After cutting through a wall during a steam generator replacement, crews at the Davis-Besse nuclear plant discovered a large air pocket in its concrete shield building.
A FirstEnergy spokeswoman told the Toledo Blade that it runs the length of a 25-foot-long cut made during a reactor pressure vessel head replacement in 2011. It varies in width from 6 to 12 inches. She said the gap likely dates back to when the concrete was repaired following the RPV head replacement, and engineers are working to ensure a similar pocket does not form when the new hole is resealed.
FirstEnergy did not suggest that it was caused by concrete delamination or the process of cutting through the wall. Unlike Florida's Crystal River 3 – where concrete delamination during a similar procedure led to the early closure of the plant – Davis-Besse's shield building is separate from the reactor's primary containment structure. According to the Nuclear Regulatory Commission, the plant near Toledo uses a Babcock & Wilcox raised-loop pressurized water reactor licensed in 1977.