05000390/LER-1917-004, Regarding Manual Reactor Trips Due to Failed Reactor Coolant Pump Power Transfer During Plant Startup
| ML17180A512 | |
| Person / Time | |
|---|---|
| Site: | Watts Bar  |
| Issue date: | 06/29/2017 |
| From: | Simmons P Tennessee Valley Authority |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| LER 17-004-00 | |
| Download: ML17180A512 (7) | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2) |
| 3901917004R00 - NRC Website | |
text
Tennessee Valley Authority, Post Office Box 2000, Spring City, Tennessee 37391 June 29, 2017 10 cFR 50 73 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 Subject: Licensee Event Report 39012017-004-00, Manua! Reactor Trips Due to Failed Reactor Coolant Pump Power Transfer During Ptant Startup This submittal provides Licensee Event Report (LER) 390t2017-004-OO. This LER provides details concerning two manual reactor trips that occurred when a Reactor Coolant Pump failed to properly transfer from its alternate to normal power supply. This report is being submitted in accordance with 10 CFR 50.73(a)(2)(ivXA). A supptement to this LER is anticipated to be submitted by August 31, 2011.
There are no regulatory commitments contained in this letter. Please direct any questions concerning this matter to Kim Hulvey, WBN Licensing Manag er, at (423) 36s-l1zo.
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Site Vice President Watts Bar Nuclear Plant Enclosure cc: See Pag e 2 ectfull
U.S. Nuclear Regulatory Commission Page 2 June 29,2017 cc (Enclosure):
NRC Regional Administrator - Region II NRC Senior Resident lnspector - Watts Bar Nuclear Plant
NRC FORM 366 (o4-2O17)
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+-a-tffi U.S. NUCLEAR REGULATORY COMMISSION LICENSEE EVENT REPORT (LER)
APPROVED BY oMB: No.31s0-0104 ExptRES: oyyEon
, the NRC may not conduct or sponsor, and a person is not required to respond to, the information collection.
- 1. FACILITY NAME Watts Bar Nuclear Plant, Unit 1
- 2. DOCKET NUMBER 05000390 10F5
- 3. PAGE
- 4. TITLE Manual Reactor Trips Due to Failed Reactor Coolant Pump Power Transfer During Plant Startup
- 5. EVENT DATE
- 6. LER NUMBER
- 7. REPORT DATE
- 8. OTHER FACILITIES INVOLVED MONTHI ORV I yrnn YEAR I ti,tr.J#.
REV NO MONTH I DAY YEAR FACILITY NAME N/A losooo 05 02 l 2017 2017 004 - 00 06 29 2017 FACILlTYNAME m
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- 9. OPERATING MODE
- 11. THIS REPORT lS SUBMITTED PURSUANT TO THE REQUIREMENTS OF 10 CFR g: (Chec k ail that appty) 1 tr zo zzol (b) tr zo zzo3(a)(3)(i) tr 50 73(aX2XiiXA) tr 50 73(a)(2)(viiiXA) tr zo zzol (d) tr zo zzo3(aX3Xii)
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X 50 73(aX2)(ivXA) tr 50 73(aX2)(x)
- 10. POWER LEVEL 26 tr zo zzo3(aX2Xii) tr 50 36(cX1)(iiXA) tr 50 73(aX2)(vXA) tr n 11 (aX4) tr 20 2203(a)(2)(iii) n 50 36(c)(2) tr 50 73(aX2XvXB) tr rc 71 (aX5) t] zo 2zo3(a)(2)(iv) tl 50 46(ax3)(ii) tr 50 73(a)(2)(vXC) tl ft zr(a)(1) tr zo 22o3(aX2Xv) n 50 73(a)(2XiXA) tr 50 73(aX2)(vXD) tr ft TT(aX2)(i) tr zo.zzo3(aX2Xvi) tl 50 73(aX2)(iXB) n 50 73(a)(2Xvii) t] ft T7(ar(2Xii) tr 50 73(aX2)(iXC) tr OTHER Specify in Abstract betow or in NRC Form 3664 LICENSEE CONTACT FOR THIS LER 12.
LICENSEE CONTACT Dean Baker, Licensing Engineer TELEPHONE NUMBER (ndude Area Code) 423-452-4589cnuse I sysrEM lcorrreoNENr I,^ts+UH;- l*t?3[$'.:l-.
CAUSE
SYSTEM I COMPONENT MANU-I REPORTABLE FACTURER I TO EPIX AITNIRLYIWESIY
- 14. SUPPLEMENTAL REPORT X VfS (ff yes, comptete 15.
EXPECTED EX PECTE D SUEMISS/Oru DATE) tr NO
- 15. EXPECTED SUBMISSION DATE MONTHT ORY I YERR 08 31 I 2017 ABSTRACT (Limit to 1400 spaces, i.e., approximately 15 singte-spaced typewritten lines)
On May 2,2017, at 1945 Eastern Daylight Time (EDT) and on May 4,2017 at 1710 EDT, Watts Bar Nuctear (WBN)
Plant Unit 1 reactor was manually tripped due to a failure of the Reactor Coolant Pump (RCP) Board 1C normal feeder breaker to close during the planned power transfer to unit power following plant startup. Concurrent with each reactor trip, the Auxiliary Feedwater system actuated as designed. All control and shutdown rods fully inserted. All safety systems responded as designed for both events.
For the first event, the cause was incorrectly attributed to a high resistance contact resulting in the normal feeder breaker failing to close. ln the investigation following the second event, a relay associated witn tne RCp Board 1C controlcircuitwas found incorrectly configured due to a human performance issue, which resulted in a standing trip signal on the RCP normal feeder breaker. To prevent recurrence, procedures will be revlsed to address material control of pretested components. Additional corrective actions are still under evaluation.
NRC FORM 366 (04-2017)
I.
PLANT OPERATING CONDITIONS BEFORE THE EVENT
Watts Bar Nuclear Plant (WBN) Unit 1 was at approximately 26 percent rated thermal power (RTp) for the first trip and at approximately 28 percent for the second trip.
II.
DESCRIPTION OF EVENT
A. Event Summary On May 2,2017, at 1945 Eastern Daylight Time (EDT) and on May 4,2017 at 1710 EDT, Watts Bar Nuclear (WBN) Plant Unit 1 reactor was manually tripped due to a failure of the Reactor Coolant Pump (RCP) {EllS:P} Board 1C normal feeder breaker {EllS:BKR} to close during the planned power transfer to unit power {EllS:EA} during plant startup following a refueling outage.
Concurrent with the manual reactor trip, the Auxiliary Feedwater (AFW) {EllS:BA} system actuated as designed. All control and shutdown rods fully inserted. All safety systems responded as designed for both events.
These events are being reported to the Nuclear Regulatory Commission (NRC) under 10 CFR 50.73(aX2)(iv)(A) for initiation of a manual reactor trip and automatic actuation of the AFW system.
B. lnoperable structures, components, or systems that contributed to the Event Control relay WBN-1-RLY-245-0152-22, associated with the RCP Board 1C power transfer logic, was configured incorrectly.
C. Dates and Approximate Times of Occurrences
Date Time Event 4t06t2017 4108t2017 4t13t2017 5102t2017 5t02t2017 5t02t2017 5t03t2017 EDT 1945 1948 2012 Work Order (WO) 117754323 steps performed to set-up replacenrent relay WBN-1-RLY-245-0 152-22. Work steps include verification of contact configuration and an energized test. Craft took relay to Fix-lt Now (FlN) shop upon completion of bench test.
Craft gave relay to foreman for storage.
WO 117543323 work resumed, relay is installed in the Main Relay board. An independent verification of wire lifts and lands for the replacement relay is performed.
Unit 1 is manually tripped when RCP 1C failed to transfer to its normal source. Enter 1-E-0, Reactor Trip or Safety lnjection.
Transition to 1-ES-O.1, Reactor Trip Response.
Transition to 1-GO-s, Unit Shutdown from 30 percent Reactor Power to Hot Standby.
Troubleshooting incorrectly concludes that high resistance on a breaker limit switch is the cause of the breaker for the RCP Board 1C normal feeder failing to close.
Date Time Event 5104t2017 5104t2017 5104t2017 5107 t2017 5t09t2017 ED 17 10 17 16 1743 Unit 1 is manually tripped when the RCP Board its normal source. Enter 1-E-0.
1C failed to transfer to Transition to 1-ES-O.1, Reactor Trip Response.
Transition to 1-GO-s, Unit Shutdown from 30 Percent Reactor Power to Hot Standby.
Troubleshooting concludes that failure to transfer is associated with misconfigured relay contacts.
ilr.
0355 RCP Board 1C successfully transferred from alternate to normal power during plant startup.
D. Manufacturer and Model Number of Components that Failed During the Event The relay that failed was an MG-6 multi-contact Auxiliary Relay with six configurable contacts, part number 289B359A2 1, manufactured by Westinghouse Electric Corporation.
E. Other Systems or Secondary Functions Affected
All safety systems and secondary functions operated as designed.
F. Method of discovery of each Component or System Failure or Procedural Error
lnspection of relay WBN-1-RLY-245-0152-22 found that the contacts were not properly configured.
G. Failure Mode and Effect of Each Failed Component With the relay misconfigured, RCP 1C could not be loaded onto the plant unit board.
H. Operator Actions
For both events, when RCP Board 1C failed to transfer to its normal operating power source, plant operators manually tripped the reactor. An automatic trip is not expected for the plant conditions and the manual reactor trip was briefed prior to the commencement of the transfer evolution. plant operators promptly stabilized the plant and transitioned from the emergency operating procedures to the normal shutdown procedure.
l. Automatically and Manually lnitiated Safety System Responses The plant operators initiated a manual reactor trip when RCP 1C failed to transfer to its operating power source. AFW automatically actuated and all automatic systems operated as designed. -
CAUSE OF THE EVENT
A. The cause of each component or system failure or personnel error, if known.
After the first event, the cause was incorrectly attributed to a high resistance contact resulting in
IV the normal feeder breaker failing to close. ln the investigation following the second event, a relay associated with the RCP Board 1C control circuit was found incorrectly configured as a resufi of a loss of material control that occurred following bench testing but prior io instaltation.
1-RLY-245-152-22 had been replaced during the Unit 1 refueling outage. The replacement relay was installed with a misconfigured contact pairwhich provided astanding trip signalon the RCp Board Normal Feeder Breaker. This event has been preliminarily determined to be caused by a loss of material control.
B. The cause(s) and circumstiances for each human performance related root cause.
Following initial setup and testing of the relay during the refueling outage, the relay was staged in the FIN shop from April 6 to April 8,2017. This inappropriate storage resulted in j loss of riaterial control.
ANALYSIS OF THE EVENT
During a normal start up at WBN, after the main generator has been synchronized to the grid, the power source for the RCPs is transferred from the Common Station Service Transformers (CSSis, offsiti power) to the Unit Station S"ry99 Transformers (USSTs) which are powered by the main generator. With ietay WBN-1-RLY-245-0'152-Z2 misconfigured, the RCP normal feeder breaker to the USSTs would not clos6.
Prior to performing this power transfer, operations personnel had briefed on actions to perform in the event the power transfer failed, which included manually tripping the reactor. Operations personnel were able to promptly stabilize the plant following these trips.
ASSESSMENT OF SAFETY CONSEQUENCES
These events are bounded by a partial loss of forced reactor coolant flow, which is an anticipated operational occurrence described in the Final safety Analysis Report (FSAR).
A. Availability of systems or components that could have performed the same function as the components and systems that failed during the event Allsafety systems operated as designed during this event.
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 residuai 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 All safety systems operated as designed during this event.
V
VI vilt vil.
CORRECTIVE ACTIONS
These events were entered into the Tennessee Valley Authority (TVA) Corrective Action program and are being tracked under Condition Reports (CRs) 1291i40 and 1292211.
A. lmmediate Corrective Actions Following the second event, the misconfigured relay was replaced and properly tested.
B. Corrective Actions to Prevent Recurrence or to Reduce Probability of Similar Events Occurring in the Future Procedures related to control of materials will be revised to ensure requirements are established to appropriately label materials to identify pretesting has been satisfactorily completed. Additional corrective actions are being evaluated and will be provided in a supplement to this report.
PREVIOUS SIMILAR EVENTS AT THE SAME SITE
A manual reactor trip was reported to the NRC in LER 391t2017-OO2 dated May 12,2017. This event was attributed to craft personnel inadvertently tripping a secondary pump, which led to a secondary plant kansient requiring operations personnel to manually trip the plant when steam generator levels could not be adequately maintained. While the event described in this LER also involveJhuman performance, the prior event involved contractor control.
ADDITIONAL INFORMATION
None.
COMMITMENTS
None.
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