DCL-15-041, Supplemental LER 2-13-004-01 for Diablo Canyon, Unit 2 Regarding Technical Specification 3.8.1 Not Met Due to Failed Wire Lug on Emergency Diesel Generator 2-3

Supplemental LER 2-13-004-01 for Diablo Canyon, Unit 2 Regarding Technical Specification 3.8.1 Not Met Due to Failed Wire Lug on Emergency Diesel Generator 2-3

ML15089A596
Person / Time
Site:	Diablo Canyon
Issue date:	03/30/2015
From:	Allen B Pacific Gas & Electric Co
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
DCL-15-041 Suppl LER 2-013-004-01
Download: ML15089A596 (5)

Text

Pacific Gas and Electric Company Barry S. Allen Diablo Canyon Power Plant Vice President, Nuclear Services Mail Code 104/6 P. 0. Box 56 Avila Beach, CA 93424 March 30, 2015 805.545.4888 Internal: 691.4888 Fax: 805.545.6445 PG&E Letter DCL-15-041 U.S. Nuclear Regulatory Commission 10 CFR 50.73 ATTN: Document Control Desk Washington, DC 20555-0001 Docket No. 50-323, OL-DPR-82 Diablo Canyon Power Plant, Unit 2 Supplemental Licensee Event Report 2-2013-004-01. Technical Specification 3.8.1 Not Met Due to Failed Wire Lug on Emergency Diesel Generator 2-3

Dear Commissioners and Staff:

In accordance with 10 CFR 50. 73(a)(2)(i)(B) and 10 CFR 50. 73(a)(2)(v)(D), Pacific Gas and Electric Company (PG&E) is submitting the enclosed Supplemental Licensee Event Report (LER) regarding Technical Specification 3.8.1, "AC Sources

-Operating," not being met due to a failed wire lug on Emergency Diesel Generator 2-3.

PG&E is issuing this supplemental LER to update the assessment of safety consequences.

PG&E makes no new or revised regulatory commitments (as defined by NEI 99-04) in this report. All the corrective actions identified in this letter will be implemented in accordance with the Diablo Canyon Power Plant Corrective Action Program.

This event did not adversely affect the health and safety of the public.

Sincerely, B~:ZnS.~

aphS/6470/50691194 Enclosure cc/enc: Marc L. Dapas, NRC Region IV Administrator Thomas R. Hipschman, NRC Senior Resident Inspector Siva P. Lingam, NRR Project Manager IN PO Diablo Distribution A member of the STARS (Strategic Teaming and Resource Sharing) Alliance Callaway

• Diablo Canyon

• Palo Verde

• Wolf Creek

NRC FORM 366 U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY OMS: NO. 3150-0104 EXPIRES: 01/31/2017 (02-2014)

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

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...t ..... *** 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 20503. If a means used to impose an information collection does not display a currently valid OMB digits/characters for each block} control number, the NRC may not conduct or sponsor, and a person is not required to respond to, the information collection.

1. FACILITY NAME 2. DOCKET NUMBER 3. PAGE Diablo Canyon Power Plant, Unit 2 05000323 1 OF 4

4. TITLE Technical Specification 3.8.1 Not Met Due to Failed Wire Lug on Emergency Diesel Generator 2-3

5. EVENT DATE 6. LER NUMBER 7. REPORT DATE 8. OTHER FACILITIES INVOLVED MONTH DAY YEAR YEAR I SEQUENTIAL NUMBER I REV NO.

MONTH DAY YEAR FACILITY NAME DOCKET NUMBER FACILITY NAME DOCKET NUMBER 06 08 2013 2013 004 - 01 03 30 2015

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) D 50 .73(a)(2)(i)(C) D 50.73(a)(2)(vii)

D 20.2201 (d) D 20.2203(a)(3)(ii) D 50.73(a)(2)(ii)(A) D 50.73(a)(2)(viii)(A) 1 D 20.2203(a)(1) D 20.2203(a)(4) D 50. 73(a)(2)(ii)(B) D 50. 73(a)(2)(viii)(B)

D 20.2203(a)(2)(i) D 50.36(c)(1 )(i)(A) D 50. 73(a)(2)(iii) D 50.73(a)(2)(ix)(A)

10. POWER LEVEL D 20.2203(a)(2)(ii) D 50.36(c)(1 )(ii)(A) D 50.73(a)(2)(iv)(A) D 50.73(a)(2)(x)

D 20.2203(a)(2)(iii) D 50.36(c)(2) D 50.73(a)(2)(v)(A) D 73.71 (a)(4)

D 20.2203(a)(2)(iv) D 50.46(a)(3)(ii) D 50.73(a)(2)(v)(B) D 73.71 (a)(5) 100 D 20.2203(a)(2)(v) D 50.73(a)(2)(i)(A) D 50 .73(a)(2)(v)(C) D OTHER Specify in Abstract below or in D 20.2203(a)(2)(vi) [2J 50.73(a)(2)(i)(B) [2J 50. 73(a)(2)(v)(D) NRC Form 366A

12. LICENSEE CONTACT FOR THIS LER LICENSEE CONTACT ITELEPHONE NUMBER (lod,de Acea Code)

Andrew Heffner, Regulatory Services Engineer 805-545-64 70

13. COMPLETE ONE LINE FOR EACH COMPONENT FAILURE DESCRIBED IN THIS REPORT MANU- REPORTABLE MANU- REPORTABLE CAUSE SYSTEM COMPONENT CAUSE SYSTEM COMPONENT FACTURER TO EPIX FACTURER TO EPIX B EK CON T198 y

14. SUPPLEMENTAL REPORT EXPECTED 15.EXPECTED MONTH DAY YEAR SUBMISSION D YES (If yes, complete 15. EXPECTED SUBMISSION DATE) [2J NO DATE ABSTRACT (Limit to 1400 spaces, i.e., approximately 15 single-spaced typewritten lines)

On June 8, 2013, at 08:40 PDT, with Diablo Canyon Power Plant (DCPP) Unit 2 in Mode 1 at 100 percent power, Emergency Diesel Generator (EDG) 2-3 failed to complete a scheduled surveillance run. Cyclic fatigue failure of a wire lug in the EDG 2-3 current differential protection circuit caused an automatic EDG shut down 21 hours2.430556e-4 days <br />0.00583 hours <br />3.472222e-5 weeks <br />7.9905e-6 months <br /> and 42 minutes into the 24-hour load run. DCPP determined the last time EDG 2-3 would have been able to complete its 24-hour surveillance run was greater than the technical specification allowed outage time. Additionally, during the time that EDG 2-3 was unable to complete its load run, EDGs 2-1 and 2-2 also had been declared inoperable on several occasions.

DCPP determined that a vibrating terminal block cover induced cyclical fatigue in the wire lug, causing it to fail.

DCPP replaced the broken wire lug and permanently removed the cover. Additionally, DCPP will revise a procedure to periodically inspect for wear on the wires and lugs.

This condition did not adversely affect the health and safety of the public.

NRC FORM 366 (02-2014)

NRC FORM 366A U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY OMB: NO. 3150-0104 EXPIRES: 01/31/2017 (02-2014)

~c..Jt~R llro(li..,> 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 />.

!~ 01)~ 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 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 Regulatory Affairs, NEOB-10202, (3150-0104), Office of Management and Budget, CONTINUATION SHEET Washington, DC 20503. If a means used to impose an information collection does not display a currently valid OMB control number, the NRC may not conduct or sponsor, and a person is not required to respond to, the information collection.

1. FACILITY NAME 2. DOCKET 6. LER NUMBER 3. PAGE YEAR SEQUENTIAL I REV Diablo Canyon Power Plant, Unit 2 05000323 I NUMBER NO.

2 OF 4 2013 004 01 NARRATIVE I. Plant Conditions At the time of the event, Unit 2 was in Mode 1 (Power Operation) at approximately 100 percent reactor [RCT]

power with normal operating reactor coolant temperature and pressure.

II. Problem Description A. Background Diablo Canyon Power Plant (DCPP) Units 1 and 2 each have three emergency diesel generators (EDGs) [DG] that provide vital backup power to each unit's three electrical buses [BU] to mitigate the consequences of a design basis accident (DBA) if off-site power sources are unavailable. DCPP EDGs are designed to function so that a single failure of any EDG will not jeopardize the capability of the remaining EDGs to start and provide power to operate the systems required to mitigate any DBA condition. In order to ensure that an EDG can perform its design function, it is tested by continuously operating at full-load for an interval of not less than 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />.

Each EDG has differential relays [87] that monitor phase currents and compare them with the corresponding phase currents on the 4 kV Bus side of the generator output breaker [BKR]. If a phase current is different between generator [GEN] and bus sides of the breaker, that differential relay actuates. This condition actuates an alarm

[ALM] in the Control Room [NA], energizes blue lights in the Control Room and on the 4 kV relay board [PL],

and energizes the diesel shutdown lockout relay [86], which shuts down the EDG.

The wire terminations for the current transformer inputs to the differential relays are located in junction boxes

[JBX]. The configuration of the junction boxes in the EDG rooms is not the same for all six EDGs. EDGs 1-1, 1-2, 1-3, 2-1, and 2-2 have their junction box mounted directly onto the generator housing, roughly 4-112 feet above ground on the generator centerline. They are lower to the ground and extremely secure, whereas the junction box on EDG 2-3 is mounted to two supports [SPT] that are connected to the top of the high voltage termination cabinet

[CAB], roughly 7 feet above ground. When EDG 2-3 is running, its junction box experiences a higher level of vibration than the other EDG junction boxes. Additionally, the equipment inside the junction boxes is not the same for all six EDGs. EDGs 1-1, 1-2, 1-3, 2-1, and 2-2 have a terminal block [BLK] inside oftheir junction boxes and no terminal block cover. EDG 2-3 has a terminal block and state switches [89] beneath a terminal block cover inside of its junction box.

B. Event Description During a performance ofDCPP Procedure STP M-9G, "Diesel Generator 24-Hour Load Test and Hot Restart Test," on June 8, 2013, the control room received two unexpected alarms for EDG 2-3. Operators recognized that 4 kV, Bus F, Differential Relay 87HFG had actuated and shut down EDG 2-3 21 hours2.430556e-4 days <br />0.00583 hours <br />3.472222e-5 weeks <br />7.9905e-6 months <br /> and 42 minutes into the 24-hour load run. DCPP determined that a broken wire lug [CON] in the Differential Relay 87HFG circuit removed an input signal to the relay. Subsequent evaluation concluded that terminal block cover vibration against the wire [WEL] induced a cyclical fatigue in the wire lug. Inspection of the junction boxes for the other EDGs showed no signs of wear.

NRC FORM 366A (02-2014)

NRC FORM 366A U.S. NUCLEAR REGULATORY COMMISSION (02-2014)

LICENSEE EVENT REPORT (LER)

CONTINUATION SHEET

1. FACILITY NAME 2. DOCKET 6. LER NUMBER 3. PAGE YEAR SEQUENTIAL I REV Diablo Canyon Power Plant, Unit 2 05000323 I NUMBER NO.

3 OF 4 2013 004 01 NARRATIVE Due to the nature of the failure, DCPP determined that the last time that EDG 2-3 would have been able to meet its surveillance requirement to complete a 24-hour load run was April 11, 2013.

C. Status of Inoperable Structure, Systems, or Components That Contributed to the Event EDG 2-3 was unable to perform its safety function from April11, 2013, until June 8, 2013. During this window, EDGs 2-1 and 2-2 were declared inoperable on multiple occasions, but remained capable of performing their safety function via manual operator action.

EDG 2-1 was declared inoperable on the following four occasions (all times PDT):

• May 1, 2013, from 01:32-04:21, for scheduled surveillance

• May 28-29, 2013, from 21:43-00:13, for scheduled surveillance

• May 2 7, 20 13, from 20: 19 - 22:5 7, for corrective maintenance

• May 29, 2013, from 03:05- 14:21, for corrective maintenance EDG 2-2 was declared inoperable on the following two occasions (all times PDT):

• April25-26, 2013, from 21:59-00:32, for scheduled surveillance

• M~y 24-25, 2013, from 10:01- 16:38, for scheduled surveillance For those periods that EDG 2-1 or 2-2 were declared inoperable, DCPP Unit 2 only had one operable EDG, when two are required to be operable to perform the designed safety function of providing vital emergency power. This condition could have prevented the fulfillment of the EDG's designed safety function to mitigate the consequences of a DBA.

D. Other Systems or Secondary Functions Affected None.

E. Method of Discovery Annunciators PK18-14, "DSL GEN 2-3 BKRDIFFERENTIAL TRIP" and PK18-15, "DSL 2-3 SHUTDOWN RELAY TRIP" alarmed in the Control Room.

F. Operator Actions Operators observed EDG 2-3 coasting down normally, DG 2-3 blue light lit on Panel VB4, and 4 kV, Bus F, Differential Relay 87HFG actuated. Operators declared EDG 2-3 inoperable.

G. Safety System Responses None.

Ill. Cause of the Problem J

The apparent cause of the EDG 2-3 trip was a broken wire lug in the Differential Relay 87HFG current transformer circuit. This broken lug removed one phase of the generator-side current input signal to the differential relay.

NRC FORM 366A (02-2014)

NRC FORM 366A U.S. NUCLEAR REGULATORY COMMISSION (02-2014)

LICENSEE EVENT REPORT (LER)

CONTINUATION SHEET

1. FACILITY NAME 2. DOCKET 6. LER NUMBER 3. PAGE YEAR SEQUENTIAL I REV Diablo Canyon Power Plant, Unit 2 05000323 I NUMBER NO.

4 OF 4 2013 004 01 NARRATIVE Subsequent evaluation concluded that terminal block cover vibration against the wire induced a cyclical fatigue in the wire lug.

IV. Assessment of Safety Consequences DCPP performed a quantitative risk analysis for a 58-day exposure period. This time frame is based on the last time that EDG 2-3 would have been able to successfully complete a 24-hour load run. EDGs 2-1 and 2-2 were capable of performing their safety function (via manual operator action) and EDG 2-3 would start, load the associated bus, and run for at least 22 hours2.546296e-4 days <br />0.00611 hours <br />3.637566e-5 weeks <br />8.371e-6 months <br /> prior to failure. In that time, the offsite power supply would likely have been recovered. Based on these considerations, DCPP concluded that the incremental conditional core damage probability was less than 1E-06.

V. Corrective Actions A. Immediate Corrective Actions DCPP replaced and reconnected the broken wire lug.

B. Other Corrective Actions DCPP permanently removed the terminal block cover, and will revise DCPP Procedure STP M-81G, Diesel Engine Generator Inspection," to include a step to inspect terminations at the generator junction box for tightness and cyclic fatigue.

VI. Additional Information A. Failed Components DCPP discovered a broken wire lug at Junction Box BTA503 in the current transformer input circuit for Differential Relay 87HFG.

B. Previous Similar Events Diablo Canyon- On December 11, 1989, EDG 1-2 tripped due to a differential relay actuation. Troubleshooting found a broken lug in the current transformer output circuit for a differential relay.

NRC FORM 366A (02-2014)