Tweak at the Creek – Faulty valve at nuclear plant draws NRC’s eye
A malfunctioning emergency valve at the Oyster Creek nuclear power plant in Lacey Township raises concern in the Nuclear Regulatory Commission (NRC), which assigned a low-to-moderate safety risk in a preliminary report.
The device, an electromatic relief valve (EMRV), is one of five that depressurize the reactor, and regulate the flow of coolant to the reactor in the event of an unplanned shutdown, according to NRC's Neil Sheehan. They are employed only in the event of an accident.
NRC inspectors called attention to it during a Problem Identification and Resolution inspection at the close of 2016. The preliminary report gives it a "white" classification for the current cycle, one step below a fully satisfactory safety categorization.
The generating station is currently under normal oversight levels. If the classification status remains as-is in the finalized report, the plant would be subject to increased scrutiny by federal regulators.
Exelon has the option of supplying relevant information in details to NRC, requesting a conference, submitting a written response, or accepting the classification. In the latter case, NRC would let the categorization stand.
Inspectors cited improper re-installation of lock washers attached to a cut-out lever for the valve, creating a level of friction between the lever and the solenoid that impaired the valve.
The valve was determined to have malfunctioned from September 5, 2014 until September 19, 2016. Sheehan explained that the period was between outages for refueling and maintenance. The EMRV malfunction was noted in inspections during the maintenance outage.
Sheehan said that Oyster Creek's technical specifications require all EMRVs to be operable when the plant is running. He added that the preliminary determination factors in all safety risk implications, including redundancies and backup systems.
A breakdown in any one valve lasting more than three days would require a reduction in reactor pressure to 110 pounds per square inch gauge (PSG) or less, within 24 hours.
During the most recent refueling outage at the end of 2016, Exelon installed new cut-out switch lever plates with greater clearances, replaced washers, and verified correct valve assembly, NRC said.
Exelon's response, in its entirety, follows.
"As part of a regular, proactive inspection, technicians found an inoperable reactor pressure relief valve, which is one of five such valves that can be used to release reactor pressure during the unlikely event of an emergency. The valve has since been repaired and returned to operable status.
The NRC has notified Oyster Creek that it will be receiving a white finding related to this event and a follow-up inspection will be conducted. We look forward to showing the NRC that we acted conservatively and with the best interest of public safety in mind."
Outmoded design, not performance, of EMRVs at the power station resulted in a "yellow" classification of "substantial" safety significance, in 2015. It was rectified that year. NRC says that the 2015 issue has no bearing on the current matter, which it considers unrelated.