury's excellent generation history is a terrific success story, especially as the site was originally planned to close in 2008.
"As a result of excellent teamwork between Magnox and the NDA, and in conjunction with our regulators, the ONR, the site's operational life was extended until February 2012. It is a testament to the skill and dedication of the workforce who have operated and maintained the reactors to such a high standard that it has been able to continue to generate safely.
"Oldbury has provided the UK with a vital source of power for over four decades, something that everyone who has worked at the site, past and present, should be very proud of."
It had been hoped the reactor would continue to generate electricity until the end of 2012.
Both of Oldbury's reactors were scheduled to close at the end of 2008, and since that time the site has generated an additional seven terawatt hours (TWh) of electricity, worth an estimated £300 million to the taxpayer and saving around six million tonnes of carbon from being released into the atmosphere.
Mike Graham, national officer of the Prospect union, said: "To have been a consistent and safe source of vital electricity since 1967 is a record to be proud of and one that sends out a positive message in terms of future new nuclear plant at Oldbury.
"The transition to defueling and decommissioning operations will mean an ongoing requirement for skilled staff on site. This continuity in employment will also ensure that there is a ready and willing skilled workforce in place in anticipation of the construction of the new Oldbury B plant."