05000390/LER-2020-001, Manual Reactor Trip Due to Lowering Steam Generator Level Caused by a Hand Station Failure
| ML20108E838 | |
| Person / Time | |
|---|---|
| Site: | Watts Bar  |
| Issue date: | 04/17/2020 |
| From: | Anthony Williams Tennessee Valley Authority |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| LER 2020-001-00 | |
| Download: ML20108E838 (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)(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)(i)(B), Prohibited by Technical Specifications 10 CFR 50.73(a)(2)(vii), Common Cause Inoperability 10 CFR 50.73(a)(2)(i) |
| 3902020001R00 - NRC Website | |
text
Tennessee Valley Authority, Post Office Box 2000, Spring City, Tennessee 37381 April 17, 2020 WBL-20-009 ATIN: 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 390/2020-001-00, Manual Reactor Trip Due to Lowering Steam Generator Level Caused by a Hand Station Failure This submittal provides Licensee Event Report (LER) 390/2020-001-00. This LER provides details concerning a manual plant trip as a result of lowering level in steam generator number 3. 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.
nthony L. Williams IV Site Vice President Watts Bar Nuclear Plant Enclosure cc: See Page 2
U.S. Nuclear Regulatory Commission WBL-20-009 Page 2 April 17, 2020 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: 04/30/2020 (04-2020) 3.Page Watts Bar Nuclear Plant, Unit 1 05000390 1 OF 5
- 4. Title Manual Reactor Trip Due to Lowering Steam Generator Level Caused by a Hand Station Failure
- 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 Month Day Year N/A 05000 Number No.
Facility Name Docket Number 02 19 2020 2020 - 001
- - 00 04 17 2020 NA 05000
- 9. Operating Mode
- 11. This Report is Submitted Pursuant to the Requirements of 10 CFR §: (Check all that apply)
D 20.2201(bl D 20.2203(aJ(3)(il D 50.73(a)(2)(ii)(A)
D 50.73(a)(2)(viii)(A)
D 20.2201(dl D 20.2203(aJ(3Hii)
D 50.73(a)(2)(ii)(B)
D 50. 73(a)(2)(viii)(B) 1 D
D D 20.2203(aJ(1)
D 20.2203(a)(4l 50.73(a)(2)(iii) 50.73(a)(2)(ix)(A)
D 20.2203(aH2J(il 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(aJ(2Hiil D 50.36(c)(1 )(ii)(A)
D 50.73(a)(2)(v)(A)
D 73.71 (a)(4)
D 20.2203(aJ(2J(iiiJ 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)
D 50.73(a)(2)(i)(B)
D 50.73(a)(2)(vii)
D 13.11(a)(2J(iil D 50.73(a)(2)(i)(C)
D OTHER Specify in Abstract below or in 2020 -
001 00
D. Manufacturer and model number of each component that failed during the event
The component that failed was a hand station (1-FIC-003-0090) provided by Foxboro.
The pushbutton in the hand station was a Honeywell, AML 21 Series CQA938E.
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 was discovered during post trip troubleshooting.
G. Failure mode, mechanism, and effect of each failed component While in manual SG level control, hand station (1-FIC-003-090) pushbutton stuck on the Loop 3 controller which provided a closing signal when open was demanded.
H. Operator actions
When operators attempted to increase feed flow to raise level in SG number 3, level continued to lower. Prior to reaching the automatic reactor trip critieria on SG level, operators manually tripped the reactor.
I.
Automatically and manually initiated safety system responses
The plant was manually tripped when the SG 3 level could not be maintained. 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 caused when, while in manual SG level control, hand station (1-FIC-003-090) pushbutton stuck on the Loop 3 controller which provided a closing signal when open was demanded, which resulted in the SG number 3 MFRV closing.
IV.
Analysis of the Event
The SG MFRVs control flow to the steam generators to maintain level within a desired operating band when operating in automatic. The isolation of a single MFRV causes the level in the associated SG to rapidly lower.
While performing a maintenance activity, 1-FIC-003-0090 was placed in manual. When operators manipulated the hand station to reduce feedwater flow to SG number 3, the decrease pushbutton became stuck. Subsequent attempts by the operators to raise feed flow resulted in the MFRV for SG number 3 going closed and the need to manually trip the unit.
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 (TVA) Corrective Action Program and are being tracked under Condition Report (CR) 1587975.
A. Immediate Corrective Actions
The valve hand station was replaced.
APPROVED BY 0MB: NO. 3150-0104 EXPIRES: 04/30/2020 YEAR 2020 -
- 3. LER NUMBER SEQUENTIAL NUMBER 001 REV NO.
00 B. Corrective Actions to Prevent Recurrence or to reduce probability of similar events occurring in the future Corrective actions include revising plant procedures to classify activities that replace automatic control availability with manual control action as risk significant and require risk evaluation and mitigation strategies.
VII.
Previous Similar Events at the Same Site
LER 390/2019-003-00 submitted on October 21, 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 October 2019 event is similar to this event, the causes are different.
VIII.
Additional Information
There is no additional information.
IX.
Commitments
There are no new commitments. Page _s_ of _s_