ML20005E661

LER 89-020-00:on 891202,turbine Controls Failed to Respond to Attempt to Counter Loss of Load & Turbine Manually Tripped.Caused by Relay Contact Failure in Turbine Electrohydraulic Control circuitry.W/900102 Ltr

ML20005E661
Person / Time
Site:	Summer
Issue date:	01/02/1990
From:	Bradham O, Higgins W SOUTH CAROLINA ELECTRIC & GAS CO.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
LER-89-020, LER-89-20, NUDOCS 9001100063
Download: ML20005E661 (6)

Text

f G yff ,

[. .hih. ' >

s:uth C!.rolina Etctric & cas CImpany..- 0110 S. Bradham '

O/; .:.- P.O. Box 88 - Vice Prtsidtnt l WF- - Jenkinsvilb, SC 29065 Nuclear Operttions :

s;av '3803) 3454 040 g -;' SCEAG 39 w%

- January 2, 1990 a s t,

Document Control Desk

, .U.-S. Nuclear Regulatory Commission Washington, DC 20555

SUBJECT:

Virgil C. Summer Nuclear Station y Docket No. 50/395 Opereting License No. NPF-12 LER 89-020 Gentlemen:

-Attached is Licensee Event Report No.89-020 for the Virgil C. Summer Nuclear

, Station.. This= report is submitted pursuant to the requirements of

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

=Should there be any questions', please call us at your convenience.  ;

Very truly yours,

/

0. S. Bradham CJM/OSB: led Attachment c: D. A. Nauman/0. W. Dixon, Jr./T. C. Nichols, Jr.

c E. C. Roberts

,R. V. Tanner J. C. Snelson S. D. Ebneter R. L. Prevatte J. J. Hayes, Jr. J. B. Knotts, Jr.

General Managers INP0 Records Center  ;

C. A. Price ANI Library '

G. J. Taylor Marsh & McLennan 1 J. R. Proper NSRC R. B. Clary NPCF F. H. Zander RTS (ON0 890107)

T. L. Matlosz Files (818.05 & 818.07) l L K. E. Nodland i

i s

s n

) 'NNC FENIt M . U.S. NUCLEAES t~t1ULATORY COneset0N

- ArenOYED oms esO 31s0-c104

'"""*8''**

. UCENSEE EVENT REPORT ILER)

1. ActLITY 8 eases N . DOCKSTasueGGR431 FAGE W Virail C. Summer Nuclear station 0 Is l o lo l o l 31915 i loFl 015 TITit tel Reactor Trip on Low-Low Steam Generator Level Followina Turbine Trin sygeff Daft Isl Lan NynetR 404 RGPORT Daft (T) OTMSA f ACILITitS 18ev0Lvt0 21

[ F ACILITV 8eAMes DOCKET NUMBER!$)

na0 NTH DAY YlAR YEAR c.

88h" h"' $ MONTH DAY YEAR 015l0l0l0 i ; i

~

1l 2 0l2 8 9 8l 9 ", 0l 2l 0 OI0 0l1 0l2 9l0 1 0 1 510 1 0 1 0 I I

,,,,,,,,,, Tues asecat e eveMiTTeo evneuaNT TO Tus neaueneassNTs Oe to Can t ten-e ., er an. s.<*waes o16 ao** * ~1 m.ami _

mw 1 mmiaH=i _

ruim ruiw g _

so .mmmm

==wmm Emwm umimH.i _

H.i 11010 _

amim _

m>=im a _ g, Mig 7;yg,g

""* "moHn emmH.ainAi = As

' s y,< _

"*WinH1HM E78tsH3Hel Et34 sit 3H.IIHW s 's' _

SIL 3 30 m6al(11M E73tnit3H6tli E73teH3Hai LtCE8dSEE C08tTACT FOst TH88 LtR H31 NAMg TELEPHONE NUMSER ARE A CODI W. R. Higgins, Supervisor, Regulatory Compliance 810 I 3- 314 i S I- l 4101412 COMPLif t Cass LINE FOR SACH C0apCdeterT FAILunt D00cm*tt0 IN THas app 0nf its)

C. Rip TA E s '

" C E s CAUSE SYSTEM COMPONENT MkAjN8 CAUSS SYSTEM ConsPONGNT N g ",TpA s B JJi RLYi i i G i q80 i N i i i i i i i E Ell' B l KI RI Gl 01810 N I l I I I I I '

GUPPLEMENTAL PGPORT EXPECTRO Hel MONTM DAY YEAR YES fid v.e. semgHne LX.tCTfD SUentIS$10N De tti NO l l l AssinACT ,u ,= ,. A. = .. .- ev, , nel On December 2, 1989, at approximately 2202 hours0.0255 days <br />0.612 hours <br />0.00364 weeks <br />8.37861e-4 months <br />, operations personnel started a load reduction to 90% power for the monthly turbine control valve testing. When the operator pushed.the load selector decrease button for the second 2% reduction in power the turbine commenced a rapid power decrease (2209 hours0.0256 days <br />0.614 hours <br />0.00365 weeks <br />8.405245e-4 months <br />). Operations personnel attempted to counter the loss of load by selecting manual increase; )

however, the turbine controls failed to respono and the turbine was manually tripped 1 when turbine power decreased below P-9 (Power Permissive < 50% Rated Thermal Power). 1 The exciter field breaker initially failed to open from the Main Control Board (MCB).

An operator was immediately dispatched to locally open the breaker. The breaker finally opened after several attempts to cycle the breaker from the MCB.

Main feedwater was manually secured /1t 2220 hours0.0257 days <br />0.617 hours <br />0.00367 weeks <br />8.4471e-4 months <br /> when the turbine runback transient caused a high level in the deareater (DA). When main feedwater was restored at 2221 hours0.0257 days <br />0.617 hours <br />0.00367 weeks <br />8.450905e-4 months <br />, the addition _of cooler (280"F) water caused a rapid RCS cooldown and steam generator levels to shrink to below the low-low steam generator level reactor trip l setpoints. A reactor trip occurred at 2222 hours0.0257 days <br />0.617 hours <br />0.00367 weeks <br />8.45471e-4 months <br /> on C" Steam Generator low-low level. With the exception of the previously mentioned problems the plant response was normal. A failed turbine control circuit board was replaced and the exciter field breaker PM'd prior to authorizing the plant restart.

Additional actions have been initiated by SCE&G to modify the turbine control circuit and increase the PM frequency on the exciter field breaker, gag, =

1

--Y < y; .

_~ ,

? ,q 8100 Pere 3BSA~

g 1, U.S hUCLECQ CEOULATOftY COMMISSION

% , '. (

) P UCENSEE EVENT REPORT (LER) TEXT CONTINUATION - L APPROVE 0 0MB NO. 3150-C104 :

. EXPIRE $

8/31/85 -

FactLtTV faseAE (14 '.

DOCKET NUMBER (2) .

LER NUMSER ($) ~: PAGE (3)

TEAR '

Na '

eTo" MrgiliC;: Summer Nuclear Stationi ~

~

TEXT (#meer spece 4 O--T, use o js lo lo j o l3 l 9) 5 8l 9 -.

0]2l 0 -

0l0 0l2 OF 0 j5' J N#C Femr JEM W (IM .

PLANT-IDENTIFICATION:

Westinghouse 2 Pressurized Water Reactor =

+

EQUIPMENT IDENTIFICATION:

Electrohydraulic Control Panel. Relay. - EIIS - JJ

w. ,

Alterex-Exciter Field Breaker - EIIS - EL 4

IDENTIFICATION OF EVENT:

' On December 2,:1989, at-approximately.2209 hours0.0256 days <br />0.614 hours <br />0.00365 weeks <br />8.405245e-4 months <br />, the turbine commenced a rapid-power decrease due'to a failure;in the turbine control system. At the time of the-occurrence,vpower was.being-decreased to approximately 90% for routine turbine-control: valve testing. . At 2217 hours0.0257 days <br />0.616 hours <br />0.00367 weeks <br />8.435685e-4 months <br /> the main generator breaker and the turbine were manually tripped.after power had decreased below P-9-(Power Permissive < 50%

Rated Thermal Power). A reactor trip occurred at 2222 hours0.0257 days <br />0.617 hours <br />0.00367 weeks <br />8.45471e-4 months <br /> on low-low steam generator _ level during-restoration of main feedwater f. low to-the steam generators.

The increased flow in.feedwater at a temperature of 280*F caused a rapid shrink. in all' steam' generator-levels.

EVENT'DATE:

December 2, 1989,-at' 2222 hours0.0257 days <br />0.617 hours <br />0.00367 weeks <br />8.45471e-4 months <br /> REPORT DATE: January 2, 1990 This report.was initiated by Off-Normal Occurrence Number 89-107.

' CONDITION PRIOR TO EVENT:

i Mode 1 - 100% Power DESCRIPTION OF EVENT:

On' December.2, 1989, at approximately 2202 hours0.0255 days <br />0.612 hours <br />0.00364 weeks <br />8.37861e-4 months <br />, operations personnel started a loadoperator

'the reduction to 90%

pushed thepower load sel for the monthly turbine control valve testing. When ector decrease button for the second 2% reduction

- in power, the turbine commenced a rapid power decrease (2209 hours0.0256 days <br />0.614 hours <br />0.00365 weeks <br />8.405245e-4 months <br />). This turbine runback resulted in an actuation of all fourteen steam dumps (including the PORV's to the atmosphere) and automatic rod insertion to compensate for the turbine runback.

Operations personnel attempted to counter the loss of load by selecting manual increase; however, the turbine controls failed to respond and the turbine was manually tripped at 2217 hours0.0257 days <br />0.616 hours <br />0.00367 weeks <br />8.435685e-4 months <br /> when g ag ,oa .

7 LICENSEE EVENT REPORT (LER) TEXT CONTINUATION areR6vEo ous no siso-oio4

4 EXPIRES 8'31/86 F ACl4tTV NAME (15 ' DOCKET NUMBER (28 LER NUMBER 16) PAGE (3) v8Aa -

" M.W. ",#v".3

' Virgil C. Summer Nuclear Station o is lo lo lo 13 l 9l5 8l 9 -

0 l 2 l0 0l0 0l3 oF 0 l5 .

TEXT t# more space a rewmt, we a#rmas/ NAC Fome 3 Hirst (17)  !

power had decreased below the P-9 setpoint. An additional problem occurred when-the' exciter _ field breaker initially failed to open from the Main Control Board (MCB)-following the' trip. An operator was immediately dispatched to locally open the breaker. The breaker finally opened after several_ attempts to cycle it from  ;

.the MCB. l Main feedwater was manually. secured by operations at 2220 hours0.0257 days <br />0.617 hours <br />0.00367 weeks <br />8.4471e-4 months <br /> when the turbine runback transient caused a high level in the deareater (DA). The rapid increase in l DA level led to a manual trip of the "B" condensate pump and the automatic tripping I of."A" condensate pump.. The condensate system was then aligned for restart and the '

"A" :ondensate pump was started. When main feedwater was restored at 2221 hours0.0257 days <br />0.617 hours <br />0.00367 weeks <br />8.450905e-4 months <br />,

-the addition of cooler (280*F) water caused a rapid RCS cooldown and steam generator levels to shrink to below the low-low steam generator level reactor trip setpoints. A reactor trip occurred at 2222 hours0.0257 days <br />0.617 hours <br />0.00367 weeks <br />8.45471e-4 months <br /> on "C" Steam Generator low-low level.. With the exception of_the previously mentioned problems, the plant response was normal. The plant was stabilized in Mode 3 until the cause of the malfunctions

'could be determined and corrected.

CAUSE OF EVENT:

The cause of the turbine runback was a relay contact failure in the turbine electrohydraulic control (EHC) load reference circuitry. Relay contacts for stator water cooling runback had shorted and remained closed when the operator pressed the load decrease button on the MCB. Instrumentation personnel replaced the circuit board which contained the defective component and returned the EHC system to operable status for a plant restart on December 3, 1989.

Subsequent investigations by engineering personnel determined that the component malfunction appeared to have resulted from a design deficiency. It is standard practice to connect a reverse biased diode across relay coils in the EHC circuitry to prevent high inductive voltages from being produced. A review of the runback circuit, which was modified in April of 1987, determined that a 24 VDC relay coil was connected to the failed contact without diodes. The contacts are rated for 500 volts; however, in a test on December 7, 1989 the vendor and South Carolina Electric & Gas Company (SCE&G) engineering personnel observed spikes of over 400 volts and that the contacts easily arced. The test confirmed that the contacts could short and cause the runback which occurred on December 2, 1989.

The failure of the Alterex exciter field breaker to open is a repeat occurrence.

The previous failure which was noted in LER 88-002 dated March 11, 1988, was due to solidification of grease, whereas the latest failure was determined to have resulted from a lack of lubrication. The cause of the repeat failure was either due to personnel error or too long of a period between lubrications. Following the previous event, the type of grease applied for lubrication of this breaker was changed to prevent binding per the recommendations of IE Information Notice 87-12

" Potential Problems with Metal Clad Circuit Breakers, General Electric Type AKF 25," and the frequency of preventative maintenance (PM) was set for every refueling outage. During an outage in November of 1988, the breaker was sent to a vendor for ungonu ma

7 f32: l F aenc Form asea c U.S NUCL6f.R 7.40VLATORY COMMISSION

'@ "9 s y - LICENSEE EVENT REPORT (LER) TEXT CONTINUATION-Arenoveo oms No. siso-oio4 9 EXPIRE 8 8/31/65

'[iI P ACILITY NAME (1)I DOCKET NUMOtR IM WR NUMSER W ,Mm I TIA" -

NEeIn YvYsIn .

[ TVirgil C.. Summer Nuclea'r Station TEKT IIImore space h requrest, use annone!NMC form 306A v (1h o p lo jo jo j3l9j5 8l9 __

0l2[0 --

0l0 0 [4 or 0l5 l

l

-refurbishment and on installation the PM was rescheduled for the next outage in -

1990.. -1

-1 ANADSIS ~ OF' EVENT:

1 This report is being submitted pursuant to the requirements of 10CFR50.73(2)(a)(iv). Notification to the NRC Operations Center via the Emergency- l Notification System was made at 0030 hours3.472222e-4 days <br />0.00833 hours <br />4.960317e-5 weeks <br />1.1415e-5 months <br /> on December 3, 1989, per the requirementsof10CFR50.72(b)(2)(ii).

'With the exception of the Alterex. exciter field breaker, the plant responded as expected to the turbine runback and subsequent reactor trip. During the runback, reactor-power was decreased through rod-insertion and emergency boration. As previously stated, increasing levels in the DA following the manual trip of the turbine.resulted.in loss of condensate pumps, and during the recovery process the ,

addition of' main feedwater led to a shrink in steam generator levels and subsequent  :

- reactor _ trip from approximately 5% RTP. The turbine driven emergency feedwater

_(TDEFW) pump started when the trip occurred due to the low-low level in all three steam generators and operated for approximately five minutes before being manually-tripped:by the operator. The plant cooled down to 530 F during the transient and was. stabilized in Mode 3.

Because of minor primary to secondary leakage in the steam generators, the TDEFW pump-and the power operated relief valve operations resulted in a release of gaseous effluents. Calculations performed in accordance with Technical Specification 3.11.2.1 determined that the release was neligible (<0.1% of allowable releases / year).

IMMEDIATE CORRECTIVE ACTION:

. Following t'he reactor trip, the operating shift placed the plant in a stable

condition in accordance with Emergency Operating Procedure (EOP) 1.0, " Reactor p -Trip / Safety Injection Actuation," and E0P-1.1, " Reactor Trip Recovery."

l Maintenance was then directed to investigate and repair the noted equipment failures. The EHC card was replaced and the exciter field breaker PM'd prior to authorizing the plant restart.

p ADDITIONAL CORRECTIVE ACTION:

L L The following additional actions were initiated by SCE&G to prevent a similar reoccurrence:

1. The circuitry of the EHC card was analyzed and determined to contain a design deficiency in that diodes were not installed to prevent high inductive voltages. This deficiency was confirmed through testing on December 7, 1989.

2. A modification to install diodes in the circuitry was performed on December 29, 1989.

l l

'NR P_ORM 366A

s.

. ie' efRC Form 3084 U.S NUCLEA11010ULATO3Y COMMIS$ tun W

J

.f UCENSEE EVENT REPORT (LER) TEXT CONTINUATION APPROVED OM8 NO. 3160-0104 EXPIRES 8/31/85

.-+-

t FActteTY NAME,til- DOCKET NUMBER (21 LER NUMBER (6) PAGE(31 YEAR stgtp pL .

mEye g

' Virgil 'C.- Summer Nuclear. Station o is lo jo l0 l3 l 9l5 8] 9 0lU[0]6OF 0l5 0l2l 0 -

TEXT tot more spese n tw, one natheonn! NMC form 366Knl(11) r.

w

3. Maintenance has been directed to inspect and lubricate if necessary the exciter field breaker at approximately six month intervals (actual time is

' dependent on frequency of outages) until the reliability of the breaker can be established. i PRIOR OCCURRENCES:

LER 88-002, dated March 11,'1988 t

1 1

l l

1 l

l l

1 NRC FORM 366A i 69 831