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On January 21, 2014, at 9:25 p.m., Unit 2 experienced an automatic reactor trip from 99.5 percent power. The reactor trip occurred when 13 kV Service Bus 21 deenergized due to a ground fault on feeder breaker 252-2104. The loss of the service bus caused a loss of power to non-safety-related 4 kV buses, which caused a loss of circulating water pumps and main condenser vacuum, requiring the use of auxiliary feedwater and atmospheric dump valves to maintain Reactor Coolant System temperature. Power was also lost to safety-related 4 kV Bus 24, which caused an automatic start of the 2B Emergency Diesel Generator to power 4 kV Bus 24.

The loss of power to non-safety-related 13 kV Service Bus 21 was caused by water intrusion when an air filter assembly located at the back of breaker 252-2104 cubicle became dislodged during a snow storm, allowing snow to enter the cubicle, melt, and cause a ground fault. This event is being reported pursuant to 10 CFR 50.73(a)(2)(iv)(A) due to Reactor Protective System actuation and the automatic start of the 2B Emergency Diesel Generator. Corrective actions include repairs to 13 kV Service Bus 21 and installation of a new filter housing. Previous events related to safety-related structures have been documented in Licensee Event Reports 317/2010-001 and 317/2011-003.

On May 21, 2013 at 0533, Calvert Cliffs Nuclear Power Plant Unit 2 initiated a manual reactor trip from 99.5 percent power in response to a trip of 22 Steam Generator Feed Pump (SGFP).

All post-trip actions were completed and the event terminated without complications. The cause of the initiating event was the failure of the 22 SGFP coupling that connects the pump to its steam turbine driver, such that the pump and steam turbine were effectively disconnected.

Inspection of the pump end of the coupling assembly revealed mechanical damage and separation along a weld seam. Forensic analysis identified areas of incomplete weld fusion on the turbine end of the failed coupling dating to the original component manufacture, combined with stresses induced by high cycle stress as being the root cause of 22 SGFP coupling failure.

Immediate corrective actions taken included the examination, inspection, and replacement of the 22 SGFP coupling.

At 11:34 AM on May 28, 2003, Calvert Cliffs Unit 2 experienced an automatic reactor trip from 100 percent power. The automatic reactor trip was initiated by the Reactor Protective System due to the high pressurizer pressure condition that resulted from the rapid loss of load. The rapid loss of load occurred when the Main Turbine Governor Valves shut unexpectedly during planned troubleshooting on the Main Turbine controls in Turbine Auxiliaries Electro-Hydraulic Control Cabinet 2T11. A short circuit created during the troubleshooting induced a loss-of-voltage to the valve position limiter causing the governor valves to shut unexpectedly.

The short circuit was caused by incorrect use of test equipment during planned troubleshooting; therefore, the root cause of the trip lies in Human Performance in the area of Work Practices. Also, contributing causes in the area of Verbal Communications and Procedural Clarity were identified.

Corrective actions include awareness training on the event, its causes and recommendations, procedure changes, and also initial and continuing training on appropriate work practices when using test equipment. The unit was restarted and paralleled to the grid on May 29, 2003 at 7:03 PM.

Calvert Cliffs Nuclear Power Plant's Technical Specifications requires one door in the emergency air lock (a containment penetration) to be closed during core alterations or during movement of irradiated fuel assemblies within the Containment Building. However, on February 24, 2003 at 1500 during a Containment Building tour, it was identified that the Unit 2 Emergency Air Lock was not in the Technical Specification required status. Specifically, "daylight" was seen around a hose penetrating the emergency air lock temporary closure device. The emergency air lock temporary closure device can be used in place of an emergency air lock door. Subsequent investigation determined that the violation occurred on February 23, 2003 at approximately 1300 when a contract employee cut through the foam sealant in the temporary closure device to install an oxygen hose needed to support steam generator replacement activities. The oxygen hose was removed and the hole was sealed on February 25, 2003, prior to commencing core off-load.

However, since core alterations (specifically control element assembly uncoupling) were performed on February 23, 2003 from 0955 until 1805, a condition existed that is prohibited by the plant's Technical Specifications.