A massive water tank, or module, has been placed atop the containment vessel and shield building roof at Georgia Power's Vogtle 3 & 4 nuclear expansion project near Waynesboro, Ga. The installation represents the final module placement for Unit 3, marking another significant milestone for the project.

The large module, known as CB-20, is a major part of the AP1000 reactor's advanced passive safety system. Standing 35 ft. tall and weighing more than 720,000 lbs., the large component will hold approximately 750,000 gal. of water ready to flow down to help cool the nuclear reactor in the unlikely event of an emergency. The water also can be directed into the used fuel pool, while the tank itself can be refilled from water stored elsewhere on site.

The modules used for Vogtle units 3 & 4 help streamline the construction process, since they were made in advance of their arrival to the project site and ready to be assembled into larger components that make up the nuclear units. Since 2011, major modules have been delivered to the site by rail and truck, including a range of plant components such as floor and wall sections, and supporting structures that surround the containment buildings and reactor vessels.

The final major module arrived at the construction site in late 2019, meaning all 1,485 key modules required to complete construction had been manufactured and safely delivered.

The placement of the CB-20 module follows the placement of the Unit 3 integrated head package (IHP) atop the reactor vessel. Standing 48 ft. tall, weighing 475,000 lbs. and containing more than 3 mi. of electrical cables, the IHP is an integral component that will eventually be used by highly-trained nuclear operators to monitor and control the nuclear reaction that will occur inside the Unit 3 reactor vessel.

Additional Units 3 & 4 milestones achieved over the last few months include:

• Completion of Open Vessel Testing, which successfully demonstrated how water flows from the key safety systems into the reactor vessel.
• Placement of the polar crane and containment vessel top for Unit 4. This signifies that all major lifts inside the containment vessels for both units are now complete.
• Operators within the Unit 3 main control room began monitoring and controlling the technology and equipment essential for testing the unit's systems and safely starting the plant.
• Crews placed the Unit 3 shield building roof, a two-million-pound structure covering the shield building. It provides an additional layer of safety around the containment vessel and nuclear reactor to protect the structure from any potential impacts.
• Final concrete placement inside the Unit 3 containment vessel allowed for the installation of machinery that will be used to load fuel into the unit.

With more than 7,000 workers on site, and more than 800 permanent jobs available once the units begin operating, Vogtle 3 & 4 is currently the largest jobs-producing construction project in the state of Georgia.

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