05000364/LER-2014-002, Regarding Manual Reactor Trip Due to Loss of 2B Startup Auxiliary Transformer and Loss of Offsite Power
| ML14346A391 | |
| Person / Time | |
|---|---|
| Site: | Farley  |
| Issue date: | 12/12/2014 |
| From: | Gayheart C Southern Co, Southern Nuclear Operating Co |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| NL-14-1825 LER 14-002-00 | |
| Download: ML14346A391 (7) | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(ii)(A), Seriously Degraded 10 CFR 50.73(a)(2) 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)(1) 10 CFR 50.73(a)(2)(v), Loss of Safety Function |
| 3642014002R00 - NRC Website | |
text
Charyl A. Gayheart Vice President
- Farley Southam Nuclear Operating Company, Inc.
Farley Nuclear Plant Post Office Drawer 470 Ashford, Alabama 36312 Tel334.814.4511 Fax 334.814.4575 SOUTHERN '*
COMPANY December 12, 2014 Docket Nos.: 50-364 U.S. Nuclear Regulatory Commission A TIN: Document Control Desk Washington, D. C. 20555-0001 Joseph M. Farley Nuclear Plant - Unit 2 Licensee Event Report 2014-002-00 Manual Reactor Trip due to Loss of 28 Startup Auxiliary Transformer and Loss of Offsite Power Ladies and Gentlemen:
NL-14-1825 In accordance with the requirements of 10 CFR 50. 73(a)(2)(iv)(A) Southern Nuclear Company hereby submits the enclosed Licensee Event Report, "Manual Reactor Trip due to Loss of 28 Startup Auxiliary Transformer and Loss of Offsite Power."
This letter contains no NRC commitments. If you have any questions regarding the submittal, please contact Ms. Julie Collier at (334) 814-4639.
Sincerely, Ms. C. A.
heart Vice President - Farley CAG/JAC Enclosure: Unit 2 Licensee Event Report 2014-002-QO
cc:
Southern Nuclear Operating Company Mr. S. E. Kuczynski, Chairman, President & CEO Mr. D. G. Best, Executive Vice President & Chief Nuclear Officer Mr. M. D. Meier, Vice President-Regulatory Affairs Mr. D. R. Madison, Vice President-Fleet Operations Mr. B. J. Adams, Vice President-Engineering Mr. R. R. Martin, Regulatory Affairs Manager - Farley RTYPE: CFA04.054 U.S. Nuclear Regulatory Commission Mr. V. M. McCree, Regional Administrator Mr. S. A. Williams, NRR Project Manager-Farley Mr. P. K. Niebaum, Senior Resident Inspector-Farley Mr. K. E. Miller, Resident Inspector-Farley
Joseph M. Farley Nuclear Plant - Unit 2 NL-14-1825 Manual Reactor Trip due to Loss of 28 Startup Auxiliary Transformer and Loss of Offsite Power Enclosure Unit 2 Licensee Event Report 2014-002-00
NRC FORM 366 U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY OMB: NO. 3150.0104 EXPIRES: 01/31/2017 (02*:!014)
Esdmated burden par raspor158 to comply with this mandatary cCIIIacti<l!l request BO hour11.
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Reported lessons learned are lncorpomled into the r~eengng process and led back Ia lndUSlly. Send commenl!l regarding burden estunatnta ll1u FOIA, PriVacy und lnformaLon Collections Branch {T*6
\\;:~'?/ LICENSEE EVENT REPORT (LER)
FSJ), U.S. Nuclear Regulatory Commission, Washington, DC 2055S.OOOI, Ill' by lnlomel o-mail to lnfocolects.Aesoun:ellnrt.gov, and Ia tho Desk OH!ter, Office ollnforma!on iVId Regulatory Aftal,
NEOlJ.1!1:02, (31~104), Ol!ico of Managom611l and Budge~ Washington, OC 20503. If a maans used tD Impose an lnforma~on cdfeclicn does not dsplay a curlefttly vahd OMB control n!lllber, 1110 NRC may not conduct 01 aponsor, and a person ts not requtred 1o rospond lo, lha lnlormalon colloclion.
- 3. PAGE Joseph M. Farley Nuclear Plant, Unit 2 05000 364 Page 1 of 4
- 4. TITLE Manu_al Reactor Trio due to los of 2B Startuo Auxilia 11 Transformer and Loss of Offsite Power
- 5. EVENT DATE
- 6. LEA NUMBER
- 7. REPORT DATE
- 8. OTHER FACILITIES INVOLVED YEAR I SEQUENTIAL I REV FACILITY NAME DOCKET NUMBER MONTH DAY YEAR NUMBER NO.
MONTH DAY YEAR 10 14 2014 2014 -
002
- - 00 12 12 2014 FACILITY NAME DOCKET NUMBER
- 9. OPERATING MODE
- 11. THIS REPORT IS SUBMITTED PURSUANT TO THE REQUIREMENTS OF 10 CFR §: {Check all that apply)
D 20.22o1(b)
D 20.22o3<a><3HI>
0 50. 73(a)(2)(1)(C) 0 50. 73(a)(2)(vli) 1 D 2o.22o1(d) 0 20.2203(a)(3)(11) 0 50.73(a)(2)(ii)(A) 0 50.73(a)(2)(vln)(A) 0 20.2203(a)(1) 0 20.2203(a}(4}
0 50.73(a)(2)(11)(B) 0 50.73(a)(2}(vlri)(B) 0 20.2203(a)(2)(1) 0 50.3B(c)(1)(i)(A)
D 50.73(a)(2)(11i) 0 50.73(a)(2)(1x)(A)
- 10. POWER LEVEL 0 20.2203(a)(2)(11) 0 50.36(c)(1)(11)(A)
[81 50.73(a)(2)(1v)(A) 0 50.73(a)(2)(x) 0 20.2203(a)(2)(111) 0 50.36(c)(2) 0 50.73(a)(2)(v)(A) 0 73.71(a)(4) 82 0 20.2203(a)(2)(1v) 0 50.4B(a)(3)(ii) 0 50.73(a)(2)(v)(B) 0 73.71(a}(5) 0 20.2203(a)(2)(v)
D 50.73(a)(2)(1)(A)
D 50.73(a)(2)(v)(C)
D OTHER 0 20.2203(a}(2)(vl)
D 50.73(a)(2)(1)(B) 0 50. 73(a)(2)(v)(D)
Sp!ctly In Abstract bolow or In Westinghouse-Pressurized Water Reactor Energy Industry Identification Codes are Identified in the text as [XX].
Requirement for Report The reactor trip Is reportable per 10 CFR 50. 73(a)(2)(lv)(A) for manual actuation of the reactor protection system. Additionally, the reactor trip resulted in a valid actuation of the Auxiliary Feedwater system which Is also reportable per 10 CFR 50.73(a)(2)(1v)(A).
Unit Status at Time of Event Prior to the event Unit 2 was operating at 82 percent power and was in a power coast-down prior to a refueling outage.
Description of Event
On 10/14/14 at 0341 COT, the Unit 2 reactor was manually tripped after a lightning strike In the HVSY led to a phase 3 to ground fault on a SOOkV transmission line resulting in a 8 train Loss of Site Power (LOSP). The fault caused the 28 SAT instantaneous overcurrent relay to actuate and resulted In de-energizing the 2B Startup Auxiliary Transformer (SAT). A missing nut in the Power Circuit Breaker
--- (PCB) protection circuitry caused a high resistance on one side of the current transformer circuit resulting in an Imbalance in current flows and an actuation in the differential instantaneous overcurrent relaying.
The B train LOSP In conjunction with the 2B Emergency Diesel Generator (EDG) being out of service for a planned maintenance outage caused a loss of Component Cooling Water (CCW) to the Reactor Coolant Pumps (RCPs). The Unit 2 Abnormal Operating Procedures for loss of CCW and loss of A or 8 Train Electrical Power were entered and the reactor was manually tripped and the RCPs were secured.
In February and March of 2013, High Voltage Switchyard (HVSY) PCB 944 and protective circuitry were installed as part of a Design Change Package (DCP) for upgrading the HVSY Bank 1 bus. This design change work was performed by Alabama Power Company (APCO) with oversight provided by Southern Nuclear Company (SNC) in accordance with approved oversight procedures. Testing was performed to verify correct Installation of the current transformers (CT) for Power Circuit Breaker (PCB) 944 and the associated wiring. These tests included insulation resistance (Megger) testing of CT and cables, continuity checks of CT cables, verification of one ground per circuit, and polarity, ratio and saturation testing for CTs. All of these were satisfactory and the DCP was completed with no issues being Identified.
Approximately 18 months after the DCP Installation, a lightning strike on the Farley-Snowdoun SOOkV transmission line on 10/14/14, led to a phase 3 to ground fault on the Farley-Snowdoun SOOkV line. The Snowdoun line relaying at Farley Transmission Substation operated as a result of the fault and tripped open HVSY PCBs 1112 and 1212. Although these PCBs tripped open, the phase 3 to ground fault did not clear due to a ground fault that was occurring Internal to PCB 1112 on the bus side of the main contacts.
The No.1 SOOkV bus secondary differential relaying operated as a result of continuation of the fault and tripped HVSY PCBs 11 02 and 1132 which cleared the fault.
Prior to the bus fault being cleared, fault current was drawn from the 230kV side of the HVSY through HVSY PCBs 840 and 944. The fault current of over 3000 amps exposed a loose termination In phase 3 of NRC r-oRM l66A !02*20t4)
PCB 944's CT circuit when the fault current passed through PCBs 840 and 944. This loose connection created a point of high resistance in PCB 944's CT circuit which caused the 2B SAT instantaneous overcurrent relay to see a difference In the current contributions from PCBs 840 and 944, indicating a fault In the 2B SAT zone of protection and causing the Instantaneous overcurrent relay to actuate.
The Instantaneous overcurrent relay then tripped HVSY PCBs 840 and 944 resulting in isolation of the 2B SAT which caused a LOSP to the B train power bus. A higher than normal resistance was created by a loose termination in the PCB 944 CT circuit to the instantaneous overcurrent relay that was caused by omitting a 5/16 inch nut when installing PCB 944 protection circuitry.
At the time of the B train LOSP, the 2B EDG was tagged out of service for a planned maintenance outage for replacement of the governor. This caused the diesel to be unavailable to start as designed to pick up the B train loads after the loss of the 2B SAT. One of the loads lost on the B train was cooling water to the RCP thermal barriers and oil coolers. This led to entry into the Abnormal Operating Procedures for loss of CCW and loss of A or B Train Electrical Power, and manually tripping the reactor and securing the RCPs at0341 COT.
Unit 2 'B' train power was restored at 0523 COT.
Cause of Event
The direct cause of this event was the loose termination from a missing nut In the PCB 944 CT circuit connection to the Instantaneous overcurrent relay, which In addition to the continued fault on the 500kV bus side of PCB 1112 led to the B train LOSP. The manual reactor trip resulted from the B train alignment of cooling water to the RCP thermal barriers and oil coolers.
The root cause was Inadequate verification practices during APCO wiring installations that led to a nut not being installed on its terminal. A contributing cause to this event Is not fully understanding the extent of the differences in verification practices performed by the organizations.
Safety Assessment
All systems responded as designed to the reactor trip and the B train LOSP. The CCW miscellaneous header was aligned to A-Train, and the B RCP was restarted. The 2C diesel generator was manually started and was aligned to B train loads. Ail equipment operated as-designed to mitigate the event.
There was no loss of safety function and no radioactive release associated with this event. There was no actual consequence detrimental to the health and safety of the public. During the event ail A-Train safe shutdown equipment responded appropriately.
Corrective Action
The missing nut was Installed and secured for the PCB 944 current transformer. Primary and secondary protective relaying for the 2B SAT was tested satisfactorily. Extent of Condition walkdowns were performed for other circuits In the HVSY and repaired as necessary. To prevent recurrence SNC will work to strengthen standards of the utility performing the maintenance for work performed In the high voltage swltchyard, ensuring that for this type of work expectations are communicated, and training and verification practices are strengthened.
Additional Information
Farley Unit 1 and Unit 2 Licensee Event Reports for the previous five years have been reviewed. In 2013 Farley Unit 1 experienced an automatic reactor trip resulting from a loss of the startup auxiliary transformer. LER 2013-001-00 was submitted. That event was caused by a degraded piece of equipment (lightning arrestor) that, over a period of time, had moisture ingress that caused a fault. The failure of the equipment caused the 1 B SAT to become de-energized resulting In a Unit 1 automatic reactor trip. The details and corrective actions for that event are not similar to this occurrence because it did not result from the human performance tool of inadequate verification practices.
NRC l;olU,I JG6A (0!.:014)