The world's largest land crane, nicknamed "Big Carl", installed the gigantic circular roof, which is more than 47 metres (154 feet) in circumference, is 14 metres high and weighs 245 tonnes, according to the French energy giant's British subsidiary.

Still weather conditions allowed the delicate manoeuvre to be undertaken and the job was completed in an hour and a half.

The metal cover now caps a 44-metre-high cylindrical concrete tower that will house the first of the plant's two reactors, due to be installed next year.

"This is a major milestone in building Britain's first nuclear reactor in a generation, and a key part of the UK government's plans to revitalise nuclear," nuclear minister Andrew Bowie said in an EDF press release.

"Generating enough zero-carbon power for six million homes, Hinkley Point C will reduce our reliance on imported energy and support our shift to net zero," he added.

EDF is also in charge of building the new Sizewell C plant in southeast England, with each site set to generate 3.2 gigawatts of power.

- Delays, ballooning costs -

The dome above Hinkley's first reactor was originally scheduled to be installed by the end of 2022 but the site has suffered several delays.

The expected cost, largely borne by EDF, has already risen to pound25-26 billion ($32-33 billion) -- or pound32.7 billion taking inflation into account, which is nearly double the original estimate of pound18 billion.

EDF is now aiming for the first reactor to come on line in June 2027, with the second due to be operational a year later.

The UK currently has nine operational nuclear reactors on five sites managed by EDF but many are nearing the end of their operating lives.

Six reactors on three sites have been shut down since 2021 and will be dismantled.

However, EDF announced in March that it was extending the life of two British power plants -- Heysham 1 and Hartlepool.

The UK intends to build up to eight new reactors by 2050.