05000321/LER-2012-002, Regarding Failure of 1C EDG Output Breaker to Close Results in Condition Prohibited by Technical Specifications

Regarding Failure of 1C EDG Output Breaker to Close Results in Condition Prohibited by Technical Specifications

ML12129A256
Person / Time
Site:	Hatch
Issue date:	05/08/2012
From:	Madison D Southern Co, Southern Nuclear Operating Co
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
NL-12-0930 LER 12-002-00
Download: ML12129A256 (8)

LER-2012-002, Regarding Failure of 1C EDG Output Breaker to Close Results in Condition Prohibited by Technical Specifications

Event date:
Report date:
Reporting criterion:	10 CFR 50.73(a)(2)(i) 10 CFR 50.73(a)(2)(vii), Common Cause Inoperability 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)(iii) 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)(i)(A), Completion of TS Shutdown 10 CFR 50.73(a)(2)(v), Loss of Safety Function 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications
3212012002R00 - NRC Website

text

Dennis R. Madison Soulhern Nuclear If,

• f'r.. oent Ha.,

Operaling Company Inc Plant ':lll n HalO 11028 Hatch ParI \\Val Nom Ba,le\\ GeOIQla 31513 fr.1912 537 58~9 Fax 91 ~ 365 2077 SOUTHERNA May 8, 2012 COMPANY Docket Nos.: 50-321 NL-12-0930 U. S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, D. C. 20555-0001 Edwin I. Hatch Nuclear Plant Licensee Event Report 2012-002-00 Failure of 1 C EDG Output Breaker to Close Results in Condition Prohibited by Technical Specifications Ladies and Gentlemen:

In accordance with the requirements of 1 OCFR50. 73(a)(2)(i)(B), Southern Nuclear Operating Company hereby submits the enclosed Licensee Event Report concerning an event of non-compliance with Technical Specification 3.8.1 for the failure of the 1 C emergency diesel generator (EDG) output breaker to close during a plant shutdown for refueling.

This letter contains no NRC commitments. If you have any questions, please contact Mr. B. D. McKinney at (205) 992-5982.

Respectfully submitted,

~yY)~

D. R. Madison Vice President - Hatch DRM/SBT/msc Enclosure: LER 2012-002-00 cc: Southern Nuclear Operating Company Mr. S. E. Kuczynski, Chairman, President & CEO Mr. D. G. Bost, Executive Vice President & Chief Nuclear Officer Mr. D. R. Madison, Vice President - Hatch Mr. B. L. Ivey, Vice President - Regulatory Affairs Mr. B. J. Adams, Vice President - Fleet Operations RTYPE: CHA02.004

U. S. Nuclear Regulatory Commission NL-0930 Page 2 U. S. Nuclear Regulatory Commission Mr. V. M. McCree, Regional Administrator Mr. P. G. Boyle, NRR Senior Project Manager - Hatch Mr. E. D. Morris, Senior Resident Inspector - Hatch

Enclosure NL-12-0930 Edwin I. Hatch Nuclear Plant - Unit 1 Licensee Event Report 2012-002-00 Failure of 1 C EDG Output Breaker to Close Results in Condition Prohibited by Technical Specifications

NRC FORM 366 U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY OMB: NO. 3150-0104 EXPIRES: 10/31/2013 (9-2007)

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. Send comments reo-arding burden estimate to the Records and FOIAlPrivacy Service Branch

- 5 F53), U.S.

LICENSEE EVENT REPORT (LER)

Nuclear Re~ulatory Commission, Washington, DC 20555-0001, or by internet e-maii to in ocollects.resources@nrc.gov, and to the Desk Officer, OHice of Information and Regulatory Affairs, NEOB-10202, (3150-0104), Office of Mana~ement and Budget, Washington, DC 20503. If a means used to impose an in ormation collection does not display a currently valid OMB control number, the NRC may not conduct or sponsor, and a person is not required to rescond to. the information collection.

13. PAGE Edwin I. Hatch Nuclear Plant Unit 1 05000321 1 OF 5 4.11TLE Failure of 1 C EDG Output Breaker to Close Results in Condition Prohibited by Technical Specifications

5. EVENT DATE

6. LER NUMBER

7. REPORT DATE

8. OTHER FACILITIES INVOLVED FACILITY NAME DOCKET NUMBER SEQUENTIAL REV MONTH DAY YEAR YEAR MONTH DAY YEAR NUMBER NO.

FACILITY NAME DOCKET NUMBER 03 10 2012 2012. 002. 00 05 08 2012

9. OPERATING MODE

11. THIS REPORT IS SUBMITTED PURSUANT TO THE REQUIREMENTS OF 10 CFR§: (Check all that apply) o 20.2201 (b) o 20.2203(a)(3)(i) o 50.73(a)(2)(i)(C) o 50.73(a)(2)(vii) 4 o 20.2201 (d) o 20.2203(a)(3)(ii) o 50.73(a)(2)(ii)(A) o 50.73(a)(2)(viii)(A) o 20.2203(a)(1) o 20.2203(a)(4) o 50.73(a)(2)(ii)(B) o 50.73(a)(2)(viii)(B) o 20.2203(a)(2)(i) o 50.36(c)(1 )(i)(A) o 50.73(a)(2)(iii) o 50.73(a)(2)(ix)(A)

10. POWER LEVEL o 20.2203(a)(2)(ii) o 50.36(c)(1 )(ii)(A) o 5O.73(a)(2)(iv)(A) o 50.73(a)(2)(x) o 20.2203(a)(2)(iii) o 50.36(c)(2) o 50.73(a)(2)(v)(A) o 73.71 (a)(4) o 20.2203(a)(2)(iv) o 50.46(a)(3)(ii) o 50.73(a)(2)(v)(B) o 73.71 (a)(5) 0 o 20.2203(a)(2)(v) o 50.73(a)(2)(i)(A) o 50.73(a)(2)(v)(C) o OTHER o 20.2203(a)(2)(vi)

[gI 50.73(a)(2)(i)(B) o 50.73(a)(2)(v)(D)

Specify in Abstract below or in NRC Form 366A

12. LICENSEE CONTACT FOR THIS LER ACILITY NAME I~ELEPHONE NUMBER (Indude Area Code)

Edwin I. Hatch / Steven Tipps - Principal Engineer - Licensing 912-537-5880 MANU-REPORTABLE MANU-REPORTABLE

CAUSE

SYSTEM COMPONENT

CAUSE

SYSTEM COMPONENT FACTURER TO EPIX FACTURER TO EPIX B

EK BKR W120 Yes

14. SUPPLEMENTAL REPORT EXPECTED

15. EXPECTED MONTH DAY YEAR SUBMISSION [gI YES (If yes, complete 15. EXPECTED SUBMISSION DATE)

ONO DATE 8

16 2012 ABSTRACT (Limit to 1400 spaces, i.e., approximately 15 single-spaced typewritten lines)

During the performance of the 1 C emergency diesel generator (EDG) loss of offsite power (LOSP) logic system functional test (LSFT), on March 10,2012, at 2350 EST, the EDG output breaker failed to close and supply power to the 1 G 4kV bus. This failure resulted in the inability to energize the 1 G bus and the safety-related buses fed by this bus. The operating crew attempted to restore normal power to the bus, but was unsuccessful. A DC ground indication was also received when the 1 C EDG output breaker failed to close.

Troubleshooting revealed a connecting screw on the circuit breaker auxiliary switch making contact between terminals 8 and 10, creating a fault between the DC positive and negative when the LOSP test permissive was applied to the closing circuit for the 1 C EDG output breaker. This short prevented the output breaker closing coil from functioning as required.

The direct cause for the failure of the breaker to close is attributed to an apparent vendor quality issue associated with the breaker that occurred at the vendor facility during the manufacturing/assembly process.

This involved the installation of a screw on an auxiliary switch termination that penetrated the insulation of an adjacent lug, thereby creating a short circuit condition that could only be manifested during an LOSP condition. The breaker was replaced and testing was performed to confirm the output breaker "close" permissive functioned as required. The condition was reviewed for applicability to 10 CFR 21 and determined to not be a 10 CFR 21 condition.

NRC FORM 366 (9-2007)

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PLANT AND SYSTEM IDENTIFICATION

General Electric - Boiling Water Reactor Energy Industry Identification System codes appear in the text as (EllS Code XX).

DESCRIPTION OF EVENT

During the performance of the 1 C emergency diesel generator (EDG)(DG) loss of offsite power (LOSP) logic system functional test (LSFT), on March 10,2012, at approximately 2350 EST, with Unit 1 in a refueling outage in cold shutdown (Mode 4), the EDG output breaker (EK) failed to close and supply power to the 1 G 4kV bus. This failure resulted in the inability to energize the 1 G bus and the safety related loads fed by this bus. The operating crew attempted to restore normal power to the bus, but was unsuccessful. A DC ground indication was also received when the 1 C EDG output breaker failed to close. There was an indicated ground on the positive leg of the 125 VDC battery system associated with this diesel generator. Initial attempts to isolate the ground were unsuccessful until the ground indication cleared during tagout of the circuit containing the undervoltage relay (EK) approximately 4 hours4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br /> later.

Additionally, the 125 VDC control power breaker for the normal and alternate supply breakers to the 1 G 4kV bus was also opened during the same interval in which the ground cleared. An undervoltage relay (27GDX) in the closing circuit for the 1C EDG output breaker was subsequently determined to have experienced arcing during the breaker closure failure. Later it was determined that this short damaged the 1 C EDG undervoltage relay in addition to preventing the closure of the output breaker. Subsequent to the "breaker close" failure, attempts to re-energize 4kV bus 1 G from the normal supply breaker were unsuccessful with that breaker closing and then immediately tripping. The nature of the failure of the 1 C EDG output breaker to close was determined to be limited to the condition that resulted in a grounded condition as a result of the relay failure which was subsequent to the electrical short that was created by a fault between the DC positive and negative when the LOSP test permissive was applied to the closing circuit for the 1 C EDG output breaker.

CAUSE OF EVENT

The direct cause for the failure of the breaker to close is attributed to an apparent vendor quality issue associated with the breaker that occurred at the vendor facility during the manufacturing/assembly process. Troubleshooting revealed a connecting screw on the circuit breaker auxiliary switch making contact between terminals 8 and 10, creating a short between the DC positive and negative when the LOSP test permissive was applied to the closing circuit for the 1 C EDG output breaker which prevented the closing coil from functioning properly. The apparent manufacturing/assembly error involved the installation of a screw on an auxiliary switch termination by the vendor that penetrated the insulation of an adjacent lug, thereby creating a short circuit condition that could only be manifested during an LOSP condition.

The root cause investigation and final report has not yet been completed and will address further technical and organizational causes as they are identified. Based on the results of this investigation a revision to this report will be submitted. The condition was reviewed for applicability to 10 CFR 21 and determined to not be a 10 CFR 21 condition.

REPORTABILITY ANALYSIS AND SAFETY ASSESSMENT This event is reportable as required by 1 OCFR50. 73(a)(2)(i)(B), in that an event and associated condition occurred and existed that was prohibited by the Technical Specifications (TS) LCO 3.8.1, requiring the 1 C EDG to be operable during the preceding operating cycle. The breaker containing the breaker auxiliary switch quality issue had a receipt inspection performed in February 2004. The receipt inspection involved visual inspection and complete preventive maintenance (PM) being performed on the NRC FORM 366 (9-2007)

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~-----------------------------LICENSEE EVENT REPORT (LER) u.s. NUCLEAR REGULATORY COMMISSION (10-2010)

CONTINUATION SHEET

1. FACILITY NAME

2. DOCKET

6. LER NUMBER

3. PAGE SEQUENTIAL IREVISION YEAR NUMBER NUMBER Edwin I. Hatch Nuclear Plant Unit 1 05000321 I

3 OF 5

2012 002 00 breaker that included checks of the cam, links, continuity tests and resistance checks with satisfactory results. This PM was developed based on direction from the vendor to the level of detail used by the vendor in performing similar PM and inspections in their shop. Because of the nature of the internal short caused by the vendor quality issue, functional tests consistent with plant procedures and industry best practices did not identify the presence of the short circuit condition. At the time of this receipt inspection the latent manufacturing/assembly quality issue was present.

The affected breaker was initially installed in the safety related 1 E 4kV switchgear as the normal supply breaker, which is fed by the 1 A EDG during LOSP conditions. When installed in this breaker location, the shorted points within this cubicle logic are both connected to DC negative and as a result did not affect the breaker function since there was no potential difference. The LOSP LSFT for the 1 A EDG was performed March 2004 and every 24 months thereafter with no problems noted.

The affected breaker remained installed as the normal supply breaker for the 1 E 4kV switchgear normal supply breaker until the Unit 1 2010 refueling outage. When the LOSP LSFT for the 1 C EDG was performed on 3/11/2010, the affected breaker was having PM performed on it and was not installed at that time. Following the PM on the breaker that included a visual inspection, continuity checks of the switch, and performance of a hi-pot test on the auxiliary switch and contacts, it was functionally tested in accordance with the normal functional test requirements for a 4kV breaker prior to installation in the field with no problems noted. The breaker containing the apparent breaker auxiliary switch quality issue was then placed into the 1 G 4kV switchgear as the alternate supply breaker on 3/16/2010. It should be noted that the circuit containing the shorted connection was not in the logic string for normal EDG testing and loading of the EDG that is performed on a monthly basis. Only during the LOSP LSFT would the affected logic string be in the circuit. During the 2012 1 C EDG LOSP LSFT the latent condition manifested itself when the shorted circuit was made up during the test. This condition prevented the 1 C EDG output breaker from closing and re-energizing the 1 G 4kV switchgear. As a result this latent condition has existed since 3/16/2010 which would have prevented the automatic closure of the 1 C EDG output breaker in the event of an LOSP condition during that operational window. The condition was discovered during the Unit 1 2012 refueling outage at a time when the 1 C EDG was not required to be operable, but a review of the condition and associated timeline was performed and it was determined that the condition had existed for a time frame greater than that allowed by the TS.

This event occurred during the performance of routine TS surveillance testing of EDG 1 C during the Unit 1 refueling outage during which time the 1 C EDG was not one of the EDGs required to be operable. The 1 A and 1 B EDGs were operable at the time the 1 C EDG failed to tie to its emergency bus_ During the preceding operating cycle the 1 A EDG was inoperable on three occasions ranging from approximately 34 hours3.935185e-4 days <br />0.00944 hours <br />5.621693e-5 weeks <br />1.2937e-5 months <br /> to 101 hours0.00117 days <br />0.0281 hours <br />1.669974e-4 weeks <br />3.84305e-5 months <br /> not considering the very brief periods of inoperability during monthly surveillance testing. The 1 B EDG was inoperable on 10 occasions ranging from approximately 8 hours9.259259e-5 days <br />0.00222 hours <br />1.322751e-5 weeks <br />3.044e-6 months <br /> to 126 hours0.00146 days <br />0.035 hours <br />2.083333e-4 weeks <br />4.7943e-5 months <br /> not considering the very brief periods of inoperability during monthly surveillance testing. At no time during the operating cycle were both the 1 A and 1 B EDGs inoperable at the same time. With either the 1 A or 1 B EDG inoperable and given the fact that the 1 C EDG could not tie to its emergency bus due to the latent equipment problem, there were periods of time during the preceding operating cycle when two of the three Unit 1 EDGs were inoperable. In determining the impact of this condition on nuclear safety a review was performed to determine what the impact would be of having periods of time when one diesel was operable and available to perform the required safety function in the event of a design basis accident involving an loss of coolant accident (LOCA)/LOSP.

The methods and models used to analyze the consequences of the LOCAILOSP have been refined during the plant lifetime in the form of the SAFER/GESTR-LOCA analysis. This analysis provides results and consequences associated with the LOCA using realistic evaluation methods as documented in the FSAR. The SAFER/GESTR-LOCA analyses were performed with a bounding maximum average planar heat generation rate at the most limiting power and exposure combination and concluded that the peak clad temperature for the nominal or expected case is insufficient to NRC FORM 366 (9-2007)

PRINTED ON RECYCLED PAPER U.S. NUCLEAR REGULATORY COMMISSION LICENSEE EVENT REPORT (LER)

(10-2010)

CONTINUATION SHEET

1. FACILITY NAME

2. DOCKET

6. LER NUMBER

3. PAGE SEQUENTIAL IREVISION NUMBER NUMBER Edwin I. Hatch Nuclear Plant Unit 1 05000321 YEAR I

4 OF 5

2012 002 00 cause perforation of the fuel cladding_ As a result no cladding perforations were considered for the LOCA and no fuel damage results_ This analysis concludes that the reactor can be brought to a cold shutdown condition and maintained in that condition on a long term basis with either two RHR low pressure coolant injection (LPCI) pumps or one core spray pump and one LPCI pump. The 1A EDG provides power for the 'A' LPCI pump, the 'A' RHRSW pump and the 'A' core spray pump. The 1 B EDG serves the 'C' and 'D' RHR LPCI pumps and 'C' RHRSW pump. The 1 C serves the 'B' LPCI pump, the 'B' core spray pump, and the 'B' and 'D' RHRSW pumps_ Either the 1A or 1 B EDG can provide the needed low pressure pumps and RHRSW pump(s) to satisfy the minimum assumptions in the SAFER/GESTR-LOCA analysis for Unit 1_ For this reason there was no loss of function on Unit 1 during the previous operating cycle.

The 1G 4kV bus also provides normal emergency power to the Unit 2 'B' RHR LPCI valve load center which contains the 'B' LPCI injection valve. The 1 E 4kV bus provides the normal emergency power to the Unit 2 'A' RHR LPCI valve load center that contains the 'A' LPCI injection valve. The alternate emergency power supply for the Unit 2 'A' RHR LPCI valve load center is provided by the Unit 2 2F 4 kV bus which requires a manual alignment to use this power source for the desired valve load center.

During the previous operating cycle, the 1 A EDG was inoperable on three occasions ranging from approximately 34 hours3.935185e-4 days <br />0.00944 hours <br />5.621693e-5 weeks <br />1.2937e-5 months <br /> to 101 hours0.00117 days <br />0.0281 hours <br />1.669974e-4 weeks <br />3.84305e-5 months <br /> not considering the very brief periods of inoperability during monthly surveillance testing_ The 1 A EDG provides emergency power to the 1 E 4kV bus that provides the normal emergency power to the Unit 2 'A' RHR LPCI valve load center. Prior to removing the 1 A EDG from service for planned maintenance, plant procedures required the Unit 2 2F 4kV bus to be realigned to provide the alternate emergency power to the Unit 2 'A' RHR LPCI valve load center.

The same SAFER/GESTR-LOCA analysis for Unit 2 assumes the presence of the same combination of low pressure pumps in order to automatically restore reactor vessel inventory and to bring the unit to cold shutdown and allow it to be maintained long term in that condition. In the case of a DBA LOSP/LOCA on Unit 2 and an LOSP on Unit 1 with the 1A and 1 C EDGs inoperable, both Unit 2 core spray pumps remain operable and will recover Unit 2 reactor vessel inventory and allow the reactor to be safely shut down. With the LOCAILOSP occurring on Unit 2, the swing EDG would normally be realigned to provide power to the Unit 2 2F 4kV bus and therefore restore alternate emergency power to the Unit 2 'A' LPClioad center. However, in the assumed condition the 1A EDG is out of service for maintenance and the 1 C EDG output breaker will fail to close. For these reasons the swing EDG will remain dedicated to Unit 1 to maintain this unit in a safe condition during LOSP conditions. Based on the nature of the direct cause for the 1 C EDG output breaker failing to close, Operations would identify this condition on the 1 C EDG and their procedures provide the needed direction to manually close the 1 C EDG output breaker. Based on discussions with licensed Operations personnel this could be reasonably expected to be accomplished within 1 to 2 hours2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br /> from the occurrence of the event. This action restores the Unit 2 'B' RHR LPCl/shutdown cooling flow path before reaching the conditions necessary to allow shutdown cooling to be placed into service. Once RHR shutdown cooling has been placed into service the reactor will be brought to cold shutdown and maintained in that condition_

During the previous operating cycle, when either the 1 A or 1 B EDG was inoperable there was always one of these EDGs that would remain operable and capable of performing its safety function on Unit

1. Additionally, based on the discussion in the previous paragraph, if a design basis LOCA had occurred on Unit 2 along with an LOSP on both units when the 1 A EDG was inoperable, there would be no loss of safety function on Unit 2_ In the event that the swing EDG was inoperable with the same conditions present the Unit 2 'N RHR LPClioad center would continue to have its emergency power source operable which also assures there is no loss of safety function on Unit 2. Based on the nature of the direct cause for the 1 C EDG output breaker failing to close, Operations procedures provide the needed direction to allow closure of the 1 C EDG output breaker in a matter of 1 to 2 hours2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br /> thereby providing additional margin in the event of a design basis accident (DBA) LOSP/LOCA condition for either unit.

NRC FORM 366 (9-2007)

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5 u.s. NUCLEAR REGULATORY COMMISSION LICENSEE EVENT REPORT (LER)

(10-2010)

CONTINUATION SHEET

1. FACILITY NAME

2. DOCKET

6. LER NUMBER

3. PAGE YEAR SEQUENTIAL I REVISION NUMBER NUMBER I

Edwin I. Hatch Nuclear Plant Unit 1 05000321 5

OF 2012 002 00 Based on the fact that the safety function is retained with one EDG on Unit 1 and considering the impact this would have on Unit 2 should the events described actually occur during the previous operating cycle, there was always one Unit 1 EDG operable and adequate low pressure pumps operable on Unit 2 such that this event did not result in a loss of function on either unit. This being the case the event was determined to be of low safety significance.

CORRECTIVE ACTIONS

The LOSP/LOCA LSFT was successfully completed that demonstrated that the 1 C EDG output breaker would close as required to perform its safety function. The breaker was replaced by a different breaker and testing of the circuit that had previously contained the apparent latent manufacturing/assembly quality issue was performed to confirm the output breaker "close" permissive functioned as required. Similar breakers on the remaining Unit 1 emergency 4kV switchgear were inspected to confirm the manufacturing/assembly quality issue was not present on these breakers. Plans are to inspect the safety related Unit 2 breakers in an upcoming outage. A search of industry operating experience and contact with the vendor revealed no similar conditions in the industry that caused a similar failure. Based on the information learned thus far this condition is considered to be isolated to the breaker that failed to function.

The root cause investigation and final report have not yet been completed and will address further technical and organizational causes as they are identified, and will result in additional corrective actions.

Based on the results of this investigation a revision to this report will be submitted.

ADDITIONAL INFORMATION

Other Systems Affected: None

Failed Components Information

None Commitment Information: This report does not create any new permanent licensing commitments.

Previous Sim ilar Events NRC FORM 366 (9-2007)

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