December 07, 2012

 A U.S. Nuclear Regulatory Commission report claims an "organizational mindset" is one reason why the degradation of structural concrete in what may amount to more than 130 locations at the Seabrook Station nuclear power plant went undetected for so long.

"This ...; 'mindset' prevented a more timely and thorough investigation and examination of the effected concrete reinforced structures on site," the report, dated Dec. 3, states. This mindset was "that groundwater infiltration was more of an 'operational nuisance' than a structural integrity concern."

This infiltration caused damp conditions in many plant structures. It has been cited as the cause of a reaction in the concrete used to build the structures, known as alkali-silica reaction, or ASR, that can change the physical properties of the concrete and, potentially, affect structural performance.

While plant officials confirmed the nuclear power plant, built in the Seabrook marsh, has been experiencing groundwater infiltration since its construction in the 1970s, it took until 2009 for plant officials to identify potential degradation in some below-grade concrete structures. That discovery, made the year before a request to extend the operating license of the plant until 2050, has now extended the time frame for granting that license extension and prompted increased oversight by the NRC.

While plant personnel included this cause in a Root Cause Evaluation of the degradation prepared for the NRC in May, the inspection team noted it was not mentioned in the RCE's evaluation summary. NextEra-Seabrook, operators of the plant, agreed to include this information in a revised RCE to be submitted soon.

The report and RCE also indicated another cause of the existing degradation was that "the monitoring program for plant systems and structures does not contain a process for periodic reassessment of failure modes."

While the NRC report concluded that the affected "structures were suitable for continued service," it stated a final assessment of the "operability" of those structures would not be made until a proposed "large scale testing program" is completed. That testing is being conducted by a structural engineering lab in Texas and is scheduled to be completed next year with results to be reported in 2014.

"Given the current known extent of ASR, there is reasonable expectation that the affected reinforced concrete structures at Seabrook Station will remain capable of performing their intended functions while NextEra continues to monitor the condition and complete detailed testing and further engineering analysis," the report stated.

NextEra's reporting initially addressed five plant structures thought to have been affected by ASR. They are: the containment building that encloses the plant's nuclear reactor, a tunnel through which the radiologically controlled areas of the plant are accessed, a pump house used in emergencies to pump water into the reactor to cool it, the vault in which the equipment that removes residual heat from the reactor is kept, and the building that houses the emergency diesel generators, which supply electricity to plant safety systems when outside power is lost. All are considered important safety-related structures.

In addition, NextEra identified cracking, potentially caused by ASR, in 11 other structures, including the waste-processing building and the building in which nuclear fuel is stored. Work to determine ASR deterioration in other areas is continuing based on cracking found elsewhere, the report indicates.

"The ASR walk-downs identified 131 locations with some level of pattern cracking (which is the result of the chemical reaction)," the report states. "Of the 131 localized areas, 26 exceeded the initial screen criteria (for lengths of the cracks)."

The full extent and effect of the ASR at the Seabrook plant remains unknown at this time, the report concludes.

"The (NRC inspection) team confirmed that NextEra's position is that all reinforced concrete structures on site are susceptible to ASR, dependent upon the exposure to moisture," the NRC report states. "NextEra does not intend to exclude any structure from ASR monitoring without confirmation (via advanced testing) that ASR is nonexistent."

NRC staff will hold a meeting and open house Tuesday, Dec. 11, to update the public on its ongoing review of concrete degradation at the plant. The open house is from 5:30 to 6:45 p.m. at the One Liberty Lane Conference Center, at 1 Liberty Lane East in Hampton. A public meeting will follow at 7 p.m., when NRC staff will provide a presentation on the review and take questions from audience members.

http://www.seacoastonline.com/articles/20121207-NEWS-212070401