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On June 22, 2001, the 'C' emergency diesel generator (EDG) heat exchanger cooling water outlet relief valve opened when two pumps were operating in the 'A' Safety Auxiliaries Cooling System (SACS) loop. The relief valve was set to open at 120 psig instead of the design setpoint of 150 psig.

During a postulated design basis event, pressure could have exceeded the lift setpoint, causing the valve to open. If automatic makeup to the 'A' SACS loop head tank was not available, operator action would be required to identify and correct the condition before loss of inventory resulted in loop inoperability. At the time of discovery, scheduled maintenance prevented the 'B' train of the Control Room Emergency Filtration (CREF) System from performing its design function. Thus, it is possible that neither CREF train would have been available during a postulated design basis event. The root cause was the failure to update the Bill of Material for relief valve 1EGPSV-2409C as part of a design change package. Upon discovery, the 'A' SACS loop was placed in a configuration that ensured system pressure would not exceed the lift setpoint for 1 EGPSV-2409C. The relief valves on the 'A', 'B', and 'D' EDGs were verified to have the correct lift setpoint. The 'B' CREF train was returned to OPERABLE status. Relief valve 1EGPSV-2409C was replaced with a valve with the correct lift setpoint.