Entergy’s Pilgrim Nuclear Power Station outside Boston just can’t seem to shake its problems with unplanned shutdowns. The most recent one occurred on Aug. 22, when a broken air-nitrogen line caused a main steam isolation valve to close, trigging a reactor scram.

This was the plant’s third unplanned shutdown in 2015. Pilgrim was forced offline during a blizzard in January when the distribution lines taking its electricity failed.

Though no damage or significant safety issues have occurred as a result of the shutdowns, they have drawn oversight from the Nuclear Regulatory Commission (NRC). Pilgrim has been in the NRC’s Degraded Cornerstone column since 4Q 2013, indicating that the plant has fallen short in one of the NRC’s plant performance criteria.

The NRC oversight stems from several other unplanned shutdowns in 2013. A subsequent investigation resulted in the NRC issuing two white Performance Indicators (PIs), finding that Entergy had not corrected the underlying problems at the time. A white PI is the lowest level of severity, indicating an incident of low-to-moderate safety significance triggering increased regulatory oversight.

In addition to the white PIs, two green inspection findings (a deficiency in performance that has very low risk significance and little or no impact on safety) were later issued as a result of the shutdowns, one in December 2014 and one in March 2015. The first was related to an August 2013 shutdown, finding that Entergy did not fully investigate the cause. The second was related to the shutdown this January, when a diesel air compressor failed, leading to a loss of instrument air during the event.

Though the 685-MW boiling water reactor in Plymouth has been on anti-nuclear activist hit lists for decades, Entergy remains committed, at least publicly, to keeping it open. The plant is licensed to operate through 2032.

—Thomas W. Overton, JD is a POWER associate editor (@thomas_overton, @POWERmagazine).