05000390/LER-2013-004, Plant Trip on 500kV Transmission Line Fault
| ML13240A218 | |
| Person / Time | |
|---|---|
| Site: | Watts Bar  |
| Issue date: | 08/27/2013 |
| From: | Cleary T Tennessee Valley Authority |
| To: | Office of Nuclear Reactor Regulation, Document Control Desk |
| References | |
| LER 13-004-00 | |
| Download: ML13240A218 (6) | |
| Event date: | |
|---|---|
| Report date: | |
| LER closed by | |
| IR 05000390/2015000 (30 April 2015) | |
| 3902013004R00 - NRC Website | |
text
{{#Wiki_filter:TennesseeValleyAuthority,PostofficeBox2000,Springcit'ffi August 27, 2013 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 Nos. 50-390 Subject: Licensee Event Report 50-390/2013-004-00 Enclosed please find Licensee Event Report (LER) 50-390/2013-004-00 that has been prepared and submitted pursuant to 10 CFR 50.73. This LER reports a Unit 1 plant trip that occurred on June 28,2013. This condition is reported as an LER in accordance with 10 CFR 50.73(aX2XivXA), an event or condition that resulted in an automatic actuation of a safety system. There are no new regulatory commitments contained in this letter. Should you have questions regarding this report, please contact Donna Guinn, WBN Site Licensing Manager, at (423) 365-1 589. Respectfully, ,*--A ^ AA
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tJ / Timothy P. Cleary Site Vice President Watts Bar Nuclear Plant Enclosure cc (Enclosure): NRC Regional Administrator - Region ll NRC Senior Resident Inspector - Watts Bar Nuclear Plant, Unit 1
RC FORM 366 U.S. NUCLEAR REGULATORY COMMISSION (10-2010) LICENSEE EVENT REPORT (LER} APPROVED BY OMB NO. 3150.0104 EXPIRES 1OI31NA13 , 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 (WBN) Unit 1
- 2. DOCKET NUMBER 05000390
- 3. PAGE 1of5
- 4. TITLE Plant Trip on 500kV Transmisslon Line Fault
- 5. EVENT DATE
- 6. LER NUMBER
- 7. REPORT DATE
- 8. OTHER FACILITIES INVOLVED MONTH I DAY YEAR YEAR lt=-tt=JLts.
REV NO. MONTHI DAY YEAR FACILITY NAME DOCKET NUMBER 06 t28 2013 2A13 - 004 r 00 08 27 2013 FACILITY NAME DOCKET NUMBER
- 9. OPERATING MODE 1
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A. Cause of the Event
Preliminary findings from a root cause investigation that is in progress revealed a possible equipment cause (failure mode) could be a loose (A-phase) wire connection on a digital fault recorder connected to the CT of feeder breaker 5084. This determination was made based on available off-line testing and the exact equipment Root Cause is indeterminate untilfurther online testing can be performed. WBN is developing mitigating actions with support from external experts to reduce the likelihood of a plant trip in the event of another high resistance 500kV fault. No plant safety parameters exceeded their anticipated limits during this event, and no radiological and chemistry abnormalities were encountered post-trip. No safety functions were prevented or inhibited during this event and off-site power capabilities were maintained with the plant safety features responding as designed. There were no safety systems that were rendered inoperable or discovered to be degraded during this event and designed redundancy was maintained. There were no safety system functional failures.
NRC FORM 3664 U.S. NUCLEAR REGULATORY COMMISSION (ro-zoro) LTCENSEE EVENT REPORT (LER) CONTINUATION SHEET FACILITY NAME (1 DOCKET QI LER NUMBER (6) PAGE (3) Watts Bar Nuclear (WBN) Unit 1 05000390 YEAR ISEOUENTTAL IREVlSION I NUMBER I NUMBER 4of5 2013 -- 004 -- 00 NARRATIVE
B. Automatically and Manually Initiated Safety System Responses
The plant trip occurred when A-Phase protective differential relay 187TF received current above the actuation setpoint of 1.5 amperes (A) (i.e., registered a false fault in protected zone). The relay responded by actuating the 186GB relay [EllS: RLY94] resulting in a turbine trip. Since the reactor was above 50 percent power, the turbine trip resulted in an automatic reactor trip. When the main feedwater pumps tripped, an automatic start of all Auxiliary Feedwater (AFW) Pumps was initiated. There were no safety system failures that adversely affected technical specification parameters/conditions during this event. Post-trip review revealed that the event was not a scram with complications. C. Manufacturer and Model Number (or other identification) of each component that failed during the event At this time, WBN has not conclusively determined how the protective relaying scheme or its individual components failed.
D. Method of Discovery of Each Component or System Failure or Procedural Error
A root cause evaluation is in progress which has preliminarily identified that a potential human performance error associated with the installation of field wiring completed in 2011.
III. CAUSE OF THE EVENT
A. The cause of each component or system failure or personnel error, if known: Preliminary findings from a root cause investigation that is in progress revealed that a possible equipment cause (failure mode) could be a loose wire connection on a digitalfault recorder connected to the current transformer for feeder breaker 5084. Due to the ongoing root cause investigation, WBN has not conclusively determined how the protective relaying scheme or its individual components failed. A supporUrefute Kepner-Tregoe (K-T) matrix was developed to determine why the 187TF relay circuit mis-operated. The K-T analysis contained 14 possible causes that could be tested offline to determine the Equipment Cause. Testing included, continuity, megger, polarity, and CT Turns ratio testing, relay calibration, and design drawing walkdown of wiring, and push/pull testing of plug type connections (RTXP-8 wires). The only item from the K-T that was supported as a possible cause once testing was completed was a loose RTXP-8 connection found on A-Phase wiring from Breaker 5084 to the digitalfault recorder. Initial inspection found the RXTP-8 connection not fully engaged. Therefore, a possible equipment cause is a loose A-Phase RTXP-8 connection on wire 5082A21 from the Feeder Breaker 5084 CT to DFR #2. Additional causes may be identified depending on the results from the continuing cause evaluation. B. The cause(s) and circumstances for each human performance related cause: A "push/pull" technique should be used when installing and verifying CT digital fault recorder type connections. The root cause evaluation team interviewed craft personneland determined that this type of installation/verification process was performed as skill-of-the-craft. The rootU.S. NUCLEAR REGULATORY COMMISSION ( ro-zoro) LTCENSEE EVENT REPORT (LER) CONTINUATION SHEET FACILITY NAME (1 DOCKET QI LER NUMBER (6) PAGE (3) Watts Bar Nuclear (WBN) Unit 1 05000390 YEAR ISEOUENTTAL IREVlSlON I ruUUBER I NUMBER 5of5 2013 -- 004 -- 00 NARRAT]VE cause evaluation revealed that WBNl does not specifically require a push/pull verification to ensure RTXP-8 connections are appropriately terminated and the procedures that govern wire terminations does not include push/pull test verifications. IV CORRECTIVE ACTIONS A lmmediate Corrective Actions The loose wire (5082A21) at connector L-6A on the digital fault recorder was secured. B. Corrective Actions to Prevent Recurrence or to reduce probability of similar events occurring in the future The procedure governing the installation of these type connections will be revised to include requirements that these type connections are to be field verified by performing a push/pull test. Additional corrective actions may be developed depending on the results from the continuing cause evaluation.
PREVIOUS SIMILAR EVENTS
A review of internal operating experience did not reveal any previous events or conditions that involved the same underlying concern or reason as this event, such as the same root cause, failure, or sequence of events.
V. ADDITIONAL INFORMATION
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