05000390/LER-2016-008, Regarding Emergency Diesel Generator Manual Start Due to Loss of Voltage on the 6.9kV Shutdown Board 1B-B
| ML16197A556 | |
| Person / Time | |
|---|---|
| Site: | Watts Bar  |
| Issue date: | 07/15/2016 |
| From: | Simmons P Tennessee Valley Authority |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| LER 16-008-00 | |
| Download: ML16197A556 (8) | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2) |
| 3902016008R00 - NRC Website | |
text
Tennessee Valley Authority, Post Office Box 2000, Spring City, Tennessee 37381 July 15, 2016 10 cFR 50 73 ATTN: Document Control Desk U.S. Nuclear Regulatory Commission Washington, D.C. 20555-0001
Subject:
Watts Bar Nuclear Plant, Units 1 and2 Facility Operating License No. NPF-90 and NPF-96 NRC Docket No. 50-390 and 50-391 Licensee Event Report 390/2016-008-00, Emergency Diesel Generator Manual Start Due to Loss of Voltage on the 6.9kV Shutdown Board 1B-B This submittal provides Licensee Event Report (LER) 390/2016-008-00. This LER provides details concerning an emergency diesel generator manual start due to loss of voltage on the 6.9kV Shutdown Board 1B-B during installation of the new open phase protective relays. This report is being submitted in accordance with 10 CFR 50.73(a)(2)(ivXA).
Please direct any questions concerning this matter to Gordon Arent, WBN Licensing Director, at (423) 365-2004.
Respectfully, Paul Simmons Site Vice President Watts Bar Nuclear Plant Enclosure cc. See Page 2
U.S. Nuclear Regulatory Commission Page 2 July 15, 2016 cc (Enclosure):
NRC Regional Administrator - Region II NRC Senior Resident lnspector - Watts Bar Nuclear Plant
NRC FORM 366 U.S. NUCLEAT. xEGULATORY COMMISSION (1 1-2015) a"ft"to""o-in4i LT.ENSEE EVEN' REP.RT (LER)
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-,,*r, APPROVED BY OMB:..v. 3150-0104 EXPIRES: 1013112018 Estimated burden per response to comply with this mandatory collection request 80 hours9.259259e-4 days <br />0.0222 hours <br />1.322751e-4 weeks <br />3.044e-5 months <br />.
Reported lessons leamed are incorporated into the licensing process and fed back to industry.
Send comments regarding burden estimate to the FOIA, Privacy and lnformation Collections Branch (T-5 F53), U.S. Nuclear Regulatory Commission, Washington, DC 2055S0001, or by internet +mail to lnfocollects.Resource@nrc,gov, and to the Desk fficer, Office of lnformation and Regulatory Affairs, NE0B-10202, (3150-0104), Office of Management and Budget, Washington, DC 20503. lf a means used to impose an information oollection does not display a cunenfly valid OMB confol number, the NRC may not conduct or sponsor, and a person is not required to respond to, the information collection.
- 1. FACILIW NAME Watts Bar Nuclear Plant, Unit 1
- 2. DOCKET NUMBER 05000390
- 3. PAGE 10F6
- 4. TITLE Emergency Diesel Generator Manual Start Due to Loss of Voltage on the 6.9kV Shutdown Board 1B-B
- 5. EVENT DATE
- 6. LER NUMBER
- 7. REPORT DATE
- 8. OTHER FACILITIES INVOLVED MONTHI DAY I YEAR YEAR I ti,t"t$sL REV NO.
MONTH I DAY YEAR FACILITY NAME I
DOCKET NUMBER Watts Bar Nuctear Plant, Unit 2 IOSOOO391 05 17 I 2A16 2016 r 008 00 07 15 2016 FACILITY NAME I
DOCKET NUMBER N/A INN
- 9. OPERATING MODE
- 11. THIS REPORT lS SUBMITTED PURSUANT TO THE REQUIREMENTS OF 10 CFR $: (Check ail thatapplfi Unitl-Mode1 Unit2-Mode3 n zo.22o1(b) tr 2o.2zo3(a)(3)(.)
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C. Dates and Approximate Times of Occurrences
Date Time (EDT) Event 05117116 1428 Clearance lifted to allow restoring protective relays to service.
05117116 1630 Loss of 6.9kV Shutdown Bd. 1B-B.
05117116 1630 Entered TS LCO 3.8.9, Action Condition A, One or more AC electrical power distribution subsystems inoperable.
05117116 1630 Entered 0-AOl-43.02, Loss of Unit 1 train B Shutdown Boards.
05117116 1630 Manually started EDGs 1A-4, 2A-A and 2B-B.
05117116 1630 Entered TS LCO 3.8.4, Action Condition A, One vital DC electrical subsystem inoperable.
05117116 1630 Entered TS LCO 3.7.11, Action Condition A, One CREATCS train inoperable.
05117116 1632 Entered TS LCO 3.7.8, Action Condition A, One ERCW train inoperable.
05117116 1802 Offsite power restored to 6.9kV Shutdown Bd. 1B-B.
D. Manufacturer and Model Number of Components that Failed There were no component failures.
E. Other Systems or Secondary Functions Affected
No other systems or functions were affected.
F. Method of discovery of each Component or System Failure or Procedural Error
The event was self-evident at the time the 6.9kV Shutdown Board 1B-B lost power.
G. Failure Mode and Effect of Each Failed Component During restoration of dc control power, it was noted that the B-phase relays for the LOV (phase B-C),
DV (phase B-C) and OV (phase A-C), did not reset while the other relays did. After trouble shooting, the decision was made to pull PK Test Block 1-PK-211-81714 to isolate the ac sensing voltage from the newly installed OP relays and eliminate any associated wiring as a possible cause for inability to reset the above relays. This action created a voltage transient on the PT secondary that caused the remaining LOV relays to trip. Once the protective relay trip logic for the LOV relays was satisfied the 6.9kV Shutdown Board 1B-B tripped isolating the bus from offsite power. This event was attributed to vulnerabilities in board restoration procedures due to reliance on the same dc control power fuses to isolate control power to both the sensing relays and the protective relay trip logic circuit.
H. Operator Actions
- 1. Operators entered TS LCO 3.8.9, Distribution System, Condition A, One or more AC electrical power distribution subsystems inoperable, for Units 1 and2 with a Completion Time of 8 hours9.259259e-5 days <br />0.00222 hours <br />1.322751e-5 weeks <br />3.044e-6 months <br />.
- 2. Operators entered AbnormalOperating Instruction, 0-AOl-43.02, Loss of Unit 1 Train B Shutdown Boards, and manually started EDGs 1A-A, 2A-4, and 2B-8. Allequipment operated properly. The EDGs were not required to be paralleled to the boards because offsite power was available.
- 3. Operators entered TS 3.8.4, Condition A, One vital DC electricalsubsystem inoperable, for Units 1 and 2 due to Battery Board ll voltage below 128VDC following loss of power. Operators transferred Battery Charger ll normal power supply to the alternate supply within the required 2 hour2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br /> Completion Time.
- 4. Operators entered TS 3.7.1 1, Condition A, One CREATCS train inoperable for Units 1 and 2. Entry was due to high oil temperature alarm on the B-train Main Control Room (MCR) Chiller following loss of power. Operators transferred control room cooling functions to the Atrain MCR Chiller.
- 5. Operators entered TS 3.7.8, Condition A, One ERCW train inoperable for Units 1 and2. Operators place B-train ERCW pumps E-B and G-B in the Stop Pull to Lock Position following loss of power to the 6.9kV Shutdown Bd. 1B-B. However, Btrain ERCW pumps F-B and H-B were available because these pumps are powered by the 6.9kV Shutdown Bd. 2B-B which did not lose offsite power and the EDG 2B-B was operable.
CAUSE OF THE EVENT
A. The cause of each component or system failure or personnel error, if known.
There was no component or system failure or personnel error.
B. The cause(s) and circumstiances for each human performance related root cause.
The cause was attributed to inadequate restoration procedures due to reliance on the same dc control power fuses to isolate control power to both the sensing relays and the protective relay trip logic circuit.
ANALYSIS OF THE EVENT
As described in Section ll.G, the LOV relays initiated the trip sequence to separate the offsite power circuits from the 6.9kV Shutdown Board 1B-B due to cycling dc and ac sensing voltage to the protective relays.
When dc control power was restored, the B-phase LOV, DV, and OV relays were in the tripped state with the protective relay trip logic circuit enabled. When the PK test block was pulled during trouble shooting to remove the ac sensing voltage to the OP relays it created a voltage transient on the PT secondary circuit which caused the remaining LOV relays to trip. Once the 2 out of 3 trip logic for the LOV relays was satisfied the feeder breakers to the 6.9kV Shutdown Board 1B-B tripped isolating the bus from offsite power.
Based on discussion with the relay vendor the preferred sequence for restoring dc control power for the protective relays is to remove PK Test Block 1-PK-211-8717 from the protective relay trip logic circuit, restore dc control power (i.e., install dc control fuses), and then a final step to restore ac sensing voltage (i.e., install PT primary fuses). The above PK test block should not be reinstalled until all protective relays are verified reset (i.e., not tripped).
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V. ASSESSMENT OF SAFETY CONSEQUENCES
A. Availability of systems or components that could have performed the same function as the components and systems that failed during the event.
The design bases for the 6.9kV shutdown boards are that two shutdown boards within the same load group must be available to mitigate an accident on one unit and maintain the other non-accident unit in hot standby (Mode 3). There are two load groups A and B. Load group A is supported by 6.9kV Shutdown Boards 1A-A and 2A-A. Load group B is supported by 6.9kV Shutdown Boards 1B-B and 2B-B. Since a minimum of one load group (i.e., Shutdown Board 1A-A and 2A-A) was Operable, the design bases as defined in Chapters 8 and 15 of the Updated Final Safety Analysis Report (UFSAR) for the 6.9kV Shutdown Boards were met.
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. At the time of event WBN Unit 1 was in Mode 1 at 100 percent rated thermal power.
WBN Unit 2 was in Mode 3.
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.
The 6.9kV Shutdown Board 1B-B was inoperable for t hour and 32 minutes before offsite power was restored.
VI. CORRECTIVE ACTIONS
This event was entered into the Tennessee Valley Authority Corrective Action Program and is being tracked under Condition Report (CR) 1172243.
A. lmmediate Corrective Actions Operators entered AbnormalOperating lnstruction, 0-AOl-43.02, Loss of Unit 1 Train B Shutdown Boards, and manually started EDGs 1A-A, 2A-A, and 2B-8. All equipment operated properly. The EDGs were not required to be paralleled to their respective shutdown boards because offsite power was available.
B. Corrective Actions to Prevent Recurrence WBN will revise General Operating lnstruction 0-GOl-7, Generic Equipment Operating Guidelines, to include general guidance for disabling and restoring the 6.9kV protective relay trip logic circuits.
VII. ADDITIONAL INFORMATION
A. Previous similar events at the same plant
No previous similar events have occurred because the protective relays are not normally de-energized for any preventative maintenance. The configuration of de-energizing the relays was a requirement for installing the new open phase relays.
B. Additional Information
None.
C. Safety System Functional Failure Consideration This event did not result in a safe$ system functionalfailure because as a minimum load group A (i.e., Shutdown Board 1A-A and 2A-A) were available to mitigate the design bases events described in the UFSAR for either Unit 1 or 2.
D. Scrams with Complications Consideration There was no scram associated with this event.
VIII. COMMITMENTS
None.