05000259/LER-2018-007, Main Steam Relief Valves Lift Settings Outside of Technical Specifications Required Setpoints
| ML19042A158 | |
| Person / Time | |
|---|---|
| Site: | Browns Ferry  |
| Issue date: | 02/11/2019 |
| From: | Hughes D Tennessee Valley Authority |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| LER 2018-007-00 | |
| Download: ML19042A158 (8) | |
| 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)(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)(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) |
| 2592018007R00 - NRC Website | |
text
Tennessee Valley Authority, Post Office Box 2000, Decatur, Alabama 35609-2000 February 11, 2019 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 50-259/2018-007-00 10 CFR 50.73 The enclosed Licensee Event Report provides details of the inoperability of two 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, Acting Nuclear Site Licensing Mana r, at (256) 729-787 4.
D. L. Hughes Site Vice President Enclosure: Licensee Event Report 50-259/2018-007 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 NRC Project Manager - Browns Ferry Nuclear Plant
NRC FORM 366 U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY 0MB: NO. 3150-0104 EXPIRES: 03/31/2020 (04-2018)
, lhe NRC may not conduct or sponsor, and a person is no1 required to respond to, lhe infoonation collection.
3.Page Browns Ferrv 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 I
Sequential I Rev Facmty Name Docket Number Month Day Year Year Month Day Year NIA NIA Number No.
12 12 2018 2018 007 00 02 11 2019 Facility Name Docket Number NIA NIA
- 9. Operating Mode
- 11. This Report is Submitted Pursuant to the Requirements of 1 O CFR §: (Check all that apply) 0 20.2201 (b)
D 20.2203(a)(3)(i) 0 50.73(a)(2)(ii)(A)
D 50.73(a)(2)(viii)(A) 1 0 20.2201 (d)
D 20.2203(a)(3)(ii) 0 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) 0 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) 0 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) 086 D 20.2203(a)(2)(iv)
D 50.46(a)(3)(ii)
D 50.73(a)(2)(v)(C)
D 73.77(a)(1)
D 20.2203(a)(2)(v) 0 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)
[8J 50. 73(a)(2)(i)(B)
D 50.73(a)(2)(vii)
D 73.77(a)(2)(ii) 0 50.73(a)(2)(i)(C) 0 OTHER Specify in Abstract below or in
C. Dates and approximate times of occurrences
Dates & Approximate Times November 2, 2016 October 14, 2018 December 12, 2018 Occurrence Unit 1 entered Mode 2, beginning the cycle.
BFN, Unit 1, entered Mode 4, ending the 1 R12 refueling outage.
NWS Technologies provided the TVA with the as-found testing results of the thirteen Unit 1 MSRV pilot valves removed during the 1 R 12 refueling 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
Failure was discovered at NWS Technologies, during their as-found testing of the thirteen MSRV two-stage pilot valves which were removed during the 1 R 12 refueling outage.
G. The failure mode, mechanism, and effect of each failed component
Troubleshooting determined that MSRV Line B failed by corrosion bonding to its valve seat as a result of its platinum anti-corrosion coatings flaking off. It was also determined that the failure of MSRV Line C was most likely caused by a relaxation of the setpoint spring over time.
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.
00 Ill.
Cause of the event
A. Cause of each component or system failure or personnel error Main Steam Line B Relief Valve, BFN-1-PCV-001 -0018, failed above its setpoint band due to valve disc corrosion bonding to the valve seat, as a result of its platinum anti-corrosion coating flaking off.
Main Steam Line C Relief Valve, BFN-1-PCV-001 -0034, failed below its setpoint band due to a faulty valve spring.
No human performance related root causes were identified.
IV.
Analysis of the event
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 1 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 a +/- 3 percent band of their setpoint values, in accordance with Surveillance Requirement 3.4.3.1. BFN, Unit 1, has thirteen MSRVs to satisfy this requirement with margin.
After the installation of the S/RVs, the as-left lift setpoints for S/RV, BFN-1-PCV-001 -0018 was 1145 psig (+/-1 percent), and SRN, BFN-1-PCV-001 -0034, was 1135 psig (+/- 1 percent).
However, during as-found testing at NWS Technologies, the Main Steam Line B Relief Valve BFN-1 -PCV-001 -0018 lifted at 1195 psig (+4.37 percent); and the Main Steam Line C Relief Valve, BFN-1-PCV-001-0034, lifted at 1090 psig (-3.96 percent). During the fuel cycle, these valve lift setpoints gradually drifted outside of the +/- 3 percent margin which is required for their operability. The valve which exceeded its setpoint band failed due to corrosion bonding between the valve disc and its seat. The valve which failed below the setpoint band failed due to a faulty valve spring.
Prior to startup from the Unit 1 Refueling Outage 12, 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 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 November 2, 2016, and October 14, 2018, the MSRV inoperability was conservatively declared to have been inoperable for an indeterminate period of time between November 2, 2016, and October 14, 2018, and longer than permitted by plant TS 3.4.3.
00 V.
Assessment of Safety Consequences
System availability was not impacted by this event. The failed MSRV pilot valves were not a part of the Automatic Depressurization System (ADS). The failure of the MSRV pilot valves to meet their TS 3.4.3 specified mechanical setpoints does not impact their remote-manual operation or activation through the MSRV Automatic Actuation Logic, since these operating modes and functions rely upon electrically signaled control air solenoids to open the MSRV pilot valves.
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. Therefore, as defined in NEI 99-02, failure of the MSRV pilot valves was not a safety system functional failure.
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 1375 psig is not exceeded and that the vessel pressure does not exceed the limit of 1404 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.
For the A TWS analysis, one valve is assumed to be out of service (OOS), as permitted by Tech Spec 3.4.3. For conservatism, one of ttie valves with the lowest setpoint is assumed to be OOS. Valves opening at a lower pressure will result in a less severe pressure transient. Main Steam Line C Relief Valve, BFN-1-PCV-001-0034, failed low at 1090 psig which is 3. 96 percent below the 1135 setpoint. Therefore, this valve was within the bounds of the analysis assumptions.
Since Main Steam Line B Relief Valve, BFN-1-PCV-001-0018, failed high at 1195 psig (+4.37 percent), this valve was considered to be OOS for the analysis. Therefore, 12 out of 13 valves are within the assumptions of the A TWS analysis, and assures the licensee that the A TWS analysis remains valid and peak pressure limits would not have been exceeded for an actual event.
Therefore, there was no impact on the MSRVs to perform their specified safety function.
Based on the above, the TVA has concluded that sufficient systems were available to provide the required safety functions needed to protect the health and safety of the public.
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 00 2018 007 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 two failed MSRV pilot valves rendered the entire S/RV system inoperable for the duration of the fuel cycle, from November 2, 2016 to October 14, 2018.
VI.
Corrective Actions
Corrective Actions are being managed by the TV/\\s corrective action program under Condition Reports (CRs) 962223, 1252419, and 1475055.
A. Immediate Corrective Actions
All thirteen of the Unit 1 MSRV pilot valves were replaced with refurbished valves during the 1 R 12 refueling outage. These valves had platinum coatings applied in accordance with the revised procedure. 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 Prior to the 1 R 12 refueling outage, a flaking issue was noted with the platinum coated pilot discs. Actions included revising the valve's inspection, repair, and reassembly procedure to add nitrogen leak testing of the pilot valves prior to platinum coating. This procedure requirement was added in 2017, and the valves removed from the 1 R 12 refueling outage did not have this step of nitrogen leak testing prior to platinum coating within the scope of their rebuilds. The valves installed during the 1 R 12 refueling outage received nitrogen leak testing before and after the platinum coating.
The corrective action to reduce the probability of similar events occurring in the future include preparing the pilot discs for platinum coating in accordance with the revised procedure which required nitrogen pressure testing to verify valve seal functionality prior to coating.
REV NO.
00 YEAR 2018
- 3. LER NUMBER SEQUENTIAL NUMBER 007 Additionally, the discs will be platinum coated, the setpoint spring for Pilot 1069 will be replaced, and the remaining springs will be tested and replaced as necessary.
VII.
Previous Similar Events at the Same Site
A search of BFN LERs for Units 1, 2, and 3, identified six LERs for this same issue within the last five years.
A search of the Corrective Action Program for BFN, Units 1, 2, and 3, identified nineteen 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, 1237184, 1294336, and 1416743.
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 BWROG to resolve setpoint drift issues.
CR 56793 identifies the corrosion-prone materials used in the construction of Target Rock two-stage S/RVs 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 recurrence. CR 166147 verified that these platinum coatings were in place.
VIII. Additional Information
There is no additional information.
IX.
Commitments
There are no new commitments.
REV NO.
00 Page _ 7_ of _ 7_