Building a nuclear reactor piece by piece, inside its own containment structure, is slow — every weld, every panel, constrained by the space it has to go into. Vogtle Units 3 and 4 took a different approach: build the heaviest sections somewhere else first, then lift them in whole.

The AP1000 reactor design's modular construction method meant large structural and mechanical sections were pre-assembled off to the side, in a dedicated modular assembly building, before being hoisted as complete units into the nuclear island — including the largest of them all, an 840-tonne module lifted by the world's largest crawler crane.

840 t
Heaviest single-module lift (CA20)
2
New AP1000 reactor units
3 hrs
CA20 module lift duration
2009–24
Construction span
Phase 1 — Off-site modular assembly
Building the reactor's interior before the reactor exists
Large structural and mechanical modules — including the CA20 module housing plant and equipment for used fuel storage, heat exchange, and waste collection — were assembled from prefabricated wall and floor sections inside a dedicated modular assembly building at the Vogtle site, ahead of being moved into position.
Phase 2 — The heaviest lift
840 tonnes, three hours, one crane
The completed CA20 module — 20 m long, 14 m wide, and 20 m high, weighing approximately 840 tonnes — was installed within Vogtle Unit 4's nuclear island in a three-hour lift operation using the world's largest crawler crane, the largest component used anywhere in AP1000 construction.
Phase 3 — Shield building panels
A double-decker lift method to save time
The shield building encasing each unit's containment vessel was built from 160 steel panels, some weighing more than 136 tonnes. A double-decker six-panel assembly method allowed crews to set two full courses in just four lifts — a new technique developed specifically to shorten the shield building erection schedule.
Phase 4 — The final major lift
Closing out with a safety-critical tank
The project's last major crane lift set the Passive Containment Cooling Water Storage Tank (module CB-20) atop Unit 4's containment vessel and shield building roof — a tank standing roughly 11 m tall, weighing over 325 tonnes, and holding approximately 750,000 gallons of water for the reactor's passive emergency cooling system.

Build the heaviest sections somewhere else first, then lift them whole — modular construction turned a nuclear reactor's interior into a sequence of crane lifts rather than a sequence of welds.

Bechtel completed construction of Vogtle Units 3 and 4 under the management of Southern Nuclear, with construction beginning on Unit 3 in March 2013 and Unit 4 in November 2013. Vogtle stands as a reference case for modular nuclear construction: shifting as much fabrication as possible away from the confined, safety-critical space of the reactor building itself, and turning final assembly into a series of precisely sequenced heavy lifts.

For further reading on complex erection sequencing, see Erection Engineering in Industrial Construction

Related case studies: Prelude FLNG · Mahlsdorf Wind Farm · Baihetan Dam

Sources: Georgia Power — owner's build record: the Heavy Lift Derrick took eight months to assemble, has a 560 ft main boom rigged with 12 miles of steel cable, rotates 360° to serve both units, and needs five people to operate; World Nuclear News — the 840-tonne CA20 module placed into Unit 4's nuclear island on 20 August 2016 in a three-hour operation; Georgia Power (Unit 3 CA20 placement). CA20 module weights are published as roughly 840 tonnes / 2 million lb for Unit 4 and 2.2 million lb for Unit 3 — the two units' modules differ. Unit 3 entered commercial operation in July 2023, Unit 4 in April 2024.

Frequently Asked Questions

Vogtle Units 3 and 4 used the AP1000 reactor design's modular construction approach: large structural and mechanical sections were pre-assembled off to the side of the nuclear island, in a dedicated modular assembly building, and then lifted as complete units into their final position — rather than being built up piece by piece inside the containment structure itself.

The CA20 module, installed at Vogtle Unit 4 in August, was the largest component used in AP1000 construction — measuring 20 m long, 14 m wide, and 20 m high, and weighing approximately 840 tonnes. It was hoisted into position using the world's largest crawler crane in a three-hour lift operation.

The last major crane lift at Vogtle was the CB-20 module — the Passive Containment Cooling Water Storage Tank, part of the AP1000 reactor's advanced passive safety system. The tank measures roughly 11 m tall with an 26 m outer diameter, weighs more than 720,000 lb (over 325 tonnes), and holds approximately 750,000 gallons of water for emergency reactor cooling.

Bechtel completed construction of Vogtle Units 3 and 4 under the management of Southern Nuclear, a subsidiary of Southern Company. Construction on Unit 3 began in March 2013 and Unit 4 in November 2013.