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Cracks at Nuclear Site Spur Violation
A New Hampshire nuclear power plant was cited by regulators last week for failing to respond properly to problems with cracking concrete.
The operators of Seabrook Station, in Seabrook, NH, have been aware of issues in some of its concrete structures, caused by the alkali-silica reaction (ASR), since 2009. In 2013, the Nuclear Regulatory Commission approved measures to address the problem.
Inspections in 2015 revealed more cracking, but the NRC has been quick to point out that the issues don’t pose any immediate threat.
On March 24, the NRC performed another inspection at Seabrook, this time finding that NextEra Energy, the plant’s owner, allegedly failed to act promptly on information it had received about the condition of the concrete. The agency’s findings were released in a report on May 6.
The NRC issued one violation, which is classified as “Green,” meaning it’s of very low safety significance.
Proper Procedures
According to the NRC, on two separate occasions in 2015, NextEra received information from engineering firms that should have been immediately followed up with operability determinations, per NRC rules.
Both Wiss, Janney, Elstner Associates and Simpson Gumpertz & Heger Inc. provided NextEra with reports that cited structural loading due to ASR as causing deformation in concrete elements at the plant. While the reports were entered and acknowledged by the company, the NRC says, they were not followed up with the appropriate Immediate Operability Determination or Prompt Operability Determination.
“NextEra received information from vendors identifying non-conforming conditions adversely impacting two reinforced concrete structures at Seabrook Station, and did not complete an appropriate IOD or initiate a follow-up POD to evaluate the impact of that non-conforming conditions on structural performance,” the agency says in its Notice of Violation.
The Alkali-Silica Reaction
The ASR can take place in concrete in the presence of water; alkaline cement reacts with reactive silica in the aggregate, forming a gel and eventually causing cracking.
According to the Portland Cement Association, ASR can be indicated by “random map cracking and, in advanced cases, closed joints and attendant spalled concrete.”
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| U.S. Nuclear Regulatory Commission |
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Alkaline cement reacts with reactive silica in the aggregate, forming a gel and eventually causing cracking. |
The micro-cracks caused by ASR can “change the physical structural properties of the concrete, including compressive and tensile strength, modulus of elasticity, and Poisson Ration,” according to the NRC report on Seabrook.
Evidence of ASR has been found in an electrical tunnel, the residual heat removal vault, the diesel generator building, and the containment enclosure building, according to the NRC’s reports. The NRC says staff deemed the cracking and deformation in these locations to be of “very low safety significance because the safety function of these structures was not affected.”
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| U.S. Dept. of Transporation |
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According to the Portland Cement Association, ASR can be indicated by “random map cracking and, in advanced cases, closed joints and attendant spalled concrete.” |
“To be very clear, this is not a safety issue,” NextEra spokesman Al Griffith told the Newburyport Daily News. “While we believe our plan to monitor and manage alkali-silica reaction for the long term is effective and comprehensive, we are committed to continuous improvement, and we will continue our efforts to ensure that the actions we are taking on ASR are appropriate and timely.”
Relicensing Controversy
The original ASR findings came to light as part of NextEra’s application for an extension of Seabrook’s license to operate. When the concrete issues were revealed, some area leaders called for a delay in granting the plant’s extension.
Seabrook is currently licensed through 2030; the license renewal would extend its license to operate through 2050.
In the most recent NRC schedule for the relicensing project, which the agency issued March 31, NRC officials pushed back a scheduled meeting pending more information about the ASR situation.
Last fall, NRC and NextEra went back and forth on the issue, the agency requesting more information as part of the relicensing program, because it had “not received any information to support a basis for long term functionality of affected structures and structural systems.”
NextEra applied for relicensing in 2010. According to the company’s website, when the relicensing process began, the company expected a decision from the NRC by 2012.
