This 60-day optional report as allowed by
10 CFR 50.73(a)(1), is being made under the reporting requirement in
10 CFR 50.73 (a)(2)(iv)(A) to describe an invalid actuation of a specified system, specifically the Nuclear
Service Water System (NSWS).
While performing changeout of a Nuclear Service Water (RN) current module, there was an unexpected auto swap from the normal heat sink (Lake Wylie) to the ultimate heat sink {Standby Nuclear Service Water Pond (SNSWP)} occurred and the system responded as designed. Work was stopped when notified by Operations.
This event occurred when technicians attempted to isolate power to the module prior to replacing. Unable to do so, they decided to perform a changeout under hot conditions. While tracing power utilizing wire tabs, the technicians did not identify that removing wire from terminal 12 of the module disturbs the power path to other channels. The channel associated with the bad module remained in the trip condition throughout, and when power to other channels was disturbed, the logic for a swap from the normal heat sink to the ultimate heat sink was completed and the automatic swap occurred as designed. This event was entered into the site corrective action program for evaluation.
The licensee will inform local and state agencies and has informed the NRC Resident Inspector.
