A nuclear power station in Somerset is to be decommissioned within the next two years.
EDF says Hinkley Point B power station near Bridgwater will be moved into the de-fuelling phase by July 2022 - a year earlier than planned.
Hinkley B started generating electricity in 1976 and since then has produced more than 300 terawatt hours of power - an amount of energy that would meet the electricity requirements of every UK home for three years.
Station director Peter Evans says: "This station has delivered more low-carbon energy during its lifetime than any other UK nuclear station.
"This is an outstanding achievement and a testament to the dedication of all those who have worked here over the decades.
"When work started on this generation of nuclear reactors in the 1960s, few could have anticipated how important it has become to generate our power with little or no emissions."
Peter Evans adds: "Over its life, this station has helped the UK avoid millions of tonnes of carbon dioxide going into the atmosphere and provided rewarding jobs for thousands of people and supply chain partners across Britain.
"Although there is much change to come, this is a moment to be proud of what we have achieved."
It means the future of some 700 workers is uncertain.
'Humbled by their support'
Mr Evans says: "It's not a surprise, when you look at the outstanding performance of this plant, they're still very very proud to work here.
"We started to synchronise the grid in 1976. It's generated low carbon electricity for over 40 years and they're just so proud of that.
"It's a tight team here, it's a lot of trust. This wasn't a surprise.
"I've talked to them over the last 18 months about this date coming and I'm just humbled by their support".
In 2012, EDF extended the estimated generating life of Hinkley Point B by seven years from 2016 to March 2023.
The announcement means the site will stop production almost a year before this.
Once Hinkley Point B stops generating power for good, EDF will begin de-fuelling the station - the first stage of nuclear decommissioning.
The station is not currently generating power. It was suspended in June 2020 for inspection and maintenance.
EDF has developed the safety case required to re-start operations, which will have to be approved by the Office for Nuclear Regulation before work can start again.
As Hinkley B enters its final stages, a new generation nuclear power station is taking shape next door. Hinkley Point C, a pressurised water reactor, is due to start generating electricity by 2025.