05000361/LER-1999-001, :on 990201,automatic Start of EDG Was Noted. Caused by Workers Closing Breaker 2A0418 by Discharging Closing Springs.Operators Restored SDC in Approx 26 Minutes. with

:on 990201,automatic Start of EDG Was Noted. Caused by Workers Closing Breaker 2A0418 by Discharging Closing Springs.Operators Restored SDC in Approx 26 Minutes. with

ML20207F668
Person / Time
Site:	San Onofre
Issue date:	03/03/1999
From:	Krieger R SOUTHERN CALIFORNIA EDISON CO.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
REF-PT21-99 LER-99-001, LER-99-1, NUDOCS 9903110295
Download: ML20207F668 (6)

LER-1999-001, on 990201,automatic Start of EDG Was Noted. Caused by Workers Closing Breaker 2A0418 by Discharging Closing Springs.Operators Restored SDC in Approx 26 Minutes. with

Event date:
Report date:
Reporting criterion:	10 CFR 50.73(a)(2)(iv), System Actuation 10 CFR 50.73(a)(2)(v), Loss of Safety Function 10 CFR 50.73(a)(2)(1)
3611999001R00 - NRC Website

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An EDISON INTLIWATIONAL Company j

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March 3,1999 i

U. S. Nuclear Regulatory Commission l

Document Control Desk Washington, D.C. 20555

Subject:

Docket No. 50-361 30-Day Report Licensee Event Report No. 1999-001 San Onofre Nuclear Generating Station, Unit 2 Gentlemen:

1 This letter provides Licensee Event Report (LER) 1999-001 in accordance with 10CFR50.73(a)(2)(iv),10CFR50.73(a)(2)(v), and 10CFR21 for an occurrence involving an Engineered Safety Feature actuation (automatic start of an emergency diesel generator).

The health and safety of neither the public nor plant personnel were affected by this occurrence.

Any actions listed are intended to ensure continued compliance with existing commitments as discussed in applicable licen:ing documents; this LER contains no new commitments. If you require any additiona information, please so advise.

i Sincerely, M

rubfbe d

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LER No. 1999-001 l

E. W. Merschoff, Regional Administrator, NRC Region IV cc:

/

J. A. Sloan, NRC Senior Resident Inspector, Units 2 and 3

[

Institute of Nuclear Power Operations (INPO) 7f 9903110295 990303 '

PDR ADOCK 05000361 S

PDR L P. O. Box 128 San Clemente. CA 92674 0128 714 368-6255 Fax 714-168-6183

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NRC FORM 366 U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY OMS No. 3160-0104 EXPIRES MM/DD/YYYY (MMM-YYYY)

NO C"'O " $,l,0,,'*O U"L',L""Ms',"L",,*,'"O LICENSEE EVENT REP 0RT (LER)

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t and to the Pacernort Reduction Dreject (3150-0104), Office of lunagemet and Budget, (See' reverse for required nueber of Washington Dr 20503. If a dricwent used to incose an infornution collection does not disoie a carmatly und as control aster, the set say not conduct or sponsor,4,s. a digits / characters for each block) 8'"5" "t '**"*' # '"8oad 2. I"f**t '" "H'ct1"-

FACILITY NAME (1)

Docket Musber (2)

Page (3)

San Onofre Nuclear Generating Station (SONGS) Unit 2 05000-361 1 of 5 TITLE (4): Automatic Start of an Emergency Diesel Generator (EDG)

EVENT DATE LER NUMBER (6)

REPORT DATE (7)

OTHER FACILITIES INVOLVED (8) l REVISION dONTH DAY YEAR YEAR SEQUENTIAL MONTH DAY YEAR FACILITY NAME DOCKET NUMBER NUMBER NUMBER 2

01 1999 1999 001 00 3

3 1999 FACILITY NAME 00CKE) NUMBER J

E 6

THIS REPORT IS $U8MITTED PUR$UANT TO THE REQUIREMENTS OF 10 CFR 5: (Check One or More) (11) l 20.2201(b)

20. 22(,3 ( a ) ( 2 ) ( v )

50.73(a)(2)(1) 50,73(a)(2)(viii)

POWER 000 LEVEL 20.2203f8)(1) 20.2203falf3)fi) 50.73(alf?)ffi) 50.73falf2)fx) 20.2203(a)(2)(1) 20.2203fa)(3) fit) 50.73 f a)(2)(111) 71 71 N

20.2203(a)(2)(ii) 20.2203falf4)

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50.73falf2)ftv)

V OTHER 20.2203(a)(2)(111) 50 16feif11 Y

E0 71(aif?ifv)

Part 21 20.2203falf2)fiv) 50.36fe)(2) 50.73falf2)(v11)

LICENSEE CONTACT FOR THIS LER (12)

NAME TELEPHONE NUMBER (Include Area R.W. Krieger, Vice President, Nuclear Generation 949-368-6255 1

COMPLETE ONE LINE FOR EACH COMPONENT FAILURE DESCRIBED IN THIS REPORT (13)

CAUSE

SYSTEM COMP 0hENT MANUFACTURER REPORTABLE

CAUSE

SYSTEM COMPONENT MANUFACTURER REPORTABLE TO EP!1 TO EPIX l

SUPPLEMENTAL REPORT EXPECTED (14)

EXPECTED MONTH DAY l

YEAR SUBMISSION Yes (l' ses, complete X

No DATE (15)

EXPECTit SUBMISSION DATE)

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

On 2/1/1999 (event date), Unit 2 was in Mode 6 (000 percent power) for a planned refueling outage. At 0959 PST, while removing a supply breaker for a 4.16 kV Class IE bus from its cubicle, a worker discharged the bres.ker's closing springs, closing the breaker. As a result, power was lost to the bus, Shutdown Cooling was lost, and the Emergency Diesel Generator started. Southern California Edison (SCE) promptly notified the NRC Operations Center (NRC Event Log Number 35336) that an Unusual Event had been declared for the loss of Reactor Coolant System heat removal capability for greater than 10 minutes (10CFR50.72(a)(i)) and an Engineered Safety Feature actuation (10CFR50.72(b)(2)(ii)). This LER is provided in accordance with 10CFR50.73(a)(2)(iv),10CFR50.73(a)(2)(v), and 10CFR21.

All equipment operated as expected. Operators restored SDC in approximately 26 minutes.

SCE has implemented or planned corrective actions to prevent recurrence.

The incremental increase in core damage probability was "very small."

In the past 3 years SCE has not reported an event with similar causes and corrective actions.

nd LICENSEE EVENT REPORT (LER) u.s. NuttEaR REcutAtoRv consissich (4-95)NRC FORM TEXT CONTINUATION FACILITY NAME (1)

DOCKET LER NUMBER (6)

PAGE (3)

San Onofre IJuclear Generating Station YEAR SEQUENTIAL REvist 3

~

(SONGS) Unit 2 05000-361 N M ER NUM ER t

l 1999

-- 001 --

00 Plant:

San Onofre Nuclear Generating Station Unit 2 Reactor Vendor:

Combustion Engineering Event Date:

February 1,1999 Event Time:

0959 PST Unit 2 Unit 3 Mode:

6, Refueling 1, Power operation Power:

000 percent 99.9 percent Temperature:

65.3 degrees F 546.5 degrees F Pressure:

Atmospheric 2250 psia

Background:

At the time of this event, Unit 2 was in day 30 of a planned 60-day refueling outage. The reactor core was approximately 50 percent reloaded with no core alterations in progress at the time of the event. The refueling cavity was filled to 23' above the flange. Figure i shows the Class IE 4.16 kV (EB) ciectrical distribution system for Unit 2.

Train A safety components were in-service with bus 2 A04 powered by the Unit Auxiliary Transformer (UAT)(FK) through breaker 2 A0419. One Saltwater Cooling (SWC)(BS) pump, one Component Cooling Water (CCW)(CC) pump, one Containment Spray (CS)(BE) pump, and one Low Pressure Safety injection (LPSI) (BP) pump to provide Shutdown Cooling (SDC) and Spent Fuel Pool (SFP) cooling were being powered from 2 A04.

Bus 2 A04 (EB) was being credited as the alternate source of offsite power to Unit 3 bus 3 A04.

The Reserve Auxiliary Transformer (RAT) 2XRI (FK) was disconnected from the switch yard and all three ground disconnect switches on the high side (220 kV) wcre closed. (See the Cause of the Event section.)

Train B safety components were unavailable due to scheduled component work in-progress.

Breaker (BKR) 2 A0418 is a 5 kV,3,000 amp (continuous) ABB model 511K-350 Class IE circuit breaker. The breaker is closed by springs. The closing springs are normally released electrically to close the breaker. However, the breaker can be closed manually. The circuit breaker is mounted on a rolling chassis for case of racking it in and out of the switchgear. (See the Additional Information section.)

Description of the Event:

Scheduled activities were underway to clear the R AT 2XRI (a primary power supply for the 2 A04, Train A 416 kV bus, and an alternate power supply to bus 3 A04 in Unit 3), to support other maintenance. Problems were encountered whi!e trying to rack out breal:er 2 A0418, the supply breaker from the RAT. (See Additional l

Information section.) A multi-discipline team (utility, licensed and non-licensed), assembled to troubleshoot I

removing the breaker, concluded the likelihood of the breaker inadvertently closing could be reduced by discharging the closing springs using the trip lever on the bottorn of the breaker.

On February 1,1999 (event date), at 0959 PST, when the worker (utility, non-licensed) discharged the closing springs on breaker 2 A0418, the breaker closed. When the breaker closed, the high side ground on the RAT 2XR1 created a three phase to ground fault through the ground disconnect switch. The fault current path was from Main /UATs 2XM and 2XUI through bus 2A04 via breaker 2A0419 to RAT 2XR1 via breaker 2A0418. The fault l

lasted about 1.5 seconds and the voltage on bus 2 A04 dropped to approximately 2.2 kV.

l

ud LICENSEE EVENT REPORT (LER) u.s. NuctEAR REcutAtoav commission (4-95)NRc FORM TEXT CONTINUATION FACILITY NAME (1)

DOCKET 1.ER NUMBER (6)

PAGE (3)

San Onofre Nuclear Generating Station YEAR SEQUENTIAL REVIS!

(SONGS) Unit 2 05000-361 NUMBER NU ER 1999

-- 001 --

00 As a result of the undervoltage, breaker 2 A0419 opened and bus 2 A04 was de-energized. Breaker 2 A0418 remained closed, as expected, because its de control power had been removed as part of the operation in progress.

Consequently, no alternate source breaker could close because the supply breakers are interlocked such that only one can be closed at a time. EDG 2G002 (EK) started and its breaker did not close. The pumps required for SDC and SFP cooling (one LPSI, one CS one CCW, and one SWC) also tripped automatically, All systems and equipment operated as expected.

i Southern California Edison (SCE) promptly notified the NRC Operations Center (NRC Event Log Number 35336) in accordance with 10CFR50.72(a)(i) that an Unusual Event (UE) had been declared at 1009 PST for the loss of 4

Reactor Coolant System (RCS) heat removal capability for greater than 10 minutes. (The UE was exited approximately 30 minutes later.) Because the start of the Emergency Diesel Generator (EDG) is an Engineered Safety Feature (ESP) actuation, that notification was also provided in accordance with 10CFR50.72(b)(2)(ii).

i This LER is provided in accordance with:

1.

10CFR50.73(a)(2)(iv). The start of the EDG was an ESF actuation.

)

2.

10CFR50.73(a)(2)(v). Because of the plant's electrical configuration, specifically the ground on the i

RAT 2XRI and the de control power removed from breaker 2 A0418, the EDG was unable to fulfill its j

safety function of powering bus 2 A04.

3.

10CFR21. As described in the Additional Information section, a contributing cause of this event was a mis-positioned roller on breaker 2 A0418.

Cause of the Condition:

l l

This event was caused by workers closing breaker 2 A0418 by discharging the closing springs. Based on previously observing that discharging the closing springs using the lever on the bottom of the breaker when the breaker was removed from its cubicle did not close the breaker, the workers assumed, but did not confirm, similar operation when in the racked-in position (cognitive personnel error).

Two contributing conditions were identified as necessary for the direct cause to have resulted in the event.

1.

The switching order for the R AT directed installing the high side grounds before racking out the low side breakers. Without the grounds installed, closing breaker 2A0418 would not have resulted in the loss of bus 2 A04.

2.

Breaker 2 A0418 did not rack out properly. The cause of the difficulty in racking out the breaker is discussed in the Additional Information section.

Corrective Actions

Operators restored SDC and SFP cooling approximately 26 minutes after the event by clearing the fault, re-energizing bus 2 A04 by closing breaker 2A0419, and restarting CCW, SWC, LPSI and a CS pump.

SCE conducted a station Work Stand Down to brief employees on the event, and to reinforce management's expectation regarding following programs, recognizing error likely situations, response to deviations from normal expected outcomes, and the significant consequences of this event including loss of SDC, declaration of an UE, and local containment evacuation.

LICENSEE EVENT REPORT (LER) u.s. huCLEAR REsutAtoRY comstssion 3eeA (4-95)hRC FORM TEXT CONTINUATION FACIL1fY NAME (1)

DOCKET LER NUMBER (6)

PAGE (3)

San Onofre Nuclear) Generating Station YEAR SEQUENTIAL REVis!

(SONGS) Unit 2 05000-361 NUMBER NU ER 1999

-- 001 --

00 Management required approval by the Octage Managers and Operations Manager or Vice President for emergent work and use of safety related blanket Maintenance Orders on Defense in Depth credited components and systems.

Inspections, tests and evaluations of affected electrical equipment and the EDG showed no apparent or predicted damage.

Breaker 2 A0418 was removed from its cubicle for inspection. (See the Additional Information section.)

Corrective action

planned or takch to address the causes include

Developing program controls that set Management's expectations for work control of high consequence activities.

Sharing lessons learned from this event, including the need to validate assumptions, with appropriate e

Operations, Maintenance and Technical personnel.

Pevising the switching order procedure to include racking out low side breakers prior to closing ground disconnects.

Safety Significance

The risk impact assessment of the loss of 2A04 considered the following:

1.

Bus 2 A04 recovery, SDC, and SFP cooling restoration scenarios.

2.

The risk impact of the loss of SDC. Without a concurrent loss ofinventory event, the times to bulk l' oiling and core uncovery were conservatively estimated to be 28 hours3.240741e-4 days <br />0.00778 hours <br />4.62963e-5 weeks <br />1.0654e-5 months <br /> and 170 hours0.00197 days <br />0.0472 hours <br />2.810847e-4 weeks <br />6.4685e-5 months <br /> (approximately 7 days), respectively.

3.

Loss of offsite power events.

4.

Loss of inventory events.

5.

Seismic events.

The incremental increase in core damage probability was less than 1 E-8, and, based on Regulatory Guide 1.174, is characterized as "very small."

Additional information

The difficulty in racking out breaker 2 A0418 was caused by an incorrectly placed shuttes roller pin e

which is mounted on the chassis of the breaker. The breaker had been recently overhauled by the vendor (ABB Service Incorporated of The Woodlands, Texas) who incorrectly reinstalled the shutter roller pin into a spare hole on the *ide of chassis. With the shutter roller pin in the wrong hole, the shutter roller pin bccame trapped behind the lever arm which actuates the cubicle stab shutter. The lever arm mechanically interfered with the movement of the roller when racking out of the breaker.

SCE notified the vendor, and the vendor is evaluating this condition in accordance with 10CFR21.

SCE will revise its breaker overhaul procedure to show proper location of the shutter roller pin.

r.

'nh LICENSEE EVENT REPORT (LER) u.s. NuctuR REcuuToRY commission (4-95)NRC FORM TEXT CONTINUATION FACILITY NAME (1)

DOCKET LER NUMBER (6)

PAGE (3)

Scn Onofre Nucleap Generating Station YEAR SEQUENTIAL REVIst (SONGS) Unit 2 05000-361 NMR 5 0F 5 NU R 1999

-- 001 --

00 in the past 3 years, SCE reported (LER 2 1998-021) an emergency chiller unit was made inoperable e

when workers failed to implement programmatic requirements for lifting and landing electrical leads i

on the low temperature cutout switch and the retest did not reveal this error. The event reported herein had similarities to the chiller event (misunderstanding of how equipment operated and failure to verify assumptions). Ilowever, the team involved in deciding to discharge the closing springs were working within the bounds of an approved work process and had the authorization of the Shift Manager. Retest was not a factor because discharging the springs directly caused the event.

Figure 1 - Class IE 4.16 kV Electrical Distribution System 230 KV SWNCHYARo FOSW ON No. 8 GENERATOR I L UNW 2 "I

"" N M 7 2.Kv 4

2EV 22KY 8.9KV i

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2A0418 1

TO UNIT 3 N{ K 2A0419 w

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omaa GENERATOR