The NRC classifies inspection findings at nuclear plants as being one of four colours: green, white, yellow or red. A “red” category indicates high safety significance, and would normally result in “strong actions by the NRC to improve plant performance.” In this case, the NRC established a special oversight panel which has compiled a list of actions to be taken by FirstEnergy “to demonstrate that plant safety systems will perform as designed and that the plant’s safety culture and management problems have been addressed.” The oversight panel will meet with FirstEnergy officials on 11 March to review recent activities at the plant. Refuelling of Davis Besse was completed last month, and FirstEnergy hope the reactor can be restarted in April.
Utility inspections found evidence of cracks in control rod drive mechanism tubes which pass through the top of the reactor vessel. During repairs to one of the tubes, workers found a cavity in the vessel head next to the tube which was later determined to have been caused by boric acid corrosion.
Following the discovery of vessel head degradation at Davis Besse, the NRC has issued a reactor pressure vessel head inspection order to all licensees operating PWRs in the USA. The order requires that licensees conduct bare metal visual examinations of the entire vessel head surface and non-visual examinations of each head penetration. The NRC said that the order is considered an interim measure until enhanced inspection requirements acceptable to the NRC are incorporated into the American Society of Mechanical Engineers Boiler and Pressure Vessel Code and related NRC regulations.
