05000275/LER-2011-004, For Diablo Canyon Power Unit 1, Regarding Emergency Diesel Generators Actuated Upon 230-kV Isolation Due to Maintenance Activities on Relay Panel

For Diablo Canyon Power Unit 1, Regarding Emergency Diesel Generators Actuated Upon 230-kV Isolation Due to Maintenance Activities on Relay Panel

ML11194A052
Person / Time
Site:	Diablo Canyon
Issue date:	06/30/2011
From:	Becker J Pacific Gas & Electric Co
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
DCL-11-078, OL-DPR-80 LER 11-004-00
Download: ML11194A052 (6)

LER-2011-004, For Diablo Canyon Power Unit 1, Regarding Emergency Diesel Generators Actuated Upon 230-kV Isolation Due to Maintenance Activities on Relay Panel

Event date:
Report date:
Reporting criterion:	10 CFR 50.73(a)(2)(iv)(A), System Actuation 10 CFR 50.73(a)(2)(v), Loss of Safety Function 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)(i)(B), Prohibited by Technical Specifications
2752011004R00 - NRC Website

text

It' L"I' Pacific Gas and Electric Company' James R. Becker Site Vice President Diablo Canyon Power Plant Mail Code 104/5/601 P 0. Box 56 Avila Beach, CA 93424 805.545.3462 Internal: 691.3462 Fax: 805.545.6445 June 30, 2011 PG&E Letter DCL-1 1-078 U.S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, DC 20555-0001 10 CFR 50.73 Docket No. 50-275, OL-DPR-80 Diablo Canyon Unit 1 Licensee Event Report 1-2011-004-00 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).

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

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

Sincerely, dnpo/50402706 Enclosure cc/enc:

Elmo E. Collins, NRC Region IV Michael S. Peck, NRC Senior Resident Inspector 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 9 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)

, the NRC may sfor each block) not conduct or sponsor, and a person is not required to respond to, the digits/characters finformation collection.

3. PAGE Diablo Canyon Power Plant Unit 1 05000 275 1

OF

4. TITLE Emergency Diesel Generators 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 MONTH DAY YEAR YEAR SEQUENTIAL REV FACILITY NAME DOCKET NUMBER NUMBER NO.

MONTH DAY YEAR 05000 FACILITY NAME DOCKET NUMBER 05 17 2011 2011 4

0 06 30 2011 05000

9. OPERATING MODE

11. THIS REPORT IS SUBMITTED PURSUANT TO THE REQUIREMENTS OF 10 CFR §: (Check all that apply) jj 20.2201(b) jJ 20.2203(a)(3)(i)

E] 50.73(a)(2)(i)(C)

El 50.73(a)(2)(vii)

El 20.2201(d)

[] 20.2203(a)(3)(ii) fl 50.73(a)(2)(ii)(A)

[

50.73(a)(2)(viii)(A)

E] 20.2203(a)(1)

E] 20.2203(a)(4)

[] 50.73(a)(2)(ii)(B)

E] 50.73(a)(2)(viii)(B)

E] 20.2203(a)(2)(i)

El 50.36(c)(1)(i)(A) 5 50.73(a)(2)(iii) 5 50.73(a)(2)(ix)(A)

10. POWER LEVEL

[] 20.2203(a)(2)(ii)

I] 50.36(c)(1)(ii)(A)

[] 50.73(a)(2)(iv)(A)

I] 50.73(a)(2)(x)

[] 20.2203(a)(2)(iii) r] 50.36(c)(2)

F] 50.73(a)(2)(v)(A)

E] 73.71(a)(4) 100

[] 20.2203(a)(2)(iv) 5 50.46(a)(3)(ii)

[] 50.73(a)(2)(v)(B)

El 73.71(a)(5)

E] 20.2203(a)(2)(v)

El 50.73(a)(2)(i)(A)

El 50.73(a)(2)(v)(C)

[

OTHER

[] 20.2203(a)(2)(vi)

I] 50.73(a)(2)(i)(B)

EJ 50.73(a)(2)(v)(D)

Specify in Abstract below or in

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 1 12 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.

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 52VU12 and isolating startup power.

B. CAUSE

Cause to be provided in a supplemental report following the completion of a root cause evaluation (RCE).

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 1E onsite EDGs remained available and would have provided power following a loss of offsite power.

The voltage on operating buses was not affected by the isolation of 230 kV startup power, and the EDGs were not required since all vital buses were powered by the Unit I 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 affect on the health and safety of the public.

V. CORRECTIVE ACTIONS

A. IMMEDIATE CORRECTION ACTIONS PG&E restored startup power and identified sensitive devices in the electrical panel that would need to be isolated or protected. Clearances were modified to add relays in the "cut out" position and maintenance ceased cutting methods involving a reciprocating saw. Instead, personnel were instructed to use a cutting wheel in order to minimize vibration.

B. CORRECTIVE ACTIONS TO PREVENT RECURRENCE (CAPRs)

CAPRs to be detailed in a supplemental report following the completion of a RCE.

VI. ADDITIONAL INFORMATION

A. FAILED COMPONENTS All components functioned as designed.

B. PREVIOUS SIMILAR EVENTS

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