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| Entered date | Event description | |
|---|---|---|
| ENS 53817 | 8 January 2019 08:12:00 | On November 12, 2018, at 1331 EST, Unit 1 secondary containment isolated and Standby Gas Treatment (SBGT) systems started on Unit 1 and Unit 2 due to a blown fuse. The blown fuse was caused by a degraded refuel floor radiation monitoring relay, causing the radiation monitor to trip and resulted in an invalid actuation of the Unit 1 Group 10 and Group 11 primary containment isolation valves, all Unit 1 secondary containment isolation valves, and auto start of the Unit 1 and Unit 2 SBGT system. The Unit 1 Fission Product Monitor isolated and tripped and both Unit 1 H202 Analyzers isolated. This event is reportable per 10 CFR 50.73(a)(2)(iv)(A) since the containment isolation and auto-start of SBGT on both units was not part of a pre-planned sequence and the event resulted in the invalid actuation of general containment isolation valves in more than one system. All primary and secondary containment isolation valves, with the exception of the 2T41F003A, Refueling Floor Inboard Vent Supply Isolation valve, functioned successfully. The refuel floor inboard vent supply isolation valve failed to travel fully closed on the secondary containment isolation signal and was therefore declared inoperable. The 2T41F003B refuel floor outboard vent supply isolation valve was verified to go fully closed and therefore isolation of that associated penetration line was successful. After assistance from maintenance, the valve was verified to be fully closed. All SBGT systems functioned successfully. The associated fuse and relay were replaced, and secondary containment was returned to normal service. The licensee notified the NRC Resident Inspector. |