ML20044D228

LER 93-003-00:on 930424,manual Reactor Trip Initiated Due to Erratic Feedwater Flow Indications to SG C & Excessive Main Feedwater Regulating Valve Oscillations.Caused by Design Instabilities.Secondary Sys secured.W/930512 Ltr

ML20044D228
Person / Time
Site:	North Anna
Issue date:	05/12/1993
From:	Kane G VIRGINIA POWER (VIRGINIA ELECTRIC & POWER CO.)
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
LER-93-003-02, LER-93-3-2, NUDOCS 9305180359
Download: ML20044D228 (5)

Text

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VOPCO VIRGINIA ELECTRIC AND POWE R COMPANY NORTH AN h A POWE R S TATION

• P. O. BO K 4 02 WIN E RAL. VIRGINI A 23117 t

10 CFR 50.73 May 12,1993 1.

U. S. Nuclear Regulatory Commission NAPS:M?W ,

Attention: Document Control Desk Docket No- 50-339 Washington, D.C. 20555 License No. NPF-7 >

Dear Sirs:

The Virginia Electric and Power Company hereby submits the following Licensee Event Report applicable to Nonh Anna Unit 2.

Repon No. 50-33993-003-00 This Report has been reviewed by the Station Nuclear Safety and Operating Committee and i will be forwarded to the Corporate Management Safety Review Committee for its review.  ;

Very Truly Yours, G. E. e I Station Manager Enclosme: j a: U.S. Nuclear Regulatory Commission 101 Marietta Street, N.W.

Suite 2900 Atlaea, Georgia 30323 Mr. D. R. Taylor NRC Resident Inspector Nonh Anna Power Station 170139 l

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NRC FoRW ke US kJCLI AR REGULATQ3V CAMO gppitDVED OWB NO. 3?504104 f4 Epi EXPIRES:GTAl2 '

ESTlWATED BURDEN PER RESPONSE TO CoWPLY WITH THis WFORMATON i NTON REWESn no HRS. FORWARD CoWWENU REGARDWG BURDEN UCENSEE EVENT REPORT (LER) ESTadATE TO THE RCCoR3S AND REPORTS MANAGEWENT BRANCH (P $33. U.S.

NUCEEAR REGULATORY CoWWISSION, WASHINGTON DC 20655. AND TO THE PAPERWORK REDUCTON PROJECT (31504104L OFFICE oF WANAGEWENT AND 6

BUDGET. WASHINGTON.DC 205c3.

FaciLTTY NAME 0) DOCKET Muud R gn *G m North Anna Power Station Unit 2 nitIninio!3l319 1 lOQOj4 TITLE tal MANUAL RFACTOR TRIP INITIATED DUE TO EXCESSIVE MAIN FEE 0 WATER REGUIATING VALVE OSCILIATIONS EVENT DATE (5) LER NUWBE R (e) REPORT DATE (7) OTHER FACILITIE3 INv0LVED (8)

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UCEN5E E CONTACT FOR IH15 LER O2)

NAME TELEPHONE NUWBER  ;

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On April 24, 1993, at 0530 hours0.00613 days <br />0.147 hours <br />8.763227e-4 weeks <br />2.01665e-4 months <br /> with Unit 2 in Mode 1, 71 percent power, a manual reactor trip was initiated due to erratic feedwater flow indications to the "C" Steam Generator, abnormally high vibration alarms for the "B" Reactor Coolant Pump, and suspected water and steam leakage from the "C" Main Feedwater line. Emergency procedures were entered and immediate actions were performed. All Engineered Safety Feature system equipment responded as designed. At 0602 hours0.00697 days <br />0.167 hours <br />9.953704e-4 weeks <br />2.29061e-4 months <br /> an " Alert" was declared, based on Shift Supervisor judgment, in accordance with Emergency Plan Implementing Procedures and the required notifications were made. A 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br /> report was made to the NRC at 0620 hours0.00718 days <br />0.172 hours <br />0.00103 weeks <br />2.3591e-4 months <br /> pursuant to 10CFR50. 72 (a) (ii) (3) . At 0816 hours0.00944 days <br />0.227 hours <br />0.00135 weeks <br />3.10488e-4 months <br /> with the unit in a '

stable condition the " Alert" classification was down graded to a Notification Of Unusual Event (NOUE) . The NOUE was terminated at 1045 hours0.0121 days <br />0.29 hours <br />0.00173 weeks <br />3.976225e-4 months <br /> on April 24, i 1993. The event is reportable pursuant to 50.73 (a) (2) (iv) .

The cause of the event has been attributed to the inherent instabilities with l the design of the main feedwater regulating valve and positioner controls. J

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1 No significant safety consequences resulted f rom the main feedwater concerns because auxiliary feedwater was available and provided cooling to the steam generators throughout the event. Therefore, the health and safety of the public were not af fected at any time during this event.

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l NRC FoRW 3EA US CM11AA REGULATORY CouME510h AppitDVED oWB No. 3160.osos De {

EXPIRES: &JG'92 I ESTauATED BURDEN PER RESPONSE To COMPLY WITH THIS INFoRuATON UCENSEE EVENT REPORT (LER) couiCTON REcuEST: 50.0 HRS. FORWARD CoWWENTS REGARDING BURoEN TEXT CONTINUATION ESTlWATE To THE RECORDS AND REPORTS MANAGEWENT BRANmi(P430L U.S.

NUCLEAR REGULATORY CoWWLSSON, WASHINGTON. DC 20555. AND To THE PAPERWORK REDUCTON PROJECT (3tS0 010sk orFCE oF MANAGEWENT AND BUDGET, WASHINGTON.DC 20h01

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0 l 0 I3 O l0 012 or 014 TEzT pm mi. ww eee emc *w= nu a 07) i 1_0 Dmriptinn cf the Event On April 24, 1993, at 0530 hours0.00613 days <br />0.147 hours <br />8.763227e-4 weeks <br />2.01665e-4 months <br /> with Unit 2 in Mode 1, 71 percent power, a manual reactor trip was initiated due to erratic feedwater flow indications to the "C" Steam Generator (EIIS System AB, Component SG), abnormally high ,

vibration alarms (EIIS System IV, Component VA) for the "B" Reactor Coolant Pump (EIIS System AB, Component P), and suspected water and steam leakage from ,

the "C" Main Feedwater line (EIIS System SJ). Emergency procedures were entered and immediate actions were performed. All Engineered Safety Feature system (EIIS System JE) equipment responded as designed. At 0602 hours0.00697 days <br />0.167 hours <br />9.953704e-4 weeks <br />2.29061e-4 months <br /> an

" Alert" was declared, based on Shift Supervisor judgment, in accordance with i Emergency Plan Implernent ing Procedures and the required notifications were made. A 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br /> report was made to the NRC at 0620 hours0.00718 days <br />0.172 hours <br />0.00103 weeks <br />2.3591e-4 months <br /> pursuant to '

10CFR50.72 (a) (ii) (3) . At 0816 hours0.00944 days <br />0.227 hours <br />0.00135 weeks <br />3.10488e-4 months <br /> with the unit in a stable condition the

" Alert" classification was down graded to a Notification Of Unusual Event (NOUE) . The NOUE was terminated at 1045 hours0.0121 days <br />0.29 hours <br />0.00173 weeks <br />3.976225e-4 months <br /> on April 24, 1993. The event is reportable pursuant to 50.73 (a' (2) (iv) .

On April 24, 1993, at 0255 hours0.00295 days <br />0.0708 hours <br />4.21627e-4 weeks <br />9.70275e-5 months <br /> "C" Steam Generator (SG) feed flow began to

• oscillate. At 0320 hours0.0037 days <br />0.0889 hours <br />5.291005e-4 weeks <br />1.2176e-4 months <br /> "B" SG feed flow escillated for approximately 10 minutes then reached steady state. At 0500 hours0.00579 days <br />0.139 hours <br />8.267196e-4 weeks <br />1.9025e-4 months <br /> "B" SG feed flow began to oscillate again. At 0517 hours0.00598 days <br />0.144 hours <br />8.54828e-4 weeks <br />1.967185e-4 months <br /> "C" feed flow oscillation worsened and both "B" and "C" Main Feed Regulating Valves (MFRV) (EIIS System SJ, Component FCV) l were placed in manual. An operator was dispatched to the Mechanical Equipment Room and reported that the feed lines were moving and the "C" MFRV was cycling. Feedline noises and pipe movement worsened. The "B" Reactor Coolant Pump vibrations alarm was received and the "B" SG Loose Parts alarm (EIIS System II, Component ALM) was received.

At 0530 hours0.00613 days <br />0.147 hours <br />8.763227e-4 weeks <br />2.01665e-4 months <br /> after vibrations were felt and heard in the Control Room the Senior Reactor Operator ordered a manual reactor trip. The immediate actions of Emergency Procedure 2-E-0, Reactor Trip or Safety Injection, were performed. Initially, Reactor Coolant System (RCS) (EIIS System AB) pressure decreased to approximately 2000 psig and temperature decreased to approximately 538 degrees F. All Engineered Safety Feature system equipment i responded as designed. Upon transition to Emergency Procedure 2-ES-0.1, Reactor Trip Response, the secondary systems were secured. At this point the noises and vibrations were no longer heard or felt in the Control Room. At 0602 hours0.00697 days <br />0.167 hours <br />9.953704e-4 weeks <br />2.29061e-4 months <br /> an " Alert" was declared, based on Shift Supervisor judgment, in ,

accordance with Emergency Plan Implementing Procedures. Notification of State and Local Governments occurred at 0609 hours0.00705 days <br />0.169 hours <br />0.00101 weeks <br />2.317245e-4 months <br />. The NRC Emergency Operations  !

Center was notified of the " Alert" at 0620 hours0.00718 days <br />0.172 hours <br />0.00103 weeks <br />2.3591e-4 months <br /> pursuant to 10CFR5 0.72 (a) (ii) (3) . At 0816 hours0.00944 days <br />0.227 hours <br />0.00135 weeks <br />3.10488e-4 months <br /> with the unit in a stable condition the ,

" Alert" classification was down graded to a Notification Of Unusual Event (NOUE). The NRC was notified at 1045 hours0.0121 days <br />0.29 hours <br />0.00173 weeks <br />3.976225e-4 months <br /> that the NOUE was terminated. At 1253 hours0.0145 days <br />0.348 hours <br />0.00207 weeks <br />4.767665e-4 months <br /> the unit entered Hot Shutdown with RCS temperature less than 350  ;

degrees F. At 1735 hours0.0201 days <br />0.482 hours <br />0.00287 weeks <br />6.601675e-4 months <br /> the unit entered Cold Shutdown wit h RCS temperature less than 200 degrees F.  ;

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%AC FORet 2n6A US CACW RhTARSDRV N aPPRo0ED ouB No. 31500104 4em EXPIRES: 4'3CvD2 ESTIMATED BURoEN PER RESPONSE To CCWPLY WITH THis INFORMATON UCENSEE EVENT REPORT (LER) CouECTON REC 1 JEST: 50.0 HRS. FORWARD CoWWENTS REGARDh3 BURDEN TEXT CONTINUATION ESNATE To THE RECORDS AND REPORTS MANAGEWENT BRANCH (P-EX)L U.S.

NUCLEAR REGULATORY CoWW:SSON WASHNGioN. Oc 2065&. AND To THE PAPERWORK REDUCTON PROJECT (315acios). OFFCE OF WANAGEWENT AND BUDGET, W ASHINGToN.DC 20603.

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O l0 0I3 cf 0l4 TLET irme =am = w u amene.wie re= asen es 07) 2.0 Sionificant Safety Cen=erences and Irrlications No significant safety consequences resulted from the main feedwater concerns because auxiliary feedwater was available to provide cooling to the steam generators throughout the event. Therefore, the health and safety of the public were not affected at any time during this event.

3.0 Cause of the Event The cause of the event has been attributed to the inherent instabilities with the design of the main feedwater regulating valve and positioner controls.

4.0 I m diate Corrective Actions Following the manual reactor trip Emergency Procedure 2-E-0, Reactor Trip or Safety Injection, was entered and the immediate actions performed.

1.0 Additional Corrective Actions Upon transition to Emergency Procedure 2-ES-0.1, Reactor Trip Response, the secondary systems were secured. The unit was brought to cold shutdown without incident.

The flow and pressure transmitters for the "C" main feedwater lines were satisfactorily calibrated and verified operable. The MFRVs and Main Feedwater Bypass Regulating Valves were visually inspected, stroked, calibrated, and verified operable. The feedwater piping and supports downstream of "C" MFRV up to and including the feed ring inside "C" SG were inspected. Adjustments were made to the MFRVs pneumatic boosters to reduce sensitivity and overshoot.

6.0 Actions to Prevent Recurrena Guidance to mitigate oscillations was provided to all operations shifts.

Early recognition of feedwater system oscillation during power ascension will allow appropriate operator actions to occur to preclude a similar event.

Parameters that will be monitored include: feedwater pump suction pressure, feedwater header pressure, feedwater flow, and the individual pressure indications at the discharge of each MFRV.

Requirements are in place to ensure the reactor trip event is included in the Licensed Operator Requalification Program. Actions taken are sufficient to preclude recurrence.

7.0 Similar Events None am e- ma im

NRC FoRW 38hA US NgCdAR RKmKSTDV NWh gpp g g g g 3 g g N' EKPERES: W3MI2 EST:WATED BURDEN PER RESPONSE TO CoWPLY W:TM THIS INFORWATON UCENSEE EVENT REPORT (LER) COLLECTION REQUEST: 504 HRS. FORWARD CoWWENTS REGARDING BURDEN TEXT CONTINUATION ESWATE TO NE RECORDS AND REPORTS WANAGEMENT ERANCH (P430L U.S.

NUCLEAR REGULATORY COWWISSON. vt ASHINGTON. DC 20555 AND TO THE PAPERwoRat REDUCTION PROJECT (315t>ctoak OFTCE OF WANAGEWENT AND BUDOET.% ASHINGTON.DC 20hD1.

F ACILITY NAME (1) DCXAET mMER 2 GA mR ts) pace m 9 E, SE;hJEETag m Rete,A North Anna Power Station wa M WJaeER Unit 2 al ci a l $ l a l31319 913 -l1 0 l0 i 3 -l O

! IO 014 0F 014 luTin . e .e. mac e anamn(17) 9.0 Additional Inf0N21 tion Component failures resulting from the main feedwater line oscillations ,

include: broken air line to the "B" Main Feedwater Regulating Valve, broken.

air line to the "B" Main Feedwater Bypass Regulating Valve, broken snubber extension rod on the "C" Main Feedwater Bypass line, broken spring hanger on ,

"C" Feedwater line, and a broken yoke en "C" main feedwater bypass regulating i valve.

The broken air lines to the "B" MFRV and "B" Main Feedwater Bypass Regulating Valve were repaired. The "C" Main Feedwater Bypass line snubber was replaced.

Snubbers were also replaced on the "A" and "C" feedwater headers. The spring hanger on "C" Feedwater line was repaired and the yoke on "C" main feedwater i bypass regulating valve was replaced.

Unit I was in Mode 1, 100 percent power, and was not affected by the event.

The Unit 1 MFRVs were modified during the recent refueling outage with a [

] pneumatic open and close operator. This modification was performed to eliminate oscillations of the MFRVs. The Unit 1 MFRV are of a different '

I design than Unit 2 and experience to date indicates they do not have similar instabilities. ,

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