05000271/LER-2003-004, Hearing - Entergy Exhibit 13, LER 2003-004-00, Brunswick, Unit 2, Loss of Generator Excitation Results in Reactor Protection System and Other Specified System Actuations

Hearing - Entergy Exhibit 13, LER 2003-004-00, Brunswick, Unit 2, Loss of Generator Excitation Results in Reactor Protection System and Other Specified System Actuations

ML062640219
Person / Time
Site:	Vermont Yankee, Brunswick  File:NorthStar Vermont Yankee icon.png
Issue date:	01/05/2004
From:	Hinds D Progress Energy Co
To:	Document Control Desk, NRC/SECY
Byrdsong A T
References
50-271-OLA, BSEP 03-0158, Entergy-Licensee-13, RAS 12263 LER 03-004-00
Download: ML062640219 (8)

LER-2003-004, Hearing - Entergy Exhibit 13, LER 2003-004-00, Brunswick, Unit 2, Loss of Generator Excitation Results in Reactor Protection System and Other Specified System Actuations

Event date:
Report date:
Reporting criterion:	10 CFR 50.73(a)(2) 10 CFR 50.73(a)(2)(v)(A), Loss of Safety Function - Shutdown the Reactor 10 CFR 50.73(a)(2)(viii) 10 CFR 50.73(a)(2)(iv)(A), System Actuation
2712003004R00 - NRC Website

text

Progress Energy DOCKET NUMBER PROD. & UTIL. FAC. 5O 47/-

A..

January 5, 2004 SERIAL: BSEP 03-0158 10 CFR 50.73 U. S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, DC 20555-0001

Subject:

Brunswick Steam Electric Plant, Unit No. 2 Docket No. 50-324lLicense No. DPR-62 Licensee Event Report 2-03-004 Gentlemen:

In accordance with the Code of Federal Regulations, Title 10, Part 50.73, Progress Energy Carolinas, Inc. submits the enclosed Licensee Event Report. This report fulfills the requirement for a written report within sixty (60) days of a reportable occurrence.

Please refer any questions regarding this submittal to Mr. Edward T. O'Neil, Manager-Support Services, at (910) 457-3512.

Sincerely,C David H. Hinds Plant General Manager Brunswick Steam Electric Plant Oft C,,

CDP C3

=n CRE/cre Enclosure: Licensee Event Report U-iULMMa~woma I.,L IRY0M19 by:

icantyUcense Intervenor_7_______

Progress Energy1 Caroflnas. Inc.

Brnswick Nuclear Plant P.O. Box 10429 Scuthrot. NC 24841 7-

- Fe/n 1&+c = s eC-r Y-o.~Y as-CY- 0111-

Document Control Desk BSEP 03-0158 /Page 2 cc (with enclosure):

U. S. Nuclear Regulatory Commission, Region H ATTN: Mr. Luis A. Reyes, Regional Administrator Sam Nunn Atlanta Federal Center 61 Forsyth Street, SW, Suite 23T85 Atlanta, GA 30303-8931 U. S. Nuclear Regulatory Commission ATWN: Mr. Eugene M. DiPaolo, NRC Senior Resident Inspector 8470 River Road Southport, NC 28461-8869 U. S. Nuclear Regulatory Commission ATTN: Ms. Brenda L. Mozafari (Mail Stop OWFN 8G9) (Electronic Copy Only) 11555 Rockville Pike Rockville, MD 20852-2738 U. S. Nuclear Regulatory Commission ATFN: Ms. Margaret Chernoff (Mail Stop OWFN 8G9A) (Electronic Copy Only) 11555 Rockville Pike Rockville, MD 20852-2738 Ms. Jo A. Sanford Chair - North Carolina Utilities Commission P.O. Box 29510 Raleigh, NC 27626-051

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1. FACILITY NAME L DOCKET NUMBER

3. PAGE Brunswick Steam Electric Plant (BSEP), Unit 2 05000324 1 OF 6 4.rTITLE Loss of Generator Excitation Results in Reactor Protection System and Other Specified System Actuations

5. EVENT DATE

8. LER NUMBER

7. REPORT DATE

6. OTHER FACILITIES INVOLVED MO DAY YEAR YEAR SEOUENTIAL REV MO DAY YEAR FACUTY NAME DOCK-ETNuMd0K NUMBER NO BSEP, Unit 1 05000325 11 04 2003 2003 -

004 00 01 05 2004 05000 S. OPERATING

11. THIS REPORT IS SUBMITTED PURSUANT TO THE REOUIREMENTS OF 10 CFR !i oChe aoter more)

MODE I

1202201(b) 20*2o3(a)(3)(,)

6O.73(a)t2)M,)(b) 50.73(a__2)(_____

10. POWER 20.2201{d) 20.2203(a)(4) 50.73(a)(2J(iii)

W0.73na(2)(x)

LEVEL 96 20,2203(a)(1) 50.36(c(1t)() M 50.73(a)(2)(m)(A) 7331(a)t4) 202203(a)(2)(0) 50.36(c1)iiXA) 50.73(a)(2)(v)(A) 7J. 1,aXO )

20.2(a)C2)(it) 50,26(c)(2) 50.T3(a)(2)(v)(B)

OTHER 202203(a)(2)(ii) 50A6(a)(3Xi) 50.73(a)(2)(vXC)(

low or 202203(a)(2)(iv) 60.73(a)(2Xi(A) 50.73,a)f2)(v D) 36_

20.2203(a)(2)(v) 5o.73(,X2X)(B, 50.-7(a)(2)(vh) 202203(a)(2Kvi) 50.73(a)(2)(G)

TW.73(8)(2)(v0II)(A) 20.2203(a)(3)(i) 50.73(a)2)(ii)XA) 50.73(a)(2)(viii)nB)

12. UCENSEE CONTACT FOR THIS LER NAM R

Charles R. Elberfeld, Lead Engineering Technical Support Specialist (910) 457-2136 I

On November 4,2003, at approximately 1732 hours0.02 days <br />0.481 hours <br />0.00286 weeks <br />6.59026e-4 months <br />, Unit 2 received a generatodturbine trip due to loss of generator excitation, which resulted in a Reactor Protection System (RPS) actuation. All control rods fully inserted into the core. Plant response to the transient also resulted in High Pressure Coolant Injection and Reactor Core Isolation Cooling System actuations on low reactor pressure vessel (RPV) coolant level with injection into the RPV. Additionally, Primary Containment Isolation System (PCIS) actuation signals for Valve Groups 1, 2, 3, 6, and 8 were received and the valves closed as required. All four Emergency Diesel Generators automatically started but did not load because electrical power was not lost to the emergency buses.

The initiator of the plant transient event and system actuations was the failure of the generator exciter inner collector ring and brush holders, which resulted in loss of excitation to the generator. The root cause of the failure is a fabrication deficiency due to poor workmanship at the time of original installation of the collector ring onto the exciter shaft. Weaknesses in brush maintenance, preventive maintenance, monitoring, and trending were also identified as the root cause of the event.

The damaged components were replaced. Enhanced exciter brush monitoring has been implemented on both Units 1 and 2. This event is being reported in accordance with 10 CFR 50.73(a)(2)(iv)(A). The safety significance of this occurrence is considered minimal.

NRC FORM 366 (1-201)

(11more space Is required, use aeditonal copies of NRG Form =A36) (17)

Energy Industry Identification System (EIIS) codes are identified in the text as [XXI.

INTRODUCTION

On November 4, 2003, at approximately 1732 hours0.02 days <br />0.481 hours <br />0.00286 weeks <br />6.59026e-4 months <br />, Unit 2 received a generator/turbine trip due to loss of generator excitation [TL], which resulted in a Reactor Protection System (RPS) [JC] actuation. All control rods fully inserted into the core. Plant response to the transient also resulted in High Pressure Coolant Injection (HPCI) [BJ] and Reactor Core Isolation Cooling (RCIC) [BN] System actuations on low reactor pressure vessel (RPV) coolant level, with injection into the RPV. Additionally, Primary Containment Isolation System (PCIS) [3M] actuation signals for Valve Groups 1, 2, 3, 6, and 8 were received and the valves c-osed as required. As a result of the associated electrical transient, a PCIS Valve Group 6 isolation was also received on Unit 1. All four Emergency Diesel Generators (EDGs) [EK] automatically started but did not load because electrical power was not lost to the emergency buses. At the time of the event, Unit 2 was in Mode 1, (i.e., Run) at approximately 96 percent of rated thermal power (RTP) and Unit I was in Mode I at 93 percent of RTP, with all Emergency Core Cooling Systems operable for both units. At approximately 1857 hours0.0215 days <br />0.516 hours <br />0.00307 weeks <br />7.065885e-4 months <br />, with Unit 2 in Mode 3 (i.e., Hot Shutdown), another RPS actuation was received due to low RPV coolant level while cycling Safety Relief Valves (SRVs) [RV]. At 2120 hours0.0245 days <br />0.589 hours <br />0.00351 weeks <br />8.0666e-4 months <br />, notification was made to the NRC (i.e., Event Number 40297) in accordance with 10 CFR 50.72(b)(2)(iv)(A),

(b)(2)(iv)(B), and (b)(3)(iv)(A). This event is being reported in accordance with 10 CFR 50.73(a)(2)(iv)(A) as manual and automatic actuation of specified systems.

EVENTDESCRIPTION On November 4, 2003, at approximately 1732 hours0.02 days <br />0.481 hours <br />0.00286 weeks <br />6.59026e-4 months <br />, the Unit 2 generator exciter [EXC] inboard collector ring (i.e., Alterrex Serial # CH8371544, General Electric Company, Reference TAB 32'S GEK 18539C Figure 7, Mechanical Outline Drawing GEK 34D105050) and brush holders failed resulting in a loss of generator excitation. The loss of generator excitation resulted in a decrease in generator voltage and AC bus voltages on Unit 2 for about three to four seconds, with a dip to approximately 40 percent of nominal voltage values. After the generator tripped, the Unit 2 bus loads were automatically transferred from the Unit Auxiliary Transformer to the Site Auxiliary Transformer (SAT). Additionally, all four EDGs automatically started, as a result of the generator trip, but did not load because electrical power was not lost to the emergency buses. Upon transfer to the SAT, the bus voltages returned to nominal values. Details of this event will be discussed in two sections: (1) Unit 2 Scram and Associated Transients, and (2) Plant Responses to the Voltage Transient.

Unit 2 Scram and Associated Transients On November 4, 2003, at approximately 1732 hours0.02 days <br />0.481 hours <br />0.00286 weeks <br />6.59026e-4 months <br />, and approximately three seconds into the voltage transient, the Unit 2 generator/turbine tripped, resulting in an RPS actuation. The voltage decrease also resulted in PCIS Valve Group 1 (i.e., Main Steam Isolation valves (MSIVs), Main Steam Line Drain valves, and Reactor Recirculation Sample valves), Group 3 (i.e., Reactor Water Cleanup isolation valves), and Group 6 (i.e., Containment Atmosphere Control/Dilution, Containment Atmosphere Monitoring, and Post NRCFORM 3S6A (-400t)

NRC FORM 3M6A U.S. NUCLEAR REGULATORY COMMISSION LICENSEE EVENT REPORT (LER)

FACILITY NAME (1)

DOCKET (2)

LER NUMBER (6)

PAGE (3)

YEAR ISEQUENTIAL I REVISION Brunswick Steam Electric Plant (BSEP), Unit 2 05000324 NUMBER NUWMER 3OF6 2003 O4 00 NARRATIVE (ltrnore space Is required, use additional copies of (it more space Is required. usp add'itonal copies at (It more space Is required, use additional copies of NRC Form 3664) (17) Low Level I RPS Actuation due to RPV Coolant Level Shrink The cause of the Low Level 1 RPS actuation is attributed to the level shrink caused by manual SRV cycling until the MSIVs could be re-opened. Although this method is allowed by plant procedures, pressure control using manual SRV cycling is not as stable as using the HPCI System, in the pressure control mode of operation, and the RCIC System.

Unit 2 SGT System Train A Failure to Automatically Start on Demand Each SGT System train is designed to be able to automatically start after a complete loss of electrical power, and incorporates a specific relay logic scheme to allow that capability. On November 4, 2003, the electrical transient resulted in a short-term voltage drop to approximately 40 percent of the nominal voltage value. The voltage value during the transient decreased to a value where some relays in the start logic may or may not have dropped out. For the Unit 2 SGT System Train A only, the relays responded such that the logic had to be reset before the train could start.

CORRECTIVE ACTIONS

• The damaged components (i.e., the collector ring, the anti-rotation key, the brushes, and brush rigging) were replaced. The collector ring was properly installed on the rotor shaft.

" Preventive maintenance, exciter brush vibration monitoring, and trending program improvements are being developed and will be implemented by February 20,2004. Program improvements for other brush applications on site arm also being considered.

" Enhanced exciter brush monitoring has been implemented on both Units I and 2. Unit 1 exciter collector rings are scheduled to be replaced during the next refuel outage, which is scheduled to begin in February 2004.

" Design improvements to the exciter brush holders and inspection windows are being reviewed and developed.

• Training is being developed for appropriate engineering, operations, and maintenance personnel on brush maintenance topics.

As part of the approved licensed operator training program, this event and the lessons learned associated with RPV coolant level control will be reviewed with the operating crews.

" A modification has been installed in the logic for both SGT System trains for both units to enhance logic response under degraded voltage conditions such as those experienced during this event.

NRC FORM 86A (14-001)

i (it more space Is equired, uss additional coples of NRC Form 366A) (17)

SAFETY ASSESSMENT

The safety significance. of this occurrence is considered minimal. Plant systems responded as designed to the transient and so the consequences of the transient on the fuel and vessel overpressure were minimal.

The analyses in Chapter 15 of the Updated Final Safety Analysis Report fully bounded this event.

PREVIOUS SIMILAR EVENTS

A review of events occurring within the past three years has not identified any previous similar occurrences.

- COMMITMENTS Those actions committed to by Progress Energy Carolinas, Inc. (PEC) in this document are identified below.

Any other actions discussed in this submittal represent intended or planned actions by PEC. They are described for the NRC's information and are not regulatory commitments. Please notify the Manager Support Services at BSEP of any questions regarding this document or any associated regulatory

commitments

• Preventive maintenance, exciter brush vibration monitoring, and trending program improvements are being developed and will be implemented by February 20, 2004.

NRC FOR.! 366A (I-I1)