The last of six gigantic modules in the nuclear island for Unit 3 at the Vogtle AP1000 reactors under construction near Augusta, Ga., have been placed.

The CA02 and CA03 modules, weighing 52 tons and 237 tons respectively, are critical components and part of the In-Containment Refueling Water Storage Tank (IRWST), Georgia Power said on May 31. The IRWST is a 75,300 cubic foot tank that, once the units are operational, will be filled with borated water, providing a passive heatsink within containment and backup cooling for the reactor vessel.

The modules were assembled onsite and moved to the nuclear island as single pieces. They were then lifted into place by a 560-foot-tall heavy lift derrick—one of the largest cranes in the world, the Southern Co. subsidiary said.

The 5,000 workers building the Westinghouse reactors at Plant Vogtle have achieved several milestones over the past few weeks (see video). Unit 3 was initially slated to begin operations this April, but delays have pushed that back to June 2019. Unit 4 is now expected to come online in mid-2020. Cost overruns have also pushed Georgia Power’s share of the price tag from $6.1 billion to $7.4 billion.

“The projected overall peak rate impact of the Vogtle nuclear expansion continues to be significantly less than when the project was originally certified due to lower financing rates, other benefits the company has proactively pursued and the fuel savings of nuclear,” Georgia Power said. “The company projects that, even with the new costs and schedule forecast, the peak rate impact will be approximately 6 to 7 percent – which is nearly half of the original rate impact forecast. Of this, approximately 4.5 percent is already in rates.”

Last week, the company announced that vertical construction of the Unit 4 cooling tower is now complete at 601 feet. Earlier in May, the stator assembly, weighing 417 tons, and a deareator was lifted into place by the derrick. Six new shield building panels for Unit 3 have also been recently placed.

A slideshow of construction in progress can be viewed here on Georgia Power’s website.

Sonal Patel, associate editor (@POWERmagazine, @sonalcpatel)