05000281/LER-2016-001, Regarding Reactor Trip Due to Generator Differential Lockout
| ML16350A101 | |
| Person / Time | |
|---|---|
| Site: | Surry  |
| Issue date: | 12/02/2016 |
| From: | Lane N Virginia Electric & Power Co (VEPCO) |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| 16-419 LER 16-001-00 | |
| Download: ML16350A101 (4) | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 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)(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) 10 CFR 50.73(a)(2)(iv)(A), System Actuation |
| 2812016001R00 - NRC Website | |
text
December 2, 2016 U. S. Nuclear Regulatory Commission Attention: Document Control Desk Washington, D. C. 20555-0001
Dear Sir or Madam,
10CFR50.73 Virginia Electric and Power Company Surry Power Station 5570 Hog Island Road Surry, Virginia 23883 Serial No.:
16-419 SPS:
TSC Docket No.: 50-281 License No.: DPR-37 Pursuant to 10CFR50.73, Virginia Electric and Power Company hereby submits the following Licensee Event Report applicable to Surry Power Station Unit 2.
Report No. 50-281/2016-001-00 This report has been reviewed by the Station Facility Safety Review Committee and will be forwarded to the Management Safety Review Committee for its review.
Enclosure Commitment contained in this letter: None Very truly yours, f),k}~
N. L. Lane Site Vice President Surry Power Station cc:
U.S. Nuclear Regulatory Commission, Region II Marquis One Tower, Suite 1200 245 Peachtree Center Ave., NE Atlanta, GA 30303-1257 NRC Senior Resident Inspector Surry Power Station
NRC FORM 366 U.S. NUCLEAR REGULATORY COMMISSIO~ APPROVED BY OMB: NO. 3150-0104 EXPIRES: 1013112018 (11-2015)
~~t.P.Alo"'*>o 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 />.
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Reported lessons learned are incorporated into the licensing process and fed back to industry.
Send comments regarding burden estimate to the FOIA, Privacy and Information Collections
~~i-.,.,........q..: LICENSEE EVENT REPORT (LER)
Branch (T-5 F53), U.S. Nuclear Regulatory Commission, Washington, DC 20555-0001, or by internet e-mail to lnfocollects.Resource@nrc.gov, and to the Desk Officer, Office of Information and (See Page 2 for required number of.
Regulatory Affairs, NEOB-10202, (3150-0104), Office of Management and Budget, Washington, DC digits/characters for each block) 20503. If a means used to impose an information collection does not display a currently valid OMB control number, the NRG may not conduct or sponsor, and a person is not required to respond to, the information collection.
- 3. PAGE Surry Power Station, Unit 2 05000 - 281 1 OF 3
- 4. TITLE Unit 2 Reactor Trip due to Generator Differential Lockout
- 5. EVENT DATE
- 6. LER 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 09 2016 2016 - 001 -
FACILITY NAME DOCKET NUMBER 00 12 08 2016
- 9. OPERATING MODE
- 11. THIS REPORT IS SUBMITTED PURSUANT TO THE REQUIREMENTS OF 10 CFR §: (Check all that apply)
D 20.2201 <bl D 20.2203(a)(3)(i)
D 50.73(a)(2)(ii)(A)
D 50.73(a)(2)(viii)(A)
N D 20.2201 (d)
D 20.2203(a)(3)(iil D 50.73(a)(2)(ii)(B)
D 50.73(a)(2)(viii)(B)
D 20.2203(a)(1 l D 20.2203(a)(4)
D 5o.73(a)(2)(iiil D 50. 73(a)(2)(ix)(A)
D 20.2203(a)(2)(i)
D 50.36(c)(1)(i)(A)
[8] 50. 73(a)(2)(iv)(A)
D 50.1:3(a)(2)(x)
- 10. POWER LEVEL D 20.2203(a)(2)(ii)
D 50.36(c)(1)(ii)(A)
D 50.73(a)(2)(v)(A)
D i3.7*1{a)(4)
~.
D 20.2203(a)(2)(iiil D 5o.36(c)(2)
D 50.73(a)(2)(v)(B)
D 13.11(a)(5) 100 D 20.2203(a)(2)(iv)
D 5o.46(a)(3)(ii)
D 50.73(a)(2)(v)(C)
D 13.77(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)
D 50.73(a)(2)(i)(B)
D 50.73(a)(2)(vii)
D 13.77(a)(2)(ii)
c.**i*-~***
(
- .!.~~ D 50.73(a)(2)(i)(C)
D OTHER Specify in Abstract below or in NRG Form 366A
- 12. LICENSEE CONT ACT FOR THIS LER
.~.
LICENSEE CONTACT I
TELEPHONE NUMBER (Include Area Code)
Barry Garber (757) 365-27?5 ' -
CAUSE
SYSTEM COMPONENT MANU-REPORTABLE
CAUSE
SYSTEM COMPONENT MANU-REPORTABLE FACTURER TO EPIX FACTURER TO EPIX B
EA IPBU C712 y
'i
- 14. SUPPLEMENTAL REPORT EXPECTED 15.EXPECTED MONTH DAY YEAR 0 YES (If yes, complete 15. EXPECTED SUBMISSION DATE)
[8J NO SUBMISSION DATE ABSTRACT (Limit to 1400 spaces, i.e.. approximately 15 single-spaced typewritten lines)
On October 9, 2016 at 0254 hours0.00294 days <br />0.0706 hours <br />4.199735e-4 weeks <br />9.6647e-5 months <br />, with Unit 1 and Unit 2 at 100 percent power, Unit 2 experienced an automatic reactor trip initiated by a turbine trip due to generator differential lockout relay actuation. At the time of the trip, high wind and heavy rain conditions existed due to the effects of Hurricane Matthew. All three auxiliary feedwater pumps automatically started on low-low steam generator water level as expected. All plant systems functioned as required, and Unit 2 was stabilized at hot shutdown. The trip response was not affected by any previously inoperable systems, structures, or components.
The direct cause of the generator differential lockout was an electrical ground overcurrent initiated by water accumulation in the "A" phase of the "A" station service transformer leads termination enclosure. Affected electrical enclosures were drained, the system was tested, and modifications to the enclosures to prevent recurrence of water intrusion were completed prior to returning Unit 2 to power operation on October 13, 2016.
This report is being submitted pursuant to 10CFR50.73(a)(2)(iv)(A) as an event that resulted in the automatic actuation of the Reactor Protection System and the Auxiliary Feedwater System.
NRG FORM 366 (11-2015)
Page 2 of 3 1.0 DESCRIPTION OF THE EVENT SEQUENTIAL NUMBER 001 REV NO.
00 On October 9, 2016 at 0254 hours0.00294 days <br />0.0706 hours <br />4.199735e-4 weeks <br />9.6647e-5 months <br />, with Unit 1 and Unit 2 at 100 percent power, Unit 2 experienced an automatic reactor trip initiated by a turbine trip due to generator differential lockout relay actuation. At the time of the trip, high wind and heavy rain conditions existed due to the effects of Hurricane Matthew. All three auxiliary feedwater (AFW) pumps [EllS-BA-P] automati_cally started on low-low steam generator (SG)
[EllS-AB-SG] water level providing flow to the SGs as expected. Operation of the main steam power operated relief valves (PORVs) [EllS-SB-RV] and the main steam dump valves [EllS-SB-TCV], coincident with the initiation of AFW, resulted in the Unit 2 reactor coolant system (RCS) temporarily cooltng to 542
"'\\.:
degrees F. RCS temperature was restored to nominal average temperature of 547 degreesf ~t 0320
'~i hours. Main feedwater flow was re-established to control SG level, and AFW was secured at 0336 hours0.00389 days <br />0.0933 hours <br />5.555556e-4 weeks <br />1.27848e-4 months <br />.
At 0609 hours0.00705 days <br />0.169 hours <br />0.00101 weeks <br />2.317245e-4 months <br />, a four-hour report to the NRC was made pursuant to 10CFR50.72(b)(2)(iv)(B) due to valid automatic actuation of Reactor Protection Systems and an eight-hour report was made pursuant to 10CFR50.72(b)(3)(iv)(A) due to automatic actuation of the AFW system.
2.0 SIGNIFICANT SAFETY CONSEQUENCES AND IMPLICATIONS
This event resulteq in no safety consequences or implications. There were no testing or surveillance procedures in progress when the reactor trip occurred. Appropriate operator actions were ta~~.ri in accordance with station procedures, and the unit was brought to a stable condition. Station eqµipment relied upon to mitigate the event responded as designed. Normal offsite and emergency power supplies were available during the event. *The health and safety of the public were not affected.
3.0 CAUSE
The 22 KV electric output of the main generator is sent to the Main Transformers and the Station Service Transformers (SST) [EllS-EA-XFMR] through the Isolated Phase Bus Duct (IPBD) [EllS-EA-IPBU] System.
The current Unit 2 IPBD system and SST leads termination enclosures were installed by design changes in 2011 and 2015, respectively. As part of the October 2016 post-trip inspection, water was found in two leads termination enclosures and in some IPBD horizontal runs. Water appears to have entered the system during ongoing heavy rain and wind conditions through gaps at mechanical joints associated with the SST leads termination enclosure and the IPBD.
The direct cause of the reactor trip was a ground of the 'A' phase on the high side (22 KV) of the 'A' S~T due to water accumulation in the 'A' SST leads box, resulting in the actuation of the generator differential lockout relay. Without a drain path, the water level in the enclosure increased up the insulator creating a path to ground.
The root cause for the water intrusion and the resulting trip was the lack of testing and inspection of mechanical joints to ensure a weather tight system was accomplished after modifications. The design change specifications included provisions to ensure weather tightness, including detailed instructions for testing of welds and an array of electrical tests. However, no guidance was provided for inspection or *,,:,_.*.
Page 3 of 3 (11-2015)
U.S. NUCLEAR REGULATORY COMMISSION LICENSEE EVENT REPORT (LER)
CONTINUATION SHEET YEAR Surry Power Station, Unit 2 05000 - 281 2016
- 6. LER NUMBER SEQUENTIAL NUMBER 001 REV NO.
00 testing of mechanical connections for the bus duct insulator hardware and gaskets, or for the termination enclosures.
4.0 IMMEDIATE CORRECTIVE ACTIONS
Following the reactor trip, control room operators acted promptly to stabilize the unit in a safe, hot shutdown condition in accordance with station procedures.
5.0 ADDITIONAL CORRECTIVE ACTIONS
A root cause evaluation (RCE) team was assembled to determine the cause of this event and to recommend corrective actions. While Unit 2 was shut down, water was removed from the IPBD and leads termination enclosures, and breaches that allowed water intrusion were sealed. Additionally, the 'A' phase SST and IPBD systems were dried using forced dehumidified air. Weep holes were installed at low points in the SST leads termination enclosures and Generator Step-Up transformer (GSU) [EllS-EL-XFMR] leads termination enclosures to allow drainage of potential moisture intrusion. All three phases of the IPBD system were meggered to verify no further grounds existed.
6.0 ACTIONS TO PREVENT RECURRENCE Weep holes installed in the transformer termination enclosures as described in section 5.0 above will prevent the possibility of creating a ground path by water accumulation. Design change testing procedures will be revised to include more rigorous instructions for non-safety design changes and common tests for electrical enclosures. Engineering qualification requirements will be updated to ensure~that engineers are trained on lessons learned from this event. Additionally, upcoming design changes associated.with Reserve Station Service Transformers (RSST) [EllS-EA-XFMR] will be reviewed and revised as neededAo capture lessons learned from this event. *
7.0 SIMILAR EVENTS
None 8.0 MANUFACTURER/MODEL NUMBER AZZ - Calvert Isolated Phase Bus I 7085
9.0 ADDITIONAL INFORMATION
Unit 1 was at 100 percent power at the time of this event and was unaffected by the Unit 2 reactor trip. Unit 1 entered a refueling outage on October 23, 2016. The corresponding Unit 1 IPBD and SST leads termination enclosures were inspected for the accumulation of water. Water was identified on the low side (4 KV) of the 'B' SST leads termination enclosure on Unit 1. As in Unit 2, weep holes were installed on the Unit 1 SST and GSU. leads termination enclosures, and connections were inspected and sealed as necessary. Other transformer terminations (including those associated with emergency power supplies) are not enclosed by bus ducts, and therefore are not affected by this event.