The Ayrshire plant has produced 297.4 terrawatt hours of electricity since it began operating in 1976 – enough to power every home in Scotland for 31 years.
The plant, located between Largs and West Kilbride on the west coast, has been in service for almost twice its original 25-year life expectancy.
It would have been due for decommissioning in 2001, but ongoing maintenance enabled its operational lifespan to be extended for an additional 21 years.
Hunterston B has been described as “the most productive clean energy asset in Scottish history" – saving an estimated 103 million tonnes of greenhouse gas emissions, compared to fossil fuel sources.
Reactor 4 at the site, which is operated by EDF Energy, will be shut down by station director Paul Forrest at midday today – 45 years and 11 months after the station started producing electricity.
“The contribution Hunterston B power station has made to this country cannot be underestimated,” he said.
The station’s other unit, Reactor 3, was taken offline in November 2021.
Although the plant will no longer generate power, there is still work to be carried out at Hunterston B.
Both reactors will now undergo a statutory outage to make sure they are ready for defueling, which involves removing all the radioactive waste and transporting it by rail to Sellafield in Cumbria for storage.
It is expected that defueling at Hunterston B will take around three years.
Fears over the power station’s safety have been raised in recent years after inspections revealed cracks in graphite bricks at the reactors’ cores.
The retirement of the plant has sparked mixed reactions, including concerns over future energy supplies.
Tom Greatrex, chief executive of the Nuclear Industry Association, said: “Hunterston B has shown the best of what nuclear can provide for Scotland – clean, reliable power to keep the lights on and save our planet, and long-term skilled jobs, on which people can build a life and a family.
“The dedicated staff who have helped keep Scottish homes warm and light for 46 years deserve our gratitude.
“As the current energy crisis demonstrates, without nuclear the cost of the electricity we rely on is higher, causes pollution and leaves us reliant on burning imported fossil fuels.
“That’s why we need new nuclear – to get to net zero and provide the reliable, secure and clean power to live our lives.”
Lang Banks, director of environment charity WWF Scotland, said: “The repeated failure to solve the problem of hundreds of cracks in the graphite bricks surrounding the reactor core means the closure of Hunterson B was inevitable.
“Thankfully Scotland has massively grown its renewable power generating capacity, which means we’ll no longer need the electricity from this increasingly unreliable nuclear power plant.
“As the expensive and hazardous job of cleaning up the radioactive legacy Hunterston leaves in its wake now begins, Scotland must press on with plans to harness more clean, renewable energy.”
GMB Scotland secretary Louise Gilmour said: “Hunterston B has been a work-horse for Scotland’s energy mix, it’s helped keep the lights on and delivered opportunity and prosperity on the west coast for nearly fifty years.”