05000259/LER-2011-002

LER-2011-002, 1 of 12 I

Browns Ferry Nuclear Plant (Bfn) Unit 1
Event date:	04-28-2011
Report date:	03-21-2012
Reporting criterion:	10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications 10 CFR 50.73(a)(2)(v)(B), Loss of Safety Function - Remove Residual Heat 10 CFR 50.73(a)(2)(iv)(B), System Actuation 10 CFR 50.73(a)(2)(iv)(A), System Actuation
2592011002R01 - NRC Website

I. PLANT CONDITION(S)

On April 27, 2011, severe weather in the Tennessee Valley Service Area caused grid instability and a loss of all 500-kV offsite power sources that resulted in a scram of all three Browns Ferry Nuclear Plant (BFN) units. At the time of the event being reported [April 28, 2011, at 2338 hours0.0271 days <br />0.649 hours <br />0.00387 weeks <br />8.89609e-4 months <br /> Central Daylight Time (CDT)], BFN Units 1, 2, and 3 were in Mode 4 (Cold Shutdown) with shutdown 4-kV buses supplied by seven of eight onsite emergency diesel generators (EDG) [EK].

II. DESCRIPTION OF EVENT

A. Event

On April 28, 2011, at 2338 hours0.0271 days <br />0.649 hours <br />0.00387 weeks <br />8.89609e-4 months <br /> CDT, seven of eight EDGs were in service to provide AC power for emergency core cooling loads. Operations personnel observed a small leak on the governor hydraulic oil system piping for the Unit 1/2 C EDG. When the piping was found leaking, Operations personnel began to switch Residual Heat Removal (RHR) [BO] pumps to unload the Unit 1/2 C EDG. The leak rapidly progressed from 1 drop per minute to a steady stream/spray and upon witnessing worsening voltage and frequency fluctuations; Operations personnel initiated an emergency shutdown of the Unit 1/2 C EDG. Upon loss of the Unit 1/2 C EDG, the C 4-kV Shutdown Board [EB] de-energized. This resulted in a loss of Shutdown Cooling (SDC) on Units 1 and 2. Unit 1 SDC was lost due to a Group 2 Primary Containment Isolation System (PCIS) [JE] actuation from the loss of the C 4-kV shutdown board. SDC was restored to Unit 1 in 47 minutes after the PCIS actuation and SDC was restored to Unit 2 four minutes after the failure. While the Unit 1/2 C EDG was out of service, the failed fitting was replaced with a like-for-like fitting. The failed fitting was sent to an offsite laboratory for failure analysis.

As a result of performing a past operability evaluation on the Unit 1/2 C EDG, it was determined the Unit 1/2 C EDG would have been unable to perform its specified safety function from April 1, 2011, at 1526 hours0.0177 days <br />0.424 hours <br />0.00252 weeks <br />5.80643e-4 months <br /> CDT until April 30, 2011, at 1047 hours0.0121 days <br />0.291 hours <br />0.00173 weeks <br />3.983835e-4 months <br /> CDT, when the failed fitting was replaced and post maintenance testing was successfully completed. In addition, it has been determined, as a result of performing a separate past operability evaluation on the Unit 1/2 A EDG, that the Unit 1/2 A EDG would have also been unable to perform its specified safety function during this time period. The Unit 1/2 A EDG inoperability is addressed in B. Inoperable Structures, Components, or Systems that Contributed to the Event Loss of offsite power was a contributor to this event.

C. Dates and Approximate Times of Major Occurrences April 5, 2011, at 2208 hours0.0256 days <br />0.613 hours <br />0.00365 weeks <br />8.40144e-4 months <br /> CDT Unit 2 enters Mode 2 from refueling outage that started on February 26, 2011, at 0001 hours1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br /> Central Standard Time.

1 1 April 24, 2011, at 2003 hours0.0232 days <br />0.556 hours <br />0.00331 weeks <br />7.621415e-4 months <br /> CDT April 27, 2011, at 1636 hours0.0189 days <br />0.454 hours <br />0.00271 weeks <br />6.22498e-4 months <br /> CDT April 28, 2011, at 0243 hours0.00281 days <br />0.0675 hours <br />4.017857e-4 weeks <br />9.24615e-5 months <br /> CDT April 28, 2011, at 0545 hours0.00631 days <br />0.151 hours <br />9.011243e-4 weeks <br />2.073725e-4 months <br /> CDT April 28, 2011, at 1337 hours0.0155 days <br />0.371 hours <br />0.00221 weeks <br />5.087285e-4 months <br /> CDT April 28, 2011, at 2330 hours0.027 days <br />0.647 hours <br />0.00385 weeks <br />8.86565e-4 months <br /> CDT April 28, 2011, at 2338 hours0.0271 days <br />0.649 hours <br />0.00387 weeks <br />8.89609e-4 months <br /> CDT April 28, 2011, at 2342 hours0.0271 days <br />0.651 hours <br />0.00387 weeks <br />8.91131e-4 months <br /> CDT April 29, 2011, at 0025 hours2.893519e-4 days <br />0.00694 hours <br />4.133598e-5 weeks <br />9.5125e-6 months <br /> CDT April 30, 2011, at 1047 hours0.0121 days <br />0.291 hours <br />0.00173 weeks <br />3.983835e-4 months <br /> CDT May 2, 2011, at 2010 hours0.0233 days <br />0.558 hours <br />0.00332 weeks <br />7.64805e-4 months <br /> CDT 1

D. Other Systems or Secondary Functions Affected

There were no other systems or secondary functions affected.

E. Method of Discovery

Operations personnel were continuously monitoring the EDGs for leaks, abnormal noises, and vibration. Operations personnel observed a small leak (1 drop per minute) on the governor hydraulic oil system piping for the Unit 1/2 C EDG.

F. Operator Actions

The Unit 1/2 C EDG oil leak rapidly progressed from 1 drop per minute to a steady stream/spray. Upon witnessing worsening voltage and frequency fluctuations, Operations personnel initiated an emergency shutdown of the Unit 1/2 C EDG.

G. Safety System Responses

During the loss of SDC event, the Technical Specifications (TS) required Emergency Core Cooling System (ECCS) subsystems were Operable to ensure adequate core cooling.

III. CAUSE OF THE EVENT

This LER addresses the cause of the failure of the Unit 1/2 C EDG. The cause of the failure of the Unit 1/2 A EDG is addressed in LER 50-259/2011-003-01.

A. Immediate Cause

The immediate cause of this event was a leaking 1/8-inch threaded brass fitting on the governor-to-governor booster pump hydraulic oil piping of the Unit 1/2 C EDG.

B. Root Cause

The root cause was determined to be less than adequate design of the Unit 1/2 C EDG governor hydraulic oil piping to compensate for vibration loading. As a result, the 1/8-inch threaded brass fitting failed due to fatigue from cyclic vibration loads transmitted from the EDG governor.

IV. ANALYSIS OF THE EVENT

The Tennessee Valley Authority (WA) is reporting this event in accordance with 10 CFR 50.73(a)(2)(iv)(A), as any event or condition that resulted in manual or automatic actuation of any of the systems listed in 10 CFR 50.73(a)(2)(iv)(B). This event is also reportable in accordance with 10 CFR 50.73(a)(2)(v)(B), as an event that could have prevented the fulfillment of a safety function for systems needed to remove decay heat.

The Unit 1/2 C EDG is a common EDG which feeds Unit 1 and Unit 2 equipment. Loss of the Unit 1/2 C EDG also caused a loss of the 1B Reactor Protection System (RPS) [JC] because the 1B RPS is fed from the 480V Reactor Motor Operated Valve Board [ED] 1B, which is fed from the 480V Shutdown Board [ED] 1B, which is fed from the C 4-kV Shutdown Board. Loss of power to the 1B RPS caused PCIS Group 2, 3, 6, and 8 isolations. Unit 1 SDC was lost due to the Group 2 PCIS isolation. SDC was restored 47 minutes later for Unit 1 in accordance with Abnormal Operating Instruction (A01) 1-A01-74, Loss of Shutdown Cooling. In addition to the loss of SDC, automatic initiation of the three trains of Standby Gas Treatment (SGT) System [BH], automatic initiation of one train of Control Room Emergency Ventilation (CREV) System [VI], a trip of the Reactor Water Cleanup System [CE] (due to loss of suction on PCIS isolation), and loss of the A Control Air System [LE] compressor occurred.

The 2B RHR pump is fed by the C 4-kV Shutdown Board, so that pump was lost resulting in a momentary suspension of SDC to Unit 2. The 2D RHR pump was used to restore SDC to Unit 2 four minutes after the Unit 1/2 C EDG was shutdown.

Based on the following, TVA is also reporting this event in accordance with 10 CFR 50.73(a)(2)(i)(B), as an operation or condition that is prohibited by the plant's TS.

As a result of performing a past operability evaluation on the Unit 1/2 C EDG, it was determined the Unit 1/2 C EDG would have been unable to perform its specified safety function from April 1, 2011, at 1526 hours0.0177 days <br />0.424 hours <br />0.00252 weeks <br />5.80643e-4 months <br /> CDT until April 30, 2011, at 1047 hours0.0121 days <br />0.291 hours <br />0.00173 weeks <br />3.983835e-4 months <br /> CDT, when the failed fitting was replaced and post maintenance testing was successfully completed. The determination was based on the results of an evaluation of the Unit 1/2 C EDG operating history and the cause of the failure. In addition, it has been determined, as a result of performing a separate past operability evaluation on the Unit 1/2 A EDG, that the Unit 1/2 A EDG would have also been unable to perform its specified safety function during this time period. The Unit 1/2 A EDG inoperability is addressed in LER 50-259/2011-003-01. Based on the results of these past operability evaluations, two Unit 1/2 EDGs were inoperable concurrently.

During this time period, the status of the three BFN units was as follows.

• Unit 1 was in Mode 1 until the unit automatically scrammed on April 27, 2011, at 1636 hours0.0189 days <br />0.454 hours <br />0.00271 weeks <br />6.22498e-4 months <br /> CDT (entering Mode 3) as a result of the loss of all 500-kV offsite power sources. Unit 1 subsequently entered Mode 4 on April 28, 2011, at 1337 hours0.0155 days <br />0.371 hours <br />0.00221 weeks <br />5.087285e-4 months <br /> CDT.

• Unit 2 was in a refueling outage and started up from this refueling outage and subsequently transitioned to Mode 1 and remained there until the unit automatically scrammed on April 27, 2011, at 1636 hours0.0189 days <br />0.454 hours <br />0.00271 weeks <br />6.22498e-4 months <br /> CDT (entering Mode 3) as a result of the loss of all 500-kV offsite power sources. Unit 2 subsequently entered Mode 4 on April 28, 2011, at 0545 hours0.00631 days <br />0.151 hours <br />9.011243e-4 weeks <br />2.073725e-4 months <br /> CDT.

• Unit 3 was in Mode 1 until the unit automatically scrammed on April 27, 2011, at 1636 hours0.0189 days <br />0.454 hours <br />0.00271 weeks <br />6.22498e-4 months <br /> CDT (entering Mode 3) as a result of the loss of all 500-kV offsite power sources. Unit 3 subsequently entered Mode 4 on April 28, 2011, at 0243 hours0.00281 days <br />0.0675 hours <br />4.017857e-4 weeks <br />9.24615e-5 months <br /> CDT.

BFN Units 1 and 2 TS Limiting Condition for Operation (LCO) 3.8.1, "AC Sources - Operating," requires, in part, that Unit 1/2 EDGs be Operable in Modes 1, 2, and 3.

The Unit 1/2 EDGs consist of the A, B, C, and D EDGs. If two or more Unit 1/2 EDGs are inoperable, TS 3.8.1 Required Action H.1 requires all but one EDG to be restored to Operable status within 2 hours2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br />. If this TS 3.8.1 Required Action is not met within 2 hours2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br />, then both Units 1 and 2 are required to be in Mode 3 within 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br /> and in Mode 4 within 36 hours4.166667e-4 days <br />0.01 hours <br />5.952381e-5 weeks <br />1.3698e-5 months <br />. Since it was not recognized that the two Unit 1/2 EDGs were inoperable concurrently until the completion of the two past operability evaluations, BFN Units 1 and 2 operated with inoperable EDGs longer than allowed by the TS.

In addition, BFN Unit 2 started up from a refueling outage and transitioned from Mode 4 to Mode 2 on April 5, 2011, at 2208 hours0.0256 days <br />0.613 hours <br />0.00365 weeks <br />8.40144e-4 months <br /> CDT while the Unit 1/2 A EDG and Unit 1/2 C EDG were inoperable. LCO 3.0.4 prohibits Mode changes when a LCO is not met except under certain conditions that were not applicable to this event.

Therefore, BFN Unit 2 entered the applicability of TS LCO 3.8.1 without the required EDGs Operable contrary to the requirements of LCO 3.0.4.

BFN Units 1 and 2 TS LCO 3.8.1, also requires, in part, that two qualified circuits between the offsite transmission network and the onsite Class 1 E AC Electrical Power Distribution System be Operable in Modes 1, 2 and 3. Upon loss of all required offsite power sources concurrent with the two inoperable Unit 1/2 EDGs, TS 3.8.1 Required Action J.1 requires immediate entry into LCO 3.0.3. LCO 3.0.3 requires action be initiated within 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br /> to place the unit in Mode 2 within 10 hours1.157407e-4 days <br />0.00278 hours <br />1.653439e-5 weeks <br />3.805e-6 months <br />, Mode 3 within 13 hours1.50463e-4 days <br />0.00361 hours <br />2.149471e-5 weeks <br />4.9465e-6 months <br />, and Mode 4 within 37 hours4.282407e-4 days <br />0.0103 hours <br />6.117725e-5 weeks <br />1.40785e-5 months <br />. These requirements were satisfied as a result of the automatic scrams that occurred on April 27, 2011, at 1636 hours0.0189 days <br />0.454 hours <br />0.00271 weeks <br />6.22498e-4 months <br /> CDT, placing each unit in Mode 3, and subsequent cooldown of each of the units to Mode 4 within the required time periods.

BFN Units 1 and 2 TS LCO 3.8.2, "AC Sources - Shutdown," requires, in part, two of the four Unit 1/2 EDGs each capable of supplying one 4-kV shutdown board of the onsite Class 1 E AC electrical power distribution subsystems required by LCO 3.8.8, "Distribution Systems - Shutdown," to be Operable. LCO 3.8.8 requires the necessary portions of the AC and DC electrical power distribution subsystems to be Operable to support equipment required to be Operable in Modes 4 and 5 and during movement of irradiated fuel assemblies in the secondary containment. In the event, one or more required Unit 1/2 EDGs are inoperable, TS 3.8.2 Required Actions B.1.1, B.1.2, B.1.3, and B.1.4 require immediate suspension of Core Alterations, suspension of movement of irradiated fuel assemblies in secondary containment, initiation of action to suspend operations with the potential for draining the reactor vessel (OPDRVs), and initiation of action to restore the required Unit 1/2 EDGs to Operable status.

During the time period that Unit 2 was in Mode 4 at the end of its refueling outage (April 1, 2011, to April 5, 2011), it is likely that either the Unit 1/2 A EDG and/or Unit 1/2 C EDG were credited with satisfying the requirements of LCO 3.8.2. However, no Core Alterations, no movement of irradiated fuel assemblies in secondary containment, and no OPDRVs were in progress. Therefore, the associated TS 3.8.2 Required Actions were satisfied. Because the inoperability of the Unit 1/2 A EDG and Unit 1/2 C EDG was not recognized, the TS 3.8.2 Required Action B.1.4 to immediately initiate action to restore the required Unit 1/2 EDGs to Operable status was not satisfied.

After BFN Units 1 and 2 automatically scrammed on April 27, 2011, and Mode 4 was entered for each of the units, no Core Alterations, no movement of irradiated fuel assemblies in secondary containment, and no OPDRVs occurred. Therefore, the associated TS 3.8.2 Required Actions were satisfied. Because the inoperability of the Unit 1/2 A EDG and Unit 1/2 C EDG was not recognized, the TS 3.8.2 Required Action B.1.4 to immediately initiate action to restore the required Unit 1/2 EDGs to Operable status was not satisfied.

BFN Unit 3 TS LCO 3.8.1 requires, in part, that Unit 3 EDGs be Operable and the Unit 1/2 EDGs capable of supplying the Unit 1 and 2 4-kV shutdown boards required by LCO 3.8.7, "Distribution Systems - Operating," be Operable in Modes 1, 2, and 3.

Unit 3 TS LCO 3.8.7.g requires the Unit 1 and 2 AC and DC boards required by LCO 3.6.4.3, "Standby Gas Treatment (SGT) System," and LCO 3.7.3, "Control Room Emergency Ventilation (CREV) System," to be Operable (i.e., the Unit 1/2 A EDG and Unit 1/2 D EDG are required to be Operable). The Unit 3 EDGs consist of the 3A, 3B, 3C, and 3D EDGs. If one Unit 3 EDG is inoperable, TS 3.8.1 Required Action B.4, applicable at the time of this event, required the Unit 3 EDG to be restored to Operable status within 7 days. The 3B EDG was declared inoperable for a planned maintenance outage on April 24, 2011, at 2003 hours0.0232 days <br />0.556 hours <br />0.00331 weeks <br />7.621415e-4 months <br /> CDT. If this TS 3.8.1 Required Action is not met, then Unit 3 is required to be in Mode 3 within 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br /> and in Mode 4 within 36 hours4.166667e-4 days <br />0.01 hours <br />5.952381e-5 weeks <br />1.3698e-5 months <br />. For the 3B EDG, the TS 3.8.1 Required Actions were satisfied as a result of the automatic scram that occurred on April 27, 2011, at 1636 hours0.0189 days <br />0.454 hours <br />0.00271 weeks <br />6.22498e-4 months <br /> CDT, placing the unit in Mode 3, and subsequent cooldown of the unit to Mode 4 within the required time periods. However, with one or more required Unit 1/2 EDGs inoperable (in this case, the Unit 1/2 A EDG), TS 3.8.1 Required Action K.2 requires the affected SGT and CREV subsystems to be declared inoperable within 30 days. Since it was not recognized that the Unit 1/2 A EDG was inoperable until the completion of the past operability evaluation, BFN Unit 3 operated with an inoperable required Unit 1/2 EDG (i.e., Unit 1/2 A EDG) longer than allowed by the TS.

BFN Unit 3 TS LCO 3.8.1 also requires, in part, that two qualified circuits between the offsite transmission network and the onsite Class 1 E AC Electrical Power Distribution System be Operable in Modes 1, 2 and 3. Upon loss of required offsite power sources concurrent with one Unit 3 EDG inoperable, TS 3.8.1 Required Action J.1 requires immediate entry into LCO 3.0.3. LCO 3.0.3 requires action be initiated within 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br /> to place the unit in Mode 2 within 10 hours1.157407e-4 days <br />0.00278 hours <br />1.653439e-5 weeks <br />3.805e-6 months <br />, Mode 3 within 13 hours1.50463e-4 days <br />0.00361 hours <br />2.149471e-5 weeks <br />4.9465e-6 months <br />, and Mode 4 within 37 hours4.282407e-4 days <br />0.0103 hours <br />6.117725e-5 weeks <br />1.40785e-5 months <br />. These requirements were satisfied as a result of the automatic scram that occurred on April 27, 2011, at 1636 hours0.0189 days <br />0.454 hours <br />0.00271 weeks <br />6.22498e-4 months <br /> CDT, placing the unit in Mode 3, and subsequent cooldown of the unit to Mode 4 within the required time periods.

BFN Unit 3 TS LCO 3.8.2 requires, in part, two of the four Unit 3 EDGs each capable of supplying one 4-kV shutdown board of the onsite Class 1 E AC electrical power distribution subsystems required by LCO 3.8.8 to be Operable. LCO 3.8.8 requires the necessary portions of the AC and DC electrical power distribution subsystems to be Operable to support equipment required to be Operable in Modes 4 and 5 and during movement of irradiated fuel assemblies in the secondary containment. In the event, one or more required Unit 3 EDGs are inoperable, TS 3.8.2 Required Actions B.1.1, B.1.2, B.1.3, and B.1.4 require immediate suspension of Core Alterations, suspension of movement of irradiated fuel assemblies in secondary containment, initiation of action to suspend OPDRVs, and initiation of action to restore the required Unit 3 EDGs to Operable status. After BFN Unit 3 automatically scrammed on April 27, 2011, and Mode 4 was entered, no Core Alterations, no movement of irradiated fuel assemblies in secondary containment, and no OPDRVs occurred. In addition, actions continued to restore the 3B EDG to Operable status. Therefore, these associated TS 3.8.2 Required Actions were satisfied.

WA is also submitting this report in accordance with 10 CFR 21 due to the root cause determination of inadequate design of the Unit 1/2 C EDG governor-to-governor booster pump hydraulic oil line. See Part VII.F of this report for details.

V. ASSESSMENT OF SAFETY CONSEQUENCES

This event could have been significant from a nuclear safety standpoint. The EDGs are one of the most important BFN systems as determined by the plant's Probabilistic Risk Assessment. Loss of an EDG limits the capability for the unit to respond to an accident or transient when accompanied by a loss of offsite power. The Unit 1/2 C EDG operated for approximately 31 hours3.587963e-4 days <br />0.00861 hours <br />5.125661e-5 weeks <br />1.17955e-5 months <br /> prior to Operations personnel performing an emergency shutdown. The 31 hours3.587963e-4 days <br />0.00861 hours <br />5.125661e-5 weeks <br />1.17955e-5 months <br /> of operation did not meet the 7-day mission time of the Unit 1/2 C EDG. In addition, the Unit 1/2 A EDG operated for approximately 4 days and 13 hours1.50463e-4 days <br />0.00361 hours <br />2.149471e-5 weeks <br />4.9465e-6 months <br /> prior to the output breaker trip. This period of operation did not meet the 7-day mission time of the Unit 1/2 A EDG. If multiple EDGs had experienced these failures concurrently, BFN could have lost its ability to provide power to components essential for core cooling, heat removal, and accident mitigation. However, in actuality the Unit 1/2 C EDG was returned to Operable status prior to the Unit 1/2 A EDG output trip breaker event. Based on this operating experience, it is reasonable to assume that both the Unit 1/2 A EDG and Unit 1/2 C EDG would not have been concurrently unavailable.

During the loss of SDC event, there was sufficient redundancy to support the core cooling requirements for Units 1 and 2 since the remaining two Unit 1/2 EDGs and the remaining three Unit 3 EDGs were Operable and the required ECCSs were Operable. In addition during the remainder of the time of concurrent EDG inoperabilities, the Unit 1/2 EDGs and the Unit 3 EDGs could have been paralleled, as shown in the Updated Final Safety Analysis Report Figure 8.5-24 (e.g., 4-kV shutdown board A to 4-kV shutdown board 3EA), to provide power to the necessary components to maintain adequate core cooling, heat removal capability, and SGT and CREV subsystem capabilities for each of the units. Therefore, this event was of minimal safety significance.

and Unit 2. Unit 1 restored SDC in 47 minutes after the failure and SDC was restored on Unit 2 four minutes after the failure. This information is relevant because the time to boil was approximately 2 hours2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br /> for each unit. In addition, TS 3.4.8, "Residual Heat Removal (RHR) Shutdown Cooling System - Cold Shutdown," contains provisions that allow both RHR Shutdown Cooling subsystems to be out of service for up to one hour. Therefore, while this event could have been significant from a radiological safety standpoint, in actuality it had minimal safety significance.

In addition, the equivalent 1/8-inch threaded brass fittings for the Unit 1/2 A, B, and D EDGs were removed and submitted for laboratory analysis to determine if there was any evidence of cracking as identified on the Unit 1/2 C EDG. A Liquid Penetrant Testing (PT) nondestructive examination was performed on each of the fittings and no indication of cracking was identified. The Unit 1/2 A, B, and D EDGs ran for approximately 5 days following the loss of offsite power event that began on April 27, 2011. Based on the approximate 5-day run time of these EDGs and the laboratory analysis that found no cracking of the fittings, it can be concluded that the 7-day mission time for these EDGs would most likely have not been affected by this failure mode.

Evaluations of the risk associated with the separate unavailability of Unit 1/2 A EDG and the unavailability of the Unit 1/2 C EDG were also performed. The evaluation for the Unit 1/2 A EDG considered that this EDG was unavailable from May 2, 2011, at 0626 CDT until May 7, 2011, 0439 CDT. The evaluation for the Unit 1/2 C EDG considered that this EDG was unavailable from April 28, 2011, at 2338 CDT until April 30, 2011, at 1047 CDT. For the Unit 1/2 A EDG unavailability and Unit 1/2 C EDG unavailability, the risk impacts were determined to be small.

TVA has concluded that there was no significant reduction to the health and safety of the public for this event.

VI. CORRECTIVE ACTIONS - The corrective actions are being managed by TVA's corrective action program. The corrective actions addressed in this LER address the cause of the failure of the Unit 1/2 C EDG. The corrective actions that address the cause of the failure of the Unit 1/2 A EDG are addressed in LER 50-259/2011-003-01.

A. Immediate Corrective Actions

The following immediate corrective actions were taken:

• Operations personnel performed an emergency shutdown of the Unit 1/2 C EDG and all loads were transferred to an operating EDG.

• Replaced failed 1/8-inch brass threaded fitting (like-for-like) on the Unit 1/2 C EDG governor hydraulic oil system.

• The failed fitting was recovered and sent to Alstom TTTM Laboratory, Chattanooga, Tennessee, for failure analysis.

• Performed vibration testing on all four Unit 1/2 EDG governor oil piping.

Other corrective actions:

• Verify as-found torque values on the Unit 1/2 C EDG governor bolting.

Perform analysis of the results.

• Review the small bore ( Pressure Coolant Injection System [BJ] and determine its acceptability for vibration loading considering tubing weight, dimensions, operating experience, and any available vibration data.

• Review the small bore ( Core Isolation Cooling System [BN] and determine its acceptability for vibration loading considering tubing weight, dimensions, operating experience, and any available vibration data.

• Review the small bore ( EDGs and determine acceptability for vibration loading considering tubing weight, dimensions, operating experience, and any available vibration data.

B. Corrective Actions to Prevent Recurrence

The governor-to-governor booster pump hydraulic oil lines were redesigned and replaced with flexible hose rather than hard tubing. The hard tubing was replaced on all four Unit 1/2 EDGs. In addition, the sister fittings on the Unit 1/2 A, B, and D EDGs were removed for lab analysis to determine if there was any evidence of cracking. A PT nondestructive examination was performed on each of the fittings and no indication of cracking was identified.

The four Unit 3 EDG governor-to-governor booster pump hydraulic oil lines were originally supplied with flexible hose. Therefore, no modifications were necessary for those components.

A. Failed Components

Unit 1/2 C EDG

B. Previous Similar Events

A search of BFN LERs for Units 1, 2, and 3 for approximately the past five years did not identify any similar issues involving cracked or failed tubing threaded fittings for EDGs.

Review of BFN Work Orders (WO) concluded that numerous oil leaks have occurred on the EDGs. However, none of them appeared to be major leaks that caused the EDG to be declared inoperable. There were also no WOs that indicated the failed fitting for this event had ever been replaced. This indicates that the fitting is originally installed equipment (Unit 1/2 EDGs delivered in 1970).

A search of the BFN corrective action program was performed. There were several Problem Evaluation Reports (PERs) that documented oil leaks and oil level issues.

None of the PERs reviewed were associated with fitting failures similar to the current event, in that there were no low stress high cycle fatigue cracks on the EDGs previously identified.

C. Additional Information

The corrective action document for this report is PER 362395.

D. Safety System Functional Failure Consideration

In accordance with NEI 99-02, this event is considered a safety system functional failure due to the loss of shutdown cooling on Unit 1 and Unit 2.

E. Scram With Complications Consideration

This event did not include a reactor scram.

F. 10 CFR Part 21 Reporting Requirements The following information is provided to meet the requirements of 10 CFR 21.21(d)(4)(i) thru (viii) (i) Name and address of the individual or individuals informing the Commission.

K. J. Polson Site Vice President Tennessee Valley Authority Browns Ferry Nuclear Plant Post Office Box 2000 Decatur, Alabama 35609-2000 (ii) Identification of the facility, the activity, or the basic component supplied for such facility or such activity within the United States which fails to comply or contains a defect.

Facility: Browns Ferry Nuclear Plant Basic component which contains a defect:

Unit 1/2 C EDG, Model 999-20, (Engine Model Number 20-645E4, order number 9464).

(iii) Identification of the firm constructing the facility or supplying the basic component which fails to comply or contains a defect.

Basic component supplier:

General Motors, Electro-Motive Division, La Grange, Illinois (iv) Nature of the defect or failure to comply and the safety hazard which is created or could be created by such defect or failure to comply.

Nature of the defect:

The root cause was determined to be less than adequate design of the Unit 1/2 C EDG governor hydraulic oil piping to compensate for vibration loading. As a result, the 1/8-inch brass threaded fitting failed due to fatigue from cyclic vibration loads transmitted from the EDG governor.

Safety hazard which could be created by such defect:

Loss of an EDG limits the capability for the unit to respond to an accident or transient when accompanied by a loss of offsite power.

1 (v) The date on which the information of such defect or failure to comply was obtained.

BFN Site Engineering (Procurement Engineering Group) completed the Part 21 evaluation on June 21, 2011.

(vi) In the case of a basic component which contains a defect or fails to comply, the number and location of all such components in use at, supplied for, or being supplied for one or more facilities or activities subject to the regulations in this part.

Other 1/8-inch brass threaded fittings of this type were used in designs supplied by the vendor for the BFN Unit 1/2 A, B, and D EDGs.

(vii) The corrective action which has been, is being, or will be taken; the name of the individual or organization responsible for the action; and the length of time that has been or will be taken to complete the action.

As stated in Section VI.B of this report, the governor-to-governor booster pump hydraulic oil lines were redesigned and replaced with flexible hose rather than hard tubing. The hard tubing was replaced on all four of the Unit 1/2 EDGs.

The four Unit 3 EDG governor-to-governor booster pump hydraulic oil lines were originally supplied with flexible hose. Therefore, the failed component does not exist on the four Unit 3 EDGs.

The individual responsible is K. J. Poison, Site Vice President of BFN.

The action was completed on June 27, 2011.

VIII. COMMITMENTS

There are no commitments.