North / South America
Nuke plant concrete woes worse than previously believed
Apr, 24 2012
Seabrook Station tells NRC plant is operating safely, tests will continue
(New Hampshire) -- The cause of concrete degradation at Seabrook Station is more pervasive than originally reported, has already brought some of the structures below licensing standards and could further delay the nuclear plant's effort to extend its operating license to 2050.
NextEra Energy, operators of the Seabrook nuclear plant, told the U.S. Nuclear Regulatory Commission on Monday in Bethesda, Md., that the concrete structures are still safe and operable. The alkali-silica reaction (ASR, caused by the interaction of water and concrete) that has been identified as the reason for the degradation is "outside current licensing requirements, but certainly remain above the levels needed for structural integrity," according to Michael Collisions, design engineer manager for NextEra Energy.
Monday's meeting was called to get NextEra's input in three areas of concern as it relates to the 2010 discovery of ASR at the Seabrook plant, according to Chris Miller, the NRC's regional director of reactor safety. Those areas are how the concrete has already been affected by the reaction, what effect the reaction has had on the rebar that supports the concrete, and the rate of degradation.
"There are many parts (of the ASR situation at Seabrook) to be considered," Miller said. "It is complicated and effects current operations, as well as the (license) renewal."
ASR was first noted at the plant in 2010, in work done in preparation for the submission of a request from the plant to extend its operating license for 20 years. The plant's current license runs until 2030, 40 years from its start-up date in 1990. The extension, if granted, would allow the plant to operate until 2050.
The NRC's concerns were heightened after further testing at the plant last year indicated that in one of the areas where ASR was found, the "B" electrical tunnel, the strength of the concrete had been reduced by 22 percent compared to samples taken at the time the concrete was poured during construction in 1979. On Monday, NextEra representatives said that information was misleading because different testing methods were used.
"The original testing was done on cylinders (taken at the time the pour was made), not on cores (such as were taken from the cement structures in 2011)," said Dr. Oguzhan Bayrak, a professor at University of Texas who has been hired by NextEra as a consultant on the ASR issue. Bayrak said there is normally at least a 15 percent disparity in concrete strength seen in comparisons of those two methods.
NextEra officials also tried to quell NRC concerns by indicating that the cracking of the concrete caused by ASR is more pronounced in the external layers than in portions where rebar supports the structure.
"Cracking is contained in the reinforced concrete structure," said Richard Noble, NextEra's director of engineering.
The investigation into the effects of ASR on Seabrook Station have already pushed the license extension process back approximately 11 months, NRC officials said. NextEra indicated that more in-depth testing of core samples taken last year by staff at the University of Texas will not be completed until 2014, and that a long-range plan for mitigating the effects of ASR will be developed at the conclusion of the testing, potentially pushing the licensing extension back further.
NextEra will submit more information on its proposed Aging Management Program in late May, the company representatives told NRC officials Monday.
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