05000482/LER-2016-002, Regarding Loss of Switchyard Bus Results in Emergency Diesel Generator Actuation
| ML17024A061 | |
| Person / Time | |
|---|---|
| Site: | Wolf Creek  |
| Issue date: | 01/16/2017 |
| From: | Shawn Smith Wolf Creek |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| WO 17-0001 LER 16-002-00 | |
| Download: ML17024A061 (5) | |
| 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)(ix)(A) 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) |
| 4822016002R00 - NRC Website | |
text
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'NUCLEAR OPERATING CORPORATION Stephen L. Smith Plant Manager U. S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, DC 20555 January 16, 2017 WO 17-0001
Subject:
Docket No. 50-482:
Licensee Event Report 2016-002-00, "Loss of Switchyard Bus Results in Emergency Diesel Generator Actuation" Gentlemen:
The enclosed Licensee Event Report (LER) 2016-002-00 is being submitted pursuant to 1 O CFR 50.73(a)(2)(iv)(A) regarding a valid actuation of one of the emergency diesel generators at Wolf Creek Generating Station.
This letter contains no commitments. If you have any questions concerning this matter, please contact me at (620) 364-4093, or Cynthia R. Hafenstine (620) 364-4204.
SLS/rlt Enclosure cc:
K. M. Kennedy (NRC), w/e B. K. Singal (NRC), w/e N. H. Taylor (NRC), w/e Senior Resident Inspector (NRC), w/e Sincerely, Stephen L. Smith P.O. Box 411 /Burlington, KS 66839 /Phone: (620) 364-8831 An Equal Opportunity Employer M/F/HCNET
NRC FORM366 U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY OMB: NO. 3150-0104 EXPIRES: 10/31/2018 (06-2016)
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 learned are incorporated into the licensing process and fed back to industry.
~
LICENSEE EVENT REPORT (LER)
Send comments regarding burden estimate to the FOIA, Privacy and Information Collections
)
Branch (T-5 F53), U.S. Nuclear Regulatory Commission, Washington, DC 20555-0001, or by e-mail (See Page 2 for required number of digits/characters for each block)*
to lnfocollects.Resource@nrc.gov, and to the Desk Officer, Office of Information and Regulatory Affairs, NEOB-10202, (3150-0104), Office of Management and Budget, Washington, DC 20503. If a (See NUREG-1022, R.3 for instruction and guidance for completing this form means used to impose an information collection does not display a currently valid OMB control htt[l://www.nrc.gov/reading-rm/doc-collections/nuregs/staff/sr1022/r3Q number, the NRG may not conduct or sponsor, and a person is not required to respond to, the information collection.
- 3. PAGE Wolf Creek Generating Station 05000 482 1 OF4
- 4. TITLE Loss of Switchyard Bus Results in Emergency Diesel Generator Actuation
- 5. EVENT DATE
- 6. LER NUMBER
- 7. REPORT DATE
- 8. OTHER FACILITIES INVOLVED I
SEQUENTIAL I REV FACILl1Y NAME DOCKET NUMBER MONTH DAY YEAR YEAR NUMBER NO.
MONTH DAY YEAR 05000 11 16 2016 2016 -
002 00 01 16 2017 FACILl1Y NAME DOCKET NUMBER 05000
- 9. OPERATING MODE
- 11. THIS REPORT IS SUBMITTED PURSUANT TO THE REQUIREMENTS OF 10 CFR §: (Check all that apply)
D 20.2201 (b)
D 20.2203(a)(3)(i) 0 50.73(a)(2)(ii)(A)
D 50.73(a)(2)(viii)(A) 5 D 20.2201 (d)
D 20.2203(a)(3)(ii) 0 50.73(a)(2)(ii)(B)
D 50.73(a)(2)(viii)(B)
D 20.2203(a)(1)
D 20.2203(a)(4)
D so.73(a)(2)(iii)
D 50.73(a)(2)(ix)(A)
D 20.2203(a)(2)(i)
D 50.36(c)(1)(i)(A) t8l 50. 73(a)(2)(iv)(A)
D 50.73(a)(2)(x)
- 10. POWER LEVEL D 20.2203(a)(2)(ii) 0 50.36(c)(1)(ii)(A)
D 50.73(a)(2)(v)(A)
D 73.71(a)(4)
D 20.2203(a)(2)(iii)
D so.36(c)(2)
D 50.73(a)(2)(v)(B)
D 73.71(a)(S) 000 D 20.2203(a)(2)(iv)
D so.46(a)(3)(ii)
D 50.73(a)(2)(v)(C)
D 73.77(a)(1)
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) 0 50.73(a)(2)(i)(B)
D 50.73(a)(2)(vii)
D 73.77(a)(2)(ii)
D 50.73(a)(2)(i)(C) 0 OTHER Specify in Abstract below or in DESCRIPTION (cont.)
i YEAR SEQUENTIAL i
NUMBER
! 2016:-I 002 REV NO.
1-G The TX7 digital differential relay scheme provides a standard configuration with "primary" and "secondary" protective relays, each with the capability of isolating TX7. Troubleshooting activities focused on the reason the primary relay tripped and the secondary relay did not trip. Wolf Creek technicians identified a jumper on the TX7 primary differential relay CT circuit had been improperly landed. The jumper was designed to run from the neutral circuit of one CT to the neutral circuit of the other. However, technicians had incorrectly landed the jumper from the neutral of the first CT onto the "C" phase of the other. This allowed current from the TX6 fault event to be detected in the TX7 primary differential relay circuit.
BASIS FOR REPORTABILITY The actuation of the Train "A" EOG described in this event is reportable per 10 CFR 1 O CFR
- 50. 73(a)(2)(iv)(A), which requires reporting of "Any event or condition that resulted in manual or automatic actuation of any of the systems listed in paragraph (a)(2)(iv)(B) of this section." Paragraph (B)(8) of 10 CFR
- 50. 73(a)(2)(iv) includes "Emergency ac electrical power systems, including: emergency diesel generators (EDGs)."
CAUSE
The preliminary apparent cause was a human performance error that led to the CT neutral circuit wiring on the TX7 primary differential relay being landed on the incorrect termination point. This cause is supported by the fact that this incorrect termination allowed additional current to be introduced onto the "C" phase relay circuit, which initiated the trip circuit actuation following the fault on TX6.
A preliminary contributing cause was identified that verification techniques and post-modification testing failed to identify an improperly landed termination.
The cause analysis is ongoing and includes a reconstruction of the wiring circuit.
CORRECTIVE ACTIONS
The wiring termination error on the TX7 primary differential protective relay was corrected, and its functionality was verified through testing of the circuit. The secondary differential protective relay wiring was verified to be correct. TX7 was tested to ensure it was not damaged or faulted. The East Switchyard Bus, the TX7 differential relays and TX7 were restored to service satisfactorily. Further corrective actions will continue to be evaluated as part of Condition Report 109467.
SAFETY SIGNIFICANCE
l 05000-1 I YEAR SEQUENTIAL ID NUMBER 1 ~-I 002 482 The safety significance of this event is low. The Train "A" EOG automatically started properly when a loss of AC power to NB01 was detected. The Train "A" EOG then supplied power to NB01 as designed. All other systems functioned normally including the shutdown sequencer. Shutdown cooling was being provided by Train "B" RHR and was uninterrupted. The plant remained in Mode 5 through troubleshooting and restoration. The West Switchyard Bus and NB02 remained stable.
OPERATING EXPERIENCE/PREVIOUS EVENTS LER 2012-001-01 described a catastrophic failure of the Main Generator output breaker which resulted in the subsequent loss of the East Switchyard 345 kV Bus and a trip of the main turbine. Coincident with the loss of the East Switchyard Bus, a rapid transfer of the non-safety busses from the Unit Auxiliary Transformer to the Startup Transformer occurred. A differential relay trip on the Startup Transformer resulted in a loss of the West Switchyard Bus and a loss of offsite power. The cause for the loss of the Startup Transformer (and the subsequent loss of offsite power) was that there was a phase-to-phase short circuit between two unused current transformer wires that were missing insulation sleeves. Corrective actions included repairing the wires by installing insulating sleeves, performing additional inspections on the Startup Transformer and satisfactory testing of the Startup Transformer. Additionally, Wolf Creek procedures were revised to ensure the work controls process has sufficient controls to address site vendor performance., Page 4
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