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Utility Touts New Fix for Nuke Rebar

Saturday, August 11, 2012

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Its first idea shot down by federal regulators, Southern Nuclear has proposed additional concrete reinforcement to remedy noncompliant rebar being used in new construction at the Vogtle Nuclear Power Plant near Waynesboro, GA.

 Vogtle Unit 4

 Photos: Southern Nuclear

Construction is continuing on the Unit 4 containment vessel head and assembly stand.

The company says the problem at its new Unit 3 reactor could be resolved by increasing the strength of the concrete that is to be poured around the steel reinforcing bar, according to a new filing with the Nuclear Regulatory Commission.

Southern Nuclear is building two new units at the plant, where construction began in 1971 and the first unit went online in 1987. Unit 3 is scheduled to begin operation in 2016; Unit 4, in 2017. The $14 billion project would launch the U.S.’s first new nuclear units in more than 30 years.

Reinforcing Foundations

The company is proposing to change the specified concrete compressive strength from 4000 psi to 5000 psi for the new unit’s basemat. The basemat is the six-foot-thick, cast-in-place, reinforced concrete foundation for the nuclear island’s steel containment vessel, coupled auxiliary and steel buildings, and containment internal structures.

In April, federal inspectors determined that the manner in which pieces of rebar were connected differed from the specifications approved for the Westinghouse AP1000 reactors being built at the site.

Vogtle

The American Concrete Institute’s Code Requirements for Nuclear Safety-Related Concrete Structures (ACI 349) require that the embedment of the reinforcing bars be sufficient to fully develop the yield strength of the reinforcement bar at the inside face of the associated wall.

The April inspection found that the Unit 3 basemat reinforcement fell short, although NRC documents indicate that the rebar was a point of discussion as long ago as 2008.

Plan B

Initially, Southern Nuclear proposed modifying the rebar that was already in place, but NRC rejected the plan.

The company now says that increasing the compressive strength of the concrete will satisfy requirements for the three seismic Category 1 structures and bring the structures into full design compliance.

The changes would also apply to the basemat at the new Unit 4, according to Southern Nuclear.

The changes would require amendment of the NRC licenses approved in February for the project. The company requested a prompt decision in order to avoid construction delays.

Tentative Approval

In a letter to Southern Nuclear, the NRC tentatively allowed the company to proceed with the plan at its own risk while regulators evaluate the formal amendment request.

If the NRC rejects the plan later, however, Southern Nuclear will have to go back and “return the plant to its current licensing basis,” the letter said.

   

Tagged categories: American Concrete Institute; Certifications and standards; Concrete; Construction; Nuclear Power Plants; Rebar; Steel

Comment from William Goldman II, (8/14/2012, 11:04 AM)

Oops..why did it take so long to notice the non-conformance? Was there anyone witnessing the installation? Sounds like some heads will roll if they have to revet back to original permit requirements.


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