Standing 250 meters above a Somerset shoreline, the world’s largest crane hung a 500-ton steel cylinder over an open hatch, and the number that stopped every worker’s breath was not the weight

Something happens on a construction site when a number is written on a whiteboard and no one speaks.

That number was 40 millimeters: the gap, on each side, between a 500-ton steel cylinder and the walls of the hatch it had to pass through.

The cylinder was 13 meters long, forged from high-strength steel, and it held the future power supply of six million British homes inside its curved walls.

Hinkley Point C is Britain’s first new nuclear plant in roughly three decades, and its two EPR units are the largest reactors ever built in the United Kingdom.

The crane swinging it overhead was the largest land-based crane on earth.

And the Somerset shoreline below had been waiting for this moment for the better part of a decade.

A machine so big it has its own nickname

Most cranes are named by model number.

This one is called Big Carl.

Formally designated the Sarens SGC-250, it stands up to 250 meters high in its tallest configuration and can lift up to 5,000 tons, making it the world’s largest land-based crane.

To picture that capacity: 5,000 tons is roughly the combined weight of three Eiffel Towers.

The 500-ton reactor pressure vessel for Unit 2 was hoisted into the reactor building by Big Carl before being handed to the building’s internal polar crane for final positioning.

The operation ran for two full days.

Every centimeter of the lift had been rehearsed in digital simulation for months before the hook was ever attached.

Through the side of a building, upright in the dark

The vessel did not drop straight down from above.

Big Carl lifted it sideways onto a rail-based transport system, which moved it through a hole in the side of the reactor building.

Inside, the building’s own polar crane took over: a massive overhead bridge crane running on a circular track near the top of the reactor chamber.

The 13-meter long vessel was then lifted, rotated vertical, and lowered onto a support ring with just 40 millimeters of clearance on either side.

Forty millimeters is roughly the width of two fingers.

The vessel weighs as much as 333 family cars.

Those two facts sat beside each other in every engineer’s head for the duration of the drop.

Learning from the first time to go faster the second

Unit 1 had its own reactor vessel installed years earlier, but the method was entirely different.

The Unit 2 vessel was lifted using Big Carl rather than the large temporary overhead system built specifically for the first unit.

EDF Energy said the decision aimed to save space, reduce costs, and enhance efficiency, and the new approach contributed to a faster build.

Unit 2 is progressing 20 to 30 percent faster than Unit 1, with more materials in place and advanced structural work completed.

The reactor pressure vessel was manufactured at Framatome’s Saint-Marcel factory in Chalon-sur-Saône, eastern France, and shipped to the site in January 2026.

A forged steel heart, born along the Saône, carried to Somerset by sea.

Hinkley Point C just sealed its second reactor

On June 1, 2026, the reactor pressure vessel was installed for the second of the two EPR reactors at the Hinkley Point C nuclear power plant in Somerset, England.

Hinkley Point C is Britain’s first new nuclear plant in roughly three decades, and its two EPR units are the largest reactors ever built in the United Kingdom.

Together, the two reactors are expected to generate enough low-carbon electricity to power around six million homes.

The completion date for Unit 1 was delayed by 12 months to 2030, and the overall project cost is expected to have roughly doubled.

Yet the vessel is now seated, bolted, and waiting for fuel, and transport rules for nuclear components are being updated to match the pace of new construction.

The planned Sizewell C plant will follow a similar EPR design, with its baseline construction cost set at 22 percent lower than the current Hinkley estimate, built on lessons won in Somerset.

A clearance thinner than a thumb, and what it proves

The 40-millimeter gap is already something engineers are writing into the Sizewell C playbook.

Every lesson absorbed at Hinkley, from the rail transport system to the polar crane handoff, reduces risk and cost at every EPR that follows.

That learning curve is the real lasting asset, a point not lost on developers watching factory-built platforms promise the same compounding efficiency gains at much smaller scale.

The reactor vessel installation came less than a year after Big Carl placed the steel dome on top of the second reactor building, completing its external structure.

The Somerset coast now holds two sealed reactor chambers, side by side, both waiting for the moment a control room operator steps forward and opens the first valve.

The cost overruns are real, and first power is still years away.

But a 500-ton cylinder now sits, precisely, in a space that left just two fingers of daylight on either side, and the margin held.