05000259/LER-2011-002, Regarding Loss of Safety Function (SDC) Resulting from Loss of Power from C EDG Due to Oil Leak
| ML11180A267 | |
| Person / Time | |
|---|---|
| Site: | Browns Ferry  |
| Issue date: | 06/27/2011 |
| From: | Poison K Tennessee Valley Authority |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| LER 11-002-00 | |
| Download: ML11180A267 (11) | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(iv)(A), System Actuation 10 CFR 50.73(a)(2)(iv)(B), System Actuation 10 CFR 50.73(a)(2)(v)(B), Loss of Safety Function - Remove Residual Heat 10 CFR 50.73(a)(2)(i) 10 CFR 50.73(a)(2)(vii), Common Cause Inoperability 10 CFR 50.73(a)(2)(ii)(A), Seriously Degraded 10 CFR 50.73(a)(2)(viii)(A) 10 CFR 50.73(a)(2)(ii)(B), Unanalyzed Condition 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)(x) 10 CFR 50.73(a)(2)(v)(A), Loss of Safety Function - Shutdown the Reactor 10 CFR 50.73(a)(2)(i)(A), Completion of TS Shutdown 10 CFR 50.73(a)(2)(v), Loss of Safety Function 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications 10 CFR 21.21(d)(4)(i) |
| 2592011002R00 - NRC Website | |
text
Tennessee Valley Authority, Post Office Box 2000, Decatur, Alabama 35609-2000 June 27, 2011 10 CFR 50.73 ATTN: Document Control Desk U.S. Nuclear Regulatory Commission Washington, D.C. 20555-0001 Browns Ferry Nuclear Plant, Unit 1 Facility Operating License No. DPR-33 NRC Docket No. 50-259
Subject:
Licensee Event Report 50-25912011-002-00 On April 27, 2011, severe weather in the Tennessee Valley Service Area caused grid instability and loss of all 500-kV offsite power sources that resulted in a scram of all three Browns Ferry Nuclear Plant (BFN) units. On April 28, 2011, with all three BFN units in cold shutdown and power supplied by onsite emergency diesel generators (EDGs), BFN Operations personnel performed an emergency shutdown of the Unit 1/2 C EDG. This resulted in a Primary Containment Isolation System actuation which caused the loss of Shutdown Cooling for BFN Units 1 and 2.
The Tennessee Valley Authority (TVA) is submitting this report in accordance with 10 CFR 21.2(c), reporting of defects; 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); and 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.
U.S. Nuclear Regulatory Commission Page 2 June 27, 2011 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. Po son Vice President
Enclosure:
Licensee Event Report 259/2011-002 - Loss of Safety Function (SDC)
Resulting from Loss of Power from C EDG Due to Oil Leak cc (w/ Enclosure):
NRC Regional Administrator - Region II NRC Senior Resident Inspector - Browns Ferry Nuclear Plant
Enclosure Browns Ferry Nuclear Plant Unit I Licensee Event Report 259/2011-002 Loss of Safety Function (SDC) Resulting from Loss of Power from C EDG Due to Oil Leak See Attached
NRC FORM 366 U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY OMB NO. 3150-0104 EXPIRES 10/13/2013 (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 (BFN) Unit 1 05000259 1 OF 8
- 5. EVENT DATE
- 6. LER NUMBER
- 7. REPORT DATE
- 8. OTHER FACILITIES INVOLVED SEQUENTIAL REV MONTH DAY YEAR FACILITY NAME DOCKET NUMBER MONTH DAY YEAR YEAR NUMBER NO.
BFN Unit 2 05000260 FACILITY NAME DOCKET NUMBER 04 28 2011 2011 -
002 -
00 06 27 2011 N/A 05000
- 9. OPERATING MODE
- 11. THIS REPORT IS SUBMITTED PURSUANT TO THE REQUIREMENTS OF 10 CFR §: (Check all that apply)
E0 20.2201(b)
El 20.2203(a)(3)(i)
El 50.73(a)(2)(i)(C)
[] 50.73(a)(2)(vii) o[ 20.2201(d)
[] 20.2203(a)(3)(ii)
El 50.73(a)(2)(ii)(A)
El 50.73(a)(2)(viii)(A)
El 20.2203(a)(1)
El 20.2203(a)(4)
El 50.73(a)(2)(ii)(B)
El 50.73(a)(2)(viii)(B)
[I 20.2203(a)(2)(i)
Cl 50.36(c)(1)(i)(A)
[I 50.73(a)(2)(iii)
[1 50.73(a)(2)(ix)(A)
- 10. POWER LEVEL El 20.2203(a)(2)(ii)
[I 50.36(c)(1)(ii)(A) 0 50.73(a)(2)(iv)(A)
El 50.73(a)(2)(x)
El 20.2203(a)(2)(iii)
El 50.36(c)(2) 0l 50.73(a)(2)(v)(A)
El 73.71(a)(4)
El 20.2203(a)(2)(iv)
El 50.46(a)(3)(ii) 0 50.73(a)(2)(v)(B)
El 73.71(a)(5) 000 [1 20.2203(a)(2)(v)
El 50.73(a)(2)(i)(A)
El 50.73(a)(2)(v)(C) 0 OTHER - Part 21 El 20.2203(a)(2)(vi)
[E 50.73(a)(2)(i)(B)
El 50.73(a)(2)(v)(D)
Specify in Abstract below or in April 28, 2011, at 23:42 hours CDT April 29, 2011, at 00:25 hours CDT April 30, 2011, at 10:47 hours CDT May 2, 2011, at 2010 hours0.0233 days <br />0.558 hours <br />0.00332 weeks <br />7.64805e-4 months <br /> CDT Unit 2 SDC restored by starting 2D RHR pump.
Unit 1 SDC restored by resetting PCIS signal and establishing SDC.
Unit 1/2 C EDG operable after replacement of failed hydraulic oil piping fitting and successful post maintenance testing.
All shutdown boards are powered from qualified 161-kV offsite power sources, and all EDGs are shutdown and in standby readiness.
D. Other Systems or Secondary Functions Affected
None
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 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:
All onsite safe shutdown equipment was available with the exception of the 38 EDG, which was inoperable and unavailable due to planned maintenance.
Ill. CAUSE OF THE EVENT 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.
NRC FORM 366 (10-2010)
IV. ANALYSIS OF THE EVENT
The Tennessee Valley Authority (TVA) 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 1 B Reactor Protection System (RPS) because the 1 B RPS is fed from the 480V Reactor Motor Operated Valve Board [ED] 1 B, which is fed from the 480V Shutdown Board [ED] 1 B, which is fed from the C 4kV Shutdown Board. Loss of power to the 1 B 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 (AOI) 1-AOI-74, Loss of Shutdown Cooling. In addition to the loss of SDC, automatic initiation of the three trains of Standby Gas Treatment System [BH], one train of Control Room Emergency Ventilation System [VI], a Reactor Water Cleanup System [CE]
trip (due to loss of suction on PCIS isolation), and loss of the A Control Air System [LE]
compressor.
The 2B RHR pump is fed by the C 4kV 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 shut down.
TVA is currently evaluating the potential that this condition may have resulted in past inoperability of the C EDG. If this is found to be the case, a revision to this LER will be submitted.
TVA 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 Probability 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 C EDG. If multiple EDGs had experienced the same failure under the same event scenario, BFN could have lost its ability to provide power to components essential for heat removal from the reactor vessel.
However, since the remaining three Unit 1/2 EDGs remained operable and all of the Emergency Core Cooling Systems were operable, there was sufficient redundancy to support the core cooling requirements for Units 1 and 2. Therefore, this event was of minimal safety significance.
NRC FORM 366 (10-2010)
The oil leak caused a loss of the Unit 1/2 C EDG and subsequent loss of SDC on Unit 1 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 Spent Fuel Pool Water (airborne radioactive contamination risk) 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 (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 been met.
VI. CORRECTIVE ACTIONS
Corrective actions are being managed within TVAs Corrective Action Program.
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 to be performed:
Verify as-found torque values on the Unit 1/2 C EDG governor bolting. Perform analysis of the results.
Review the small bore (<1/2-inch) tubing/piping connections on the High 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 (<1/2-inch) tubing/piping connections on the Reactor 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 (<1/2-inch) tubing/piping connections on all eight EDGs and determine acceptability for vibration loading considering tubing weight, dimensions, operating experience, and any available vibration data.
NRC FORM 366 (10-2010)
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.
VII. ADDITIONAL INFORMATION
A.
Failed Components:
Unit 1/2 C Emergency Diesel Generator B.
Previous LERS or 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.
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:
This event is a safety system functional failure in accordance with NEI 99-02.
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)
NRC FORM 356 (10-2010)
(i) Name and address of the individual or individuals informing the Commission.
K. J. Poison 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 Emergency Diesel Generator, 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.
(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.
N RC FORM 366 (10-2010)
(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.
VIII. COMMITMENTS
None NRC FORM 366 (10-2010)