This 60-day telephone notification is being made per the reporting requirements specified by
10 CFR 50.73(a)(2)(iv)(A) and
10 CFR 50.73(a)(1) to describe an invalid actuation of a
Primary Containment Isolation System (
PCIS) Group 1 for
Main Steam Isolation Valves (
MSIVs), Group 3 for
Reactor Water Cleanup (
RWCU), Group 6 for
Secondary Containment isolation, Group 7 for Reactor Water Sampling, Diesel Generator,
Reactor Core Isolation Cooling (
RCIC) System logic, and
Residual Heat Removal (
RHR) logic.
Group 1, Group 6, Diesel Generator actuation, RCIC actuation and RHR actuation are within scope of 10 CFR 50.73(a)(2)(iv). Group 3 and Group 7 are not within scope as they affect only one system.
Cooper Nuclear Station [CNS] was shut down in Mode 5 at the time of the event with the reactor cavity flooded. On October 13, 2018, at 0028 Central Daylight Time, CNS received full PCIS Groups 1, 3, and 6, and a half Group 7 on the Division 1 side. The MSIVs and RWCU isolation valves were already closed for maintenance. The Secondary Containment isolated. Control Room Emergency Filter and the Standby Gas Treatment Systems initiated. The inboard Reactor Water Sample valve isolated. Diesel Generator #1 started but was not required to connect to the critical bus. Reactor Core Isolation Cooling System logic actuated with no expected response due to being isolated for shutdown conditions.
Division 1 RHR pump logic actuated. Division 1 RHR system was operating in shutdown cooling mode. The actuation caused the Division 1 RHR outboard injection and heat exchanger bypass valves to open. Shutdown cooling was unaffected and remained in service throughout the event.
The plant systems responded as expected with no Emergency Core Cooling System injection.
At the time of the event, an in-service inspection of welds inside the reactor vessel was taking place using a robot scanner that uses two vortex thrusters to hold the robot to the vessel wall. The robot inadvertently passed over an instrument penetration, drawing suction on the process leg, resulting in low reactor water level indications and the subsequent invalid Level 1 and 2 system actuations. Actual reactor vessel water level remained steady at cavity flooded conditions.
The NRC Resident Inspector has been notified of this event.
