ML20045A232

LER 93-008-00:on 930505,determined That Electrical Starter for Both Charging Pumps Inoperable.Caused by Program Failure.Administrative Controls Have Been Established to Ensure Minimum TS requirements.W/930601 Ltr

ML20045A232
Person / Time
Site:	Millstone
Issue date:	06/01/1993
From:	Deslandes K, Scace S NORTHEAST NUCLEAR ENERGY CO., NORTHEAST UTILITIES
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
LER-93-008, LER-93-8, MP-93-442, NUDOCS 9306090554
Download: ML20045A232 (4)

Text

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3 Usf.7Ila$sIeD[.'t$7 coEaY P.O. BOX 270 I$EE*It t*NEEc5$'o2can, H ARTFORD. CONNECTICUT 06141-0270 L 'T' Nutt, east rue.ea Ewg, comr;any

                                                                          -{203}665-5000 June 1, 1993 MP-93-442 1

Re: 10CFR50.73(a)(2)(v)(D) U.S. Nuclear Regulatory Commission Document Control Desk Washington. D.C. 20555

Reference:

Facility Operating License No. DPR-65 Docket No. 50-336 Licensee Event Report 93-00S-00 Gentlemen: Thic letter forwards Licensee Event Report 93-00S-00 required to be submitted within thirty (30) days pursuant to 10 CFR50.73(a)(2)(v)(D) any event or condition that alone could have prevented the fulfillment of the safety function of structures or systems that are needed to mitigate the consequences of an accident. Very truly yours, NORTHEAST NUCLEAR ENERGY COh1PANY

                                                                        .         -/
                                                              / p)hj W                . c o c.c._
                                                           / Ftephen E. Scl ace Vice Pre;ident - h1illstone station SES< KDD:bjo

Attachment:

LER 93-005-00 cc: T. T. N1artin, Region 1 Administrator P. D. Swetland. Senior Resident inspector, hiillstone Unit Nos.1, 2 and 3 G. S. Vissing, NRC Project blanager, N1illstone Unit No. 2

                                                                                     /

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                                                                                                                                                              < PE u_. - u s e ssicu VE5        ves cc :r s,e'e E (?EcT ED Su?MS$ TON c A*El                               NO                                                                                    l       l       l Ass r A:: m : s a mes. , e , an m g < we s g..maa wwmr m ae; On Ntav 5.1993 at lo45 hours with the plant at 1009 power and normal operation an engineenng evaluanon                                                                                               !

determned the electrical (tarter for the A", "B" (aligned to the facihty Z2 power supply) and "C" Charging  ; pump could bas e msufficient control power (120 voh AC) dunng a degraded voltage condition, and f ati to start the Charging pumpt The Charging pumps in quesunn have long lengths of cable which mcrease$, the resistance of the control circuit, and thus reduces the as ailable vohage f or the starter. This n hemp reported as an etent or condnion that could hase prevented the fulfillment of the safety funcuan i of structures or system that are needed to mingate the consequences of an accident. This condinon is only a concern durmg a degraded gnd toltage condition, which is lugher than the lesel two bislable inp setpoint for a . Lou of Nortnal Power (LNP). If an LNP uas to occur, which starts and loads the Diesel Generators, the control power returns to normal leselt and is no longer a conce:n. The unmediate response was to proside admmstrause controls which identihed the operatmg configuration that would ensure the rmrumum Technical Specincauons requirements for the Chargmg system are satished. Conuol circun modihcanons are bemg conudered to reduce the soltace drop of the cabbng which would supply suihcient voltage to the starter of the Charging pumps Similar Events: W 42 NRC Form 3% (649s

e - rac farm 366A US NUCLE AR REcaAToAv CoMMS5loN APPAov5D ovs rc 3160-0104 g-gg; ExPAES 4'30'92 Estimated burden per resoonse to comony with this

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                     . LICENSEE EVENT REPORT (LER)                                 Commer'tS regardPQ Durc"en estirnate to 1%e ReCo"d5 TEXT CONTINUATION                                       a,e neaarti vanagement eranes co-53cn u s. osaisar Repatory Commssion. wasnington. Dc 20555 anc ic toe Pape won Recuchon Pro,e:t 13150-OR41 off4ee of Management anc Buopet. Wasnm;: ton Dc 20503 F AcCTY N AME [1,                                          DOCKET NJ.fBER (2)                t rm typp.: p                        PAGE (31 ygg        SCADma6          P?'EICN PA.N904        MMMQ Millstone Nuclear Pou er Stanon Unn 2                                                                             -                ~

OF 013 0l 5l 0l ol 0l3 l3 l6 9l3 0l0l8 0l0 0l 2 TE AT d mye soa e s recscee use aad t ona! rac Fom %6A s) (17 ; L Descrmoon of Es ent On May 5,1993 at 1045 hours w th the plant at 100cc power and normal operation an engineering evaluauon determined the electrical starter for the " A~, "B" (abgned to the facihty Z2 power supply) and "C" Charging pumps could have insuffiaent control power (120 volt AC) during a degraded voltage condiuon, and f ail to start the Chargmg pumps. The Charging pumps m quesuon have long lengths of cable which mcreases the resistance of the control circuit. and thus reduces the available voltage for the

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Other control ciretuts are bemg reviewed to determine the adequacy of control power schage during a degraded bus voltage condition. There were no automatic or manual mitiated safet) actuations, or degraded grid voltage conditions. Therefore, there were no safety consequences frorn this event.

11. Cause of Event The root cauce of the event is procram failure. In 1976, Millstone Urut 2 experienced a degraded voltage and the Charpmg pumps did not start (start signal was generated and control power supply fuses wert found to be blown due to excessive current). To correct for the excessive amount of current, the voltage taps of the loadcenter transformers were adjusted to compensate for the reduction in voltage. j Howeser, dunng the recent review of the histancal records, the reviewer noted cable lengths were not ,

considered previoush, and thus the voltages at the starter could be lower than expected. Therefore, the + increase m soltage by adjusting the taps at the loadcenter transformers would not be sufficient to start the Charpmg pumps dunnp a denraded voltage condinon. A calcu! anon was prepared usmg the cable lengths installed for each charging pump applicanon. The calculanon has documented the assumpoons made for soltage drop due to cable lengths and has incorporated the results learned from bench testing of starter units of the same size as those used in the Charpmg pump control circuits. Conunumg activines are planned and the calculations will also be extended to determine if other components, that use smaller starter units, can be affected in a similiar manner. Ill. Anah us of Event Thic esem is bemg reported pursuant to the requirements of 50 73(a)(2)(vuD), wh ch  ! requires the reporung of any esent or condiuon that alone could have presented the fulfillment of the safety funcuon of structures or spiems that are needed to mitigate the consequences of an accident. This was determmed to be a reportab!e event, based on the review of the potential impact of a degraded voltap condition, unh a SI AS sienal present. The runnmg pump would not be affected, but the standby pump rna) not start due to insulhaent soltage at the starter relay coil. There were no automatic or manual truuated safety acutations, or degraded gnd voltage conditions. Therclore. there were no safety consequences from this event. This condition is only a concern during a degraded gnd voltage condiuon, which is higher than the level two bistable inp for a Loss of Normal Pow er (LN P). 11 an LNP was to occur, which starts and loads the Diesel Generators. the control power ieturns to normal lesels and is no longer a concern.

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                                                                                  'o'"30 0' co"*:# '*us t 50.0 hrs F orw a*C LICENSEE EVENT REPORT (LER)                                c'"omments reca d ng tween estimate ic tne Recorcs TEXT CONTINUATION                                    ano sems va,agemem erae e-s30t u s Nseies-Re;siatory cemsson W asNngton DO 20555 and to tne Fa:wwo a Recsetion Pro,ect (3150-0104) Of' ce of Marageme-! ano Bso;et Wasmrcton DO 20503 FAclL*Y N AME s 's                                      DOCGT NMER (2;                   J D N. 9 9tA 4A; PA3E Oi YE A.R uuusm              emon Millstone Nuclear Pouer Station Urut -                                         ol 5l ol ol oja l3 l5 9l3                                          OF
                                                                                              ? l 0l S           0l0 0l 3           0l3 Te xt e mye soa:. -s wec use miva Nac re r- aca si m IV.       Correcuo Action To avoid ihn potendal s:tuanon. admmistratne controls hase also been estabbshed to ensure the mmimum Techmcal Specifications requirements for the Charpmg system are satisfied.

The long term solunon is to install larger control power transformers or mierpo>mg relays. Both modificauons will reduce the voltage drop across the cabbng, and provide sufficient voltage at the starter relas coih The f ailure to mclude soitage drops due to caHe length resstance is beine corrected b perforrning addinonal voltage drop calculations on similar class IE equipment All class IE component which are pouered from the Motor Control Cemers u:ll be res neued and corrected as necessary. V. .\diud Informanon Nmilar LER'S: W42 There were no failed components aveciated with this esent. Ells Code Identifiers 1 120 Volt Control Power - ED-JC-GOs0

2. Charging Pump - ClbP-GOU 3 4 th0'-40 Volt I;udcenter Transformers - ED-XFMR-GO50 1

4 i l 1 r+n: w- n (6491

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