05000259/LER-2016-005, Regarding Main Steam Relief Valves Lift Settings Outside of Technical Specifications Required Setpoints
| ML17030A311 | |
| Person / Time | |
|---|---|
| Site: | Browns Ferry  |
| Issue date: | 01/30/2017 |
| From: | Bono S Tennessee Valley Authority |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| LER 16-005-00 | |
| Download: ML17030A311 (9) | |
| 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)(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)(v)(A), Loss of Safety Function - Shutdown the Reactor 10 CFR 50.73(a)(2)(v)(B), Loss of Safety Function - Remove Residual Heat 10 CFR 50.73(a)(2)(v), Loss of Safety Function 10 CFR 50.73(a)(2)(i)(A), Completion of TS Shutdown 10 CFR 50.73(a)(2)(vii), Common Cause Inoperability 10 CFR 50.73(a)(2)(i) |
| 2592016005R00 - NRC Website | |
text
Tennessee Valley Authority, Post Office Box 2000, Decatur, Alabama 35609-2000 January 30, 2017 ATTN: Document Control Desk U.S. Nuclear Regulatory Commission Washington, D.C. 20555-0001
Subject:
Browns Ferry Nuclear Plant, Unit 1 Renewed Facility Operating License No. DPR-33 NRC Docket No. 50-259 Licensee Event Report 50-259/2016-005-00 10 CFR 50.73 The enclosed Licensee Event Report provides details of the inoperability of three Main Steam Relief Valves for longer than allowed by plant Technical Specifications. The Tennessee Valley Authority is submitting this report in accordance with Title 10 of the Code of Federal Regulations 50.73(a)(2)(i)(B), as any operation or condition which was prohibited by the plant's Technical Specifications.
There are no new regulatory commitments contained in this letter. Should you have any questions concerning this submittal, please contact M. W. Oliver, Nuclear Site Licensing Manager, at (256) 729-2636.
Enclosure: Licensee Event Report 50-259/2016-005 Main Steam Relief Valves Lift Settings Outside of Technical Specifications Required Setpoints cc (w/ Enclosure):
NRC Regional Administrator - Region II NRC Senior Resident Inspector - Browns Ferry Nuclear Plant
ENCLOSURE Browns Ferry Nuclear Plant Unit 1 Licensee Event Report 50-259/2016-005-00 Main Steam Relief Valves Lift Settings Outside of Technical Specifications Required Setpoints See Enclosed
NRC FORM 366 U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY OMB: NO. 3150-0104 EXPIRES: 1013112018 (06-2016) /¥\\
Estimated burden per response to comply with this mandatory collection recuest: 80 hours9.259259e-4 days <br />0.0222 hours <br />1.322751e-4 weeks <br />3.044e-5 months <br />.
Reported lessons learned are incorporated into the licensing process and fed back to industry.
LICENSEE EVENT REPORT (LER)
Send comments regarding burden estimate to the FOIA, Privacy and Information Collections
\\,
':Ii Branch (T-5 F53), U.S. Nuclear Regulatory Commission, Washington, DC 20555-0001, or by e-mail
~o to lnfocollects.Resource@nrc.gov, and to the Desk Officer, Office of lnfomnation and Regulatory Affairs, NEOB-10202, (3150-0104), Office of Management and Budget, Washington, DC 20503. If a means used to impose an infomnation collection does not display a currently valid OMB control number, the NRC may not conduct or sponsor, and a person is not recuired to respond to, the infomnation collection.
- 3. PAGE Browns Ferry Nuclear Plant, Unit 1 05000259 1 OF 7
- 4. TITLE Main Steam Relief Valves Lift Settings Outside of Technical Specifications Required Setpoints
- 5. EVENT DATE
- 6. LER NUMBER
- 7. REPORT DATE
- 8. OTHER FACILITIES INVOLVED YEAR I SEQUENTIAL I REV FACILITY NAME DOCKET NUMBER MONTH DAY YEAR NUMBER NO.
MONTH DAY YEAR N/A NIA 11 30 2016 2016 005 00 01 FACILITY NAME DOCKET NUMBER 30 2017 N/A NIA
- 9. OPERATING MODE
- 11. THIS REPORT IS SUBMITTED PURSUANT TO THE REQUIREMENTS OF 10 CFR §: (Check all that apply)
D 20.2201(b)
D 20.2203(a)(3)(i)
D 50.73(a)(2)(ii)(A)
D 50.73(a)(2)(viii)(A) 1 D 20.2201(d)
D 20.2203(a)(3)(ii)
D 50.73(a)(2)(ii)(B)
D 50.73(a)(2)(viii)(B)
D 20.2203(a)(1)
D 20.2203(a)(4)
D 50.73(a)(2)(iii)
D 50. 73(a)(2)(ix)(A)
D 20.2203(a)(2)(i)
D 50.36(c)(1 )(i)(A)
D 50. 73(a)(2)(iv)(A)
D 50. 73(a)(2)(x)
- 10. POWER LEVEL D 20.2203(a)(2)(ii)
D 50.36(c)(1 )(ii)(A)
D 50.73(a)(2)(v)(A)
D 73. 71 (a)(4)
D 20.2203(a)(2)(iii)
D 50.36(c)(2)
D 50.73(a)(2)(v)(B)
D 73. 71 (a)(5)
D 20.2203(a)(2)(iv)
D 50.46(a)(3)(ii)
D 50.73(a)(2)(v)(C)
D 73. 77(a)(1) 100 D 20.2203(a)(2)(v)
D 50.73(a)(2)(i)(A)
D 50. 73(a)(2)(v)(D)
D 73.77(a)(2)(i)
D 20.2203(a)(2)(vi)
IZ! 50.73(a)(2)(i)(B)
D 50.73(a)(2)(vii)
D 13.77(a)(2)(ii)
D 50.73(a)(2)(i)(C)
D OTHER Specify in Abstract below or in
C. Dates and approximate times of occurrences
Dates & Approximate Times October 9, 2014 October 29, 2014 October 30, 2014 October 1, 2016 November 4, 2016 November 30, 2016 Occurrence The MSRV pilot valves are replaced, as part of the Unit 1 Refueling Outage 10. PMT was delayed until after the outage ends, since the surveillance used as a PMT requires a minimum reactor pressure of 935 psig.
Unit 1 enters Mode 1, beginning the fuel cycle.
BFN, Unit 1 enters Mode 5, to begin the U1 R11 refueling outage.
Replacement of MSRV pilot valves and their associated post maintenance testing is completed, as part of the U1 R11 refueling outage.
NTS Laboratories provided TVA with the as-found testing results of the thirteen Unit 1 MSRV pilot valves removed during the U1 R11 outage.
D. Manufacturer and model number of each component that failed during the event
The failed components were all Target Rock Corporation two-stage pressure control valves, model number 7567F.
E. Other systems or secondary functions affected
No other systems or secondary functions were affected by this event.
F. Method of discovery of each component or system failure or procedural error
REV NO.
00 Failure was discovered at NTS Laboratories, during their as-found testing of the thirteen MSRV two-stage pilot valves which were removed during the Fall 2016 U1 R11.
G. The failure mode, mechanism, and effect of each failed component
The two-stage pilot valves failed due to the corrosion bonding of the valve disc to the valve seat.
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H. Operator actions
There were no operator actions associated with this event.
I. Automatically and manually initiated safety system responses
There were no automatic or manual safety system responses associated with this event.
Ill.
Cause of the event
A. Cause of each component or system failure or personnel error The two-stage pilot valves failed due to the valve disc corrosion bonding to the valve seat.
No human performance related root causes were identified.
IV.
Analysis of the event
The Tennessee Valley Authority is submitting this report in accordance with Title 10 of the Code of Federal Regulations 50.73(a)(2)(i)(B), as any operation or condition which was prohibited by the plant's TS. It was determined that the MSRV pilot valve inoperability resulted from their setpoints gradually drifting during the course of their operating cycle, which began on October 29, 2014, and lasted until October 1, 2016, when Unit 1 entered Mode 4.
00 BFN, Unit 1, TS Limiting Condition for Operation (LCO) 3.4.3 requires twelve Operable S/RVs during Modes 1, 2, and 3. If one or more required S/RVs becomes inoperable, Required Action A.1 requires BFN, Unit 1, to enter Mode 3 within 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br />, and Required Action A.2 requires entering Mode 4 within 36 hours4.166667e-4 days <br />0.01 hours <br />5.952381e-5 weeks <br />1.3698e-5 months <br />. S/RV Operability is defined as being within +/- 3 percent of their setpoint values, in accordance with Surveillance Requirement (SR) 3.4.3.1. BFN, Unit 1, has thirteen MSRVs to satisfy this requirement with margin.
After their installation on October 9, 2014, the as-left lift setpoint for Main Steam Line C Relief Valve was 1145 psig, and the Main Steam Line D Relief Valves had as-left lift setpoints of 1155 psig.
However, during as-found testing at NTS Laboratories, the lift setpoint for Main Steam Line C Relief Valve BFN-1-PCV-001-0030 was found to be 1181 psig (+ 3.14 percent), and the setpoints for Main Steam Line D Relief Valves BFN-1-PCV-001-0041 and BFN-1-PCV-001-0180 were found to be 1278 psig (+10.65 percent) and 1209 psig (+4.68 percent), respectively. During the fuel cycle, these valve lift setpoints gradually drifted outside of the +/- 3 percent margin which is required for their operability. This failure was due to corrosion bonding between the valve discs and their seats which occurred after their installation but before Unit 1 entered Mode 4 on October 1, 2016. Therefore, BFN, Unit 1, operated with inoperable S/RVs for longer than what is allowed by TS.
SEQUENTIAL NUMBER 005 REV NO.
00 On October 9, 2014, all thirteen BFN, Unit 1 MSRV pilot valves were replaced with refurbished valves which were certified to lift within +/- 1 percent of their setpoint. Operating experience (OE) has shown that Target Rock two-stage MSRV setpoint drift is not a uniform, linear process. The corrosion bonding increases at a random rate. Without an accurate and reliable model for predicting or estimating the setpoint drift development, the point in time where the setpoint exceeded the +/- 3 percent limit cannot be reliably determined. Since this drift occurred between the beginning of the fuel cycle on October 29, 2014, and October 1, 2016, when Unit 1 entered Mode 4, the MSRV inoperability was conservatively declared to have been inoperable for an indeterminate period of time between October 29, 2014, and October 1, 2016, and longer than permitted by plant TS 3.4.3.
V.
Assessment of Safety Consequences
System availability was not impacted by this event. The failure of BFN-1-PCV-001-0030, an Automatic Depressurization System (ADS) valve, to meet the mechanical setpoint identified in TS 3.4.3 does not impact its remote-manual operation, or activation through the ADS or MSRV Automatic Actuation Logics since these operating modes and functions rely upon an electrical signal to energize the MSRV control air solenoid which electrically opens the pilot valve.
TS Bases 3.4.3 states that the overpressure protection system must accommodate the most severe pressurization transient. The MSRVs remained capable of maintaining the reactor pressure below 1375 psig, which is the ASME code limit (110 percent of the vessel design pressure). The valves remained capable of performing their required safety function.
The bounding maximum over-pressurization analyses are performed each fuel cycle to show that the requirements of the ASME code regarding overpressure protection are met. The analyses are performed specifically to show that the dome pressure TS limit of 1325 psig is not exceeded and that the vessel pressure does not exceed the limit of 1375 psig. In addition, the Anticipated Transient Without Scram (A TWS) pressurization analyses are also performed to demonstrate that the 1500 psig peak vessel pressure limit is not exceeded.
NUREG-0800 defines bases the acceptance criteria for reactor coolant pressure on the ASME Service Level C limits, which are approximately 10.3 MPa (1500 psig) for BWRs. For the ATWS analysis, the setpoint groupings conservatively bound the ten lowest as-found MSRV opening setpoints; however, the three highest valve setpoints fall outside the bounds of the valve groupings.
Therefore the limiting ATWS overpressurization event, identified as the ATWS pressure regulator failed open at 100% rated power and 81% rated flow at the beginning of cycle exposure, was re-analyzed by AREVA. The results from this analysis indicate that despite the three MSRV pilot valves which exceeded their as-found setpoint, the maximum vessel pressure and maximum dome pressure reaches a maximum of 1398 psig, and therefore does not exceed the A TWS vessel pressure limit of 1500 psig. Therefore, there was no impact on the MSRVs to perform their specified safety function.
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YEAR 2016
- 3. LER NUMBER SEQUENTIAL NUMBER 005 Based on the above, TVA has concluded that sufficient systems were available to provide the required safety functions needed to protect the health and safety of the public.
REV NO.
00 A. Availability of systems or components that could have performed the same function as the components and systems that failed during the event Each BFN operating unit has a non-safety related, electrical logic system (MSRV Actuation Logic) installed, which provides defense-in-depth against MSRV setpoint drift by electrically opening MSRV groups based upon setpoints at 1135 psig, 1145 psig and 1155 psig. Therefore, during a reactor pressure transient event, the four 1135 psig group MSRVs, followed by the four 1145 psig group MSRVs, and finally the five 1155 psig group MSRVs would receive an electrical open signal, providing a defense-in-depth function to allow the valves to perform their safety function.
B. For events that occurred when the reactor was shut down, availability of systems or components needed to shutdown the reactor and maintain safe shutdown conditions, remove residual heat, control the release of radioactive material, or mitigate the consequences of an accident This event did not occur when the reactor was shutdown.
C. For failure that rendered a train of a safety system inoperable, estimate of the elapsed time from discovery of the failure until the train was returned to service TS 3.4.3 requires twelve of the thirteen S/RVs to be operable for S/RV system operability. The three failed MSRV pilot valves rendered the entire S/RV system inoperable for the duration of the fuel cycle, from October29, 2014, to October 1, 2016.
VI.
Corrective Actions
Corrective Actions are being managed by TVA's corrective action program under Condition Report (CR) 962223.
A. Immediate Corrective Actions
All thirteen of the Unit 1 MSRV pilot valves were replaced with refurbished valves during the U1R11 Refueling Outage. As-left testing verified that these refurbished pilot valves were within 1 percent of their name plate setpoints.
B. Corrective Actions to Prevent Recurrence or to reduce the probability of similar events occurring in the future The discs from the previous failed pilot valves were analyzed, and their results were documented under CR 962223.
NRC FURM 366A (06-2016)
Page _6_ of _7_
SEQUENTIAL NUMBER 005 REV NO.
00 Steps were added to procedure MCl-0-001-VLV002, Main Steam Relief Valves Target Rock Model 7567 Disassembly, Inspection, Rework and Reassembly, to use a borescope, microscope and a Root Mean Square (RMS) optical comparator and a microscope to verify that the pilot disc finish quality is 32 RMS or better, optimally 16 RMS, prior to platinum coating VII.
Previous Similar Events at the Same Site
A search of BFN LERs for Units 1, 2, and 3, identified eight LERs for this same issue within the last eight years. This is a common issue throughout the industry, as corrective actions have only been able to mitigate the problem. By documenting and trending the issue, incremental improvement is being made towards a resolution.
A search of the Corrective Action Program for BFN, Units 1, 2, and 3, identified seventeen MSRV failure events since 1999. These failures were captured by CRs 37328, 59786, 50084, 61823, 81376, 102298, 124944, 146189, 175990, 159200, 226627, 294506, 372047, 558488, 962223, 1157981 and 1237184. These individual failures were collectively evaluated and addressed by CR 112190.
CR 55557 identified that corrosion bonding between the valve discs and their seat surfaces were strong enough to cause significant drifts in their opening pressure and reset setpoints. As a corrective action, a design change was implemented to update/install a safety related pressure switch logic that was endorsed by the BWR Owners Group to resolve setpoint drift issues.
CR 56793 identifies the corrosion-prone materials used in the construction of Target Rock two-stage safety-relief valves presented a fundamental design deficiency. An alternate MSRV design/logic/manufacturer was sought, but industry OE demonstrated that the use of platinum coated valve discs provided the best results.
The Corrective Actions for CR 146189 required platinum coated MSRV discs to be installed in future outages to prevent reoccurrence. CR 166147 verified that these platinum coatings were in place.
While the use of platinum coated valve discs has mitigated the occurrence of corrosion-induced setpoint, drift, it continues to occur. Industry OE shows that this is a result of platinum coatings flaking off due to the rough Stellite surfaces of valve discs.
VIII. Additional Information
There is no additional information.
IX.
Commitments
There are no new commitments. Page _7_ of _7_