05000362/LER-1996-001, :on 960304,voltage Signal Actuation Loss Due to Inadvertent Relay Trip.Enhanced Turbine Startup Sequence by Slowing (from 2.5 Seconds to 8 Seconds) Operation of Trip/ Throttle Valve

:on 960304,voltage Signal Actuation Loss Due to Inadvertent Relay Trip.Enhanced Turbine Startup Sequence by Slowing (from 2.5 Seconds to 8 Seconds) Operation of Trip/ Throttle Valve

ML20108C975
Person / Time
Site:	San Onofre
Issue date:	05/02/1996
From:	Krieger R SOUTHERN CALIFORNIA EDISON CO.
To:
Shared Package
ML20108C957	List: 05000362/LER-1996-001, :on 960304,voltage Signal Actuation Loss Due to Inadvertent Relay Trip.Enhanced Turbine Startup Sequence by Slowing (from 2.5 Seconds to 8 Seconds) Operation of Trip/ Throttle Valve 05000362/LER-1996-001-01, Forwards Supplemental LER 96-001-01,providing Addl Info on Safety Significance of Occurrence Involving Inadvertent ESFs Actuation
References
LER-96-001, LER-96-1, NUDOCS 9605070224
Download: ML20108C975 (2)

LER-1996-001, on 960304,voltage Signal Actuation Loss Due to Inadvertent Relay Trip.Enhanced Turbine Startup Sequence by Slowing (from 2.5 Seconds to 8 Seconds) Operation of Trip/ Throttle Valve

Event date:
Report date:
Reporting criterion:	10 CFR 50.73(a)(2)(v), Loss of Safety Function 10 CFR 50.73(a)(2)(iv), System Actuation 10 CFR 50.73(a)(2)(1) 10 CFR 50.73(a)(2) 10 CFR 50.73(a)(2)(viii)(B) 10 CFR 50.73(a)(2)(x)
3621996001R00 - NRC Website

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LICENSEE EVENT REPORT (LER)

Ftcility Name (1)

Docket NL.mber (2)

Poae e3)

SAN ONOFRE NUCLEAR GENERATING STATION. UNIT 3 01Sl010101316l2 1

of 0

2 i

Title (4)

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Loss of Voltage Signal Actuation Due to Inadvertent Relay Trip EVENT DATE (5)

LER NUMBER (6)

REPORT DATE (7)

OTHER FACILITIES INVOLVED (8)

Month Day Year Year

/// Sequential

/// Revision Month Day Year Facility Names Docket Number (s)

///

Ntmiber

///

Ntaber NONE 01510101Of I l 01 3 01 4 91 6 91 6 010l 1 011 015 01 2 91 6 01 51 01 01 01 l l l

OPLRATINb THib REPORT'IS SUBM TTED' PURSUANT'TO 'HE'REuulREMLNTS OF 10CFR MODE (9) 1 (Chirck one or more of the follggina) (11)

POWER 20.405(a)(1)(li) 50.36(c)(2) 50.73(a)(2)(v)

73. 71(b) 20.405(a)(1)(1) 20.405(c) 2 50.73(a)(2)(iv) 20.402(b)

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20.405(a)(1)(iv) 50.73(a)(2)(1) 50.73(a)(2)(vil) 73.71(c) 50.36(c)(1)

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20.405(a)(1)(v) 50.73(a)(2)(li)

50. 73(a)(2)(vi i i )( A)

Other (Specify in LEYEL 20.405(a)(1)(ill)

Abstract below and f10) 1 1 0l 0 50.73(a)(2)(viii)(B) in text)

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50.73(a)(2)(lii) 50.73(a)(2)(x) i

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LICENSEE CONTACT FOR THIS LER (12)

Name TELEPHONE NUMBER AREA CODE R. W. Krieaer. Vice President. Nuclear Generation 7l 1 14 316181-l6121515 COMPLETE ONE LINE FOR EACH COMPONENT FAILURE DESCRIBED IN THlU REPORT'(13a

~CAUSE SYSTEM COMPONENT MANUFAC-REPORTABLE

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CAUSE

SYSTEM COMPONENT MANUFAC-REPORTABLE

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TURER TO NPR!1, ///////

TURER TO NPRDS

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I l l l l l l

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l l l l l l l

//////

l i l l I l I

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l l I l l 1 l f/////

$UPPLEMENTAL'REPOR EXPECTED (14)

Month Day Year Expected Submission i_

Date (15)

Yes (If ves. comotete EXPECTED SUBMISSION DATE)

IX No l

I l

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

On 03/04/96 with Unit 3 at 100% power, Electrical Test Technicians (utility maintenance personnel) were preparing to obtain post-maintenance in-service readings on reserve auxiliary transformer 3XRl.

At 1333, while obtaining a reading on a differential protective relay, a voltmeter wire inadvertently caught and actuated a contact switch for the relay.

This personnel error (cognitive) caused the ralay to trip.

The protective circuitry operated as designed, tripping open the 220kV breakers supplying all 3 reserve auxiliary transformers and the 4kV breakers supplying both class lE 4kV buses.

The resulting Loss of Voltage Signal (LOVS) caused both Unit 3 emergency diesel generators (EDGs) to start.

Because power for the Unit 3 class lE 4kV buses successfully fast transferred to the Unit 2 class lE 4kV buses, as designed, the EDGs did not load.

Because there was a valid Engineered Safety Features Actuation Signal, Edison made a 4 hour4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br /> non-emergency report at 1515, and submitted this report in accordance with l

10CFR50. 73 (a) (2 ) (iv).

Edison is submitting this supplemental report to provide additional l

information on the safety significance of this occurrence.

l As required by the Technical Specifications, Edison surveilled the A. C.

sources for both Units.

Edison also verified the integrity of the Unit 3 reserve auxiliary transformers, stopped the running EDGs, reset the 3XR1 protective relay, and, at 1531, completed restoration of the normal Mode 1 electrical configuration.

Maintenance supervision reviewed this event with all station Electrical Test Technicians and reemphasized the importance of attention to detail.

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9605070224 960502 PDR ADOCK 05000362 S

PDR

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bo LICENSEE EVENT REPORT (LER) TEXT CONTINUATION 1

I SAN ONOFRE NUCLEARnGENERATION STATION DOCKET NUMBER LER NUMBER PAGE UNIT 3 05000362 96-001-01 2 of 2 1

On 03/04/96 with Unit 3 at 100% power, Electrical Test Technicians (utility maintenance personnel) were preparing to obtain post-maintenance in-service readings on reserve

' auxiliary transformer 3XR1 [XFMR). At 1333, while obtaining a reading on a differential protective relay (87), a voltmeter wire inadvertently caught and actuated a contact switch for the relay.

This personnel error (cognitive) caused the relay to trip. The j

protective circuitry operated as designed, tripping open the 220kV oreakers supplying all

)

3' reserve auxiliary transformers and the 4kV breakers (52) supplying both class 1E 4kV i

buses (EB).

The resulting Loss Of Voltage Signal (LOVS) (JE) caused both Unit 3 emergency diesel generators (EDGs) to start.

Because power for the Unit 3 class 1E 4kV buses successfully fast transferred to the Unit 2 class 1E 4kV buses, as designed, the EDGs did not load.

Because there was a valid Engineered Safety Features Actuation Signal (JE), Edison made a l

4 hour4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br /> non-emergency report at 1515, and submitted this report in accordance with l

10CFR50.73 (a) (2) (iv).

Edison is submitting this supplemental report to provide l

additional information on the safety significance of this occurrence.

l As required by the Technical Specifications, Edison surveilled the A.

C.

sources for both Units.

Edison also verified the integrity of the Unit 3 reserve auxiliary transformers, stopped the running EDGs, reset the 3XR1 protective relay, and, at 1531, completed restoration of the normal Mode 1 electrical configuration. Maintenance supervision reviewed this event with all station Electrical Test Technicians and reemphasized the importance of attention to detail.

Because all protective features operated as designed, Edison originally reported that l

this event had little safety significance.

Subsequent to this event, on 3/12/96, the l

Unit 3 turbine-driven auxiliary feedwater (BA) pump turbine [TRB) tripped during startup l

for a routine inservice test.

Edison re-evaluated the safety significance of the LOVS l

event in light of potentially reduced pump reliability.

l 1

Utilizing probabilistic risk assessment techniques and employing conservative assumptions l

for pump reliability, Edison estimates the conditional (i.e. instantaneous) core damage l

frequency due to internal initiating events during the LOVS event on 3/4/96 to have been l

about 8.5E-4/ year.

While this level of risk is relatively high, the brief duration of l

the LOVS event resulted in an increase in the annual core damage probability attributable l

to internal initiating events of less than 2E-7 l

l In the followup investigation of the turbine-driven auxiliary feedwater pump trip, the l

startup trip could not be reproduced despite approximately 20 starts of the turbine over l

a 60 hour6.944444e-4 days <br />0.0167 hours <br />9.920635e-5 weeks <br />2.283e-5 months <br /> period and another 4 starts spaced geometrically over a 23 day period.

Edison l

completed a formal root cause analysis identifying several potential causes for the l

turbine trip.

Edison concluded after further investigation that some of the potential I

causes could be dismissed.

To bound the remaining potential causes, Edison enhanced the I

turbine startup sequence by slowing (from 2.5 seconds to 8 seconds) operation of the I

trip / throttle valve.

I Edison submitted LER 3-94-002 to report an inadvertent LOVS actuation caused by a worker jarring a door-mounted protective relay while attempting to repair a door retaining screw.