Jan. 21--PLYMOUTH -- A valve that is part of a fan system that keeps one of Pilgrim Nuclear Power Station's two emergency diesel generators from overheating had not been inspected or maintained since it was installed 16 years ago, according to a report from Entergy Corp., Pilgrim's owner-operator, posted on the Nuclear Regulatory Commission website Thursday.
The diesel generators kick in when offsite power is lost, keeping critical safety systems running and cooling down the nuclear reactor. Each of the two is capable of powering all essential systems.
Plant workers discovered oil had leaked from the gearbox on a fan system used to cool "Emergency Generator A" during a routine monthly check on Sept. 28.
According to Entergy's report, the oil pressure relief valve on the fan's gearbox had loosened, causing the oil to leak. There was enough oil left in the gearbox for Emergency Generator A to start up, said the report, but "it would have been losing gearbox oil, and we conservatively assumed it would have overheated due to failure of the cooling fan from gearbox damage."
Federal standards state each emergency generator should be capable of powering systems for 30 days. Emergency Diesel Generator A was declared inoperable until the gearbox problem was fixed.
The longest the system can be out of service under federal regulations is 72 hours.
According to Entergy's report, plant workers had replaced the gearbox in question in May 2000. The new gearbox had a relief valve on the outside that the original gearbox didn't have. "Changes to the gearbox inspections were not updated to include any inspections or preventive maintenance for the relief valve," stated Entergy's report.
On Sept. 15, before the oil leak was detected but during the period when the leak would have prevented Emergency Diesel Generator A from running for an extended period, the second emergency diesel generator was taken out of service for testing. "This created a condition that could have prevented the fulfillment of the safety function of a system needed to shut down the reactor and maintain it in a safe condition," the Entergy report stated.
NRC spokesman Neil Sheehan wrote in an email that his agency is "continuing to review this issue."
"It is among the items being assessed by our Phase 'C' inspection team, which completed its onsite reviews on Jan. 13," Sheehan wrote.
"This was the first time that oil had spilled from the new design of the gearbox since 2000," Entergy spokesman Patrick O'Brien said. "We promptly addressed the issue and reported the event upon discovery."
Equipment problems have been frequent at Pilgrim, and the plant is currently classified by the Nuclear Regulatory Commission as one of the worst in the country.
Two dampers designed to automatically close so radioactivity can't escape into the environment in an emergency failed to fully shut when tested during a routine maintenance check at Pilgrim Nuclear Power Station Monday.
It turned out the dampers simply needed to be cleaned and lubricated. While the issue took only 15 minutes to address, there is no way to know how long they had not been working.
The Nuclear Regulatory Commission received the report on the leaky valve Dec. 9, but it was just posted on the NRC website Thursday.
"The delay is not unusual," Sheehan wrote. "It's a function of how long it takes to process documents. There were also a number of holidays and that may have been a factor."
- Follow Christine Legere on Twitter: @ChrisLegereCCT.
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