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| Entered date | Event description | |
|---|---|---|
| ENS 50565 | 24 October 2014 14:49:00 | 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 general containment isolation signals affecting containment isolation valves in more than one system. On August 27, 2014, at 1109 hours Central Daylight Savings Time (CDT), while in a forced unit outage with the reactor noncritical (Mode 3) and with all control rods fully inserted, instrument mechanics were attempting to backfill reactor water level transmitter (LT) 3-53 sensing lines following performance of LT replacement. During this effort, water levels in both the variable and reference legs of the LT were disturbed resulting in a Browns Ferry Nuclear Plant (BFN) Unit 1 full scram and Primary Containment Isolation System (PCIS) Groups 2, 3, 6, and 8 isolation signals due to receipt of an invalid low reactor water level signal. The PCIS Groups 2, 3, 6, and 8 isolations caused the initiation of Trains B and C of the Standby Gas Treatment (SBGT) System and Control Room Emergency Ventilation (CREV) Subsystem 'A'. The Reactor and Refuel Zone ventilation fans tripped and the secondary containment dampers isolated. Train A of the SBGT System was tagged out of service during the event. Operations personnel responded to the PCIS initiation, ensured all equipment operated as designed, and placed affected systems back in service. Plant conditions which initiate PCIS Group 2 actuations are Reactor Vessel Low Water Level (Level 3) or High Drywell Pressure. The PCIS Group 3 actuations are initiated by Reactor Vessel Low Water Level (Level 3) or Reactor Water Cleanup Area High Temperature. The PCIS Group 6 actuations are initiated by Reactor Vessel Low Water Level (Level 3), High Drywell Pressure, or Reactor Building Ventilation Exhaust High Radiation (Reactor Zone or Refuel Zone). The PCIS Group 8 actuations are initiated by Low Reactor Vessel Water Level (Level 3) or High Drywell Pressure. At the time of the event, these conditions did not exist; therefore, the actuation of the PCIS was invalid. There were no safety consequences or impact to the health and safety of the public as a result of this event. This event was entered into the Corrective Action Program as Problem Evaluation Report 928777. The NRC Resident Inspector has been notified of this event. |