DCL-11-119, LER 11-04-001 for Diablo, Unit 1, Regarding Emergency Diesel Generator Actuated Upon 230 Kv Isolation Due to Maintenance Activities on Relay Panel

LER 11-04-001 for Diablo, Unit 1, Regarding Emergency Diesel Generator Actuated Upon 230 Kv Isolation Due to Maintenance Activities on Relay Panel

ML113130078
Person / Time
Site:	Diablo Canyon
Issue date:	11/08/2011
From:	Becker J Pacific Gas & Electric Co
To:	Office of Nuclear Reactor Regulation, Document Control Desk
References
DCL-11-119 LER 11-04-001
Download: ML113130078 (6)

Text

Pacific Gas and Electric Company James R. Becker Diablo Canyon Power Plant Site Vice President Mail Code 104/5/601 P. O. Box 56 Avila Beach, CA 93424 805.545.3462 Internal: 691.3462 November 8,2011 Fax: 805.545.6445 PG&E Letter DCL-11-119 U.S. Nuclear Regulatory Commission 10 CFR 50.73 ATTN: Document Control Desk Washington, DC 20555-0001 Docket No. 50-275, OL-DPR-80 Diablo Canyon Unit 1 Licensee Event Report 1-2011-004-01 Emergency Diesel Generators Actuated Upon 230 kV Isolation Due to Maintenance Activities on Relay Panel

Dear Commissioners and Staff:

Pacific Gas and Electric Company submits the enclosed Licensee Event Report (LER) regarding the Diablo Canyon Power Plant Unit 1 emergency diesel generators actuation after 230 kV startup power was isolated due to an inadvertent relay actuation. This LER is submitted in accordance with 10 CFR 50.73(a)(2)(iv)(A) and 10 CFR 50.73(a)(2)(v)(D). This supplement provides the cause for the event, along with associated corrective actions.

There are no new or revised regulatory commitments in this report.

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

Since*rely, dnpo/50412203 Enclosure celene: Elmo E. Collins, NRC Region IV Michael S. Peck, NRC Senior Resident Inspector James T. Polickoski, NRR Project Manager Alan B. Wang, NRR Project Manager INPO Diablo Distribution A member of the STARS (Strategic Teaming and Resource Sharing) Alliance Callaway. Comanche Peak. Diablo Canyon. Palo Verde. San Onofre. South Texas Project. WolfCreek

NRC FORM 366 U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY OMB: NO. 3150-0104 EXPIRES: 10/31/2013 (10-2010)

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 regarding burden estimate to the FOIA/Privacy Section (T-5 F53), U.S. Nuclear Regulatory Commission, Washington, DC 20555-0001, or by internet e-mail to infocollects.resource@nrc.t>ov, and to the Desk Officer, Office of Information and Regulatory Affairs, NE B-10202, (3150-0104), Office of Management and LICENSEE EVENT REPORT (LER) Budget, Washington, DC 20503. If a means used to impose an information (See reverse for required number of 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 digits/characters for each block) information collection.

1. FACILITY NAME 2. DOCKET NUMBER 3. PAGE Diablo Canyon Power Plant Unit 1 05000 275 1 OF 5

4. TITLE Emergency Diesel Generator Actuated Upon 230 kV Isolation Due to Maintenance Activities on Relay Panel

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

MONTH DAY YEAR NUMBER 05000 05 17 2011 2011 . 4 . 1 11 08 2011 FACILITY NAME DOCKET NUMBER 05000

9. OPERATING MODE 11. THIS REPORT IS SUBMITTED PURSUANT TO THE REQUIREMENTS OF 10 CFR §: (Check all that apply) 1 o 20.2201(b) o 20.2203(a)(3)(i) o 50.73(a)(2)(i)(C) o 50.73(a)(2)(vii) 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) D 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) D 50.73(a)(2)(ix)(A)

10. POWER LEVEL D 20.2203(a)(2)(ii) o 50.36(c)(1)(ii)(A) ({] 50.73(a)(2)(iv)(A) D 50.73(a)(2)(x) o 20.2203(a)(2)(iii) o 50.36(c)(2) D 50.73(a)(2)(v)(A) o 73.71(a)(4) 100 D 20.2203(a)(2)(iv) o 50.46(a)(3)(ii) D 50.73(a)(2)(v)(B) o 73.71(a)(5) o 20.2203(a)(2)(v) o 50.73(a)(2)(i)(A) D 50.73(a)(2)(v)(C) D OTHER o 20.2203(a)(2)(vi) o 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 FACILITY NAME ITELEPHONE NUMBER (Include Area Code)

Thomas R. Baldwin, Manager, Regulatory Services (805) 545-4720

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

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

On May 17,2011, at 0954 PDT, with Unit 1 at 100 percent power, 230 kV startup power was isolated following the actuation of the 230 kV Line Differential Relay 287. As a result, all Unit 1 emergency diesel generators (EDGs) started in standby mode as designed, with no problems observed. No vital loads were affected by the loss of startup power as they remained powered by the Unit 1 main generator. At the time, Unit 2 was in a refueling outage with the core offloaded and startup power cleared; therefore, it was unaffected by the event. All Unit 1 EDGs were shut down and returned to auto, Startup Transformers 1-1 and 1-2 were returned to service, and on May 17,2011, at 1125 PDT, Unit 1 startup power was declared operable.

The actuation of Differential Relay 287 was due to modifications being performed on the 12 kV startup relay board (Panel RU) that contains components for both units. Mechanical vibration induced by a reciprocating saw caused the relay to actuate, thus opening the 12 kV Feeder to Startup Bus Breaker 52VU12 and isolating Unit 1 230 kV startup power.

The cause was that plant personnel failed to perform an adequate risk assessment during the planning stage of the modification, misjudging the possible impact of mechanically agitating an adjacent active relay while cutting. Corrective actions include revising procedures to assure adequate risk assessments are performed when working on or near equipment that can potentially impact both units, and strengthening the consistent use of human performance tools.

NRC FORM 366 (10-2010)

NRC FORM 366A LICENSEE EVENT REPORT (LER)U,S, NUCLEAR REGULATORY COMMISSION (10-2010)

CONTINUATION SHEET

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

05000 275 2 OF 5 2011 .. 004 .. 01 NARRATIVE I. PLANT CONDITIONS When the event occurred, Unit 1 was in Mode 1 (Power Operation) at 100 percent power.

II. DESCRIPTION OF PROBLEM 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. Nonvital4.16 kValternating current (AC) auxiliary buses are energized by either offsite power or power from the main generator. Vital AC buses [EA]

[BU] have an additional available source, which includes onsite power delivered by diesel generators. The electrical systems are designed so that failure of anyone electrical device will not prevent operation of the minimum required engineered safety feature (ESF) equipment.

General Design Criteria (GDC) 17 states, in part, "An onsite electric power system and an offsite electric power system shall be provided to permit functioning of structures, systems, and components important to safety. The safety function for each system (assuming the other system is not functioning) shall be to provide sufficient capacity and capability to assure that (1) specified acceptable fuel design limits and design conditions of the reactor coolant pressure boundary are not exceeded as a result of anticipated operational occurrences and (2) the core is cooled and containment integrity and other vital functions are maintained in the event of postulated accidents."

DCPP offsite power is supplied by two systems that are physically and electrically separated and independent of each other: a 230 kV system and a 500 kV system. This satisfies requirements established by GDC 17. The 230 kV system provides startup and standby power, and is immediately available following a loss-of-coolant accident (LOCA) to assure that core cooling, containment integrity, and other vital safety functions are maintained. To make power available to the vital 4.16 kV buses, the 230 kV system provides power to Startup Transformer (SUT)[EA][XFMR] 1-1 (230 kV to 12 kV),

which then feeds SUT 1-2 (12 kV to 4.16 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.

Technical Specification (TS) 3.8.1 requires two qualified circuits between the offsite transmission network and the onsite Class IE AC Electrical Power Distribution System. If one required offsite circuit is inoperable, TS Action 3.8.1 is entered and the following actions are required: DCPP must perform Surveillance Requirement (SR) 3.8.1 for the required operable offsite circuit within 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br /> and once every 8 hours9.259259e-5 days <br />0.00222 hours <br />1.322751e-5 weeks <br />3.044e-6 months <br /> thereafter, and restore the required offsite circuit to operable status within 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> and 14 days from discovery of failure to meet the Limiting Condition for Operation (LCO).

To produce onsite power, each unit has three emergency diesel generators (EDGs)[EK][DG], which supply power to the 4.16 kV vital AC buses when power is unavailable or voltage degrades below a point at which required ESF loads would be operable. After the EDGs have started, they will supply power to their respective vital bus if the buses are deenergized. If the vital buses are not deenergized, the EDGs will continue to run in standby mode, ready to provide power if required.

NRC FORM 366A (10-2010)

NRC FORM 366A (10-2010)

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

1. FACILITY NAME 2. DOCKET 6. LER NUMBER 3. PAGE Diablo Canyon Power Plant Unit 1 YEAR SEQUENTIAL I REV 05000 275 I NUMBER NO.

3 OF 5 2011 004 01 NARRATIVE B. EVENT DESCRIPTION At the time of the event, Unit 2 Sixteenth Refueling Outage (2R16) was ongoing and modifications were being made to the 230 kV startup system. On May 17,2011, at 0954 PDT, while work was being performed on a relay panel containing components for both units, the 230 kV Line Differential Relay 287 actuated. This opened the 12 kV Feeder to Startup Bus Breaker 52VU12 and resulted in a loss of power to the Unit 112 kV startup bus.

The isolation of the offsite standby power source, and subsequent loss of power to startup feeder breakers for the 4.16 kV operating buses, caused all Unit 1 EDGs to start in standby mode. The EDGs started as designed with no problems observed.

All Unit 1 EDGs were shutdown and returned to auto. SUTs 1-1 and 1-2 were returned to service, and on May 17,2011, at 1125 PDT, Unit 1 startup power was declared operable.

Startup power on Unit 2 was cleared due to the maintenance activities being performed; therefore, it was unaffected by the event.

On May 17,2011, at 1542, Pacific Gas & Electric (PG&E) made an 8-hour nonemergency report (Reference NRC Event Notification 46856) in accordance with 10 CFR 50.72(b)(3)(iv)(A).

C. STATUS OF INOPERABLE STRUCTURE, SYSTEMS, OR COMPONENTS THAT CONTRIBUTED TO THE EVENT There were no inoperable structures, systems, or components that contributed to the event. All systems functioned as designed.

D. OTHER SYSTEMS OR SECONDARY FUNCTIONS AFFECTED No other systems or secondary functions were affected.

E. METHOD OF DISCOVERY The event was immediately known to licensed plant operators by alarms and indications received in the control room.

F. OPERATOR ACTIONS Plant operators performed required surveillances, secured the Unit 1 EDGs, and proceeded to restore the availability of startup power to Unit 1.

G. SAFETY SYSTEM RESPONSES All Unit 1 EDGs started as designed with no problems observed.

NRC FORM 366A (10-2010)

NRC FORM 366A (10-2010)

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

1. FACILITY NAME 2. DOCKET 6. LER NUMBER 3. PAGE YEAR SE.QUENTIAL I REV Diablo Canyon Power Plant Unit I 05000 275 I NUMBER NO.

OF 5 4

2011 004 ... 01 NARRATIVE III. CAUSE OF THE PROBLEM A. IMMEDIATE CAUSE The 230 kV Line Differential Relay 287 was inadvertently actuated due to maintenance activities on the 12 kV startup relay board (Panel RU) where Relay 287 is installed. As part of the maintenance work being conducted during 2R16, a reciprocating saw was used to cut an opening in Panel RU, which is common to both Units 1 and 2. Mechanical vibration induced by the power tool caused the relay to actuate, thus opening Breaker 52VUI2 and isolating startup power.

B. CAUSE Plant personnel failed to perform an adequate risk assessment during the planning stage of the modification. While evaluating the work to be performed on the panel, personnel considered electric and magnetic fields induced from welding to be performed, but overlooked the possible effects of mechanical agitation to the Unit 1 relays that inadvertently actuated during the cutting process.

IV. ASSESSMENT OF SAFETY CONSEQUENCES At DCPP, the 230 kV system is the only offsite power system which is designed to be immediately available to mitigate the consequences of postulated accidents; therefore, this event could have prevented fulfillment of a safety function of the offsite electric power system. However, the Class IE onsite EDGs remained available and would have provided power following a loss of the offsite source.

The voltage on operating buses was not affected by the isolation of230 kV startup power, and the EDGs were not required since all vital buses were powered by the Unit 1 main generator. As a result, no vital loads were affected by this event.

The increased conditional core damage probability for this event was assessed and found to be less than 4E-07.

This event had no adverse effect on the health and safety of the public.

V. CORRECTIVE ACTIONS A. IMMEDIATE CORRECTION ACTIONS Plant operators restored startup power and identified sensitive devices in the electrical panel that would need to be isolated or protected. Planners modified clearances to add relays in the "cut out" position and maintenance ceased cutting with a reciprocating saw. Instead, personnel used a cutting wheel in order to minimize vibration.

B. CORRECTIVE ACTIONS

1. Station procedures will be revised to require a risk assessment for work being performed (daily and during outage) in panels that can potentially impact both Units I and 2.

NRC FORM 366A (10-2010)

NRC FORM 366A (10-2010)

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

1. FACILITY NAME 2. DOCKET 6. LER NUMBER 3. PAGE YEAR SEQUENTIAL I REV Diablo Canyon Power Plant Unit 1 05000 275 I NUMBER NO.

5 OF 5 2011 004 01 NARRATIVE

2. Procedure AD7.DC8, "Work Planning," will be revised to include additional steps for work involving panels which contain sensitive or repositionable components or equipment that impact both Units 1 and 2. The procedure will instruct personnel to install temporary protective barriers in order to shield components or equipment associated with the opposite unit. It will also require performance of an engineering evaluation for any physical work on electrical relays (e.g., cutting, hammering), as well as recommendations for risk mitigation.

3. Personnel will install permanent signage or hardened barriers on electrical panels containing components or equipment that can potentially impact both Units 1 and 2.

4. Maintenance Services training (initial and recurring) will be developed for successful supervisor coaching. The training will focus on effective coaching for accomplishing work while demonstrating appropriate behaviors, such as correct use of human performance tools and verification practices. It will also focus on identifying opportunities for coaching.

VI. ADDITIONAL INFORMATION A. FAILED COMPONENTS All components functioned as designed.

B. PREVIOUS SIMILAR EVENTS There are no examples of previous events at where offsite power was isolated due to relay vibration at DCPP in the past three years.

NRC FORM 366A (10-2010)