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| Entered date | Event description | |
|---|---|---|
| ENS 44471 | 7 September 2008 23:12:00 | On 09/07/2008 at 1720 CDT, Browns Ferry Nuclear Plant experienced a partial loss of offsite communication to include the Emergency Notification System to the NRC, normal phone communication to offsite, the Operations Duty Specialist ring down phone to Chattanooga and the satellite phone to offsite located in the control room. This loss of communications was the result of an unplanned electrical power outage due to loss of temporary diesel generator supplying power to the communications network. The control room indications and assessment capability were not affected. Cell phones and the Health Physics Radio Network were available to be used onsite to communicate offsite. The plant radio system and sound powered phones were unaffected and plant staff communication capability was available. Communication capability was restored at 1758 CDT 09/07/2008. Operation of Unit 1, Unit 2 and Unit 3 was not affected by the event. The NRC Sr. Resident Inspector has been notified. This event is reportable under 10CFR50.72(b)(3)(xiii), 'Any event that results in a major loss of emergency assessment capability, offsite response capability, or offsite communications capability (e.g., significant portion of control room indication, Emergency Notification System or offsite notification system.' |
| ENS 44400 | 8 August 2008 17:43:00 | This is a Voluntary Notification in accordance with NUREG 1022 Section 2.7 of a controlled shutdown that can be considered to be of Generic Interest to the NRC and is not reportable otherwise per 10CFR50.72 or 10CFR50.73. Operations performed the controlled shutdown of Browns Ferry Unit 1 this morning in order to isolate and repair a small steam leak. The leak was determined to be from a Code Class 2 piping thermo-well located in the Unit 1 Steam Tunnel. The controlled shutdown was uneventful with all systems responding as expected. There was no impact to the health and safety of the public. Units 2 and 3 were operating at 50% power when Unit 1 was shutdown and were not affected by this event. The Senior NRC Resident Inspector has been notified of this Voluntary Notification. |
| ENS 43560 | 11 August 2007 21:25:00 | On 08/11/2007 at 1751 CDT, Browns Ferry Unit 1 received an Automatic SCRAM due to a Neutron Monitoring (APRM) Trip Signal . Preliminary investigation indicates the trip signal was caused by a Recirculation System Flow Transmitter sensing line becoming separated giving an indicated low flow signal to the neutron monitoring system. With the indicated low flow and high (100%) power, the neutron monitoring system initiated an APRM Simulated Thermal Power Flow Biased Reactor Scram. All control rods inserted and all systems responded as required to the automatic SCRAM signal. No Emergency Core Cooling System (ECCS) initiations occurred as a result of the SCRAM. Reactor water level lowered below Level 3 (+2") (lowest indicated level reached -33") as a result of the SCRAM and was recovered to the normal level band by the Reactor Feed Pumps (RFPs). The expected Primary Containment Isolation System (PCIS) Groups 2, 3, 6, and 8 isolations were received due to Reactor Water Level lowering below Level 3 (+2") (lowest indicated level reached -33") with all systems isolating as required. Reactor pressure is being controlled using Main Steam Bypass Valves. Reactor Level is being maintained in band using Reactor Feed Pumps. Plant to remain in Mode 3 and initiate repairs to the failed sensing line. Investigation into the event is proceeding. This event is reportable under 10CFR50.72(b)(2)(iv)(B), any event or condition that results in a valid actuation of the Reactor Protection System; 10CFR50.72(b)(3)(iv)(A), any event that results in an actuation of the specified systems. This event also requires a 60 day written report in accordance with 10CFR50.73(a)(2)(iv)(A). The NRC Senior Resident Inspector has been informed of this event. The sensing line had a flow limiter on it and the line was isolated locally. Amount of leakage not known at this time. |
| ENS 43414 | 9 June 2007 15:53:00 | On 06/09/2007 at 1100 CDT, Browns Ferry Unit 1 received an automatic SCRAM due to a Turbine Trip Signal caused by a Moisture Separator Drain Tank Level High. All control rods inserted and all systems responded as required to the automatic SCRAM signal. Two Main Steam Relief Valves (MSRVs) momentarily lifted in response to the pressure transient. No Emergency Core Cooling System (ECCS) initiations occurred as a result of the SCRAM. Reactor water level lowered below Level 3 (+2") as a result of the SCRAM and was recovered to the normal level band by the reactor feed pumps (RFPs). The expected Primary Containment Isolation System (PCIS) Groups 2, 3, 6, and 8 isolations were received due to reactor water level lowering below Level 3 (+2") with all systems isolating as required. Additionally, the expected initiation of the RPT breakers from the turbine trip was received which resulted in the trip of both reactor recirculation pumps. Reactor pressure is being controlled using Main Steam Bypass Valves. Reactor Level is being maintained in band using RFPs. Cooldown is in progress to Mode 4. Investigation into the event is proceeding. The NRC Senior Resident Inspector has been informed of this event. This event is reportable under 10CFR50.72(b)(2)(iv)(B) 'any event or condition that results in a valid actuation of the Reactor Protection System'; 10 CFR50.72(b)(3)(iv)(A), ' Any event that results in an actuation of the specified systems'. This event also requires a 60 day written report in accordance with 10CFR50.73(a)(2)(iv)(A).
Follow-up review of the reported reactor scram revealed that the Group 8 isolation did not function as required. Specifically, the licensee provided the update below concerning the function of one of the reactor's five Traversing Incore Probes (TIP) that had been used the previous day for flux mapping and were in the drywell (not fully retracted) to permit decay when the scram occurred. The Group 8 isolation signal received during Unit 1 Rx SCRAM on 06/09/2007 @ 1100 did not automatically go to completion as designed. The 'D' TIP failed to automatically withdraw as required. When the TIP was manually withdrawn, the TIP Ball valve closed as required. The local resident was notified. A work order and PER was written to correct the deficiency. The other four TIPs did retract and the corresponding ball valves shut as expected. R2DO (Fredrickson) notified.
Review of available data indicates that no Main Steam safety relief valves (MSRVs) opened in response to the Unit 1 reactor scram on 06-09-2007. There were no indications of an open MSRV on any discharge tailpipe thermocouple or acoustic monitor. Initial indications of the discharge tailpipe thermocouples for MSRVs 1-PCV-1-5, 1-PCV-1-30, and 1-PCV-1-31 did indicate slight increases in temperature (5 to 18 degrees F) as reactor pressure decreased, which resulted in the initial assumption of two SRVs opening. However, this behavior is a classical indication of slight main seat leakage. This equipment condition is under review via an open PER. The multiple reactor pressure instrumentation responses were reviewed. The peak reactor pressure was indicated at approximately 1093 psig which is 42 psi below the lowest nominal MSRV setpoint. Based upon the observed peak reactor pressure and no indication of an MSRV opening, it would appear that the MSRVs performed as required to during the reactor pressure transient event. The licensee will notify the NRC Resident Inspector. Notified R2DO(Shaeffer). |
| ENS 43381 | 24 May 2007 04:42:00 | On 05/24/2007 at 0211 CDT Browns Ferry Unit 1 initiated a Manual reactor SCRAM due to an Electro-Hydraulic Control (EHC) System pressure lowering and reservoir level lowering due to an EHC system leak. The leak was from #6 Main Turbine Combined Intermediate Valve (CIV). All Systems responded as required to the manual SCRAM signal. No Emergency Core Cooling System (ECCS) initiations occurred as a result of the manual SCRAM signal. Reactor water level was maintained in the normal band during the SCRAM. There were no Primary Containment Isolation signals received during the SCRAM. The EHC leak was stopped due to reservoir level depletion and EHC pumps being secured. There were no indications of main steam relief valves (MSRVs) opening. Reactor pressure is being controlled using Main Steam Line Drains. Reactor Level is being maintained in band using Control Rod Drive pumps. Repair of the EHC leak is in progress. The Scram was characterized as uncomplicated. All rods fully inserted. The only significant equipment out of service at the time was RCIC. When the leak was initially discovered, it was about 60 drops per minute. When repairs were attempted, the piping separated and approximately 600 gallons of EHC fluid was discharged out the break onto the turbine building floor. Cleanup of the EHC fluid is in progress and environmental monitoring is in place to assure no offsite release of the spill. The licensee notified the NRC Resident Inspector. |