05000391/LER-2019-001, Regarding Manual Reactor Trip Due to Main Feedwater Regulating Valve Failing Closed
| ML19199A085 | |
| Person / Time | |
|---|---|
| Site: | Watts Bar  |
| Issue date: | 07/18/2019 |
| From: | Anthony Williams Tennessee Valley Authority |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| WBL-19-037 LER 2019-001-00 | |
| Download: ML19199A085 (7) | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(iv)(A), System Actuation 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)(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) |
| 3912019001R00 - NRC Website | |
text
Tennessee Valley Authority, Post Office Box 2000, Spring City, Tennessee 37381 July 18, 2019 WBL-19-037 ATTN : Document Control Desk U.S. Nuclear Regulatory Commission Washington, D.C. 20555-0001 Watts Bar Nuclear Plant, Unit 2 Facility Operating License No. NPF-96 NRC Docket No. 50-391 10 CFR 50.73
Subject:
Licensee Event Report 391/2019-001-00, Manual Reactor Trip Due to Main Feedwater Regulating Valve Failing Closed This submittal provides Licensee Event Report (LER) 391 /2019-001-00. 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.
o 1ams Site Vice President Watts Bar Nuclear Plant Enclosure cc: See Page 2
U.S. Nuclear Regulatory Commission WBL-19-037 Page 2 July 18, 2019 cc (Enclosure):
NRC Regional Administrator - Region II NRC Senior Resident Inspector - Watts Bar Nuclear Plant
NRCFORM366 U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY 0MB: NO. 3150-0104 EXPIRES: 03/31/2020 (04-2018)
ES1inaled bu'den per response m COf!1Jly with this mandalory collection request 80 holn.
Repor1ed lessons leaned n incorporaled in1o the licensing process a1d led back m industy. Send ccnments regring bu'den estimala 1o the lnfcrmation SeNices Branch
'¥.'
LICENSEE EVENT REPORT (LER)
(T-2 F43), U.S. Nuclear RegiJauy Ccnmssion, Washing1on, DC 20555-0001,oc by 1HNi1 i
1o lnb:olleels. Resowce@m:.gov, and m the Desk Officer, Office of lnbmation ll1CI
\\
'I Regumy Affairs, NEOB-10202, (3150-0104), Office ri Ma1agement and Budget, Washingm, DC 20503. H a means used 1o ~
an inbnnalon colection does not clsplay a cllT8t1ly vald 0MB c:onlrol number, the NRC may not conduct oc sponsor, and a person is not reqlired 1o respond m, the lnfoonation colectlon.
- 1. Faclllty Name
- 2. Docket Number 3.Page Watts Bar Nuclear Plant, Unit 2 05000391 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 Rev Facility Name Docket Number Month Day Year Year Number No.
Month Day Year N/A 05000 Facility Name Docket Number 05 22 2019 2019 - 001
- - 00 07 18 2019 NA 05000
- 9. Operating Mode
- 11. This Report is Submitted Pursuant to the Requirements of 10 CFR §: (Check all that apply)
D 20.2201
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><m>
D 50. 73(a)(2)(ix)(A)
D 20.2203<a><2>
D 50.36(c)(1 )(i)(A) 181 50. 73(a)(2)(iv)(A)
D 50.73(a)(2)(x)
- 10. Power Level D 20.2203<a><2><n>
D 50.36(c)(1 )(ii)(A)
D 50.73(a)(2)(v)(A)
D 13. 11 <a><4>
D 20.2203<a><2><m>
D 5o.3e<c><2>
D 50.73(a)(2)(v)(B)
D 13.11<a><5>
D 20.2203(a)(2)(iv)
D 5o.4e<a><3>(ii)
D 50.73(a)(2)(v)(C)
D 13.77(a><1>
95 D 20.2203(a)(2)(v)
D 50.73(a)(2)(i)(A)
D 50.73(a)(2)(v)(D)
D 13.77(a><2>
D 20.2203(a)(2)(vi)
D 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 2019 -
001
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 the SG 2 MFRV failed closed.
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 had failed closed, 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 failed closed.
00 111.
Cause of the Event
A. Cause of each component or system failure or personnel error The SG 2 MFRV failed closed as a result of the installation of a defective valve actuator diaphragm.
The personnel performing maintenance on the SG 2 MFRV missed an opportunity to identify the diaphragm they replaced was defective.
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 May 22, 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 revealed the diaphragm in the MFRV that had been replaced during the prior unit outage had torn. This failure was due to a defective diaphragm. Additionally, maintenance personnel did not identify the defect prior to installation.
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.
- 8. 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 (TVA) Corrective Action Program and are being tracked under Condition Report (CR) 1518719.
A. Immediate Corrective Actions
The valve diaphragm was replaced with a non-defective diaphragm and the plant was returned to operation.
- 8. Corrective Actions to Prevent Recurrence or to reduce probability of similar events occurring in the future Corrective actions include revising the maintenance instructions for diaphragm inspection requirements.
VII.
Previous Similar Events at the Same Site
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 lilT UIIID: l'IU, v *-- -
CAr"l"C'°: --*-,, ___ _
Estinated bllden per response ID ~ly with this mandmy collection request 80 hours9.259259e-4 days <br />0.0222 hours <br />1.322751e-4 weeks <br />3.044e-5 months <br />.
Reporled lessons leaned n inccrpcraled Int> the licensing process and fed ba:k ID industy. Send comments r&ga'ding bu1len estimale ID the lnbmalon Services Br111Ch (T-2 F43), U.S. Nuclew Regulatory Conmssion, Washingt>n, DC 20555-0001,or by e-mail kl 1nrocoilec1S. Reso~m:.gov, and ID the Oesk Officer, Office of lnbmalion and ReglUlllly Alias, NEOS-10202, (3150-0104), Ollce fl Ma1agernenl 111d Budget, Washingt>n, DC 20503. ff a means used kl in1J()S8 an inbmalion colecion does not
<f,splay a etmntly valid 0MB coml number, the NRC may not conduct or sponsor, and a person is not n,qlired ID respond kl, the infoonalion colection.
YEAR 2019
- 3. LER NUMBER SEQUENTIAL NUMBER 001 REV NO.
00 crews inadvertently depressed the local trip button for the 2A Hotwell pump, which resulted in the secondary system transient.
LER 391/2016-007-00 submitted on October 21, 2016 documents a manual reactor trip due to a loss of main feedwater. The loss of main feedwater was due to a leak on a hydraulic fitting associated with the Main Feedwater Pump Turbine High Pressure Governor valve, resulting in the valve going partially closed. Subsequent investigation determined the leak to be caused by the installation of incompatible fittings associated with the governor valve that occurred during plant construction.
The previous similar events have different direct causes than this event.
VIII.
Additional Information
There is no additional information.
IX.
Commitments
There are no new commitments. Page _5_ of _5_