SEABROOK — Nuclear Regulatory Commission officials will soon travel south to the University of Texas to further investigate the concrete degradation problem affecting areas of NextEra Energy Seabrook nuclear power plant.
Alkali-silica reaction is a slow chemical reaction between water, the alkaline cement and reactive silica found in some aggregates used to make concrete. ASR forms a gel that expands, causing cracks that affect concrete properties, but which can take five to 15 years to show up.
More commonly found in transportation structures like dams, bridges and roads, where it has been successfully mitigated, Seabrook Station is the first nuclear power plant to discover and report the presence of ASR. It was found in an electrical conduit tunnel located about 40 feet below ground level, in one of the deepest sections of the plant. The tunnel contains wires that lead from the control room to the rest of the plant.
NRC officials have assured the public on several occasions that the presence of ASR in some walls presents no danger to the public and that they are confident the power plant is safe. The reason for their conclusion is the conservative safety factors built into the plant when it was constructed, such as the 2-foot thick walls reinforced with a lattice of steel bars — or rebar — that maintain the load-bearing capacity of the walls and meet federal standards.
Adding controversy to the discovery of ASR at the power plant is that NextEra Energy Seabrook is currently under review by the NRC for a 20-year extension of its operating license, extending it from 2030 to 2050. Agency officials have told the power plant’s owners that in order for the plant to gain approval for its license extension, proof must be provided concerning the impact ASR will have on the plant as it ages, as well as how to mitigate ASR in the plant’s concrete structures if necessary.