05000390/LER-2019-003, Manual Reactor Trip Due to Main Feedwater Regulating Valve Failing Closed
| ML19294A010 | |
| Person / Time | |
|---|---|
| Site: | Watts Bar  |
| Issue date: | 10/21/2019 |
| From: | Anthony Williams Tennessee Valley Authority |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| WBL-19-051 LER 2019-003-00 | |
| Download: ML19294A010 (7) | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 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)(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)(i)(B), Prohibited by Technical Specifications 10 CFR 50.73(a)(2)(vii), Common Cause Inoperability 10 CFR 50.73(a)(2)(i) |
| 3902019003R00 - NRC Website | |
text
Tennessee Valley Authority, Post Office Box 2000, Spring City, Tennessee 37381 October 21, 2019 WBL-19-051 ATTN : Document Control Desk U.S. Nuclear Regulatory Commission Washington, D.C. 20555-0001 Watts Bar Nuclear Plant, Unit 1 Facility Operating License No. NPF-90 NRC Docket No. 50-390 10 CFR 50.73
Subject:
Licensee Event Report 390/2019-003-00, Manual Reactor Trip Due to Main Feedwater Regulating Valve Failing Closed This submittal provides Licensee Event Report (LER) 390/2019-003-00. This LER provides details concerning a manual plant trip as a result of a main feedwater regulating valve failing closed. This condition is being reported as a safety system actuation of the reactor protection system and the auxiliary feedwater system in accordance with 10 CFR 50. 73(a)(2)(iv)(A).
There are no regulatory commitments contained in this letter. Please direct any questions concerning this matter to Tony Brown, WBN Licensing Manager, at (423) 365-7720.
thony L. Williams IV Site Vice President Watts Bar Nuclear Plant Enclosure cc: See Page 2
U.S. Nuclear Regulatory Commission WBL-19-051 Page 2 October 21, 2019 cc (Enclosure):
NRC Regional Administrator - Region II NRC Senior Resident Inspector-Watts Bar Nuclear Plant
NRC FORM 366 U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY 0MB: NO. 3150-0104 EXPIRES: 03/31/2020 (04-2018)
Estinaled Mien per response m COIT1)1y with this mandatcry collection request 80 holls.
Reporled lessons leaned ae incorporaled into the licensing process aid ild back m industy. Send conrnems regading burden estimate ID the lnbmalion Services Branch
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LICENSEE EVENT REPORT (LER)
(T-2 F43), U.S. Nuclear Regulmy Cornnission, Washlngtcn, DC 20555-0001,or by e-mail i
ID lnb:ollecls. Resoirte@m:.gov, and m the Desk Officer, Office of lnloonalion 111d
~ 1 Regulaby Affairs, NEQB.10202, (3150-0104), Office of Malagement 111d Budget, Washingmn, DC 20503. tt a means used ID Impose an inlormalion collection does not cisplay a ctmnlly vald 0MB control number, the NRC may not conduct or sponsor, and a person is not required ID respond ID, the information coleclion.
3.Page Watts Bar Nuclear Plant, Unit 1 05000390 1 OF 5
- 4. Title Manual Reactor Trip Due to Main Feedwater Regulating Valve Failing Closed
- 5. Event Date
- 6. LER Number
- 7. Report Date
- 8. Other Facilities Involved I
Sequential I Rav Facility Name Docket Number Month Day Year Year Number No.
Month Day Year N/A 05000 Facility Name Docket Number 08 31 2019 2019 - 003
- - 00 10 21 2019 NA 05000
- 9. Operating Mode
- 11. This Report Is Submitted Pursuant to the Requirements of 10 CFR §: (Check all that apply)
D 20.2201cb>
D 20.2203<a><3>
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 50.13<a><2><iii)
D 50.73(a)(2)(ix)(A)
D 20.2203<a><2>
D 50.36(c)(1)(i)(A)
~ 50.73(a)(2)(iv)(A)
D 50.73(a)(2)(x)
- 10. Power Level D 20.2203<a><2>cn>
D 50.36(c)(1)(ii)(A)
D 50.73(a)(2)(v)(A)
D 13.11ca><4>
D 20.2203<a><2>cm>
D 5o.3s<c><2>
D 50.73(a)(2)(v)(B)
D 13.11ca><5>
D 20.2203(a)(2)(iv)
D 5o.4s<a><3>(ii)
D 50.73(a)(2)(v)(C)
D 13.11<a><1>
100 D 20.2203(a)(2)(v)
D 50.73(a)(2)(i)(A)
D 50. 73(a)(2)(v)(D)
D 13.11<a><2>
D 20.2203(a)(2)(vi)
D 50.73(a)(2)(i)(B)
D 50.73(a)(2)(vii)
D 13.11(a><2><ii)
D 50.73(a)(2)(i)(C)
D OTHER Specify in Abstract below or in NRC Fonn 366A
- 12. Licensee Contact for this LER Licensee Contact ralaphona Number (Include Area Code)
Dean Baker, Licensing Engineer (423) 452-4589 Cause System Component Manufacturer Reportable to ICES
Cause
System Component Manufacturer Reportable to ICES B
SJ FCV FISHER y
- 14. Supplemental Report Expected Month Day Year D Yes (If yes, complete 15. Expected Submission Date)
~No
- 15. Expected Submission Date N/A N/A N/A Abstract (Limit to 1400 spaces, i.e., approximately 14 single-spaced typewritten lines)
On August 31, 2019, at 2055 Eastern Daylight Time (EDT), the Watts Bar Nuclear Plant (WBN) Unit 1 reactor was manually tripped due to a loss of Steam Generator (SG) number 2 level control. Concurrent with the reactor trip, the Auxiliary Feedwater system actuated as designed. All Control and Shutdown rods inserted properly. All safety systems responded as designed.
This event was likely caused by diaphragm case bolt relaxation. This relaxation resulted in additional load on the bolt holes of the diaphragm, causing tearing and failure. Corrective actions include replacement of the defective diaphragm and revising the diaphragm case bolt torque requirement in the vendor manual and maintenance procedure.
This condition is being reported as a safety system actuation in accordance with 10 CFR 50. 73(a)(2)(iv)(A).
NRC FORM 366 (04-2018)
I.
Plant Operating Conditions Before the Event
Watts Bar Nuclear Plant (WBN) Unit 1 was at 100 percent rated thermal power (RTP). Unit 2 was unaffected by this event.
- 11.
Description of Event
A Event Summary On August 31, 2019, at 2055 Eastern Daylight Time (EDT), the Watts Bar Nuclear Plant Unit 1 reactor was manually tripped due to a loss of Steam Generator (SG) number 2 level control. Concurrent with the reactor trip, the Auxiliary Feedwater (AFW) system
{EIIS:BA} actuated as designed. All Control and Shutdown rods inserted properly. All safety systems responded as designed.
This event is being reported to the Nuclear Regulatory Commission (NRC) under 10 CFR 50.73(a)(2)(iv)(A) as a safety system actuation of the Reactor Protection System (RPS) and the AFW system.
B. Status of structures, components, or systems that were inoperable at the start of the event and that contributed to the event No inoperable structures, systems, or components contributed to this condition.
C. Dates and approximate times of occurrences
Date Time (EDT}
8/31/19 2040 8/31/19 2055 8/31/19 2056 8/31/19 2057 8/31/19 2115 Entered 1-AOl-16 due to placing number 2 SG Main Feedwater Regulating Valve (MFRV){EIIS:FCV} in manual due to issues maintaining SG 2 water level.
Unit 1 Manual Reactor trip due to inability to maintain number 2 steam generator water level with the failure of SG 2 MFRV.
Entered 1-E-O, Reactor Trip or Safety Injection Transitioned to 1-ES-0.1, Reactor Trip Response Transitioned to 1-G0-5, Unit Shutdown from 30 percent Reactor Power to Hot Standby
D. Manufacturer and model number of each component that failed during the event
2019 003 00
E. Other systems or secondary functions affected
No other systems or secondary functions were affected.
F. Method of discovery of each component or system failure or procedural error
The component failure became apparent when SG 2 water level could not be maintained.
G. Failure mode, mechanism, and effect of each failed component The MFRV closed due to a failed actuator diaphragm.
H. Operator actions
Upon identifying the SG 2 MFRV was not properly controlling SG level, operations personnel manually tripped the plant and followed operations procedures in response to a plant trip.
I.
Automatically and manually initiated safety system responses
The plant was manually tripped when the SG 2 MFRV could not maintain SG 2 level. All Control and Shutdown rods inserted properly and the AFW system actuated as designed.
Ill.
Cause of the Event
A Cause of each component or system failure or personnel error This event was likely caused by diaphragm case bolt relaxation. This relaxation resulted in additional load on the bolt holes in the diaphragm, causing tearing of the valve diaphragm and its failure.
No human performance root causes were identified for this event.
IV.
Analysis of the Event
The SG MFRVs control flow to the steam generators to maintain level within a desired operating band. The isolation of a single MFRV causes the level in the associated SG to rapidly lower. On August 31, 2019 when SG 2 MFRV failed closed, SG level lowered and operations personnel manually tripped the reactor prior to reaching the SG level automatic trip setpoint.
Investigation found the MFRV actuator diaphragm case bolt torque to be at 10 ft-lbs or less, approximately 50% of the torque value specified by the MFRV maintenance instruction. This 2019 -
003 00 likely resulted in load being carried at the diaphragm bolt holes and consequently the tearing and failure of the diaphragm.
V.
Assessment of Safety Consequences
This event closely matches and is bounded by the Loss of Normal Feedwater event described in the Updated Final Safety Analysis Report (UFSAR). A probabilistic risk review of this event shows the risk from this trip is very small.
A Availability of systems or components that could have performed the same function as the components and systems that failed during the event Not applicable.
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 Not applicable.
C. For failure that rendered a train of a safety system inoperable, an estimate of the elapsed time from the discovery of the failure until the train was returned to service Not applicable.
VI.
Corrective Actions
These events were entered into the Tennessee Valley Authority (TV A) Corrective Action Program and are being tracked under Condition Report (CR) 1545537.
A. Immediate Corrective Actions
The valve diaphragm was replaced and torqued to a higher value than previously specified.
B. Corrective Actions to Prevent Recurrence or to reduce probability of similar events occurring in the future VII.
Previous Similar Events at the Same Site
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, the NRG may not conduct or sponsor, and a person is not required to respond 1D, the information collection.
YEAR 2019 -
- 3. LER NUMBER SEQUENTIAL NUMBER 003 REV NO.
00 LER 391 /2019-001-00 submitted on July 18, 2019 documents an event where the reactor was manually tripped as a result of a MFRV failing closed as a result of a failed diaphragm. While the component failure is the same, this event was due to a defective diaphragm.
LER 391/2017-002-00 submitted on May 12, 2017, documents an event where the reactor was manually tripped as a result of a secondary plant transient. This event resulted when scaffold crews inadvertently depressed the local trip button for the 2A Hotwell pump, which resulted in the secondary system transient.
VIII.
Additional Information
There is no additional information.
IX.
Commitments
There are no new commitments. Page _5_ of _5_