Inspectors determined in April that the way pieces of rebar – metal bars used to reinforce concrete – were connected differed from specifications approved for the Westinghouse AP1000 reactors being built at the Burke County site. Southern Nuclear proposed modifying the rebar in place, but the NRC staff rejected the idea.
The solution affirmed in the NRC license amendment involves increasing the compressive strength of the concrete to be poured around the rebar from 4,000 pounds per square inch to 5,000.
That change, NRC safety evaluators concluded, would give the structures the desired resistance to seismic activity and bring it into compliance.
Southern Nuclear notified the commission in March that minor settling beneath the reactor’s “mudmat” made it a few inches off level and would require changes. The mudmat lies beneath the concrete “basemat” on which nuclear buildings will sit. The original license allows a 1-inch variability in the levelness of the basemat, and the amendment will increase that to 4 inches, allowing engineers to level the surface by using more concrete as the basemat is poured.
The NRC’s decision to approve its first-ever amendment to a nuclear combined operating license was detailed in a letter, dated Oct. 18, to B.L. Ivey, Southern Nuclear’s vice president for regulatory affairs.
Georgia Power spokesman Mark Williams said there will be continued focus on safety and quality as the first new commercial reactors in a generation take shape.
In a related matter, officials announced Tuesday that the 2,300-person workforce building the reactors had passed 10 million work-hours. The time represents actual hours expended on the site, beginning in 2009.
The Unit 3 turbine’s building foundation is two-thirds complete, with about 750 tons of rebar installed and 5,800 cubic yards of concrete poured. About 50,000 cubic yards of concrete have been poured for the cooling tower foundations for both units, and assembly of the bottom half of the Unit 4 containment vessel is more than halfway complete. The world’s largest heavy-lift derrick, 560 feet tall, has been assembled and is ready for use.
Major components will begin arriving later this year and early 2013, the first of which will be the reactor vessel for Unit 3. The Unit 3 condensers have arrived from South Korea, where they were manufactured.
Unit 3 is scheduled to go online in 2016, and Unit 4 will follow in 2017. The construction project represents a $14 billion investment.