The world's oldest operating nuclear power station, Oldbury near Bristol, stopped producing electricity today after 44 years of generation.
The closure marks the start of the decommissioning process over the next few decades, which will include removal of the spent fuel, management of the waste and eventual demolition of the buildings.
The shutdown of the site's reactor one follows the closure last June of reactor two.
The shutdown was originally scheduled for 2008, but the Nuclear Decommissioning Authority (NDA) decided to extend Oldbury's operating life following reviews with the regulators.
The site is operated by Magnox Ltd, which is owned by EnergySolutions.
Oldbury is one of 11 nuclear power stations in the UK that were based on the Magnox design, developed during the post-war years and the first in the world to generate electricity on a commercial scale.
Ten are now closed and in various stages of decommissioning, with only Wylfa on Anglesey still operating.
Dr Brian Burnett, NDA head of programmes, said: "Oldbury has a long and proud history of safely generating electricity. Our thanks go to the Magnox workforce, who have been extremely committed to maximising the plant's generating life, ensuring it was safely able to continue past its original planned closure date.
"Its income has been extremely valuable in supporting our mission to decommission the UK's first generation of civil nuclear sites."