WASHINGTON, D.C. — Seeking to understand the testing initiated by owners of NextEra Energy Seabrook nuclear power plant on its concrete problem, staff from the Nuclear Regulatory Commission spent three days auditing the regimen being conducted at the University of Texas.
The purpose of the NRC's October review at the University of Texas' Ferguson Structural Engineering Laboratory in Austin was for auditors to get a better understanding of the large-scale testing program that seeks to determine the longterm impact of concrete degradation problem found at Seabrook Station, according to Neil Sheehan, spokesman for Region 1 of the NRC. One conclusion of the NRC audit is that more information is needed before a final determination can be made on how to handle the problem in the long term.
"The NRC is still reviewing NextEra’s plans for addressing concrete degradation, also known as alkalai silica reaction, at the Seabrook nuclear power plant and how it might impact the facility during a license extension period (of) an additional 20 years of operation past the original 40-year operating license," Sheehan said. "While there, the five-member NRC team observed a sample of the testing. This included two large-scale shear load tests on concrete beams to failure and material property testing."
In May, 2010, Seabrook Station made application to the NRC to extend its 40-year operating license period from 2030 to 2050. However, while preparing the application, staff at the power plant discovered signs of alkalai-silica reaction in some of the concrete walls of an electrical tunnel deep underground. NextEra staff reported the issue to the NRC. Since then, ASR has been discovered in more walls throughout the power plant.
The issues of if an how the concrete problem could impact the aging of the nuclear power plant is being investigated as the nuclear regulatory agency considers whether to approve the 20-year extension of Seabrook Station's operating license.
Alkali-silica reaction, or ASR, is a slow chemical reaction between the alkaline cement and reactive silica found in some concrete aggregates when moisture is present. Commonly found in dams and bridges, ASR forms a gel that expands, causing micro-cracks that affect concrete strength. ASR can take five to 15 years to show up.
Seabrook Station is currently the only nuclear power plant in the United States known to have ASR issues, although power plants located in Canada and Europe have experienced the problem.
After inspections and analyzing samples, the NRC has repeatedly assured the public that ASR has not affected the safety of Seabrook Station. The plant and its walls are still structurally sound, the NRC has said, for the 2-foot thick walls where the problem has been discovered still meet federal standards for load-bearing capacity due to the lattice of steel rebar reinforcement within the walls. The NRC closely monitors the condition at the plant.
The NRC has also stated repeatedly that it will not act on the license extension until it is convinced the power plant's owner can satisfactorily demonstrate it has developed a long-term plan to address ASR at the plant as the plant ages. That information is what the testing program at UT's Ferguson Structural Engineering Laboratory is meant to provide.
According to a recent report from the NRC on its October audit, the staff reviewed the testing program, interviewed various Seabrook Station representatives, toured the Texas facility and observed set up and some of the testing. Staff reviewed the merits of the testing program.
According to the report, staff observed four separate testing programs, including shear testing of large beams, rebar anchorage testing on large beams, anchor bolt testing in concrete blocks and instrument evaluation study for through-wall expansion instrumentation choosing.
Sheehan said NRC auditors concluded additional information is needed before the agency can determine whether Seabrook Station's aging management program for ASR is sufficient.
"The NRC staff will evaluate all of the company’s responses and its updated aging management program and provide those results in the agency’s Safety Evaluation Report for the plant’s license renewal application," he said.
As it relates to progress on the commission's review of the overall application to extend Seabrook Station's operating license, Sheehan said, the schedule for a meeting of an agency subcommittee of the Advisory Committee on Reactor Safeguards was pushed back from this month to next May.
"Also, some other key milestones, including the issuance of the final Safety Evaluation Report and the final decision on the application by the director of the Office of Nuclear Reactor Regulation is now listed as 'To Be Determined'" Sheehan said. "The footnote for the “TBDs” notes that new dates will be based on the company’s submittal of requested additional information."