ML20029A690

LER 90-011-01:on 900819,reactor Trip Occurred Due to Power Surge.Caused by Lightning Strike.Rod Drive Sys Will Be Modified W/New Model of Power Supply Less Likely to Cause Reactor trip.W/910221 Ltr

ML20029A690
Person / Time
Site:	Byron
Issue date:	09/13/1990
From:	Pleniewicz R, Schrock J COMMONWEALTH EDISON CO.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
BYRON-91-0110, BYRON-91-110, LER-90-011-01, LER-90-11-1, NUDOCS 9103010259
Download: ML20029A690 (6)

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..o; i / 4450 North German Church Road Byron. lilinois 61010 February 21, 1991 Ltra BYRON 91-0110 U. S. Nuclear Regulatory Commission Document Cont.rol Desk Washington, D.C. 20555 Dear Sir The enclosed supplemental Licensee Event Report from Byron Generating Station in being transmitted t.o you in a ;ordance with the requirement.s of 10CTR50.73(a)(2)(iv).

This report is number 90-011; Docket tio. 50-454.

Sincerely, s

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R. Pleniewicz Station Manager Byron Nuclear Power ?tation RP/DK/mw Enclosure Licensee Event Report No.90-011 cci A. Dort Davis, NRC Region III uministrator W. Kropp, NRC Senior Resident Inspector INPO Record Center CECO Distribution List (0716R/0081R) 9103010259 900913

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SUPFLEMENT TO DVR DVR NO.

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PART 1 lillLQ{_(yD{l Q[(MRELQ High Negative Flux Rate Reactor Trip due to Loss 08/19/10 0425 of Control Rod Drive Power Supplies during DATE 11 t't Lightning Strike BfA10tLIDi.3VffLEMENTAL P,EEQE1

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SUPPLEMENTAL REPORT APPROVED AND AUTHORIZED FOR DISTRIBUTION s I///-rL . /

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- (0716R/0081R-1)

LICENSEE EVENT REPORT (LER) 9 Fact,llty Namt (1) Docket Number (2) lagtj ] _ _ _

8yrrn. Unit 1 0.L51_0LOLollLil 4 L L or1 0 i_ 4 Title,(4) High Negative Flux Rate Reactvr Trip due to Eoss of Control Rod Drive Power Supplies during LI 2hin.ifg.1LE1).t-lten_LRaledh) . LI!LUnitidt) RepotLpejtllL _ Qlhtr_[AE111t i t1Jnt9hicl0L_

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OPERATING LCh'ALIAIIt_ng.E e f the fo1Igwlna)_(l11 MODE (9) 1 20.402(b) __ 20.405(c) .JL 50.73(a)(2)(iv) _ 73.71(b)

POWER _ 20.405(a)(1)(1) _ 50.36(c)(l) __ 50.73(a)(2)(v) _ 73.71(c)

LEVEL , , _ _ _ 20.405(a)(1)(ii) _ 50.36(c)(2) ___ 50.73(a)(2)(vil) _ Other (Specif y (101 17 i L _._ 20.405(a)(1)(lii) _

50,73(a)(2)(t) _ 50.73(a)(2)(viii)(A) in Abstract

////////////////////////// _,_ 20.405(a)(1)(iv) _ 50.73(a)(2)(ii) _. 50.73(a)(2)(viii)(B) below and in

////////////////////////// _ 20.405(a)(1)(v) _ 50.73's)(2)(lii) _ 50.73(a)(2)(x) Text)

LICENSEE CONTACT FQR THIS LER (11)

Name TELLPHQULttyMECR AREA CODE J. Schros L Qgeratin.gJnalater Exten11gnl216 8l 1 l5 21314 l -l ILaLilJ COMPLETE ONE LIME FOR EACH CQM ONEN FAILURE DESCRIBED IN THIS REPORT (13)

CAUSE' SYSTEM COMPONENT MANUFAC- REPORTABLE CAUSE SYSTEM COMPONENT MANUFAL. REPORTABLE /

TURER lQJP10L. TURER _103{PRQL. j/

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SUPfL(tiENTAL REPORT EEEECTED (14) Expected t!ontb._j.la.y llent Submission lyes (If ves. (QLnnit.ttJ)(PECTEDlVQdi$1]ON DATE) X l NO ABSTRACT (Limit to 1400 spaces, i.e, approximately fifteen single-space typewritten lines) (16) 8 l ll lI _

At 0425 on August 19, 1990, with severe lightning activity near Byron Station, a Unit I reactor trip occurred from 78% power. A lightning strike induced a voltage surge that activated nine out of ten over-voltage protection devices installed on power supplies in the rod drive (RO) ( AA) power cabinets. Inis activation released twelve out of fifteen rod control cluster assembly groups into the core and resulted in a high negative flux rate reactor trip.

Due to several Commonwealth Edison and industry wide lightning induced reactor trips, several modifications have previously been made to both the containment lightning protection system and the rod drive over voltage protectors.

The Rod Drive System will be further modi' led with a new model of power supply that is less likely to cause a reactor trip after a transient caused by lightning.

This event is reportable pursuant to 10CFR50.73 (a)(2)(iv) as a result of the automatic actuation of the Reactor Protection System.

(0716R/0081R-2)

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((. j LICEN$tE EVENT pEPORT (LER) TEXT Cot {lltiUATION Form Rev 2.Q_ ,

3- i fACl)!TY #4AME (1) DOCKET NUMDER (2) .MfLJNttDL! Lib) P Agt_.13 L._ l Year j/// $equential /j//j Revision 4 ff f

/// Number /// Number.;

Jyron; Unit' 1 0 1 5 l Q_l__QJ_Q l 4111 4 9i0 - 0 l 1 1._ l ' -

Q l1 0 12_ 0F Q,.lt TEXT Energy Industry Identification System (EMS) codes are identified in the text as (XX) "

A'.' PLANT CONQITIONS PRIOR TO EVEN{t Event Date/fime 08-19-90. / 0425 Unit 1 MODE 1 - 02ERL2 PEAL [pn Rx Power 181_ RCS ( AB) . Temperature / Pressure _gtmjLggnaling.

Unit 2 MODE I _P0rtI._QF t.tElian__ Rx Power.301_. RCS (AB]' Temperature / Pressure _ngts L gptraling_.

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B; QL M IP_ TION OF EVEN1:

AT 0425 on August 19, 1990, with severe lightning activity near Byron Station, a Unit I reactor trip occurred. f rom 78% power due to Fower range (IG) high . negative flux rate. As expected after the trip, both Auxillary Feedwater pumps (AF) (BA) automatically started on $ team Generator to+2 level. The Unit was

- stabilized and recovered in accordance with Station emergency procedures with the reactor core temperature

' being controlled by main condenser steam dumps and steam generator. level maintaleed by both the 1A Auxiliary Feedwater Pump and the Unit One Startup Feedwater Pump. The Unit was maintained in Mode 3 (Hot

' Standby). Mode 1-(power operations) was entered following a reactor startup on 8-20-90 at=1225.

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No systems or components were inoperable at the beginning of this event which contributed to this event.

Operator actions aided in restoring stable plant conditions af ter the event.

The NRC Operations Center w as notified 'of the event at 0525 on 8-19-90, pursuant to 10CFR50.72(b)(2)(ii), i An actuation of the Reactor Protection System is reportable pursuant to 10CFR50.73(a)(2)(lv).

C. 'CAUSE OF__ EVENT .

The Unit I five Rod Drive-(RO) (AA) power cabinets each contain two Lambda (model LME-24) 44 Volt direct current (VDC) power supplies and two Lambda-(model LCS-A24-6795) -24VDC power supplies. A unique feature-common._to the positive. supplies are the Over-Voltage Protection :(OVP)-devices (Lambda model LHOV-3)

. designed to protect the power cahinet's internal circuitry. If the sensed output of a positive power ,

supply excee$s +28VDC, the'0VP device will activate. This activation will short the associated power 7

-supply =and. force the;r W *i ct pnet s@ ply to pick up the cabinet load through auctioneering. Once the

.0VP device is " tripped". It can only be_ reset by de-energizing the shorted supply. Loss.of both positive  !

. power supplies in a power cabinet through OVP activation will cause all the power cabinet's Rod Control Cluster' Assemblies (RCCAs) to fall into the core and . result in a reactor high-negative flux rate trip.

Innediately prior to.the reactor trip of this event,' a lightning = strike in the vicinity of.0yron Station induced a voltage surge that activated nine out of ten Over-Voltage Protection devices installed on the. ,

positive 24 VOC power supplies in the Unit One' RD power cabinets. - This activation released twelve RCCA j groups out of the total fif teen into the corei These groups the caused the Negative Higk fluw Rate trip )

which then released the remaining three RCCA groups held t , the 2AC cabinet. l

- The most probable-root cause of the OvP activations sas lightning induced volteges on the RD system .  !

cabling, Due to the elusive nature of lightning and the unkenwn location of-the lightning strikef the -

Induced voltage carrier is unknown. The ground cables and lightning rods were e ffied intact on both units.

The positive power supplies themselves may have allowed passage of the voltage transient and contributed to this event. The RO power cabinet negative power supplies. which are not over-voltage protected, did not contribute to the cause of this event.

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(0716R/0081R-3)

LECK$LLEYEHLREP9RLIMRLJEXI._MNIINVAI19N _. _ LettnattlaQ_

s FACI,tITY NA'ME (1) DOCKET NUMBER (2) _LLILtM10LR {6)-

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pp/ Sequential j//g/ Revision llL,/ httL- LLL hntL

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- -- LLL_LIL .0L Lit TEXT Energy Industry Identification System (E!!$) codes are Identified in the tent as (XX)

D. $AFETY A%LY.113:

There were no adverse safety consequences as a result of this event, the health and safety of the public was at no time endangered. Other equipment important to safety was not affected by the storm.

E. CDELC11YLAtllMS:

After a similar event in 1985, several corrective actions were implemented to prevent recurrence.

Hodification M6-1-85-0516 improved the containment lightning protection by bypassing the containment liner in the lightning protection system and routing directly to the ground grid. This modification seems to have abated lightning influences beyond the Rod Drive system.

After the 1987 successive Unit One lightning trips, Modification M6-1-87-105 changed Unit One Rod Drive grounding such that cabinets were not separately grounded but grounded only at two points. This groundir.g scheme reduced circulating currents and is consistent with the Unit Two configuration.

Additionally, per Commonwealth Edison Engineering and Westlughouse recomendations, surge protection has been added to the RO over-voltage protectors and the trip setpoints increased on both Units. On 04-15-88, 2200 pr capacitors were installed across the base to emitter of transistor Q1 within the OVP devices on Unit One. This installation is equivalent to Lambda model LHOV-3 "$-option" and should relieve tow energy high frequency transients without activating the OVP device. On 2-16-90, Unit One OVP setpoints were changed from 26.5 Vdc to 28 Vdc.

On 10/21/90, Byron Nuclear Work Requests B80213 - 880222 were written to replace the Lambda LME-24 (+) 24 Vdc power supplies with Acopian model A24H1200 supplies. The Acoplan supplies will prevent unwarranted reactor trips with an automatic " reset" function. Upon activation of an OVP device, the Acopian supplies will cut out and re-energize in 50mS. The Acopian supplies will then provide control power to the still stationary RCCAs if the initiating over voltage condition no longer exists.

The Acoplan supplies are presently installed on the Unit Two Rod Drive System from the latest Unit Two refueling outage 02R02. The Unit One Acoplan power supply changeout will occur prior t; the completion of the the upcoming Unit One refueling outage BIR04. AIR

• 91-030 tracks completion of this activity.

i

r. ERLY10VSJCCVERENCISI Since 1985, the OVP devices on the power cabinet positive power suoplies have tripped Unit One four times during thunderstorms. Below 15 a list of the events:

1. OVP QAII UN11 ACIMA110NS LER 07-13-85 1 02 LER 85-068 07-29-87 1 09 LER 87-017 07-31-87 1 03 LER 87-017 08-19-90 1 09 LER 90-011 l

In all the above events, lightning caused a voltage surge sensed by the OVP devices which lead to their activation. Only the 1985 event caused additional damage beyond the Rod Drive system. Note also Unit Two has not experienced lightning induced reactor trips.

I (0716R/0081R-4) l

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I L1RERELLyJHLIEPML EltRL. TEXT CANTINILAJlpN F QIm_@&y.,LL i FACDifY HAME (1) DOCKET NUMBER (2) JfLEVdDERJ6) __Past L3L__

Year /// Sequential //

,j/p Revision (pppR BunktL-. lR HunktL

,J,yrok. Uni t 1 0 1 5 1 0 1 0 1 0 i d1 Sl_4 910 -

0 l_1 11 - 0l t Ljd 0F Llt TEXT Energy Industry Identification System iEIIS) codes are identified in the text as (XX)

In addition, similar events have occurred at Zion and Braidwood and throughout the industry. IE Inf ormation Notice 85-86, " lightning Strikes at Nuclear Power Generating Stations," included events at Zion and Byron and the corrective actions as a result of the 7-13-85 trip, G- CEf0NLMT FAILVELDAIA:

Component failure did not initiete this event, nor did any failures result from this event, l

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10716R/0001R-5)