Unplanned reactor trips at St. Lucie and a generator malfunction during last year’s earthquake at North Anna will result in additional inspections at the plants, the Nuclear Regulatory Commission announced Monday.

Florida Power and Light’s St. Lucie unit 1 reactor in Jensen Beach, Fla., has shut down unexpectedly three times since the third quarter of 2011, with two of those shutdowns classified as complicated trips.

St. Lucie nuclear plant. Source: NRCOperators tripped the unit manually in August after an influx of at least 1,000 pounds of jellyfish clogged the coastal plant’s water intake and caused condenser backpressure to rise, according to an NRC event report. The incident also involved a leak in the casing of a feedwater pump, according to the report, and a trip of a second feedwater pump.

The Palm Beach Post reported that reactor trips in October and March were caused by valve problems, and that the March trip is still under investigation.

The reactor’s recent performance crossed a threshold for trips per 7,000 critical hours, according to an NRC release. The agency placed the unit in the “degraded cornerstone” column of its action matrix, which entails a supplemental inspection and additional oversight. The column is the third most serious of five columns in the matrix.

In a separate release Monday, the NRC said it placed Dominion’s North Anna plant in the “regulatory response” column of the matrix, its second lowest category of severity. In August an earthquake centered near the plant in Mineral, Va., caused it to trip automatically. While the reactor shut down and cooled off safely, one of its four emergency diesel generators failed, according to NRC documents. The agency later blamed the failure on inadequate guidance for installing certain gaskets in the generators. The resulting white finding and its new position in the matrix will result in further inspections from the NRC.