On February 16, 2018, the Unit 1 reactor tripped from 100 percent power due to a human performance error. Specifically, during B train SSPS testing, technicians reached Step 12.4.6 in procedure PT/0/A/4601/008 B which instructed Technician 1 to Depress and hold
UV TEST push button for Train B in back of breaker CABINET- 1(RTB/BYB), and Technician 2 to proceed with Steps 12.4.7 through 12.4.13. Technician 2 completed the actions, out of the area, while Technician 1 stayed in the area holding the
UV TEST push button. Technician 1 proceeded, without the procedure, to Step 12.4.14, which states, Release
UV TEST push button, and proceeded to Step 12.4.15, which instructs the technicians to verify that the
reactor trip breaker (RTB) opened. Technician 2 erroneously opened the bypass breaker(BYB) cabinet to perform Step 12.4.15 and noticed that the breaker was closed. Technician 2 proceeded to trip the BYB causing a
reactor trip because the BYB was supplying power to the
control rods while the RTB was being tested. Technician 2s actions were done without the procedure in-hand and the procedure did not direct the technician to manipulate the breaker, regardless of position. Corrective Actions: Technicians were removed from dutyPost-trip fitness-for-duty testing was performedReactor Trip investigation performed Corrective Action Reference:
NCR 02185409, Unit 1
Reactor Trip during 1B SSPS Testing
