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A cracking containment structure at a troubled Ohio nuclear plant is finally likely to get the protective coating it should have received decades ago, in the wake of a new report by the Nuclear Regulatory Commission.
The NRC’s report, announced Thursday (June 21), essentially affirms the findings of an investigation earlier this year by FirstEnergy Nuclear Operating Co. into the problem at its Davis-Besse Nuclear Power Station, 21 miles southeast of Toledo.
Uncoated Safety Structure
The shield building surrounds a 1.5-foot-thick steel containment vessel that encloses the reactor. The containment vessel and the shield are 4.5 feet apart.
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Photos: Nuclear Regulatory Commission |
| A Nuclear Regulatory Commission inspector examines cracks at the Davis-Besse Nuclear Power Station Shield Building. The NRC says that this crack was probably widened by hydrodemolition. |
The 2.5-foot-thick reinforced concrete structure was “the only above-grade nuclear safety-related structure on site designed by Bechtel during original construction that was not sprayed with a white cement Thoroseal finish for sealing of exterior concrete surfaces,” FirstEnergy reported in its Root Cause Analysis Report, submitted in February.
Left unprotected, the building was vulnerable to weathering that eventually caused cracks, mostly below the surface, the NRC now agrees.
Most of the cracking occurred “in the concrete at the outer face of structural reinforcing steel located behind the architectural flute shoulder region,” according to the operator.
Design Cited
The plant went online in 1970; the cracks began with a blizzard in 1978, FirstEnergy reported. The company also cited—and NRC affirms—unspecified problems with “certain aspects of the shield building’s design.”
The NRC has determined that FirstEnergy’s 119-page report “established a sufficient basis for its conclusions” regarding both the problem’s cause and corrective measures.
Those measures will include applying a protective moisture coating on the building, according to the NRC.
‘Thorough and Independent Review’
“Our inspectors conducted a thorough and independent review of FENOC’s root cause determination to make sure that the reasons for the internal cracks in the shield building are well understood,” said NRC Region III Administrator Charles Casto.
“We evaluated the effectiveness of the company’s proposed actions to ensure the continued safety of the shield building going forward.”
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| The cracking was found as crews worked to replace the building’s reactor vessel head. The operator found that corrosion had eaten a hole in the head, leaving just three-eighths of an inch of steel cladding. |
An NRC inspection team concluded that the actions proposed by the company would prevent recurrence of the laminar cracking if properly implemented.
The NRC documented the results of its independent inspection in a report (Accession No. ML12173A023) that will be made available at http://adams.nrc.gov/wba/. The agency said it would schedule a public meeting shortly “to discuss this issue and the NRC’s plans to monitor the plant’s corrective actions.”
Corrosion Hole
The NRC began looking at the issue on Oct. 10, 2011, when FirstEnergy reported that its workers had found the cracks during a shutdown to replace the reactor vessel head.
That component had to be replaced after maintenance workers discovered a football-sized hole caused by corrosion. Discovery of the hole, in March 2002, led to a two-year plant shutdown and $33 million in fines against FirstEnergy.
The NRC reviewed the cracks and said they posed no imminent safety issue. On May 7, regulators issued an inspection report documenting their review of the building’s operability. Before the plant returned to service, the NRC issued a Confirmatory Action Letter, documenting FirstEnergy’s commitments to determine the cause of the cracks.
More Inspections Planned
The plant’s license is due to expire in 2017; operators are seeking an extension.
The NRC says that its license renewal staff is “evaluating the implications of” of the cracking issue and that the agency is “developing a program of short-term and long-term inspections” to ensure that FirstEnergy follows through on the corrective actions “in a thorough and timely manner.”
In 2006, the NRC said Davis-Besse had been the source of two of the top five most dangerous nuclear incidents in the United States since 1979.
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