More Cracks Found at Nuke Plant

WEDNESDAY, SEPTEMBER 25, 2013


The owner of an Ohio nuclear plant with a cracked concrete shield building says that it has found new cracks in the structure and that some of the old cracks have lengthened.

However, the building at the Davis-Bessee Nuclear Power Station "continues to maintain its structural integrity and ability to safely perform its functions," operator FirstEnergy Nuclear Operating Company (FENOC) reported in a release Sept. 20.

FENOC said the cracks had been discovered on a "routine inspection."

Cracked History

The 2.5-foot-thick, 250-foot-tall, reinforced concrete shield building surrounds a 1.5-foot-thick steel containment vessel that encloses the station's reactor about 21 miles outside Toledo. The containment vessel and the shield are 4.5 feet apart.

The shield building was the only above-grade structure at Davis-Besse that was not sprayed with a white cement Thoroseal finish to seal the exterior concrete surface before the facility went online in 1970. Project builder Bechtel says no coating was required at the time.

However, both FENOC and the Nuclear Regulatory Commission now agree that the lack of coating (along with some design problems) left the structure vulnerable to weathering that caused cracking beginning during the harsh winter of 1978.

The cracking first came to light in 2011, when FirstEnergy reported to the NRC that workers had found the cracks during a shutdown to replace the reactor vessel head. The replacement project, which shut down the plant for two years, followed the 2002 discovery of a football-sized hole caused by corrosion.

The cracks raised concerns among regulators that came to light only later.

Since the problem was discovered, the shield building has been coated with a protective coating, and FENOC has established a long-term inspection program to monitor the building.

3 New Cracks

The new inspection regimen apparently led to the new discovery of cracking issues.

Cracks at Davis-Besse

The subsurface cracking was documented in Nuclear Regulatory Commission photos taken in late 2011 and in core bore samples from the Shield Building.

FENOC said its "high-definition camera technology" allows "examination inside of the building's walls through a series of inspection ports—or core bores."

The new camera "provides greater clarity and mobility than previously available equipment," FENOC said.

The company has examined 43 of the shield building's 82 core bores, with the remaining examinations expected to be complete in the next several weeks.

"The improved camera has identified three very tight, subsurface pre-existing cracks in the building that were not visible with previous inspection technology," FENOC said.

"These inspections also have found that in three locations, cracks initially identified in 2011 appear to have propagated a small amount."

License Extension Sought

The cracks have become an issue in the operator’s application for a 20-year extension on the plant’s license, which is due to expire in 2017.

Davis-Besse Site Vice President Ray Lieb said the inspection results thus far "confirms the 2011 conclusion that the shield building's structural integrity is not impacted by the presence of these tight cracks."

He added: "The robust building continues to function safely and reliably. Long-term safe, reliable operation of the plant is our number one goal."

   

Tagged categories: Bechtel; Concrete defects; Cracks; Exposure conditions; Exterior coatings; Nuclear Power Plants; Power Plants; Program/Project Management; Protective coatings; Weathering

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