The Nuclear Regulatory Commission staff issued a white finding of low-to-moderate safety significance to the Dresden Nuclear Power Station, Unit 2, for the failure to establish measures to ensure the reliable operation of certain safety-related valves. The finding will result in increased oversight by the NRC.
The nuclear power plant, operated Exelon Generation, is located in Morris, Ill., about 25 miles southwest of Joliet.
The NRC will conduct an inspection to verify that the plant staff understands the cause of the problem and has taken sufficient action to make sure it does not recur.
As a result of this finding, the plant will move from Column 1 to Column 2 of the NRC’s Action Matrix, as of the second quarter of 2015.
The company has 30 days to contest the finding.
On Feb. 7, 2015, one of four valves in the reactor vessel depressurization and overpressure protection safety system failed a required maintenance test. This system controls pressure in the reactor in certain accident conditions.
A subsequent review showed that the valve failed because of improper reassembly during the last required test and maintenance in 2013 and increased vibration of plant components resulting from an extended power uprate.
The valve failure occurred when the plant was shut down and had no impact on public health and safety.
The plant began operating at extended power in 2009, which is known to increase vibration levels on certain plant components, including the valves in the reactor depressurization and overpressure protection system. NRC inspectors determined that the facility failed to develop effective installation and maintenance procedures and guidance to prevent valve damage in light of these new conditions.