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| Entered date | Event description | |
|---|---|---|
| ENS 42837 | 12 September 2006 11:47:00 | This 60-day telephone notification is being made under 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 more than one system. On July 18, 2006, at 0447 hours CDT, with Unit 2 operating at 100% thermal power, the electrical power to reactor protection system (RPS) bus 2A was interrupted during the performance of surveillance testing on RPS circuit protectors 2A1 and 2A2. The RPS buses 2A and 2B are normally powered from motor-generator (MG) sets 2A and 2B, respectively. During testing or maintenance intervals affecting either the MG set or the normal supply circuit protectors, the affected RPS bus is powered from a transformer supply through alternate power circuit protectors 2C1 and 2C2. Power to RPS bus 2A, which was being powered through the alternate power circuit protectors via a temporary transformer, was interrupted when circuit protector 2C1 actuated on a sensed undervoltage condition. The Primary Containment Isolation System (PCIS) logic circuits powered from RPS bus 2A were de energized, and PCIS logic Groups 2, 3, 6, and 8 were actuated. None of the plant conditions which require PCIS Groups 2, 3, 6, or 8 actuation (e.g., low reactor water level, high drywell pressure, abnormal area radiation levels, high area temperature, etc.) existed, therefore these actuations are considered invalid. The following actuations/isolations occurred: Group 2: Isolation of the Pressure Suppression Chamber head tank pumps; and Drywell Floor and Equipment Drains Isolation Group 3: Isolation of the reactor water clean-up system Group 6: Initiation of the Standby Gas Treatment System; Initiation of Control Room Emergency Ventilation; and Isolation of the reactor zone and refuel zone normal ventilation systems. Group 8: This logic isolates the Traversing Incore Probes (TIP) if they are inserted. The TIPs were not inserted at the time of this event. All equipment responded in accordance with the plant design. Upon loss of power from the alternate source, the surveillance testing was suspended, and RPS Bus 2A was re energized from RPS MG set 2A. The affected logic was reset, and equipment was realigned as appropriate. There were no safety consequences or impacts on the health and safety of the public. The event was entered into TVA's corrective action program for evaluation and resolution. The NRC senior resident inspector has been notified of this report. Reference corrective action document PER 106999. |
| ENS 42389 | 6 March 2006 12:00:00 | This 60-day telephone notification is being made under reporting requirements specified by 10 CFR 50.73(a)(2)(iv)(A) to describe an invalid actuation of any of the equipment specified in paragraph 50.73(a)(2)(iv)(B). In this case, the equipment actuated was emergency diesel generator (EDG) A. This EDG is common equipment for Units 1 and 2. On January 13, 2006, troubleshooting was being conducted by maintenance personnel to determine the cause of observed alarm malfunctions on the EDG A local annunciator panel. Browns Ferry Unit 1 was shutdown and defueled and Unit 2 was operating at 100% thermal power. During this troubleshooting activity, at 1157 hours CST, EDG A was inadvertently started. The exact cause of the start could not be conclusively determined. EDG A properly started and ran in response to the invalid start signal. No loss of normal plant electrical power occurred, and the EDG did not connect to its associated shutdown board. The EDG was allowed to run for approximately one hour, and then it was shut down in accordance with plant operating procedures. Since no actual plant condition existed which required the EDG to start, and since the start occurred inadvertently, most likely as a result of a human error during the electrical circuit troubleshooting effort, this EDG start is classified as invalid. There were no safety consequences or impacts on the health and safety of the public. The event was entered into TVA's corrective action program for evaluation and resolution. (Reference BFN corrective action document PER 96291). The licensee notified the NRC Resident Inspector. |
| ENS 42215 | 21 December 2005 14:01:00 | This 60-day telephone notification is being made under reporting requirements specified by 10 CFR 50.73(a)(2)(iv)(A) to describe an invalid actuation of general containment isolation signals affecting more than one system. On November 15, 2005, while operating at 100% thermal power, at 08:05 hours CST, Browns Ferry Unit 2 incurred an inadvertent, invalid actuation of the PCIS Group 6 logic. One reactor zone ventilation exhaust radiation monitor (the B channel) was indicating downscale due to a pre-existing maintenance issue, and, during activities to formally place the channel in a tripped status in accordance with the applicable Technical Specifications, the PCIS logic fuse for the opposite (A channel) radiation monitor was inadvertently removed rather than the fuse for the B channel. The PCIS logic responded as designed to the condition of both radiation monitors being downscale, and a Group 6 logic actuation resulted. The actuation was invalid because it resulted from an error related to an equipment tagging activity; there were no actual plant conditions which required the associated equipment actuations/isolations to occur. The following equipment actuations/isolations occurred: Unit 2 Group 6
* reactor zone and refuel zone normal ventilation systems * drywell-torus differential pressure compressor * drywell-torus Hydrogen/Oxygen analyzers * drywell radiation continuous air particulate monitor All equipment responded in accordance with the plant design. There were no safety consequences or impacts on the health and safety of the public. The event was entered into TVA's corrective action program for resolution. The NRC senior resident inspector has been notified. |
| ENS 41181 | 8 November 2004 11:05:00 | This 60-day telephone notification is being made under reporting requirements specified by 10 CFR 50.73(a)(2)(iv)(A) to describe an invalid actuation of general containment isolation signals affecting more than one system. On September 28, 2004, with Unit 2 operating at 100% thermal power, at 1302 hours CDT during maintenance work associated with protective relaying on 480 VAC Shutdown Board 2A, the board was inadvertently tripped. Associated RPS motor-generator (MG) set 2A lost power, and RPS bus 2A, which is powered from this MG set, was de-energized. Primary Containment Isolation System (PCIS) logic circuits powered from this bus lost power, and PCIS logic Groups 2, 3, 6, and 8 were actuated. The following actuations/isolations occurred: Group 2: Isolation of the Pressure Suppression Chamber head tank pumps (and) Drywell Floor and Equipment Drains Group 3: Isolation of the reactor water cleanup system. Group 6: Initiation of the Standby Gas Treatment System (and) Initiation of Control Room Emergency Ventilation (and) Isolation of the reactor zone and refuel zone normal ventilation system. Group 8: This logic isolates the Traversing Incore Probes (TIP) if they are inserted. The TIPs were not inserted at the time of this event. All equipment responded in accordance with the plant design. There were no safety consequences or impacts on the health and safety of the public. The event was entered into TVA's corrective action program for resolution. The NRC senior resident inspector has been notified. |
| ENS 41180 | 8 November 2004 11:05:00 | This 60-day telephone notification is being made under reporting requirements specified by 10 CFR 50.73 (a)(2)(iv)(A) to describe an invalid actuation of general containment isolation signals affecting more than one system. On September 25, 2004, with Unit 3 operating at 100% thermal power, at 1814 hours CDT, a voltage regulator problem occurred on RPS motor-generator (MG) set 3B. The associated RPS circuit protectors sensed an undervoltage condition and opened, thereby de-energizing RPS bus 3B. Primary Containment Isolation System (PCIS) logic circuits powered from this bus lost power, and PCIS logic Groups 2, 3, 6, and 8 were actuated. The following actuations/isolations occurred: Group 2: Isolation of the Pressure Suppression Chamber head tank pumps, Drywell Floor and Equipment Drains Isolation. Group 3: Isolation of the reactor water clean-up system. Group 6: Initiation of the Standby Gas Treatment System, Initiation of Control Room Emergency Ventilation, Isolation of the reactor zone and refuel zone normal ventilation systems. Group 8: This logic isolates the Traversing Incore Probes (TIP) if they are inserted. The TIPs were not inserted at the time of this event. All equipment responded in accordance with the plant design, with the exception that Unit 2 refuel zone ventilation system supply inboard isolation damper 2-DMP-064-0006 failed to close. The series damper, 2-DMP-064-0005, fully closed, therefore there would have been no impact to secondary containment integrity had this been an actual event. The damper's failure to close resulted from a sticking solenoid valve which was subsequently replaced. There were no safety consequences or impacts on the health and safety of the public. The event was entered into TVA's corrective action program for resolution. The NRC senior resident inspector has been notified. |