Pilgrim Nuclear Station operators returned the plant to service Wednesday at 11:21 a.m. when it was reconnected to the New England electric transmission grid, according to a release from Entergy, the plant's owner.
The plant was manually shut down Monday to investigate a minor leak associated with a pilot valve on one of the plant’s four safety relief valves. It was the second time in less than two weeks that the plant was shut down.
The plant was manually shut down Jan. 10 after recirculation pumps stopped operating; it was up and running again Jan. 16.
Plant technicians replaced the pilot valve and operators began the process of restarting Pilgrim Station early Wednesday.
According to a story by the Cape Cod Times, this is the sixth unplanned shutdown in the past two years.
Although officials with Entergy Nuclear, which owns Pilgrim, say the string of shutdowns at the facility never put the public in danger, the 40-year-old plant exceeds industry averages for automatic shutdowns and unplanned power changes, according to the latest available data from federal regulators and nuclear experts.
"The performance indicators for Pilgrim in both areas are currently above those averages," Nuclear Regulatory Commission spokesman Neil Sheehan wrote in an email to the Times.
In 2011 the industry averaged 0.83 unplanned power changes compared with Pilgrim's 3.3, according to Sheehan. These figures are based on a rolling average per 7,000 hours of operation.
The plant experienced 0.8 unplanned automatic shutdowns, or SCRAMs, during 7,000 hours of operation as of the end of 2012, compared with a 0.45 industry average for 2011, Sheehan said.
A full year of operation is typically 8,200 hours, he said....
Despite the higher-than-average number of problems, and even including the recent shutdowns, the plant is unlikely to trigger thresholds that automatically require more oversight by NRC inspectors, Sheehan said.
For SCRAMs, the threshold is three per 7,000 hours of operation, and for unplanned power changes the threshold is six, he said.
Although the failure of a safety release valve during the weekend is reminiscent of the failure of the same type of valve in 2011, it does not appear the problems are related to the age of the plant, Sheehan said.
At the time of Monday's shutdown, Pilgrim had been online continuously for 230 days.