DCL-15-042, Supplemental Licensee Event Report 1-2014-004-01 for Diablo Canyon, Units 1 and 2 Regarding Actuation of Six Emergency Diesel Generators Due to Loss of Offsite Power

Supplemental Licensee Event Report 1-2014-004-01 for Diablo Canyon, Units 1 and 2 Regarding Actuation of Six Emergency Diesel Generators Due to Loss of Offsite Power

ML15089A597
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-15-042 Suppl LER 1-014-004-01
Download: ML15089A597 (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-15-042 U.S. Nuclear Regulatory Commission 10 CFR 50.73 ATTN: Document Control Desk Washington, DC 20555-0001 Docket No. 50-275, OL-DPR-80 Docket No. 50-323, OL-DPR-82 Diablo Canyon Power Plant, Units 1 and 2 Supplemental Licensee Event Report 1-2014-004-01. Actuation of Six Emergency Diesel Generators due to Loss of Offsite Power Dear Commissioners and Staff; Pacific Gas and Electric Company (PG&E) submits the enclosed supplemental Licensee Event Report (LER) regarding the valid actuation of all six safety-related emergency diesel generators due to the loss of 230 kV offsite power. Both Units 1 and 2 were impacted by this event. PG&E is submitting this LER in accordance with 10 CFR 50. 73(a)(2)(iv)(A). All systems operated as designed with no problems observed.

PG&E makes no new or revised regulatory commitments (as defined by NEI 99-04) in this report. All corrective actions identified in this letter are being 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, Ba1.~n ~. AtL_

aph8/64 70/50669932 Enclosure cc/enc: Marc L. Dapas, NRC Region IV Administrator Thomas R. Hipschman, NRC Senior Resident Inspector Siva P. Lingharr1, NRR Project Manager IN PO Diablo Distribution A member of the STARS (Strat(;!gic Teaming and Resource Sharing) Alliance Callaway

• Diablo Canyon

• Palo Verde

• Wolf Creek

NRC FORM 366 U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY OMB: NO. 3150-0104 EXPIRES: 01/31/2017 (01 - 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 />. Reported

~~<,'-t.!A:au"Lt,.o lessons learned are incorporated into the licensing process and fed back to industry. Send

{. A~.r- *::. l comments regarding burden estimate to the FOIA, Privacy and Information Collections Branch (T-5 F53), U.S. Nuclear Regulatory Commission, Washington, DC 20555-0001, or by internet e-mail

\.,

...... LICENSEE EVENT REPORT (LER) 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, Washington, DC (See Page 2 for required number of 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 1 05000 275 1 OF 4

4. TITLE Actuation of Six Emergency Diesel Generators due to Loss of Offsite Power

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

MONTH DAY YEAR FACILITY NAME Diablo Canyon Unit 2 DOCKET NUMBER 05000 323 FACILITY NAME DOCKET NUMBER 10 31 2014 2014 - 004 - 01 03 30 2015

9. OPERATING MODE 11 . THIS REPORT IS SUBMITTED PURSUANT TO THE REQUIREMENTS OF 10 CFR §: (CIIeck all that apply) 0 20.22o1(b) 0 20.2203(a)(3)(i) 0 50. 73(a)(2)(i)(C) 0 50.73(a)(2)(vii) 1 n 20.2201(d) n 20.2203(a)(3)(ii) n 50.73(a)(2)(ii)(A) n 50.73(a)(2)(viii)(A) 0 20.2203(a)(1) 0 20.2203(a)(4) 0 50.73(a)(2)(ii)(B) 0 50.73(a)(2)(viii)(B) n 20.2203(a)(2)(i) n 50.36(c)(1 )(i)(A) n 50. 73(a)(2)(iii) n 50.73(a)(2)(ix)(A)

10. POWER LEVEL 0 20.2203(a)(2)(ii) 0 50.36(c)(1)(ii)(A) IKJ50.73(a)(2)(iv)(A) 0 50. 73(a)(2)(x) 0 20.2203(a)(2)(iii) 0 50.36(c)(2) 0 50.73(a)(2)(v)(A) D 73.71(a)(4) 100 0 20.2203(a)(2)(iv) 0 50.46(a)(3)(ii) 0 50. 73(a)(2)(v)(B) D 73.71(a)(5) 0 20.2203(a)(2)(v) 0 50.73(a)(2)(i)(A) 0 50. 73(a)(2)(v)(C) OOTHER D 20.2203(a)(2)(vi) 0 50.73(a)(2)(i)(B) 0 50.73(a)(2)(v)(D) Specify in Abstract below or in NRC Form 366A

12. LICENSEE CONTACT FOR THIS LER FACILITY NAME TELEPHONE NUMBER (Include Area Code)

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

13. COMPLETE ONE LINE FOR EACH COMPpJ~ENT FAILURE DESCRIBED IN THIS REPORT MANU- REPORTABLE MANU- REPORTABLE CAUSE SYSTEM COMPONENT CAUSE SYSTEM COMPONENT FACTURER TOEPIX FACTURER TOEPIX c EK N/A N/A N/A N/A N/A N/A N/A N/A I

14. SUPPLEMENTAL REPORT EXPECTED 15. EXPECTED MONTH DAY YEAR OvES (If yes, complete 15. EXPECTED SUBMISSION DATE) (K] NO SUBMISSION DATE ABSTRACT (Limit to 1400 spaces, i.e., approximately 15 single-spaced typewritten lines)

On October 31, 2014, at 17:40 PDT, during a medium to heavy rain, Pacific Gas and Electric Company (PG&E) lost its 230 kV offsite power source at the Diablo Canyon Power Plant when an insulator in the 230 kV switchyard flashed over.

This resulted in the valid start of all Unit 1 and 2 emergency diesel generators (EDGs), three per unit. All EDGs successfully started, but did not load since all associated electrical buses remained energized by auxiliary power. All systems operated as designed with no problems observed. The 230 kV offsite power source is the only offsite power system designed to be immediately available following an accident. However, the safety-related onsite EDGs would have provided power to mitigate the consequences of an accident while the 230 kV system was unavailable. On October 31, 2014, at 23:07 PDT, PG&E made an 8-hour nonemergency report to the NRC. The 230 kV offsite power was declared operable on November 1, 2014, at 02:29 PDT.

PG&E completed a root cause evaluation and determined that inadequate organizational oversight and alignment resulted in ineffective and untimely execution of planned corrective actions intended to prevent excessive buildup of environmental contaminants on the 230 kV insulators.

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

NKt; t-UKM3b6 (U1-2U14)

NRCFORM366A U.S .NLXJ..EARREGULATORY COMMISSION APPROVED BYOMB: N0.3150-0104 EXPIRES: 01/31/2017 (01-2014)

Estimated burden per response b cnmply 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 rn the licensing process and fed back to industry Send comments regarding burden estimate to the FOIA, Privacy and Information Collections Branch (T-5 F53), U.S. Nuclear Regulatory Commission, Washington ,DC 20555-0001 , or b~

internet e-mail to lnfocollects.Resource@nrc.gov, and to the Desk Officer, Office of Information LICENSEE EVENT REPORT (LER) 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 no 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 1 05000 275 NUMBER NO.

2 OF 4 2014 - 004 - 01 NARRATIVE I. Plant Conditions Just prior to, and following, the event, Unit 1 operated in Mode 1 (Power Operation) at approximately 100 percent reactor power with normal operating reactor coolant temperature and pressure. Unit 2 operated in Mode 4 (Hot Shutdown) at 0 percent power with power supplied from the 500 kV auxiliary power source.

II. Problem Description A. Background The Diablo Canyon Power Plant (DCPP) electrical systems are designed to ensure an adequate supply of electrical power to all essential auxiliary equipment during normal operation and under accident conditions. Nonvital 4 kV alternating current (AC) auxiliary buses [BU] are energized by either offsite power or power from the main generator.

Vital AC buses [EA] have an additional available source, which includes onsite power delivered by emergency diesel generators (EDGs) [DG]. The electrical systems are designed so that failure of any one electrical device will not prevent operation of the minimum required engineered safety feature (ESF) equipment.

DCPP offsite power is supplied by two systems that are physically and electrically separated and independent of each other: (1) a 230 kV system [EK] and (2) a 500 kV system [EK]. The 230 kV system provides offsite startup and standby power, and provides an immediately available source of offsite power to the 4 kV system . To make power available to the vital4 kV buses, the 230 kV system provides power to Startup Transformers (SUT)[EA][XFMR] 1-1 and 2-1 (230 kV to 12 kV), which then feeds SUT 1-2 and 2-2 (12 kV to 4 kV). The 500 kV system provides for transmission of the plant's power output, and is also available as a delayed access source of offsite power after the main generator is disconnected.

To produce onsite power, each unit has three EDGs, which supply power to the 4 kV vital AC buses when 230 kV startup power is unavailable or voltage degrades below a point at which required ESF loads would be operable. The EDGs start in standby mode on loss of 230 kV startup power. After the EDGs start, they supply power to their respective vital bus if the buses are deenergized. If the vital buses are not deenergized, the EDGs continue to run in standby mode, ready to provide power if required.

B. Event Description On October 31,2014, at 17:40 PDT, during a medium to heavy rain, Pacific Gas and Electric Company (PG&E) lost its offsite 230 kV offsite power source at DCPP due to an insulator flashover in the 230 kV switchyard, resulting in the valid anticipatory start of all Unit 1 and 2 EDGs, three per unit. This is reportable, in accordance with 10 CFR 50.73(a)(2)(iv)(A), as an event that resulted in the valid actuation of EDGs. All EDGs successfully started, but did not load since all associated electrical buses remained energized by auxiliary power. All systems operated as designed with no problems observed. However, the safety-related onsite EDGs would have provided power to mitigate the consequences of an accident while the 230 kV system was unavailable. On October 31, 2014, at 23:07 PDT, PG&E made an 8-hour nonemergency report to the NRC (Reference NRC Event Notification Number 50586). The 230 kV offsite power was declared operable on November 1, 2014, at 02:29 PDT.

C. Status of Inoperable Structure, Systems, or Components That Contributed to the Event None.

NRCFORM366A (01-2014)

NRC FORM 366A LICENSEE EVENT REPORT (LER) u.s. NUCLEAR REGULATORY COMMISSION (01-2014)

CONTINUATION SHEET 1.FACILITY NAME 2.DOCKET 6. LER NUMBER 3.PAGE YEAR I SEQUENTIAL I REV NO.

Diablo Canyon Power Plant, Unit 1 05000 275 NUMBER 3 OF 4 2014 - 004 - 01 NARRATIVE D. Other Systems or Secondary Functions Affected None.

E. Method of Discovery Licensed plant operators immediately recognized the event by alarms and indications received in the control room.

F. Operator Actions On November 1, 2014, operators restored the Unit 1 and Unit 2 EDGs, respectively, to standby service. The 230 kV offsite power system was declared operable on November 1, 2014, at 02:29 PDT.

G. Safety System Responses All Unit 1 and Unit 2 EDGs started as designed with no problems observed.

Ill. Cause of the Problem A. Root Cause:

PG&E completed a root cause evaluation and determined that inadequate organizational oversight and alignment resulted in ineffective and untimely execution of planned corrective actions intended to prevent excessive buildup of environmental contaminants on the 230 kV insulators.

IV. Assessment of Safety Consequences The 230 kV startup power is a standby system. Its loss was due to a degraded condition in the 230kv switchyard.

This event did not create a transient at the plant. A Significance Determination Process evaluation allows taking credit for the actual plant configuration at the time of an event. With the successful start of all EDGs upon the loss of startup power, the vital AC power supply to all emergency core cooling system loads would have been maintained. A bounding analysis was performed and resulted in an incremental core damage and incremental large early release probabilities that were well below their respective acceptance criteria.

V. Corrective Actions

1. A new Project Manager has been designated to implement activities to effectively prioritize action plans into one comprehensive strategy for recovery between Transmission and DCPP projects.

2. Revised the Transmission & Distribution Interface procedure to ensure a single point of contact with ownership and oversight over switchyards affecting DCPP reliability to strengthen execution of maintenance and corrective actions.

VI. Additional Information A Failed Components None.

NRC FORM 366A (01-2014)

NRC FORM 366A LICENSEE EVENT REPORT (LER) U.S. NUCLEAR REGULATORY COMMISSION (01-2014)

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

05000 275 4 OF 4 2014 - 004 - 01 NARRATIVE B. Previous Similar Events On May 12, 2007, at 10:25 PDT, during a refueling outage at DCPP, with Unit 1 in no Mode (core offloaded to the spent fuel pool) and Unit 2 in Mode 1 at approximately 100 percent power, an EDG system actuation was initiated on loss of 230 kV startup power supply due to an offsite transmission system insulator failure resulting in a phase to ground short and unanticipated protective relay response. Two Unit 1 EDGs started and loaded to provide onsite power. Unit 1 had one EDG and auxiliary offsite power cleared for maintenance. All three Unit 2 EDGs started as required, but did not load since all associated buses remained energized by auxiliary power. On May 12, 2007, at 14:30 PDT, operators restored startup power to the site. On May 12, 2007, at 15:09 PDT, operators made a nonemergency event notification (EN 43360) in accordance with 10 CFR 50. 72(b)(3)(iv)(A).

On June 23, 2013, at 21:20 PDT, PG&E lost its 230 kV offsite power source at the DCPP, due to an offsite transmission system insulator failure resulting in a phase to ground short and unanticipated protective relay response.

This resulted in the valid start of all Unit 1 and 2 EDGs, three per unit. All EDGs successfully started, but did not load since all associated buses remained energized by auxiliary power. All systems operated as designed with no problems observed. The 230 kV offsite power source is the only offsite power system designed to be immediately available following an accident. However, the safety-related onsite EDGs would have provided power to mitigate the consequences of an accident while the 230 kV system was unavailable. On June 24, 2013, at 01:35 PDT, PG&E made an 8-hour nonemergency event notification.

C. Industry Reports None.

NRCFORM366A (01-2014)