05000296/LER-2013-001, Regarding Inoperable Emergency Diesel Generators Due to Failed or Degraded Electric Generator Casing Fan Bearings
| ML13074A051 | |
| Person / Time | |
|---|---|
| Site: | Browns Ferry  |
| Issue date: | 03/11/2013 |
| From: | Polson K Tennessee Valley Authority |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| LER 13-001-00 | |
| Download: ML13074A051 (14) | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications 10 CFR 50.73(a)(2)(ii)(B), Unanalyzed Condition 10 CFR 50.73(a)(2)(v)(A), Loss of Safety Function - Shutdown the Reactor 10 CFR 50.73(a)(2)(vii), Common Cause Inoperability 10 CFR 50.73(a)(2)(i) 10 CFR 50.73(a)(2)(ii)(A), Seriously Degraded 10 CFR 50.73(a)(2)(viii)(A) 10 CFR 50.73(a)(2)(viii)(B) 10 CFR 50.73(a)(2)(iii) 10 CFR 50.73(a)(2)(ix)(A) 10 CFR 50.73(a)(2)(iv)(A), System Actuation 10 CFR 50.73(a)(2)(x) 10 CFR 50.73(a)(2)(v)(B), Loss of Safety Function - Remove Residual Heat 10 CFR 50.73(a)(2)(i)(A), Completion of TS Shutdown 10 CFR 50.73(a)(2)(v), Loss of Safety Function |
| 2962013001R00 - NRC Website | |
text
Tennessee Valley Authority, Post Office Box 2000, Decatur, Alabama 35609-2000 March 11, 2013 10 CFR 50.73 ATTN: Document Control Desk U.S. Nuclear Regulatory Commission Washington, D.C. 20555-0001 Browns Ferry Nuclear Plant, Unit 3 Facility Operating License No. DPR-68 NRC Docket No. 50-296
Subject:
Licensee Event Report 50-296/2013-001-00 The enclosed Licensee Event Report provides details of degraded or failed blower bearings on the 3A, 3B and 3D emergency diesel generators. The Tennessee Valley Authority (IVA) is submitting this report in accordance with Title 10 of the Code of Federal Regulations (10 CFR) 50.73(a)(2)(i)(B), 10 CFR 50.73(a)(2)(ii)(B),
10 CFR 50.73(a)(2)(v)(A) and (D), and 10 CFR 50.73(a)(2)(vii).
Further analysis of this condition is ongoing. Upon completion of the analysis, the TVA will submit a supplement to this LER with the results of the additional analysis of safety consequences.
There are no new regulatory commitments contained in this letter. Should you have any questions concerning this submittal, please contact J. E. Emens, Jr., Nuclear Site Licensing Manager, at (256) 729-2636.
Respectfully, K. J. Poison Vice President
Enclosure:
Licensee Event Report 50-296/2013-001 Inoperable Emergency Diesel Generators due to Failed or Degraded Electric Generator Casing Fan Bearings cc: See Page 2
ý-A
U.S. Nuclear Regulatory Commission Page 2 March 11, 2013 cc (w/ Enclosure):
NRC Regional Administrator - Region II NRC Senior Resident Inspector - Browns Ferry Nuclear Plant
ENCLOSURE Browns Ferry Nuclear Plant Unit 3 Licensee Event Report 50-29612013-001-00 Inoperable Emergency Diesel Generators due to Failed or Degraded Electric Generator Casing Fan Bearings See Enclosed
NRC FORM 366 U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY OMB NO. 3150-0104 EXPIRES 10/31/2013 (10-2010)
, the NRC may not conduct or sponsor, and a person is not required to respond to, the information collection.
- 3. PAGE Browns Ferry Nuclear Plant, Unit 3 05000296 1 of 11
- 4. TITLE: Inoperable Emergency Diesel Generators due to Failed or Degraded Electric Generator Casing Fan Bearings
- 5. EVENT DATE
- 6. LER NUMBER
- 7. REPORT DATE
- 8. OTHER FACILITIES INVOLVED M
FACILITY NAME DOCKET NUMBER SEQUENTIAL REV MONTH DAY YEAR N/A 05000 j
FACILITY NAME DOCKET NUMBER 01 09 2013 2013 001 00 03 11 2013 N/A 05000
- 9. OPERATING MODE
- 11. THIS REPORT IS SUBMITTED PURSUANT TO THE REQUIREMENTS OF 10 CFR §: (Check all that apply)
El 20.2201(b)
[I 20.2203(a)(3)(i)
El 50.73(a)(2)(i)(C)
N 50.73(a)(2)(vii)
El 20.2201(d)
[I 20.2203(a)(3)(ii)
El 50.73(a)(2)(ii)(A)
[I 50.73(a)(2)(viii)(A)
El 20.2203(a)(1) 0l 20.2203(a)(4) 0 50.73(a)(2)(ii)(B)
El 50.73(a)(2)(viii)(B) 0_ 20.2203(a)(2)(i) 0l 50.36(c)(1)(i)(A)
[] 50.73(a)(2)(iii)
El 50.73(a)(2)(ix)(A)
- 10. POWER LEVEL El 20.2203(a)(2)(ii) 0l 50.36(c)(1)(ii)(A)
El 50.73(a)(2)(iv)(A)
[: 50.73(a)(2)(x)
El 20.2203(a)(2)(iii)
El 50.36(c)(2) 09 50.73(a)(2)(v)(A)
El 73.71(a)(4)
El 20.2203(a)(2)(iv)
El 50.46(a)(3)(ii)
El 50.73(a)(2)(v)(B)
[E 73.71 (a)(5) 100 [1 20.2203(a)(2)(v)
El 50.73(a)(2)(i)(A)
El 50.73(a)(2)(v)(C)
El OTHER El 20.2203(a)(2)(vi) 0 50.73(a)(2)(i)(B) 10 50.73(a)(2)(v)(D)
Specify in Abstract below or inNRC Formn 366A
- 12. LICENSEE CONTACT FOR THIS LER FACILITY NAME TELEPHONE NUMBER (Include Area Code)
Mark Acker, Licensing Engineer 256-729-7533CAU MANU-REPORTABLE
CAUSE
SYS MANU-REPORTABLE SE SYSTEM COMPONENT FACTURER TO EPIX FACTURER TO EPIX E
EK 38 E147 Y
- 14. SUPPLEMENTAL REPORT EXPECTED
- 15. EXPECTED SUBMISSION MONTH DAY YEAR YES (If yes, complete 15. EXPECTED SUBMISSION DATE)
El NO DATE 05 10 2013 ABSTRACT (Limit to 1400 spaces, i.e., approximately 15 single-spaced typewritten lines)
On January 9, 2013, at 0400 Central Standard Time, an Auxiliary Unit Operator (AUO) performing rounds near the 3D Emergency Diesel Generator (EDG) discovered metal residue around the blower shaft.
Inspection by Maintenance determined the blower bearing had failed. This condition rendered the 3D EDG inoperable. Further investigation into the extent of this condition revealed the lubrication of the 3A and 3B EDG blower bearings was in a degraded condition.
The root causes of this condition are the shielded bearings in the EDG blowers were not adequately assessed on a component level to identify potential failure modes and impacts to EDG operability, and standard vibration data was ineffective in identifying the degradation of the lubrication in the shielded bearings of the BFN, Unit 3, EDG blowers due to the masking effect of the generators' vibrations.
Immediate corrective actions included the inspection and replacement of all diesel blower bearings that have not been replaced since 2012. The corrective actions to prevent recurrence are to determine appropriate Preventive Maintenance strategies for the population of sealed or shielded bearings associated with EDGs and safety or quality related rotating equipment, and to add an additional vibration monitoring point to the EDG blower fan bearings and relocate two existing monitoring points to the drive end bearing housing.
Further analysis of this condition is ongoing. Upon completion of the analysis, the Tennessee Valley Authority will submit a supplement to this LER with the results of the additional analysis of safety consequences.
NRC FORM 366 (10-2010)
I. PLANT CONDITION(S)
At the time of discovery, Browns Ferry Nuclear Plant (BFN), Unit 3, was in Mode 1 at 100 percent rated thermal power.
II. DESCRIPTION OF EVENT
A. Event:
On January 9, 2013, at 0400 Central Standard Time (CST), an Auxiliary Unit Operator (AUO) performing rounds near the 3D Emergency Diesel Generator (EDG) [DG] noticed grease and metallic residue around the shaft leading from the EDG to the generator blower [BLO]. Investigation of this condition led to disassembly of the generator blower assembly where it was discovered that the blower bearing [38] had failed. Further investigation revealed that the blower bearing failed 18 days earlier, on December 22, 2012, during the Post-Maintenance Test (PMT), following the 12 year Preventive Maintenance (PM) task for the 3D EDG. A Past Operability Evaluation (POE) conservatively concluded that the 3D EDG would have been unable to meet its 7 day mission time from April 27, 2011, until January 10, 2013, when the blower bearings were replaced.
Investigation into the extent of this condition revealed the lubrication of the 3A and 3B EDG blower bearings was in a degraded condition. It is unknown if the 3A and 3B EDGs could have met their 7 day mission time. The POEs conservatively concluded, based on information available at the time of the evaluations, that the 3A EDG was inoperable from April 27, 2011, until January 29, 2013, and 3B EDG was inoperable from January 18, 2009, until January 29, 2013. These dates were determined by adding up 7 days of EDG run time prior to blower bearing replacement and are provided as a conservative assumption for the extent of the past inoperability.
Further analysis of this condition is ongoing. Upon completion of the analysis, the Tennessee Valley Authority (TVA) will submit a supplement to this LER with the results of the additional analysis of safety consequences.
B. Inoperable Structures, Components, or Systems that Contributed to the Event:
There were no inoperable structures, components, or systems that contributed to this event.
C. Dates and Approximate Times of Major Occurrences
January 9, 2013, at 0400 CST An AUO discovered metal residue around the 3D EDG blower shaft resulting from blower bearing failure.
January 10, 2013, at 1500 CST The 3D EDG was declared operable after the blower bearings were replaced.
January 28, 2013, at 0044 CST The 3A EDG was declared inoperable for the performance of its 12 year PM.
NRC FORM 368A (10-2010)
January 29, 2013, at 1837 CST The 3A EDG blower bearing lubricant was discovered to be in a degraded condition.
January 29, 2013, at 1837 CST The A and 3B EDG were declared inoperable to evaluate for a common cause failure.
January 29, 2013 The 3A and 38 EDG blower bearings were replaced.
January 30, 2013, at 0030 CST The 3B EDG was declared operable.
January 30, 2013, at 1915 CST The A EDG was declared operable.
February 10, 2013, at 0655 CST The 3A EDG was declared operable after the completion of its 12 year PM.
D. Other Systems or Secondary Functions Affected
The EDGs supply required loads for the safe shutdown and cool down of all three units in the event of loss of offsite power and a design basis event in any one unit. Any system that relies on emergency power from EDGs is potentially affected by this condition.
E. Method of Discovery
On January 9, 2013, at 0400 CST, an AUO performing rounds near the 3D EDG noticed grease and metallic residue around the shaft leading from the EDG to the generator blower. Further investigation concluded the blower bearing had failed.
On January 29, 2013, the 3A EDG blower bearings were replaced during the 3A EDG's 12 year PM. The blower bearings were inspected as part of the extent of condition evaluation from the 3D EDG bearing failure. On January 29, 2013, at 1837 CST, the inspection discovered the 3A EDG blower bearing lubricant to be in a degraded condition. The 3A and 3B EDGs were immediately declared inoperable. Inspection of the 3B EDG blower bearings discovered the blower bearing lubricant was also in a degraded condition.
F. Operator Actions
Operators declared 3D EDG inoperable, entered Technical Specifications (TS) 3.8.1 Actions for BFN, Unit 3, verified that there were no redundant inoperabilities, and walked down all other EDGs for immediate indications of common cause failures.
G. Safety System Responses There were no safety system responses.
III. CAUSE OF THE EVENT
A. Immediate Cause The immediate cause was the absence of lubrication to the internal parts of the 3D EDG blower bearing due to age related breakdown of the grease.
B. Root Causes This condition has two root causes. First, the shielded bearings in the EDG blowers were not adequately assessed on a component level to identify potential failure modes and impacts to EDG operability. Second, standard vibration data was ineffective in identifying the degradation of the lubrication in the shielded bearings of the BFN, Unit 3, EDG blowers due to the masking effect of the generators' vibrations.
C. Contributing Factors Turnover by maintenance personnel was inadequately performed resulting in the night shift crew's failure to notify the day shift crew that two different vibration meters were used during the 3D EDG PMT. This event contributed to the bearing failure remaining unnoticed for 18 days.
IV. ANALYSIS OF THE EVENT
The analysis of this event is ongoing. Upon completion of the analysis, TVA will submit a supplement to this LER with the results of the additional analysis of safety consequences.
The TVA is submitting this report in accordance with Title 10 of the Code of Federal Regulations (10 CFR) 50.73(a)(2)(i)(B), as any operation or condition which was prohibited by the plant's Technical Specifications, 10 CFR 50.73(a)(2)(ii)(B), as any event or condition that resulted in the nuclear power plant being in an unanalyzed condition that significantly degraded plant safety, 10 CFR 50.73(a)(2)(v)(A) and (D), as any event or condition that could have prevented the fulfillment of the safety function of structures or systems that are needed to shut down the reactor and maintain it in a safe shutdown condition or mitigate the consequences of an accident, and 10 CFR 50.73(a)(2)(vii), as any event where a single cause or condition caused at least one independent train or channel to become inoperable in multiple systems or two independent trains or channels to become inoperable in a single system designed to shut down the reactor and maintain it in a safe shutdown condition, remove residual heat, control the release of radioactive material, or mitigate the consequences of an accident.
During the first ten minutes of design basis events, only three of the BFN, Unit 1 and 2, EDGs, along with three of the BFN, Unit 3, EDGs are required to automatically start and come to a ready to load condition. The EDGs must be capable of accepting automatically sequenced plant safety loads. For the long term (greater than 10 minutes),
three of the BFN, Unit 1 and 2, EDGs paralleled with three of the BFN, Unit 3, EDGs, are required to supply all required loads for the safe shutdown and cool down of all three
units in the event of loss of offsite power and a design basis event in any one unit. The degraded blower bearings on the BFN, Unit 3, EDGs is an unanalyzed condition that could have prevented the fulfillment of the safety function of the EDGs which are required to shut down the reactor and maintain it in a safe shutdown condition and mitigate the consequences of an accident.
The BFN, Unit 3, TS LCO 3.8.1, AC Sources - Operating, requires EDGs to be Operable, during Modes 1, 2, and 3. With one BFN, Unit 3, EDG inoperable, TS 3.8.1 Required Action B.1 requires power availability from the offsite transmission network be verified in 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br /> and once per 8 hours9.259259e-5 days <br />0.00222 hours <br />1.322751e-5 weeks <br />3.044e-6 months <br /> thereafter. TS 3.8.1 Required Action B.2 requires the availability of both temporary diesel generators be evaluated in 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br /> and once per 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br /> thereafter. TS 3.8.1 Required Action B.3 requires the required feature(s),
supported by the inoperable BFN, Unit 3, EDG, be declared inoperable when the redundant required feature(s) are inoperable within 4 hours4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br /> from discovery of one inoperable BFN, Unit 3, EDG concurrent with inoperability of redundant required feature(s). TS 3.8.1 Required Action B.4 requires Operations to determine if Operable BFN, Unit 3, EDG(s) are inoperable due to a common cause failure or perform Surveillance Requirement 3.8.1.1 for Operable BFN, Unit 3, EDG(s). With multiple BFN, Unit 3, EDGs inoperable, TS 3.8.1 Required Action H.1 requires all but one BFN, Unit 3, EDGs be restored to Operable status in 2 hours2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br />. If all but one BFN, Unit 3, EDG cannot be restored to Operable status in 2 hours2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br />, while in Mode 1, 2, or 3, TS 3.8.1 Required Actions 1.1 and 1.2 require the unit to be in Mode 3 in 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br /> and in Mode 4 in 36 hours4.166667e-4 days <br />0.01 hours <br />5.952381e-5 weeks <br />1.3698e-5 months <br />.
The BFN, Unit 3, TS LCO 3.8.2, AC Sources - Shutdown, requires two of four BFN, Unit 3, EDGs to be Operable, during Modes 4 and 5 and during movement of irradiated fuel assemblies in secondary containment. With one or more required EDGs inoperable, TS 3.8.2 Required Action B.1 requires immediate suspension of core alterations, immediate suspension of irradiated fuel assembly movement in secondary containment, immediate suspension of Operations with the Potential to Drain the Reactor Vessel, and immediate initiation of actions to restore required EDGs to Operable status.
On January 29, 2013, at 1837 CST, BFN, Unit 3, entered TS 3.8.1 Required Action H.1 due to the concurrent inoperability of 3A and 3B EDGs for blower bearing replacement.
BFN, Unit 3, then entered TS 3.8.1 Required Action 1.1 after 2 hours2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br />. BFN did not make preparations to enter Mode 3 because it was known that the 3B EDG blower bearing replacement would not exceed TS 3.8.1 Required Action 1.1. At 0030 CST on January 30, 2013, 3B EDG was declared operable and BFN exited TS 3.8.1 Required Action H. 1 and 1. 1.
As previously stated, the POEs conservatively concluded, based on information available at the time of the evaluation, that the 3A EDG was inoperable from April 27, 2011, until January 29, 2013, and 3B EDG was inoperable from January 18, 2009, until January 29, 2013.
Based on the conservative assumption in the POEs, the BFN, Unit 3, was considered to have operated with 3B EDG inoperable from January 18, 2009, until April 27, 2011, at
which time the 3A and 3D EDGs became inoperable as well. Since it was not recognized that 3B EDG was inoperable until the completion of the POE, BFN, Unit 3, operated with one inoperable EDG for longer than allowed by TS 3.8.1 Actions.
Based on the conservative assumption in the POEs, the BFN, Unit 3, was considered to have operated with multiple EDGs inoperable from April 27, 2011, until January 30, 2013. Since it was not recognized that multiple EDGs were inoperable until the completion of the POEs, BFN, Unit 3, operated with multiple inoperable EDGs for longer than allowed by TS 3.8.1 Required Action H. 1, and TS 3.8.2 Required Action B.1.
Also, LCO 3.0.4 prohibits Mode changes when an LCO is not met except under certain conditions that were not applicable to this event. Since it was not recognized that one or more BFN, Unit 3, EDGs were inoperable from January 18, 2009, to January 30, 2013, until the POEs were completed, it is conservatively assumed that BFN changed Modes in violation of LCO 3.0.4 on multiple occasions.
The BFN, Unit 3, EDG blower bearings were installed when the EDGs were manufactured in 1973. The lack of adequate preventive maintenance on the EDG blowers resulted in the 3D EDG blower bearings remaining in service until failure. On multiple occasions BFN had the opportunity to identify the need for periodic replacement PMs on the EDG blower bearings, but it was not until 2011 that PM change requests were initiated to include the bearings into the 12 year diesel generator PMs. Since the new PMs will not be added to the 12 year PM until the next time the 12 year PMs are performed, the blower bearings were replaced by corrective maintenance work orders.
At the time of the 3D EDG blower bearing failure, blower bearings had been replaced on all BFN EDGs except A, 3A, 3B, and 3D EDG since 2012. The condition of the previously replaced blower bearings is unknown because they were not inspected before being discarded.
Following the 3D EDG bearing failure, the two bearings from the 3D EDG blower were sent to SKF Group for failure analysis to identify the direct cause of the failure. The report from SKF identified the cause of failure as a lack of lubrication.
In 1986, the bearings in A, B, C, and D EDG blowers were replaced due to a 1974 bulletin that advised upgrading the original roller bearings with deep groove ball bearings. During this same timeframe, vendor recommendations were incorporated to add both a 6 and 12 year inspection to the EDGs. These inspections were defined as PMs at that time; however, personnel failed to incorporate any lifespan for the shielded bearings installed in the blower. The Maintenance Instruction included a recommendation in the six year inspection to remove the main generator bearing cover, inspect and re-grease if needed.
In 2009, self-assessment CRP-ENG-08-009 identified a learning opportunity regarding the lack of EDG blower PMs. Corrective Action (CA) 164475-003 addressed the need for PMs on the blowers and determined that the only PM needed was for replacement of the rubber inserts in the flex coupling. This conclusion was based on a lack of industry operating experience (OE), vendor guidance, Owners Group recommendations, and
vendor manual recommendations. At the time, BFN was aligned with the industry for preventive maintenance on the EDG blowers.
On multiple occasions, BFN had the opportunity to identify the need for periodic replacement of the EDG blower bearings. The need for PMs was not identified until 2011 because the shielded bearings in BFN EDG blowers were not adequately assessed on a component level to identify potential failure modes and impacts to EDG operability. This is the root cause of the bearing lubricant degradation on the 3A and 3B EDG, and the bearing failure of the 3D EDG.
The failure of the 3D EDG bearing was unexpected because degradation had not been seen in the vibration data collected monthly. A thorough review by independent vibration analysts determined that the historical vibration data did not show any signs of bearing degradation on any of the EDG blowers. The only time that the vibration data showed indications of bearing problems was when the 3D EDG blower bearing failed on December 22, 2012. Even then, signs of bearing failure did not trigger alarms on the vibration meter. The reason that the data did not show bearing issues is that the blowers are located on top of the generators and see considerable movement and induced vibrations. The vibration of the bearings was not large enough to show up over the generator vibrations, thus the bearing degradation went unnoticed.
Additionally, the industry standard for predictive vibration monitoring utilizes velocity data. No adverse trends have been noted based on the BFN Predictive Maintenance (PdM) personnel's review of the velocity data. The only signs of bearing failure were noted after the failure by discovering an increase in acceleration vibration data.
Standard vibration data was ineffective in identifying the degradation of the lubrication in the shielded bearings of the 3D EDG blower due to the masking effect of the generator.
This is the root cause of BFN's failure to identify the degradation of 3D EDG blower bearing before it failed. This is also the root cause of BFN's failure to identify the degradation of the 3A and 3B EDG blower bearings.
After the failure of the 3D EDG blower bearing was discovered, PdM was contacted to determine if vibration data detected any anomalies during the December 2012, data review. No anomalies were detected, so PdM. performed a point to point review of the data. It was discovered that several of the data points were missing.
Review into this missing data led to the discovery that two separate vibration meters were used to collect data during the 3D EDG PMT. Normally two vibration meters are taken to the jobsite in case problems arise with one, but Technical Instruction 0-TI-230V only requires one to be used in the collection of data. The nightshift crew used one meter to collect data on the 3D EDG blower and received a warning message. In order to confirm the data was valid, and not a malfunctioning meter, the second meter was used.
The night shift crew turned the vibration meter over to a supervisor on day shift because it was possible that a subsequent set of vibration readings would need to be collected.
Later into the shift, the supervisor gained confirmation that additional data collection was
unneeded. Qualified personnel were tasked with the download of the data. The day shift crew did not receive an adequate turnover; therefore they were unaware that both vibration meters had been used. This resulted in only downloading data from one vibration meter.
Turnover by maintenance personnel was inadequately performed resulting in the failure to relay that two vibration meters were used during the 3D EDG PMT. This is the contributing cause to BFN's failure to identify that the 3D EDG blower bearing had failed on December 22, 2012. This event will be addressed by briefing the Electrical Maintenance Group on the use of complete and accurate communication during shift turnovers. In addition, focused observations documenting the quality of shift turnovers will be conducted.
The inadequate turnover was a cognitive human performance error because the procedure requires the data to be downloaded. Error precursors existed because a face to face turnover was not utilized and the event occurred immediately before the Christmas holiday.
Extent of Condition The extent of condition covers equipment with vibrations that are substantially greater than the vibrations of the smaller attached components leading to the vulnerability of the individual component's vibrations being masked resulting in unidentified failures. This population includes the EDGs, Aggreko package units, the Security Diesel Generator, Diesel Fire Pumps, the EDG Room coolers, and the starting air compressors.
On January 28, 2013, the 3A EDG's blower bearings were inspected during its 12 year PM due to the failure on 3D EDG. The bearings were discovered to be in a degraded condition due to age related degradation of the bearing lubricant, and it was unknown if 3A EDG could have met its mission time. The A EDG and 3B EDG were the only remaining EDGs with blower bearings that had not been recently replaced since 2012.
Both EDGs were immediately declared inoperable until their blower bearings could be replaced. Inspection of the bearing during replacement determined that the A EDG blower bearings were in satisfactory condition; however, 3B EDG blower bearings were in a degraded condition due to age related degradation of the bearing lubricant.
The fuel oil transfer pumps and engine turbochargers located on the EDGs are also vulnerable to an unidentified failure due to the movement of the diesel engine and generator during the collection of vibration data. Based on multiple unpredicted EDG turbocharger failures, vibration data on the turbochargers has shown to be ineffective in identifying underlying degradation. The condition is being addressed by the installation of an additional oil system to provide pre-lubrication and post-lubrication to the turbochargers and by reevaluating the turbochargers maintenance strategy. The fuel oil transfer pump vibration data can also be masked by the diesel generator; therefore, PM change request will be submitted to require periodic replacement on all eight EDGs.
All EDG turbochargers have recently been replaced and the fuel oil transfer pumps were inspected for degradation or signs of failure. It was determined that there are no current operability concerns.
Extent of Cause The extent of cause for the failed blower bearing includes sealed and shielded bearings on the diesel generators and other safety or quality related rotating equipment where failure would result in BFN's inability to meet TS. An assessment will be performed to identify the population of sealed or shielded bearings associated with EDGs and other safety or quality related systems at BFN. These components will be analyzed to determine the potential failure modes and impact of each failure mode to the operability of the associated system. This analysis will be used to determine the appropriate PM strategy for maintaining this equipment.
The extent of cause for BFN's failure to identify the failed blower bearing extends to vibration monitoring on all eight EDG blowers. To address this condition, an additional vibration monitoring point will be added to the EDG blower fans and 2 existing vibration monitoring points will be moved to the drive end bearing housing. The new vibration monitoring point will monitor for velocity and acceleration and high value alarms will be tied to both parameters.
V. ASSESSMENT OF SAFETY CONSEQUENCES
There are a total of eight EDG units which serve BFN, Units 1, 2, and 3. A set of four EDG units, designated as A, B, C, and D, are located in the BFN, Unit 1/2, EDG building.
Another set of four EDG units, designated as 3A, 3B, 3C, and 3D, are located in the BFN, Unit 3, EDG building.
During the first ten minutes of design basis events, only three of the BFN, Unit 1 and 2, EDGs, along with three of the BFN, Unit 3, EDGs are required to automatically start and come to a ready to load condition. The EDGs must be capable of accepting automatically sequenced plant safety loads. For the long term (greater than 10 minutes),
three of the BFN, Unit 1 and 2, EDGs paralleled with three of the BFN, Unit 3, EDGs, are required to supply all required loads for the safe shutdown and cool down of all three units in the event of loss of offsite power and a design basis event in any one unit.
The analysis of this event is ongoing. Upon completion of the analysis, TVA will submit a supplement to this LER with the results of the additional analysis of safety consequences.
VI. CORRECTIVE ACTIONS - The corrective actions are being managed by TVA's corrective action program.
A.
Immediate Corrective Actions
- 1. Reviewed the vibration data for the A, B, C, D, 3A, 3B, and 3C EDG to ensure that there no signs of supply air blower fan bearing failure following discovery of the 3D EDG bearing failure. No signs of failure were found.
- 2. Walked down the A, B, C, D, 3A, 3B, and 3C EDG to ensure that there were no signs of supply air blower fan bearing failure following discovery of the 3D EDG bearing failure. No signs of failure were found.
B.
Corrective Actions to Prevent Recurrence
- 1. The population of rotating equipment containing shielded or sealed bearings associated with the EDGs will be analyzed to determine the potential failure modes and impact of each failure mode to the operability of the EDGs. This analysis will be used to determine the appropriate PM strategy.
- 2. Identify the population of sealed or shielded bearings associated with safety and/or quality related rotating equipment at BFN. These components will be analyzed to determine the potential failure modes and impact of each failure mode to the operability of the associated system. This analysis will be used to determine the appropriate PM strategy.
- 3. Two existing vibration monitoring points will be relocated to the drive end bearing housing and an additional vibration monitoring point will be added to the EDG blower fans on the drive end bearing housing on all EDGs. This point shall monitor for velocity and acceleration and high value alarms shall be tied to both parameters.
VII. ADDITIONAL INFORMATION
A.
Failed Components The failed components are Model 3312C deep groove, single row, double shielded ball bearings, manufactured by New Departure Hyatt (NDH), and installed while the EDG was being manufactured in 1973.
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 events.
A search was performed on the BFN corrective action program. Similar Problem Evaluation Reports (PERs) 164475, 369956, 488208, 667866, 675339, and 675952 were identified.
Corrective actions from PER 369956 created the corrective maintenance work orders to replace the blower bearings on all EDGs. The corrective actions did not prevent this event because the 3D EDG blower bearing failed before the work orders could be completed.
C.
Additional Information
The corrective action document for this report is PER 665217.
D.
Safety System Functional Failure Consideration:
In accordance with NEI 99-02, this issue is considered a safety system functional failure.
E.
Scram With Complications Consideration:
This condition did not include a reactor scram.
VIII. COMMITMENTS
There are no commitments.