NRC: Limerick Nuclear Generator ‘Scrams’ For Second Time In 36 Hours

NRC: Limerick nuclear generator ‘scrams’ for second time in 36 hours (Montgomery News, June 03, 2011):

The same nuclear reactor at Exelon’s Limerick Generating Station that shut down unexpectedly early Sunday morning did so again Monday, according to an official at the Nuclear Regulatory Commission.

Neil Sheehan, a spokesman for the NRC office in King of Prussia, wrote in an e-mail that “Limerick Unit 2 experienced another scram Monday.”

“As the plant was being started up, two reactor re-circulation pumps tripped. The reactor was at zero-percent power when this occurred,” Sheehan wrote.

According to NRC documents, the second “scram” occurred at 11:50 a.m.

“Licensee is investigating a potential issue with the relay logic associated with the scram bypass feature. Offsite power circuits and emergency diesel generators are operable and available. There was no increase in plant risk associated with this event,” read an update in status posted on an NRC daily log of events.

It was the second time in less than 36 hours that the reactor had to be shut down unexpectedly.

Unit 2 shut down at 5:02 a.m. Sunday “after the turbine tripped following scheduled testing and maintenance on an electrical system in the non-nuclear section of the plant,” according to a news release issued Sunday by Exelon.

The company has not yet released any complete explanation for the first “scram.”

On Sunday, Sheehan said that when a reactor “scrams,” the NRC begins to analyze if a unit has more than three scrams in its 7,000 hours of operations in a service quarter.

In Tuesday’s e-mail he wrote: “I’m told this would not count as a hit on the plant’s Performance Indicator for Unplanned Scrams per 7,000 Hours of Online Operation because it occurred while the reactor was subcritical [at zero-percent power].”

In February, the same reactor, Unit 2, shut down unexpectedly due to problems with systems related to recirculating pumps. That shutdown lasted for more than two days.

According to NRC documents, Unit 1, experienced a scram on June 23, 2010, also because of problems with the re-circulation pumps.

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