05000362/LER-2002-001, /27/2002, Loss of Offsite Power with Consequential Rps/Esf Actuations Due to Maintenance Error

/27/2002, Loss of Offsite Power with Consequential Rps/Esf Actuations Due to Maintenance Error

ML021200004
Person / Time
Site:	San Onofre
Issue date:	04/24/2002
From:	Krieger R Southern California Edison Co
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
LER 02-001-00
Download: ML021200004 (7)

LER-2002-001, /27/2002, Loss of Offsite Power with Consequential Rps/Esf Actuations Due to Maintenance Error

Event date:
Report date:
Reporting criterion:	10 CFR 50.73(a)(2)(iv)(A), System Actuation 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)(v), Loss of Safety Function 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications
3622002001R00 - NRC Website

text

SOUTHERN CALIFORNIA EDISON An EDISON\\ INTER4AT10INAL"' Company R. W. Krieger Vice President Nuclear Generation April 24, 2002 U.S. Nuclear Regulatory Commission Document Control Desk Washington, DC 20555

Subject:

Docket No. 50-362 60-Day Report Licensee Event Report No. 2002-001 San Onofre Nuclear Generating Station, Unit 3 Gentlemen:

This submittal provides Licensee Event Report (LER) 2002-001 describing the loss of offsite power event that occurred at Unit 3 on February 27, 2002. Four consequential events (reactor trip, starting both emergency diesel generators, initiation of the Auxiliary Feedwater System, and initiation of the Emergency Containment Cooling System) are reportable in accordance with 1 OCFR50.73(a)(2)(iv)(A).

These events did not affect the health and safety of either plant personnel or the public.

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

Sincerely,

Enclosure:

cc:

E. W. Merschoff, Regional Administrator, NRC Region IV C. C. Osterholtz, NRC Senior Resident Inspector, San Onofre Units 2 & 3 P. 0. Box 128 San Clemente. CA 92674-0128 949-368-6255 Fax 949-368-6183

NRC FORM 366 U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY OMB NO. 3150-0104 EXPIRES MM-YYYY II1M-YYYY)

, the NRC may not conduct or sponsor, and a person is not required to respond to, the information collection.

FACILITY NAME (1)

DOCKET NUMBER (2)

PAGE (3)

San Onofre Nuclear Generation Station (SONGS) Unit 3 L

05000-362 1 of 6 TITLE (4)

Loss of Offsite Power With Consequential RPS/ESF Actuations Due To Maintenance Error EVENT DATE (5)

LER NUMBER (6)

REPORT DATE (7)

OTHER FACILITIES INVOLVED (8)

MONTH DAY YEAR YEAR SEQUENTIAL REVISION MONTH DAY YEAR FACILITY NAME DOCKET NUMBER NUMBER NUMBER 2

27 2002 2002 001 00 4

24 2002 FACILITYNAME DOCKET NUMEER OPERATING 1 THIS REPORT IS SUBMITTED PURSUANT TO THE REQUIREMENTS OF 10 CFR §: (Check all that ply) (11)

MODE (9) 1 j

20.2201(b) 20.2203(a)(3)(i) 50.73(a)(2)(i)(C) 50.73(a)(2)(vii)

POWER LEVEL l 00 20.2201(d) 20.2203(a)(3)(ii) 50.73(a)(2)(ii)(A) 50.73(a)(2)(viii)(A)

(10) 20.2203(a)(1) 20.2203(a)(4) 50.73(a)(2)(ii)(B) 50.73(a)(2)(viii)(B) 20.2203(a)(2)(i) 50.36(c)(1)(i)(A) 50.73(a)(2)(iii) l 50.73(a)(2)(ix)(A) 20.2203(a)(2)(ii) l 50.36(c)(1)(ii)(A)

X 50.73(a)(2)(iv)(A) l 50.73(a)(2)(x) 20.2203(a)(2)(iii) 50.36(c)(2) 50.73(a)(2)(v)(A) 73.71 (a)(4) 20.2203(a)(2)(iv) 50.46(a)(3)(ii) 50.73(a)(2)(v)(B) 73.71 (a)(5) 20.2203(a)(2)(v) 50.73(a)(2)(i)(A) 50.73(a)(2)(v)(C)

OTHER 20.2203(a)(2)(vi) l 50.73(a)(2)(i)(B) 50.73(a)(2)(v)(D)

Specify in Abstract below or inLICENSEE CONTACT FOR THIS LER (12)

NAME lTELEPHONE NUMBER (Include Area Code)

R W Krieer, Vice President, Nuclear Generation 1949-368-6255 COMPLETE ONE LINE FOR EACH COMPONENT FAILURE DESCRIBED IN THIS REPORT (13 RPOTAL

CAUSE

SYSTEM COMPONENT MANUFACTURER REPORTAIXLETO j

CAUSE

SYSTEM COMPONENT MANUFACTURER TOEPIX I

E PI I

,1,_

1_

T O E P SUPPLEMENTAL REPORT EXPECTED (14)

EXPECTED M

DAY YEAR l_YES I X lINO I

I SUBMISSION l

[ _

I (If yes, complete EXPECTED SUBMISSION DATE).

F DATE (15) l l

l ABSTRACT (Limit to 1400 spaces, i.e., approximately 15 single-spaced typewritten lines) (16)

On 2127/02 at 1043 PST, a technician was performing maintenance and testing in the San Diego Gas &

Electric (SDG&E) portion of the San Onofre switchyard. As planned for the work, the South West bus was de-energized. All the transmission lines from SDG&E territory, Unit 3 reserve auxiliary transformer (RAT), and Unit 3 main transformer (main generator) were aligned to "South East" bus. The technician's approved work scope was to test the Breaker Failure Local Backup (BFLBU) scheme on the South West bus breakers. The technician exceeded the authorized work scope and chose also to test the cross bus BFLBU trip from a breaker on the South East bus. While doing so, the technician also failed to isolate a trip signal between the South West bus and the South East bus and the resulting signal tripped all the breakers connected to the South East bus, including the Unit 3 main transformer breaker and Unit 3 RAT breakers. Consequently, the Unit 3 main turbine/generator tripped, the reactor tripped, both emergency diesel generators started and Auxiliary Feedwater started. Operators manually started the Emergency Containment Coolers.

The loss of offsite power and associated Reactor Protection System and Engineered Safety Features actuations were reported to the NRC in accordance with 1 OCFR50.72(b)(2)(iv)(B) and 10CFR50.72(b)(3)(iv)(A). This written report is provided in accordance with 1QCFR50.73(a)(2)(iv)(A).

Offsite power was restored in about 32 minutes. Future switchyard detailed work plans will be reviewed and approved by SONGS Operations prior to the commencement of work.

The event had minimal safety significance.U.S. NUCLEAR REGULATORY COMMISSION (MM-YYYY)

LICENSEE EVENT REPORT (LER)

TEXT CONTINUATION l

FACLWY NAME(1)

DOCKET (2)

L LER NUMBER (6 1

PAGE (3) l SEQUENTIAL REVISION San Onofre Nuclear Generating Station (SONGS) Unit 3 05000-362 2 002 NUMBER l

NUMBER 2 of 6 11 2002

-- 001--_

00 I

Plant:

San Onofre Nuclear Generation Station (SONGS) Unit 3 Event Date:

February 27, 2002 Unit 2 Unit 3 Reactor Vendor:

Combustion Engineering Combustion Engineering Mode:

Mode 1 - Power Operation Mode 1 - Power Operation Power:

100 percent 100 percent

BACKGROUND:

Features of the San Onofre (SONGS) Units 2 and 3 electrical distribution system include the following (See Figure 1):

The 230 kV switchyard [FK] is a double bus, double circuit breaker arrangement with nineteen positions.

The Unit 3 main transformer [EL] steps up 22 kV generated by the Unit 3 main generator [TB] to 230 kV for transmission to the grid.

Non-Class 1 E 6.9 kV buses provide power to the four Unit 3 Reactor Coolant [AB] Pumps (RCP) [P]. During normal operation, the Unit 3 main generator powers these buses through the Unit 3 Unit Auxiliary Transformer (UAT). While shutdown, during startup, or when the Unit 3 UAT is not available, these buses are powered from the switchyard through Unit 3 Reserve Auxiliary Transformer (RAT). The buses can also be powered from the Unit 2 RAT, provided it is not being used to provide power to the Unit 2 RCPs.

Power to these buses can be manually or automatically transferred from one source to another without de-energizing the buses to ensure continuous operation of the RCPs.

The RATs step down switchyard voltage to supply 4.16 kV Class 1 E buses. These buses provide power to the Engineered Safety Featured (ESF) loads under normal and accident conditions, using the most preferred source of power available. The preferred sources, in order of preference, are the Unit 3 RATs, the corresponding Unit 2 Class 1 E buses, and the Unit 3 emergency diesel generators (EDGs) [EK]. The buses also provide power to selected non-ESF loads under normal and abnormal operating conditions.

The Unit 3 RATs also supply 4.16 kV non-Class 1 E buses. However, there are no provisions to power buses 3A03, 3A07, 3A08, or 3A09 from Unit 2 or an EDG.

As indicated on the attached figure, the northern section of the SONGS switchyard is controlled by Southern California Edison (SCE); the southern portion is controlled by San Diego Gas and Electric (SDG&E).

DESCRIPTION OF THE EVENT:

On February 27, 2002 (event date) at 1043 PST, a SDG&E technician (non-utility, non-licensed) was performing maintenance and testing in the SDG&E portion of the SONGS switchyard. As planned forU.S. NUCLEAR REGULATORY COMMISSION (MM-YYYY)

LICENSEE EVENT REPORT (LER)

TEXT CONTINUATION L

FACLITY NAME(l) 1 DOCKET (2)

LER NUMBER 6 PAGE (3)

F YEAR SEQUENTIAL I

REVISION San Onofre Nuclear Generating Station (SONGS) Unit 3 05000-362

_NUMBER l

NUMBER 3 of 6 11

-~[

2002

-- 001 -- I 00

~I the work, the "South West" bus was de-energized. All the transmission lines from SDG&E territory, Unit 3 RATs, and Unit 3 main transformer (main generator) were aligned to "South East" bus. The SDG&E technician's approved work scope was to test the Breaker Failure Local Backup (BFLBU) scheme on the South West bus breakers (i.e. breaker 6122). The technician completed the testing on the circuit for breaker 6122, then chose to test the cross bus BFLBU trip from breaker 4122, located on the South East bus. While doing so, the technician incorrectly generated a signal for breaker 6122 from breaker 4122, actuating the South East bus breaker failure scheme. This signal tripped all the breakers connected to the South East bus, including the Unit 3 main transformer breaker and Unit 3 RAT breakers (AR020201440). The following consequential events occurred at Unit 3 (unless otherwise stated):

The main turbine/generator tripped.

The reactor tripped. All control rods fully inserted. See Additional Information.

Both emergency diesel generators (EDGs) started on loss of voltage (LOVS) on the 1 E buses. As designed, the 1 E buses automatically transferred to their Unit 2 1 E sources, so the EDGs' output breakers did not close.

Due to the loss of non-1 E power:

1.

The main condenser circulating water pumps lost power, resulting in a loss of condenser vacuum.

2.

The condensate booster pumps lost power, resulting in the main feedwater pumps tripping (low suction pressure) and the loss of main feedwater flow. Auxiliary Feedwater (AFW) automatically started on steam generator low level and automatically controlled steam generator water level. Unit 3 was then in Mode 3 with decay heat being removed by AFW and steaming to the atmosphere through the Atmospheric Steam Dump Valves (ADVs).

3.

The containment normal coolers lost power. Operators subsequently manually started the Emergency Containment Coolers (ECC).

All Unit 3 auxiliary loads transferred to the Unit 2 RAT, as designed. All four reactor coolant pumps continued to run.

These major plant responses were normal and expected.

The loss of offsite power (LOP) and associated reactor protection system (RPS) and ESF actuations were reported to the NRC (Log No. 3873) in accordance with 1 OCFR50.72(b)(2)(iv)(B) and 10CFR50.72(b)(3)(iv)(A). This written report is provided in accordance with 10CFR50.73(a)(2)(iv)(A).U.S. NUCLEAR REGULATORY COMMISSION (MM-YYYY)

LICENSEE EVENT REPORT (LER)

TEXT CONTINUATION FACLITY NAME(1)

DOCKET (2)

LER NUMBER (6 PAGE (3)

YEAR SEQUENTIAL I

REVISION San Onofre Nuclear Generating Station (SONGS) Unit 3 05000-362 Y

I NUMBER NUMBER I

4 of 6 11 2002

--__001--_

00

CAUSE OF THE EVENT

This event was caused by cognizant personnel error. The technician performing switchyard testing exceeded his authorized work scope (the authorized clearance boundary) and decided to conduct breaker trip testing of the cleared breakers. Because the technician also failed to isolate one of the breaker trip signals, when breaker 4122 was trip tested, the South East bus BFLBU caused the South East bus section to isolate. This action then isolated Unit 3 from the grid causing it to trip.

This event could have been prevented if SCE had more effectively controlled work activities in the switchyard. SCE did not conduct a review of the planned work nor conduct a tailboard, relying instead on standard SCE and SDG&E switchyard practices.

CORRECTIVE ACTIONS

Offsite power was restored to Unit 3 at approximately 1115 PST the same day; Future switchyard detailed work plans will be reviewed and approved by SONGS Operations prior to the commencement of work; and This event and its corrective actions will be reviewed with appropriate SONGS, SCE Grid Operation and Maintenance, and SDG&E personnel who work in the SONGS Switchyard.

SAFETY SIGNIFICANCE

An assessment of the conditional core damage and large early release probabilities, and increase in core damage and large early release frequencies determined the Unit 3 conditional core damage probability (CCDP) and large early release probability (CLERP) were approximately 2.1 E-5 and 8.5E-7, respectively. This assessment was based on the reported actual component unavailability and system alignments at the time of the event. All safety-related equipment designed to mitigate the event operated as designed during the event.

This event was not caused by nor did it result in any Safety System Functional Failure (SSFF). This event did not impact the ability to shut down the Unit or mitigate the consequences of an accident. This occurrence is categorized "Green" using the latest draft of the Reactor Safety Significance Determination Process (SDP).

ADDITIONAL INFORMATION

1. At the time of the event, the non-1 E instrument bus which supplies power to the reactor core mimic board was being powered from its alternate (off-site) AC power source. Thus, when offsite power was lost, the reactor core mimic (which provides information on CEA position) was deenergized.

Alternate indications of a reactor trip were available (reactor trip breakers open and CEA status on Core Protection Calculators). However, operators initiated emergency boration of the RCS as directed by procedure due to the normal status indication being lost. Boration was suspended when the instrument bus was transferred back to its uninterruptible power supply (UPS) a few minutes later.

2. In the past three years, SCE has reported:U.S. NUCLEAR REGULATORY COMMISSION (MM-YYYY)

LICENSEE EVENT REPORT (LER)

TEXT CONTINUATION FACILITY NAME(1 DOCKET (2)

LER NUMBER I PAGE (3)

YEAR SEQUENTIAL I

REVISION San Onofre Nuclear Generating Station (SONGS) Unit 3 05000-362 l

NUMBER 5 of 6 112002

--001 -- I 00 The loss of offsite power (reactor trip, EDG start, AFW start, and ECC start) for Unit 3 (LER 3-2001-001) caused by a breaker failure and fire in the plant (not switchyard), a cause not present in this case. Therefore, corrective actions for that event would not have prevented the event reported herein.

The automatic start of the Unit 2 EDGs (LER 2-1999-001). That event was caused by personnel error when a breaker was closed on a grounded emergency bus. The corrective actions for that event would not have been expected to prevent the event reported herein.

A Unit 3 manual reactor trip and AFW initiation in response to the loss of normal feedwater flow (LER 3-1999-003). The event occurred when the main feedwater regulating valves failed closed. The corrective actions for that event would not have been expected to prevent the event reported herein.

A Unit 3 manual reactor trip and AFW initiation in response to a rapid increase in normal feedwater flow (LER 3-1999-004). The event occurred when a main feedwater regulating valve failed open at 24 percent power. The corrective actions for that event would not have been expected to prevent the event reported herein.U.S. NUCLEAR REGULATORY COMMISSION (MM-YYYY)lI LICENSEE EVENT REPORT (LER)

TEXT CONTINUATION FACLITY NAME(1l DOCKET 2)

LER NUMBER {

PAGE (3)

YEAR SECUENTIAL REVISIONl San Onofre Nuclear Generating Station (SONGS) Unit 3 05000-362

- NUME

.2002

_-001 --

00 Figure 1 - SONGS Switchyard 413 4182 426 428 6182 414 412 4 72-q15

=J 4'5 U1,-