The Nuclear Regulatory Commission will determine whether one of the reactors at the PPL Susquehanna nuclear power plant requires additional oversight following two automatic reactor shutdowns this week.
According to NRC spokesman Neil Sheehan, workers at the plant in Salem Township were testing a turbine control valve in Unit 2 at 1:56 a.m. Sunday when the plant‚??s safety systems detected an anomaly with the valve and automatically shut down the plant.
That accident occurred in the ‚??non-nuclear‚?Ě side of the plant, where steam produced by the reactor is converted to energy by the turbine, Sheehan said.
At 5:31 p.m. Wednesday workers were bringing the reactor back online after fixing the problem when another automatic shutdown was triggered. Sheehan said a feed water pump, one of three pumping water into the nuclear reactor to produce steam, malfunctioned and caused the water level in the reactor to drop.
The shutdown caused control rods to be inserted into the reactor rapidly, which stopped the fission of enriched uranium inside, he said.
Joe Scopelleti, community relations manager for the PPL‚??s Susquehanna nuclear power plant, said the water level dropped about 29 inches below where it should have been, but the nuclear material remained below more than 10 feet of water. The plant never needed to activate its emergency plan, he said.
‚??We had a water system that could add water to the reactor if needed, but we were not in an emergency,‚?Ě Scopelleti said. ‚??‚?Ľ The bottom line is, the reactor shuts down safely, and that‚??s what it‚??s designed to do.‚?Ě
Unit 2 remained offline Friday as plant workers worked to diagnose what went wrong. They are being assisted by the two NRC resident inspectors assigned to the plant and by NRC reactor safety specialists in King of Prussia. Unit 1 was online and running at full power Friday.
Sheehan said the NRC will evaluate whether the incident will trigger additional government oversight.
‚??Fundamentally, we want to make sure that the company is being very thorough in evaluating what went wrong, and we want to be aware of any corrective actions that they are taking,‚?Ě Sheehan said. ‚??‚?ĽAnd then secondly, we would evaluate whether or not we need to increase our inspection activities at the plant in response to these events.‚?Ě
The commission uses a color-coded four-tier system to rank shutdowns and other unexpected incidents at nuclear plants. Incidents are ranked from least to most severe on a scale from green to white to yellow to red. A green safety finding will not trigger additional oversight, but a white or higher level finding will, Sheehan said.
Unit 1 has been at the white inspection level since a July 2010 flooding incident prompted another shutdown. Sheehan said a plant will typically stay at that level for a year if the underlying problem is corrected, but Unit 1 remains there because the NRC is ‚??not fully satisfied with the progress they‚??ve made.‚?Ě
‚??We want to make sure they fully have their hands around the root of the problem‚?Ľ and then we want to look at any corrective actions, any changes they‚??ve made to make sure this doesn‚??t occur again,‚?Ě Sheehan said.