ML19220C444

Summary of 780829 Meeting W/Metropolitan Edison Co Re Proposed Fix for Potential Problem Involving Auxiliary Transformers

ML19220C444
Person / Time
Site:	Crane
Issue date:	09/06/1978
From:	Silver H Office of Nuclear Reactor Regulation
To:	Office of Nuclear Reactor Regulation
References
NUDOCS 7905010595
Download: ML19220C444 (41)

Text

{{#Wiki_filter:. g t d. W /jamafog*g UNITED STATES O +1 NUCLE AR REGULATORY COMMISSION s WASHINGTON. O C. 20555 SEp 6 1978 Docket No: 50-320 APPLICANT: Metrcpolitan Edisen Comcany (Met Ed) FACILITY: Bree ? tile Island Unit 2 (DII-2) SUBJECI': SL?t4\\RY OF NEETING CN AUXILIARY TRANSERMEFS Representatives of the licensee and his centractors met with members of the staff on August 29, 1978 to discuss the prcposed fix for a potential problem involving the auxiliary transformers at DE-2 reported in LER 78-35/IT. A list of attendees is enclosed. He licensee described the potential problem and the feasible alternative fixes, presented information to shcw hcw its preposed fix meets GLC-17, and discussed the reliability of the prcposed fix. His informtien is contained in the enclosed handout entitled Auxiliarr TransfoTrer Recort, dated August 25, 1978. Tne discur-ion brought out tLe follcwing points and questicas. 1. Acceptability of the prcposed fix (autcmatic 1 cud shedding) hinges on interpretation of paragraphs of GDC-17. The staff indicated concern over the complexity added by the fix, and that an additional transformer or a special centrol pcwer transformer would be preferred. Estimted costs and schedules for these altematives were discussed. He licensee stated that the addition of solid state relays du"ing the first reloading would eliminate the problem, and the staff agreed this was a meaningful point. 2. Possible failure of the automtic load shedding feature was discussed. He licensee explained its probability analysis in the Auxiliarv Iransfoner Report for the LCCA event, but agreed that safe snutdown (no LGTf in the event of loss of auxiliary transfoner and failure of the automatic Icad shedding scheme had not been addressed. 'letrcpolitan Edison will modify its report of August 25,1978 to address the concem ei safe shutdown after loss of one auxiliar/ transfomer and failure of autcmatic load shedding, and will submit the modified report en the docket by September 1, 1973. 07 l.1 - 4 / L. sa f ". ) 790501Of 6 .,h

-3 SEP 6 1978 2- 'lhe staff will examine the report of August 25 and indicate any furtlier concerns, and will revise the modified r ort expediticus ly. f! / m 'yk /(. ,, Rarle.f$ilver, Project Manager Light Whter Reactors Branch No. 4 Division of Project 5bnagement linclostires. As stated cc: See next page \\ l [. t s

s A Metrepolitan tdison (.i n. i' iny Ccs: George F. Trowbridge. Esq. Alan S. Rosenthal, Esq. C ha i rr'a n Shaw, Pi ttruan, Pot ts & Trcwbridge Atomic Safety and Licensing 1800 f1 Street, N. W. V. S. Nuclear Regulatury Cuir:ission Washington, U. L. Juu36 Washington, D. C. 20b55 fir. l. R. I lot rod Jersey Central Po e an! Ityht Compay Dr. W. Iteed Johnson, Meit er Madison Avenue at Punch Ucwl Road Atoiiic Safety and Licensing Morristown, New Jersey 07960 Appeal Board U.S. Nuclear ReguTatory Coixussion Mr. R. Conrad Washington, O. C. 20555 Pennsylvania Electr c Ccapany 1007 Broad Street Jerome E. Sharfman, Esquire, Member Johnstown, Pennsyl vania 15907 Atomic Safety and Licensing Appeal Board Chauncey R. Kepford, Esq. U.S. Nuclear Regulator y Cortunission C ha i rrian Washington, D. C. 20555 York Cor:naittee for a Safe Environment bbtropolitan Edison Company 433 Grlando Drive ATTN: Str. J. G. Herbein State College, Pennsylvania 16801 Vice President P. O. Box 542 Mr. Richard W. Heward Reading, Pennsylvania 19603 Project Manager GPU Service Corporation 260 Cherry Hill Road Parsippany, New Jersey 07054 Mr. T. Gary Broughton Safety and Licensing Manager GPU Service Corporation 260 Cherry Hill Roac Parsippany, New Jersey 07054 Edward Luton, Esq., Cha i r un Atomic Safety and Licensing 30ard U. S. Nuclear Regulatory Commission Washington, D. C. 205 % Mr. Gustave A. Linenber ger Atc, aic Safety and L icens ing Board U. S. Nuclear Regulatory Conaission Washington, D. C. 20555 Dr. Ernest O. Salo Pro f essor, Fisheries R esearch Institute, WH-10 College of Fisheries Uni versity of Washington Seattle, Washington 93195 1~ 1 Q7 4 f. I

\\ SEP 6 1979 AUXILIARY TRANSFORNER II. Silver NRC R. Tedesco NRC R. Lingel $bt Ed D. Ranft B6R F. Rosa NRC GPUSC D. Reppert R. Noll $bt Ed F. Ashe NRC R. Fitzpatrick NRC U. Potts 5bt Ed .I. Calvo NRC , t. i ;v

s SEP 6 1978 NEE MILE ISLMID ITUCLEA8 STATICII LCTIT II AU:CLIARY TRA?ISFORMER REPCRT Metropolitan.Mison Ccmpany ^ August 25, 1973 an l l. $.]o

CONTENTS I Background Information II Automatic Balance of Plant Load Shedding (Description) III Components Used IV Alternatives - D(feat of the Automatic Transfer Mechanism V Compliance with General Design Criteria 17 VI Reliability Factors VII Summary and Conclusions g / L. Iv -

1 Itackgrounu Information filed Licensee On May 9,1978, Metropolitan Edison Company (Met-Ed) Event Report (LER) 78-35/lT (see Attachment 1) with the Nuclear Regulatory Commission. LER 78-35/lT identified a potential problem involving the Auxiliary Transfonners at TMI-2. If one of the auxiliary transformers at TMi-2 were to fall, all station loads would be automatically transferred to the remaining transformer. Using a voltage study prepared by Burns and Roe (the project Architect Engineer), it was determined that with the off-site grid voltage at the lower end of its normal operating range, if the full unit load was carried by a single Auxiliary Transformer, losses in the systen would produce voltage levels low enough to blow control fuses on ES compoaents if these components were called on to start (as, for ocample, in the event that a LOCA would occur). At that tima, Met-Ed proposed several possible solutions to the problem, including the long term solution finally agreed upon (i.e. selective Balance of Plant (BOP) load shedding). On May 30, 1978, Met-Ed submitted GQL 0961 (see Attachment 2) to the Commission. This letter further explained the Auxiliary Transformer situation at IMI-2, and also identified which of the corrective actions mentioned in LER 78-35 would be taken. In determining the corrective action which would be most acceptable, Met-Ed attempted to locate NRC regulations and guidance which may have been published concerning tuxiliary Transformer and associated proble=s. Using the guidance available (i.e. the TMI-2 FSAR, GDC 17 and Reg. Guide 1.6) and sound engineering judgement, Met-Ed selected th automatic shedding of selected BOP loads as the best solut;on to the TMI-2 Auxiliary Transfor=er problem. As will be demonstrated later, the solution chosen meets all the require-ments of GDC 17. Recently, the Commission has raised several questions concerning the long ters fix which was chosen and installed. L l -] e r

m (Descrintion) II Auporatic Dalance of Plant Lead 3heddine ( Reference Dra>ing - attachment #3: Bia 3071 SH.Te) The intended functica of the Bal1nce of Plant (3CP) Lead Shedding Schene is to selectively trip sufficient 3CP loads so as to maintain sufficiently high voltages to ensure the starting of ES cc=penents should they be needed while one of the TMI-2 Auxiliary Trsnsfor=ers is out of service. Any one or six leck-out contsets from the individual auxiliary transforner protective relaying vill initiate the BCP Ioad Chedding Gehene. tic six con-follows: tacts nentioned above are identical for either transformer and are ac 1. 86/ATA-1 (AT3 M i - Auxiliary Transformer Sudden Pressure 2. 86X/3h-2 (38-2) - 230 KV Bus #k (#8) Differential Backup 3elaying 3 86X/nh-1 (38-1) - 230 <7 Dus #h (#8) Differential Primary 3elaying k. 86/ATA-2 ( AT3-2) - Auxiliary Transformer Neutral Over Current 5 86/ATA ( ATB) - Auxiliary Transfor=er Over Cur ent Differential 6. 86/ATA-P(A 3-P) - Auxiliary Transformer Fault and Time Over Current Closing of any of the above centacts will energize the EFT /1 relay. This relay has four centacts which are used in thin scheme (2 instantanecue and 2 time delay closing). If the three Cire Water Pumps CW-P-LA/13/lc are all operating and the Auxiliary Transformer fails, centact 5-1 of the EPT/1 relay closes after a 15 second time delay and thus trips CW-P-la. In addition, if the 3 remaining Cir: Jc:er Pumps (fed by bus 2-6) are all operating, contact 6-2 of the EFT /1 relay will also close 15 seccnds after the Ices of the Auxiliary Transforner, thus tripping Cire Wa'.cc Punp, un-P-13. Thus, the result of the closing of the 2 tine-delayed contacts cf relay EFT /l is to assure that no nere than h Cire Water Pumps are oterating, within 15 seconds felleving the loss of an Auxiliary Transformer. (At least 2h seconds is required in order for control fuses en E3 ccmpenents to blev. ) The instantrneous contacts of MPT/l initiate the lead chedding of a Cendensate 3ccster Pw:p (CCN-P 2), and a Ecater Drain Pu=p (ED-P-1). Dependant upon the operating pu=p lineup (2 of 3 are needed for 100% power), the EFT / l instantanecus centacts close to energize an auxiliary relay as follows: Punts Bunnine Auxiliary Relav Enerciced Puno ~'ritted CO-P-2C L CC-P-2A CO/CA CC-?-2A CC-?-20 i CC-?-23 C0/03 CO-P-23 CC-?-2A & CC-P-23 CO/A3 CC-F-23 ED-F-lO L ED-F-la D/CA .D-?-1A ED-?-1C i ED-P-13 ED/03 EJ-P-13 n gs ED-?-1A & E-F -13 ED/A3 q9 jgU E /T-13 sL s

~ . The auxiliary relay:: also pe.for= the following functicn: 1. CC/CA prevents CC-P-1A frc= tripping CC/C3 preverts CO-P-13 frc= tripping CO/AB prevents CO-P-13 frc= tripping This 1) encures that the :Ondensate pumps ccatinue to operate, supplying adequate pressure /flev and 2) prevents the backup condensate /cendensate booster pu=p frc= starting. 2. HD/CA prevents backup pu=p ED-P-13 frc= starting ED/CB prevents backup pu=p ED-P-1A from starting ED/A3 prevents backup punp ED-P-lC fre= starting Thus, the installation of this lead shedding sche =e prevents u;cn the Icss of an auxiliary transfor:er, the voltage at the safety related buses from decreasing to a level which =27 cauce the inoperability of safety related leads. By tripping the above ECP leads (i.e., 2 Cire. 'later Pu=ps,1 Ccndensate Ecoster and 1 Eeater Drain Pu=p) upco less of an auxiliary transformer, the voltage levels vill re=ain high enough to safely operate all safety-related leads if these loads veuld be required to operate. In addition, the trippirc of a Condensate Booster Pump vill cause a trip of one of the =ain Feedvater Pu=ps. This causes the !CS to initiate a plant runback to approximately the 60% power level at a rate of 50% per minute. The installaticn of this systes provides a reliable nethed of ensuring the voltaca levels of the safety related buses are adequate. As discussed above, thi ucheme can be initiated by any one of six protective relays for either auxiliary transformer, thu; pecviding backup for the initistion function. All leads not autc=2tically tripped as discussed abcVe, vill bc aute=atically transferred to the remaining Auxiliary Transforner upcn the de-energi:ation of the failed transfor=er. 4 1 i t. /J

III. Cemeenents Used Manufacturer Ccmponent EPT/l Relay Agastat Mcdel 7012 FCLL Westinghouse Medel M6-6 Auxiliary Relayc CO/CA CO/CB CO/AB HD/CA HD/CB an/A3 Transformer Lock-Out Relays Electro-Switch Corp. 86 / ATA-P ( AT B-F) Series 24 Lcck-Out Relays 86/ATA-1 ( ATB-1) 86X/B4-2 (SS-2) 86x/B4-1 (38-1) 86/ATA-2 (ATB-2) 86/ATA (ATB) All compenents used in the Automatic 30P Load Shedding Scheme are of the same quality as the of f-site power system (including the Auxiliary Transformers). 1,. G nq u jt.

IV. Alternatives - Cefest c' 9e Autc atic Transfer 'fechanis: Mring the course of discussicas with NRC staff centers, the feasibility of solving the prcble identified in LER 78-35/lT by defeating the mechanism which automatically transfers leads to the remaining Auxiliary Transformer when ene Auxiliary "'ransfer er fails was discussed. !!et-Ed considered this as a possible solutien to the prcble=, but decided against it for a number of reasons. If the transfer rechanisms vere defeated, 3 cire. vater pu=ps (instead of

2) vculd be tripped. This less of cire. vater flow veuld cause a turbine trip due to decreased cendenser vacuu: (this veuld not occur with enly 2 cire, water pumps tripp % vith a 15 minute ti=e delay).

The turbine trip eculd cause a reactor runback. '"hus, a transient ecnditien vould be intro-duced in both the primary and secondary syste=s. In addition, defeating the Aute stic Transfer vould eliminate the use of the condenser as a steam dunp. It is cur opinien that transients of this nature should not be introduced unnecessarily. Thus, a reductica in power to 600 (as veuld be introduced by the installed solution) is preferable to a unit trip. If the Autematic Tr1ns fer Mechanis: vas only partially defeated for any of the 30P Ll6CV Suses, the partial transfer eculd not be acec plirhed in such a manner as to both prevent a unit trip and trip sufficient leans to main-tain satisfactorily high voltage levels at the emergency cceponents. As vill be demonstrated later, the Aute atic DCP Lead Shedding Scheme is hi hly reliable and therefore because the Sche =e eliminates an unnecessary 6 unit transient, it is preferable to the defeat of the Autc atic Transfer Mechani:n. A second alternative which was censidered and rejected as a long tern sc1' tion was ad.inistrative centrcl of unit leads to levels which could be carried by a single Auxili1ry Transformer without jeopardizing the starting of E3 compenents. '"his veuld require lief ting unit cunput to approxi=ately 50%. For obvicus reasons, this solutien was used as a " temporary fix" caly. Both of the above centicned solutiens were presented in LIR 78-35/1T as potential solutions t, the Auxiliary Transfer:er Proble-1. The 9:ird and final colutien which was propcaed in that LER is the soluticn valch was eventually installed. M L L l.s a

V. Cc=cliance 'Jith Genersl Oesien Criteria 17 In order to de=cnstrate ec plete ec:pliance with GOC 17, ve vill, in this sec tica, review that Gener11 Cesign Criteria, and explain how ve meet the varicus requirements. General Design Criteria 17 - Electric P0ver Syste:s re2ds as foll:v : "An ensite electric pcuer system and an offsite electri: power systen shall be provided to per=it functiening of structures, systers an.1 cc penents i=portant to safety". At TMI-2 both an ensite pcver syste: (diesel generators) and an offiste power systen (supplied thrcugh the Auxiliary, Transformers) has been provided. Either of these syste=s is capable of providing adequate pcVer to assure the functiening of :afety related ec:penents. "The safety functicn of each syste: (assa:ing the other syster is not functioning) shall be to provide suf'icient capacity and capability to assure that (1) specified acceptable fuel design limits and design conditiens Of the reactor coolant pressure boundary are not exceeded as a result of anticipated operational eccurrences and (2) the core is cooled and containment integrity and other vital functicns are main-tained in the event of postulated accidents." This requirement of CCC 17 is cet by the current design at T!C-2 in that the ensite power syste: and the offsite power system are cufficiently independent to assure that if either syste: fails, its failure vill not cause the failure c' +5a - aining system. In Order to jeopardize the independence of these power systems, and their ability to start IS cc=penents, both an Auxiliary Transforce-

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+he Autcratic Lead Shedding Scheme mu:t fail to cperate. As vill be seen later, the probability of these failures cc urring sinultanecusly is extre ely re:Ote. "The ensite electric pcVer sources, including the tatteries and the ensite electric distribution system shall have aufricient independence, re-dundancy and testability to perfor: their safety fun ticas 1:su ing a single failure." Neither the original proble=, nor the installed :01ution affect the independence, redund1ncy Or testability of the casite power syrten-The Aute atic 30P Lead Shedding Scheme vill not prevent the Onsite pcVer sys-te: frc: perfor=ing its safety function, assuming a single failure. " Electric Power frc the transmission network to the ensite electric disbribution systen chall be supplied by two phycically independent circuite (not necc-mrily on separate richts-of-way) desig".ed 2nd to mininine to the extent practical the likelihoci of located s0 as their cicultanecus failure under operating and postulated 2::ilent and environmental conditions. A svi;;hy1rd cctron to both ; nits is acceptable." These requirement cf CCC 17 are met as indicated in Section 8.2.1.L.l. o f the 2C-2 FSA3 ( atta-* " - V5). The Aatematic ECP Lead Sheilim' Sc heme e dees act affect the ;h731eal ceparation or independence cf the 2 cff ite power cir:uits. na 4 r u/ L I u.

. "E1ch cf these circuits shall te designed to be available in sufficient ti=e folleving a loss of all Onsite alternating currcnt pcVer supplies and the other offsite electric power cir:uit to assure that sp?:ified a::eptable fuel design limits and design cenditicas of the r:20ter ecolant pressure boundary are not exceeded." This is the pcrti:n of 0:017 which is = cst dire:tly applicable tc the problems identified in 1E3 78-35/lT. Theref:re, this is the pertion of GCC 17 which re:eived the = cst attentien in determining the best colution to that problem. The Autceatic ECP Lcad Shedding Scheme vill, ty tripping selected ECP leads up:n the less of an Auxiliary Transformer (cne of the offsite pcVer circuits), assure that sufficient and reliable pcver 13 sup-plied to ES cc:penents to allow their Operation even if the ensite p0ver syste: 11:0 fails. "One of these circuits shall be designed to be available within a few seconds following a los;-of-coolant a :ident to assure that core ecoling, containnent integrity, and other 'rital safety functions are niintained." The TMI-2 design is for both offsite pcVer circuits to te available following a 1CCA to assure that the above centicned safety functions are raintained. H0v2ver, in the event that the less of an Auxiliary Transformer c: curs, the Autenctic EOF Load Chedding Scheme assures that the remaining Auciliary Trans-f:r er vill supply sufficient and reliable power to all ES cc penents to ac:ure that the above centioned safety functienc are maintained. "Proviciens shall be included to =inimize the probability of losing electric pcVer for any of the remaining sources as a result ef, or coincident with the less of power generated by the nuclear unit, the loss of power fr:: the transmission network er the loss of sever frcm the Oncite electric pcVer sources." Neither the loss of power generated by the nuclear unit, nor tha loss of pcVer fre: the ensite electric power sources causing the loss of the re-msining power sourcen is an is ue here, nor is the ec=plete loss of Off-sita.over sou eca. Cnly the 1 cc cf an Auxiliary Trsncforecr preventing r pov:r from reachinc E3.capencata is an issue, and as was indic.ted above, the automatic ECT La1d Shecling Scheae has been inctalled to prrtert this chain of events, by selectively tripping en0 ugh ECP losds to assure that ! control fuses en the E3 cc ponent: are not blevn. i/I ^ n) 7L \\'.J ... 4

VC Reliabilt r a c t u r s. Recent discus; ions with membera of the NRC staf f have indicated that the reliability of the Automatic BOP Load Shedding Scheme is a primary area of c onc e rn. Met-Ed has tested this scheme and found it to operate reliably. A number of factors contribute to the overall reliability of the scheme. A. As was menti med in Section II, any of six lock out relays per auxiliary tt sformer may initiate the SOP load tripping sequence. In addition i tse six relays not only initiate the 30P load tripping sequence, but 1so are used to open the breakers which energize the tr ans f o rme r. herefore, the auxiliary transformer will beccme de-energized . result of energizing a relay which is in turn used to initiate > B0P load tripping sequence. Therefore, if the trans-former beco de-energized, the 30P load tripping sequence must be initiated. B. As has already been indicated, the components used in the Automatic BOP Load Shedding Sche =e are all of industrial commercial quality. Although these acmponents do not carry the same " pedigree" as do safety-grade components, there is essentially no dif ference between these commercial quality components, and safety-grade components used elsewhere, in the industry. In addition, these components are located in areas which are not expected to see adverse enviren= ental conditions (such as a LOCA environment). C. In addition, at the first scheduled refueling outage a Solid State Undervoltage Protection System (SSUVPS) will be installed. This SSUVPS will act as a "back-up" for the Automatic B0P Load Shedding Scheme. The SSUVPS will perform this back-up functica by detecting the undervoltage condition which wculd lead to the blowing of control fuses on safety related ccmponents. h* hen such an undervoltage condition is detected the SSUVPS will attempt first to transfer the load to the f ailed auxiliary transf ormer, because this will not be possible, the emergency loads will be supplied by the on-site pcuer sources. D. The reliability of the Automatic BOP Load Shedding Scheme is further enhanced at the present time by a manual "back-up". Emergency Procedure 2202-2.8 requires, upon the loss of an auxiliary transformer and the failure of the Automatic BOP Load Shedding Scheme, that the operator manually trip the loads which the Automatic S0? Load Shedding Scheme should have tripped. In addition, Met-Ed has undertaken to determine quantatively, the reliability of the Automatic BOP Load Shedding Scheme which has been installed. The worst design basis condition only exists when the following events have occurred simultaneously: 1) An Auxiliary Transformer has failed,

2) The Autcmatic BOP Lead Shedding Schene has failed. an;

3) A LOC.\\ har occurred.

In order to determine the probability of these events ocet rrins ^ si mu ltaneous ly, the tern simultaneously must be defined. For the purpose ef cur eciculatiens, events will be ennsider_d to hr. occurred si titaneously if they u.' e occurrec itnir tha came cae minute rcr iod -

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__ The probability of a LOCA occuring (PL) is 10-4 per year ('n' ASH 1400). The probability of a Auxiliary Transformer failing (P ) is 1.445 x 10-6 A per hour (IEl:P. 500). The probability of the Automatic BOP Load Shedding Scheme f ailing (Fg) is 3.88 x 10-* per hour (IEEC 500). Che reliability of the Automatic BOP Load Shedding Scheme has been of the scheme. determined using the reliability values of each component These reliability values have been taken from the recc= mended valt s found in IEEE Standard 500. The probability of f ailure f or the Automatic B0P Load Shedding Scheme was determined by assuming the failure probabilities for all components which would prevent the scheme from completing its function. In addition no credit has been assumed for partial operation of the scheme.) each of Because the three eventa mentioned above =ust occur " simultaneously" these probabilities must be converted to probabilities on a per minute basis years and 1.66 x 10-2 hours). and then factored tcgether (one minute is 1.9 x 10-6 (1) 1.9 x 10-10 per minute PL = (10-4) (1.9 x 10-6) 2.4 x 10-8 per minute (2) (1.445 x 10-6) (1.66 x 10-2) = PA = 6.4 x 10-6 per minute (3) PS = (3.38 x 10-4) (1.66 7 10 2) = The probability of these events occurring si=ultaneously (P77) is: P, = (P,)(P3)(Pe) = 2.91 x 10-23 cer minute (4) Met-Ed This may be cc pared with the reliability of the off-site pcwer system. has found that the probability (Po) of the off-site power grid decaying to the point at which of f-site power could not be used to mitigate thein cperation is 3 x 1 consequences of a LOCA ut th two auxiliary transformers this would not be a problen unless a LOCA.securred per year. Because "st=ultaneously", it must be treated in the same canner as wa; the above-mentioned s'ituation. (5) P = (10-4) (1.9 x 10-6) 1.9 x 10-10 per minute (6) g 5.7 x 10-13 per minute P = (3 x 10-7) (1.9 x 10-6) = O Pn, = (P ) (Po) - 1. 08 x 10-22 per minute (7) 2 As demcastrated above the probability of a simultaneous LOCA, auxiliary transformer failure and Autcmatic 30P Load Shedding Scheme failure is less than the precability of simultaneous loss of of fsite power ar.d LCCA by a factor of nearly '4 It ic therefore concluded that the 30P Iced Shedding In Ecnene does not ice eace the reliacility of the offaite power cycten. fact, becance t"c uccurrence of a LCCA is ccc=on to both of the above calculations it can be eliminated. This would allov 1 cc= paris:n of the

bability cf ico:inc offsite power, with the probability er the "si=ultanerus" of an Auxiliary Transformer and the Autenatic EO? L:ad Shedding Scheme.

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' Probability of loss of of f site power PLCp = 5.7 x 10-13 per minute (8) (EQ !6) Probability of simultaaecus loss of Auxiliary Transformer and loss of Au te=a t ic J0P Load Shedding Scheme (EQ 12 and #3) PAT BOP " (P ) (P ) = (2.4 x 10-8) (6.4 x 10-0) - 1. 3 x 10-13 (9) A S per minute the combination of the Auxiliary Transf ormer and the BCP Load Shedding

Thus, Scheme is less likely tc fail and therefore does not decrease the reliability of the offsite power grid. Because the offsite power systes has been found the to be acceptably reliable for use as the preferred power source, Automatic 30P Load Shedding Scheme is also acceptably reliable. Therefore, the reliability of the pref erred power source is not appreciably af fected g

I by the installed scheme. CONSERVATISMS IN FRECEEDING ANALYSIS: l 1. The reliability of the Automatic BOP Load Shedding Scheme resulting from ite=s C and D above were not included in the determination of Ps. l failure of a component which could inhibit any portion of the 30P 2. The Load Shedding Schece was considered to cause a complete f ailure of the Schene. (i.e., no credit was taken f or partial Scheme operation). 3. The method for calculating PS (i.e. summing of individual component f ailure rates) yields core conservative results than would be expected for f ailures of the system as a whole). i f a I I -d '/ l, t i o

v tI Summarv and Conclusiens As has been demonstrated above, Metropolitan Edison Company has acted respcasibly in referencing the appropriate NRC guidance for meeting Electric Power Systems Design Criteria. All applicable NRC guidcnce (i.e. CDC 17 and Reg. Guide 1.6) are complied Vith by the installed automatic COP Load Shedding Scheme. Therefore, as has been demonstrated through probability analyses, the current TMI-2 design is acceptably reliable. Further, because all applicable design criteria are met, and because the reliability of the preferred power source is not appreciably dif ferent from that under which the plant was originally licensed, no Licensing precedent is set. For the reasons mentioned throughout this report, Metropolitan Edison Company concludes that the installation of the Autcmatic 30P Load Shedding Scheme does not involve an unreviewed safety question because-1) the probability of occurrence or the consequences of an accident or malfunction of equipment important to safety previously evaluated are not increased; 2) the probability for an accident of a different type than has been previously analyzed is not created, and 't ) the ma ry In of c.i f et y w de f ined in the bases of the Technical SpecIflcatlonn is not reduced. Therefore, we believe that the automatic BOP Load Shedding Scheme is the only solution which is required for the problem which was identified in LER 78-35/lT. ') L s ~. < /Y

.y .emen: n. - -- --- ,,,' y,.f-~ fQ r.::,, ~... ~,.am, u ' ( '/ METHOPOLITAN EDISON COMPANY 7 s.. POST C.'8tCE BOX 542 REACING. pef.NSYLVANI A 19503 TELEPHCNE 215 - 5:3-3501 May 9, 1978 GqL 0890 I Mr. 3. H. Grier, Director Cffice of Inspection er.d Enforcenent Regicn I U. S. Selcar Regulato./ Cc==issien 631 Park krenue ing or Prussia, Pennsylvania 19hC6 2 ear Sir: Three Mile Islar.d Ifuclear Station Unit 2 (TIE-2) ( Cperating License !io. DPR ~l3 Enclosed please find Licensee Event Report 78-35/1T vhich is : utzf.tted in 2:0:r?.ance with Secticn 6.9.1.8.h or cur Technical Specificaticas. Sincerely, c. :, .2. O. '.'c'..m J. G. Herbein Vice President-Generation JCH : ?JJ.,: cj g

Enclosure:

LER 73-35/1T Earley Silvcr (?!EC) cc: j - )(. ') I ~ - A,

C,'iTROL SLECK: l l lM ! l l (PLEASE PRINT ,PE ALL REQUIRED ITJFORPtATION) I W 6 b im !: la 11 l2 Igo lo I -i of of o 01 c i -1 o f o l(?) L l II :. l il 1[h[ [ lg e i 7 8 9 LiCEP.5EE COOE le 15 LICENSE NVP.18!R 25 26 L&GEP45E TYPE 40 53 CAT sa s0).c E [L_jhl 019 l0 10 IO I7 I9 10 @l0 ls 10 l7 I7 18 l@lol510!ol7l8l@ i a so si COCxET suvata 6a 62 EvtNT oATE 24 75 a EPoR i CAT E sa EVENT DESCRIPT1CN AND PROSABLE CON 3ECUENCES L o,L2J lWile in "ede 5 the TMI-? a-chiteet encineer (Burns & Ree) notified the Licensee t..2t] Isin le auxilia y transfemer eteration vithin the nor=al operating rance of the s rid I ra a o i4 19111 not provide sufficient voltage levels for operatien of the h80 V =cter centro 11er-( !o s (durin perieds of peak unit auxiliary de=and. Because the unit has not been operated ] lat a rever level reOuiring =aximu= unit auxiliaries, t_here was no potential for any l o s l adverse effect en the health and safety of the public. [ o 7 u,a i bG / 3 9 SY3TE M CAUSE (AU$E CCV7 VALVE COCE LOC 2 SL8OOCE COMPONPNT :COE SUS CO c t' SUSCOCE I z iz lO L4J@ LZJ@ I z i z i z i z i z i z l@ W@ I zi @ iDis 8 9 10 13 12 IJ 14 19 23 S E OV E N TI A L CCCURRENCE RdPCRT R EVr$1Cid tg e,pg EVENTYEAR REPCR T NO. CODE TYPE Na @ ad.'.g I7181 [ _J lof3151 [d loIlI lT I I-I LJ ._ 21 22 23 24 25 27 23 23 JG 31 32 A CTIO.N Ft. TUR E -EFFECT SHUTCOWN ATT ACHM E N T NP A D-4 PRIME COP.P. CD).!PCN E N T TAKEN ACTION CN PLAT 47 IVETHCO HOURS SUSW TTED dCEt >Us. SUPPU E R MArdVFACTURER ( l XI@[$h I Zlh lZlh l0l0l0l l W@ lNl@ lzl@ lzl9l9l9l 3J 34 35 26 31 40 48 42 43 44 47 causE OESCRIPTION ANo CCARECTIVE ACTIONS h l Single transfer er creration voltage studies corducted by the arOhitect engineer afterl i o Ii lecerleting the voltage cetiniOatien studies, shcued that within the normal crerating i TTl Irange of the grid (232 to 238r/) a single auxiliary transformer can't provide adequate i l volta:;e levels to surpert cperation of the unit Engineering Safety Features and bilaneq 3 g i of pir. auxilicries. (Continued) ers 3 0 STATUS

• A POWE R CTHE R S TA TUS ~

METHCO CF F AC:UT v CIS00VERY DISCCVE R Y OE5; Af' TIC's .2 is }Bl@ JOlolCl@l NA l lC l@l Notificat, ion by AE [ I 8_ 9 M 12 13 44 45 45 go ACT1vtTY 00'ATENT 8TELEASED ':rO!LE/5E AMOUNT OF ACTivtTY LOCATIO*: OF RELE ASE f f UA l 1 l6 l* l UA 8 3 13 11 44 45 go PE A50.' E L E XFOSUAIS r?V*.' 3 ? 2 TY8f C E $CTU P TIO*4 l l UA 0fQfO 7 E 9 Ii 12 13 33 P E R ~ ?:'. ? ; n ~;;u m E 5 r u' * * ! = O E scaiP TIO'J f UA f 9 I l '- .v g3 6 0 ti

7

~' n ") LO!3 O F '.;"I D CJ t.05 TO FAC:LITY., ^ TV'E CLSCPvTiO 4 } g, g j .f wJ l r bf ur i gg 2 9 r; VN; t of .mP r:T; l f I I I i IIIIll l!f - j') .s o n.,. y 2L5 0'G-3 ] _ [. lbO e,. ' L P 4 + : L H.. _... - P..t

!TARRATIVE TO ACCCWA:.T LER TE a l i On t'ay '.,1978, the results of the sir.cle auxtlf ary transforner vo] tage study were received fres the Architect Encineer (Burns & Hoe). The voltage values \\ calculated for the h80 V !!otor Contral Ceaters, for a normal voltage of. the ~230 ?.~/ grid vere below the required h07 V AC necessary to assure safe operation of the 2gnetic centrollers and prevent control pcVer fuse bleving. n:ese voltag, values are based on having the =axi=us unit auxiliaries in service during the su==er c:cths, with all circulating vater pu=ps in service. This ites was determined to be a violation of Technical Specification 6.91.8.h, in that the Safety 1 valuation Report states that each unit auxiliary transformer is sized to.:vry the unit full lead auxiliaries and the energized safety features auxiliaries. Since the E3F bus povered f.om the inoperable transfor=er is designed to fr.st transfer to the remaining transfor=er, the potential to disable both IST trains due to control power fuse blowing exists. Follev up stu: lies ave verified that by autc=atically shedding selected Balance S of Plant loads upon auxiliary transfor=er failure, adequate voltage levels are available at the h80 V Motor Centrol Centers throughout the nor=al operating range of the 230 K7 grid. 4 I 1 t i I e 4~ 9^ l (, l j 6- .)

• 6 MW e qq M q ee agg an.e
• mm 68 g

'r' t Cause Descriotien and Corrective Actions (. to assure adequate voltage level, one of.follo. ting corrective I.c orde: actions vill be taken: A) the unit vill not be cperated above a pc.ter level ec=patible to safe single transfor=er operatica; B) selective balance of plant load shedding vill be installed; C) or the autc=atie bus transfers to the other auxiliary transfer =er for designated bus -ill be disabled. t iL <.) W

.r / Attachment #2 I ~j..,=Jz m.,r s s ai .e.. l 7=, ~~. - u i i I METROPOLITAN EDISON COMPANY us.m oc:

n.uuauc u r.u xw.,cru r:n., /!

l PC3T CFFICE BOX 542 REAQiNC. PENNSYLVANI A 19603 TELEPHCNE 215 - 9:3 2801 l'sy 30, 1973 GQL C961 Director,:Tuclear Peactor Regalatica Attn: Mr. S. A. Varga, Chief Light Water Reactors 3 sCch :Io. b U.S. :iuclear Regulatory Connissica Washington, D. C. 20555

Dear Sir:

Th.ree Mile Island Ifuelear Station, Unit 2 (TFC-2) Operating License tio. DPR-73 Docket No. 50-320 In respense to questiens raised by Ftr. Harley Silver of your staff, enclosed please find infor atica ecccerning the potential problem as-sociated with the loss of a. auxiliary trar.sfor:er at CC-2. Sincerely, Sii;ned J. G. Herbdd J. G. Hercein Vice President-Generation JCH:RA.L:cjg ec: Directer of ::aclear Resetor Regulatien Attn: Harley Silver Light Water Reacter: Bre.nch 'Io.,4

• ~

U. S. : uelear Regulatcry Ccamissien Q) Washington, D. C. 20555 Attach ent e G. '".. ro u ght e n C. W. Smyth m bec: ,,_s. e.a u.4 4-s J. P c*a4 5 - + oo.o .3+<+.e R. M. Klingacan u p. n..-- 4, 'I* r annis (GPUSC) R. J. Stevens' 4,_, r,,,., A u .,,,,, c e. co Park Avenue ,3 - *- " - - - - - .ev ,, y . ~-, 1 L. L. lawyer .c e r.,..... ,,nge,. gg; gecretary R. a,. u. A. Chsiman GOR 3 T:C-1 C. P. ille. c.cc c c,r.(a y,l, c c"x D. G. Mitche;1* Chaine.n PCRC 7 C-1 ,n"-,.., a-Chairman PCRC T'C-2 3 C* A :lixdorr p. . Mcx 1200 . P ,,,.u.an1cn TMI GCRB Secreta:/ ^ 2," ' _ - ", <......".,,,a, %..,.,,

• tC-1 FCRC Secretary

.Ly.:hburG, u T'C-2 PCRC Sec retary' r: 7 - ew4 p-g nas,;. Sla.c,or L-

3332, pi-.._.n, Pc.= c

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9 ~ 1 AUXILIARY ""31d SFCFlER CC:!CEF IS P C-2 ) on :by 3,1978, Metropolitan Idisen Cc=pany was notified by the OE-2 Architece Engineer (Burns i Ece) that a potentie.1 proble: existed with the CC-2 Auxiliary Wans fc=ers. The results of a Eurns cnd P.oe voltage study indier.ted that vith caly cne auxiliary transformer in operation and with the plant at full lead, tne bu.s voltage vould be reduced to the extent that, in the event of a LCCA, scne safety loads veuld not be picke:1 up. This could result in the bleving of centrol fuses en the safety-related cc=ponents. Met-Ed found this situation to be reportable in acecr:iance with Section 6.9.1.8.h of the OE-2 Te:hnical Specifications. Therefore, en May 9, 1978, Met-Ed subsitted Licensee Event Report (LIR) 78-35/lT to the Cc=- =ission. This LER identified the potential proble= and offered several possible corrective actions which =ight be taken, these included: a) The unit vil.1 not be operated above a power level ec=patible with safe single transfc=er operation b) selective talance of plant lead shedding vill be installed c) or the autc=atic bus transfers to the other auxiliary transfo =er for designated buses vill be disabled. Since May 9, 1978 vhen these pctential solutiens were sub=itted to the :rPC, Met-Ed and Burns and Roe have been verking to deter =ine which solutien best meets both the safety requirements and yet allows DE-2 to operate nost satis-factorily. '"he solutica reached is as follo'c : I. Short Te = C0rrecticn Action: The Unit Auxiliary Lead vill be maintained less than er equal to h8 :~.1 whenever h RC pumps are in operation. '4 hen enly 3 RC pumps are in operation, the lead en the 4160 V buses vill be limited to 20 r4 These loading values (h8 lf1 and 20 IG) have been analyzed (for single auxiliary transf =er operation) by Burns and Roe and found to be

• aining voltage levels sufficient to pick up acceptabla N

safety-related compenents in the event of a LCCA. Maintaining unit loadings at er belev the levels indicated above has been ad=inistratively accc plished through precedural changes to the T'E-2 Unit Sta.M up 2nd Power Cperatien precelures. Essentially, these procedural changes allev SE-2 to startup and escalate power to the point at which the above-centioned loadings are established. L:adings cEthe Aunliary Transfc=ers rr.:i on the h160 V buses are conitored in the OC-2 Centrol R:cm. Cperation of additienal equipnent and the fur-ther escalation of pcVer level are then prohibited. The Burns and Rce 7c1:ase Frogra der.onstrates that with unit leadings !=' b g.t k s j l. sJJ J

,o a I\\ limited to the valuen =entioned above, the loss of an auxiliary transfor=er, and subsequent transfer of load to the remaining trans-forner vould result in voltage levels sufficient to pick up all safety-related cecpenents necessary to citigate the censequences of a LOCA, and ec= ply with General Design Criteria 17 of 10 CFR 50 Appendix A. i { The Burns and Ree Voltage Progra= used in =ating these deter =inaticas is the sa=e progra= vhich was used for the TMI-2 Voltage Opti=icatice l Studies. The accuracy of this program vas verified thrrush field measuresents at that ti=e. II. Lenz Term Corrective Action In order to operate safely throughout the normal grid range (232-23SKV) l a 1ccgters correctic'n action of selectively tripping plant leads upon the loss of any Auxiliary Transformer has been develon ' A system of relays vill be installed which vill ensure that vh* .er an Aaxiliary Transfer =er becc=es de-energiced, the following plant loads vill be tripped: A) 2 - Circulating Water Pumps B) 1 - Condensate Booster Pu=p C) 1 - heater Drain Pu=p Burns and Ece has perfor:ed an analysis (using the above-centioned voltage prcgra:) to shov that tripping the above-centioned leads vill provide the following h30 USS bus voltages: pSO V USS* Voltage (1 Auxiliary Transformer Operation) Crid '!citare Normal LCCA (Prior to Last L'S Conocnent: S t ar'. in a ) Post LOCA 232 '{V h26V hilV kob V**

• 'This is the voltage level after all ES cc=penents have started.

h07V is needed for starting ec=ponents, however, cc=penents vill safely operate at a much lever voltage (363 volts). As can be seen frca this chart, the voltage available for starting the last safety-related ec=;cnents (hll V) exceeds thTe voltage required for starting those eccpenents (h07 V). Also, the voltage available after all ssfety-related cccponents are started (hCk V) is far in excess of the voltage needed to keep these ec ponents operating (363 V). It is hoped that these long ter= corrective actions can be impla=ented within the next six weeza. "he rrsult cf tr nn:nc the above mentioned loads upon the de-energicatien of an Auxiliary Tranaf,rmer vill te an autcratic reduction of unit pcwer to approx'- 'M y 50$. (This vill be acecaplic"ed autccatically by the ICS systen due to the trip of the Ccadensate 3 coster Pu=p.) G. 9 '. I. s I l. s., w

,e 3-It should be noted that the short tem and long term corrective acticna which are being adcpted, vere presented as corrective actions A ' ' " '- LIE 78-35/10. It is our belief that thrcugh our imple=entatien of the above-mentioned short tem and long tern corrective action, TMI-2 cenplies with 10 CFR 50 Appendix A, General Design Criterion 17, and with the TXI-2 FSAR. O e 41 eo y O 4 )L Id' AG

'// O ee e S o c k.N o. Fay No. O Ca.c ';o S h._: t - cf Oraw.~ ' b. ay l' N O'U r W F O.. cu A nnrove7 ,u : e.r L'. E u c v T r: s ' 01 u_G r : r, c.:. M ce L:ir o; c w= Au 7.? s y c e r? u 9 r> r -_. ~ ~ v l G 1tA G L: l TI M E. D E LA7 3 mMD w

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T R t P r L.a c k.' cur H 0-P-I S S Lo cic c ra l2 Tn M C, --+= ' ' :.L : :. /: C:' _I m V 4 ~ Te.)9 C.W-k-lA C ,f-. CWeO. f C C J ?! t11 Al s ; ,. 1 I

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u t : : :... .:. 2 : u ~t d n :. - -. h '.'.. s. s.,... .: u:. Figure i. 2-1, the Of f sita scur:es of ausiliar t pcwer f:: :he uni: As shcv 00 s u r. L.* a ^. '.~. v -. =.. ~.'- a:/ ..a.3 ..._4 a- '.\\ a. '. ' 3 "... '.- *..- a.- ~. _- 2. c. e ^. o ^ o 1 =- Sus !. and Bus 3, :s s ec-ively, ci :he *.20 'c subs:2:1:n. The ~ 10 'cr s ub-2..a. .ae,< ..-._,e 2.., 2 u.eay,._a 2 a.ua : g u.e_a :. +4... _. a _,. u. a _, a..

s. n _e, e... e_.

4 2,..2 ._.a.y se c n e.e;. a.f. 2 .2 2_. a p..w. e., u.,.-,.. '*c t: age 's s:cpped vn.:.M bus may be c:csidated a pref e::ed scur:a. az.. e. <. e. e g. n. a.e ~..,.s.. e > _<.. _. u. u.. t.n s y,. e__ .... u. a a:.s w a ye, 3 a. egregated na tal-teci: sed bus du.:s and fu:: e

hrough catal-clad ais swi::hges: braska:s.

's consac:ed :: :ha exis:ing F.a::cpoli:a Edise Cc=pany l ~he 230 '_ci subs:a:ic , 0 ci a.__s sa_.. .,.,. o.. by.h_ee ...._..s, . o c.,...,4.. s., c.< c.. i, :o. dd., e-w

.~ Junc ica cc a d:uble ci'::ui: =cuer.

F.iddie::vn Junc:icc, locatad 1.3 =1les f := Three Pila Taland, 's a =ajor subs:2:1:n 1: ha Penss*/lvania ' Jew Jersey-u..a: /.i. aa v.a.. .4.-, . a.. s.. 30 ci. a s._ ass,n 1.4._.e c. e 4..s o..w..... o u.. a.ts...ec, ass.. <cu.w 2.4a.24 , a ; sou..w.o 2. ~. a .3.53.>, a ~* c a o sa.y cwee. and operated by ?anssylracia ?:ver and Ligh: C =pany. d gene:aci ; s:2:10: A.. au..c 2.s.e.,.._e. ...a.. ,ec.s.ie,.30.ci su.as a s.. ri. .. e .c, C 0.ci ....s de_.<va a. a,d .e. ._a.,.'s e._e 2..,. . - s s, u. s a. ~, .o ..n_a u .u - e cu...,u_. c: m .r .+4..._. as ..,.c s e s ac4,

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are:::ac:10:s are shcws cc the singla 11:e diagra=, T',gura 3.2-3.

Loca:1ce of tha ac 111ar7

ansforzars and ::u:ing of :he dis::ibucie: duc:s :s the ensi:e buses are sccva on Figura S.2-4.

The syncols used cc :he figures presen:ad in this chaptar are definad. en Figure S.2-5. c.,._,._, .L a.,,,.a. < -,, e. n e s.<. _ c.a.. e.a. a ......3.,_ C d a '.:. .s ".'a.....'.- '. ve. e.vs.e .e ._a..o-_,ss, e...c .,..s u.e c s.<.a e.4........ d s.. w... u 4 r., a c. <. cwe...- sys:e is suppli. Sv :se physically indepe den: circui:3 des -..d and 1 ca:ad so as to sini=1:e to the ex:ent ;;ac:ical :ha likalinecd of :nC.: s inu '.:an a cus f ailure.::dar operatic; and postula:ed acci:ient and anvirenzen:ai ::ndi: ions. One circui: is supplied fr : Auxiliar/ !: ass f :=e 2A cc=nac:ad :s 3us !. of .w. e c.ie. c.4 ..a. a.. A...c _4., 4a y..a e,, _ a ,.a. ..e ,.. 0 ci s..wm, s. 2.., a; c:enec:ad :: Sus 3. Iach circui: :::=2117 supplias : e-hal' of tha uni: as.e .. i. e a y e., e a '.e a. a__.,1 . a; .: cs. a_....a

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b. The liua :: Jackson f cil:ws an enciralv. differan: : u a :han :ha '..'.n.s.."..'.'..e..~~..~.a'".....'.~.n. '...e ' '..e s a. =.

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' h'y s '..- 1 ' ~.m~~.'~'..~..o c each c-her in the s:arien svi:chyard. Nevertheless, :he gecze::7 ef

ne ::vars n %as si=u'.:ane us s::::: ural d2: age unlikaly.

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an:al decign of :.a :: wars =akas i: unlikaly :ha- -hey ::",.'d both e. v...._.._., - e.e.s..

4... . aave., .2_, .e.._ c._ -. a..4..- ._e 2., ausa. 4 encush o ever:::: cne ::ver in:o :ha ::her wculd al::s car:sinly have i.* s..-. s " ' ~. *. '. *...'....- ~..'..'.' s.' a rc~-a - c. The .iddla: vn June:icn subs:a:ica is =ly 1.5 11es away, :hus reducing line exposure. 2:1:n, in:o d. An au:ctransfczner tie is p vided to tie tha 500 kv subs: which Uni: 2's genera::- discharges 1:s cu:pu:, and the 230 kv sub- ., c.. e,. L,. s s c :- s. a. < s... v...a. u. t... _<., e s aux.a.,.< a.a.es b.a a... u. e _o. u . u..e. 4. e.s.4 3.,... shu. d... u... u.., 4. e s au c.,a as. e. The breaker-and-a-half svi::hing a ange:an: in the 230 Li subs:a:ica includes :vo full capaci:y rain buses. ?:1=ary and backup relaying ,,as e p. .i<>.e,.a..ec. e a u. <.... s... .. a, - g..a.. h c < r _... >. b. e u, a. a.. a <..a. a backup svi::hing. These p rovisiens par:1: tha falleving: ue su...u.eg u.>.e. c 1_, c. e au.,. n n...a.<. a - s s... , - _... <. ez .a t. y.y vi:hou: loss od ex:ernal power scurces. sc., e. .e., _2.< .e.a. e a s<.,.,e c. ,._<- u.aa..e can.a a s u n. .s../ A c. p. a e c..' ~... o ..a.y c.'..- ".#.. y.. u.g u. 4.. a...p :.".... ". e, cuc. 3. Shar circut c f c single =2in bus will be isola:ed vi heut in:e: upting servic.e :o any cu:;;cing line c: to the plant far no a :han 6 cycles. .as_.es..,.... .s, .u..e , c s s s a, u a .e........

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1_ = Y/[-f.,q] ,$c....., i.. - n.,a a. w i>> (j/ MEINOPOUTAN EDISON COMPANY POST OFFled CcX 0'2 R E AC!t4G. rE rit.0Y LV A'.f A ICGe3 TELEPHCrtE 215 - 0 2 M; May 9, 1978 G ^.L 0390 !r. 3. H. Grier, Director Office of Inspection and Enferecnent ..ccica I U. S. ?fuelear Regulato:/ Cc:=.iscien 631 Pa-k krenue 1 19.C6 King of Prussia, Pennsylvania Ocar Sir: Three Mile Island Muelear Station Unit 2 (TIII-2) ( Operating Licence I*o. DPR-T3 .N.clcsed please find Licensee Event Report TS-35/1T vhich is cut eit.ted in t.cccrdence with Scc t.ic-6.9.1.8.h o our Techid:cl Specifications. r Sinc ert ly, c.; ,.' 0 ' ' %a J. G. IIerbein Vice Prcu bient-Generat. ion JCi!: ' ' !. : c,j c }r.c lo tu r e : LER 78-35/lT 'raricy Silver (IDE:) cc: i < t,,., L. V> 3<> Amng * '. ' ' 'Nt.'&?" R i

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,aw uua4 v.om use et Att sitouinto mroar.mTiom -. - - i i i v. o li { P 1 ;, l - !: e [I l 2 l{ 10 [ -l 0l Ol Od Ol -l 0[ ] 1 ] 1,[ 1 l j,] @,', car a]_] g a ') u:v.ucC;;E i4 is uc tnst r. van n 2c acp.a n,, u 3 CO l@[0 l 9 l0 10 l0 I7 l 's I0 @ [n_j5_.in J lr [8_]@ 01 QC l 9 I 7 {8J@ I L o si c a tt su.*aco c.5 o EveJT care n b n.m i r u.i f so EVENT DESCnt*TWJ AND proct.2tE CO'4 SEQUENCES h Io 2 h~ nile i' 'f S 5 the ':".i! 0 --ch i t e e_t enr ineer _(Bur. & Roe }.oti fic e +he i.icer.r.ce th: ! i cin 1c milicr/ transfer:ce operation within tite ner: al oncrctirr-ram e of the rr'.2 fo 2 I u la tvill ne? provide sufficient volta e levels for operatien of the LE] 7 r.otor centro 11er. IoIs [durir periode of peck unit citxiliary dc tand. Because the unit hac r.ot been operated Io ic lat a 7:v2r level recuirinc m uir.u: unit cuxiliaries, there was no potential for cny '1]_j ladverty ef fect on the hccith nnd safet/ of the public. ', OTG l s u o s ys T O.1 CAUSE Caus! COv7 vr.t v t CGO! CCCE $UCCODC CO'.*PC'frNrCCOI SUCCCOE sg c ;;'t rm i z iz i@ LxJ@ I zl@ I z i z l z i z i z i z i8 121@ l R @ i 8 3 10 II 12 13 13 l9 20 SE CU PJ TI AL OCCU A 5t E NCC PEFOnT REVISION t e e.y h. E '.T YE A R FIEPCRT NO. COOE TYPE P;O. @,N'. g [21Tl Si l-j l o l 3151 I/l Io11I EJ 1-l loj 22 23 25 26 21 23 20 JJ 31 32 C'?<. ATT ACli'?!'JT N7HO 4 f;i!* ; C C '? '. CO"PC?JENT SHUT O.40 3 A CTre. N..* EFFECT 7.' E T Hout:5. Sust/ITTED FOR.1 su3. St,,'? m a f.1 AN'J r AC TURE R y 1/ v itJ A;T6;. O'J PL ANT t I xi@LEJG I z!@ l 21 @ lololol i IYlg [Njg [Zj@ [Z 919l9 JJ 31 35 35 3/ 40 41 42 43 44 4 CaV5E OIS".m?TIO" AND CORitECTIVC ACTIONS i %t lSincle tre -former eneration voltar.e stitdies co:elueted by t he crelit i cet etmincer afte' 7[j ( c oc '. ' ' hc volta c on'. c edion studir",, che:.M that within th. r 1 en:ratint-t crid (232 to 2.97) a sInd e auxilic ry trans for.:cr c: 1' t pr Tel d< adequate j {} jr. 2 ef ti l c.:lc to cupcort cnerVion of tite unit IM,ineerint, Sa fety Yn','ircr. nnd bhinne l fjlvol:. J 1 !cf r!.'-! '<!1inrica. (Continu~d) i, ...a C V ') r e t iT,. r rnien e; S T A T'J 5

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.hPATin' TO /tCC0r?/J:Y LER 78 " -- l' Ca l'c.y 3, 1978, the re: ult of the sincic auxilicry trancroccer voltcce study ve:w I c:cived frca the Architec t Engineer (Durn: & Eoc). The volter,e values calculated for the !680 V I'otor Centrol C' enters, for a nomal voltecc of. the 230 KV r. rid were below the required I,07 V AC necco:nry to : ure cafe olieraticn of the ra.: etic controller: cnl prevent control power fuse blowing,. Th :e ve],nc v aluN are baced on having the :.axir:ur. unit auxiliarics in service durin;; the ru-e.

nths, with all circulating water pu=p: in scrrice.

Tni: itca vas determined to be a violation of Technical Specification 6.91.8.h, in that the Safety Evaluation Eeport states that etch unit cuxiliary transfc=cr in si cd to carry the unit full lead cuxiliaric and the cncrgized t,afety features auxilieries. Since the E5? bus povered fren the increrable trancfomer i= designed to fast trcnsfer to the remaining trancforner, the potentici to disable both ESF trains due to centrol power fuse bleving exists. Follav up tudies have verified that by cutomtically shedding selected llulance of Plcnt loads upon auxiliary trancforner failure, adequate voltace levels are avcilcble at the 130 V I:stor Control Centers throughout the nor:01 operating 6 ran;e of the 230 KV grid. G O e ( ) [. b-J a. gme --,.3 T.yue_ p' m 7 ' 'd3'E,:f J.,7:1MdLJWW4"_ C'" '%"NGh'MW DM3

t ( _C n:'J g eriotion an ---d Corr;c tive f,,..i.c, - a I. order to accure af:qut e voltacc levci, one of fol2 c; ting cer2 cet,-fc r.:tica; vill be taken: A) the unit vill not bv operated nb;ce, 7:vc r level couratible to saf: cir.cle transferner op:raticn; B} celective balance af plant lead sheddin; vill be installed; C) or the autc:atic bus tra:.sfer: to the other auxiliary trencforcer fcr de:icantel bus vill be disabled. O f ( 9. ') l. s ') 5 6 -b

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~. g//,g., ,e r PMt * /C t f.OCn.1 E / / ME f ROPO;.n AN EDISON COMPANY m.:ac v.. :,. e,..o,.. u.c...' sa..a u / POST CH IC: l'

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m Dirc:ter, :uclear Re:ctor Regulation At t.7 : !*r. S. A. Varga, Chier Li;ht '<.:.ter Beac tor: Bra; h :;o. 4 U.S. i.uclear Reg'.:.' atcry Cor. issica

• lashington, D. C.

20555 De - Sir : Th.ree Mile Isthnd ?!ucc ar Station, Unit 2 (T!I-2) Opere.tinc License !!o. DPR-73 Docket No. 50-320 In rc: pense to questions raised by Mr. Earley Silver of your staff, enc' oce1 pleace find infor.: tion cencerning the potential probica e.c-cc:iated

• ith the loss of en aur.ilicry transfer:.er at E!I-2.

Sincerely, Sencd J. G. lictb:M J. C. I:crLein Vice President-Generatica JCM ., : : j,; cc: Dirc tor of !!aelcai I:en:.: tor Itegulation '.ta: 1:arley 311'.mc Licht '> Tater Reseter: 1]rcr.ch I o. h r U.S. :.;;1 car Repit.' ory C:::n.insion ',/ t'. I 'l - .1...ington, D. C. 20Z~ n.....,. b:c: :.r . Fct !!!;;ir.3 G. T. Ercuchten C. U. Smy'*h *

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a b u r.T.n.,.v. 2 F m. S.-vin _. A. C n. e-..n. a<- ( z..e r. i_o ) r. a m u Ca hy 3,1978, !btrepol_ ten "lison Cc:.pany va.; notified by th: 7:.7 -2 A chite: Engineer (Darns & R e) that a potential prob]en existed.rith .. <. <_ n, u. n. a. r.i, .cc._.._ -o 3 .s..., .4 'lte rc:cits of a Eurno cr.d Roe voltace study indiented that with enly cue c.uxili.cy tran:fo:-.er in op: ration and with the plant at full lord, the bus voltasa vould be reduced to the extent that, in the event of :. LOC.;, sc:2 cafet/ loads vould not be picked up. This could rc..-:lt in the bl:eing of central fuses on the cafety-related components. l'Ot-El found thi: :;ituntion to be reportable in cecordance with Section 6.9.1.6.h of the T:!I-2 Technical Specific:_tions. 'lherefore, on 10y 9, 1973, IMt-Ed submitted Licencec Event Report (LER) 78-35/l':' to th: Cc.n- =ission. This LER identified the potential proble and offered creeral possible corrective actions which nicht be taken, these included: c) The unit vill not be operated above a power level cc patible with cafe singh transfor=cr oper:. tion b) celective talance of plant lead shedding vill ba installed c) er the autc=atic bus trancfors to the other auxiliary tr:nsformer for designated buse vill be disabled. Since 1y 9,1978 when these potential solutions were cub:.itted to the :RC, 1-St-Fi cnd Eurns and Roc h w been vorking to detercine which solution best r ~ :: atS the :nf ety rerjuire,cals and yet aHour ';'ii-2 to oln' rat e "unt en tic- 'Ph. u d ul.io n rea l d i: .e-ful l ou.< f: i I. .F.. _,_ _ _'J_'c. :-' Cu r r e c t c r /.c_t_.0.'. '. c a ih it lac:tliriry T,mul ill be m.intained Ican than or c,un2 to b W pu- ..re in opar.t b n. Inu o on]. r 3 ItC 1 U. vnen.<cer - re th" !.I O V bu w. 1:1 L1 bc.1 irti ted to N '"J. I ra t. i an, t19 lo i o in i. 't. m. - loadine,, duca ('id Cf and 20 lM) hr.vc been t.n.ly..0d (11 : s ; n -le at_d Iincy trancfor: 4r operr. tion) by Darne end Pan ar.d found Ia ha acc ep'.able for n11nt: inia; volte levelu suf fic i,er.t to pick up ra 'c,,y-related cc:npc. - i in the event of a LOCA. 1.ai.Lainic., unit loci:ng at or belv,. the levc2 s indicated chve '-ac been at.inistratively necc:cplished throuch proce. ural chance:. to tha T:'l-? L'ait Startup and Power Operation precedurcs. L'caentinuy, thane per. 'a rai chari',es al loa T 'T.-? to :tartup and coce. late potter to the p a i.- c.; t;tich t; ' c.b;. e-:...itioned landi:i;;; are en'.a.blinhed. L:2d i 'cs cr.. w.111. y 'crr-- .:..nl or the Ii100 ~i huses nre no: it0 ced in ?' the fur.. L! ',. ' C."i l r. t l 8.. ( q..; ; i t. i o " > f' th ! [!. i rn al e qu i p -"'i t-4 l <.o 1 c I m ui r pr o:i i b : 1 ., ti ti...i i.e p -' * ' 'l i n f, a a and iW '. .l' igt di .'n ' ' '. r c t m ' h n t 'il til Mai e +- r-b h j \\* y kl i. V./. ' i d L< r s. iL O ') s i / / (- l P. I,v t- .J-- ..d_' ' -. * * ' ' - - ~ - - ' ' * * ' --'a V M 'J-* WM m,,, limited to the valu;L nentionci above, the Ics: of an caxiliary transforcer, and cubsequent transfer of lead to the remaining trcnn-for:er v0uld result in voltage levels sufficient to pick up all safety-related cc:penents necessary to citigate the consequence: of a 1CCA, and cceply vith Cenar:1 Cesign Criteria 17 cf 10 CFP 50 Appendix A. The Dur:c and Ece Vcitage Progra ucc3 in : king the:e deter =inations 10 the sa:e program which was uced for the IMI-2 Voltage Cpti:1:ntion Studies. The accur:07 of this program was verified through field neat ratents at that time. II. Len Term Corrective Action In order to operate safely thrcu6 out the ner:al crid rince (232-238KV) h a leng ter: correcticn a: tion of celec tively trippinC plant loads upon the loss of any /,uxiliary Transformer has been developed. A synte= of relays vill be insti. led which vill ensure that whenever an Auxiliary Transfor:er beccces de-energized, the following plant leads vill be trip;ed: A) 2 - Circulating 'icter Pumps B) 1 - Condensate 3ccater Pump C) 1 - Heater Drain Pump Burns and Roe has perfarned an analyci: (using the above-tentiened voltage program) to chov that tripping the above-centiened losds vill provide the followins h80 USS bus voltages: h80 V USS" Voltano (1 Auxiliary Trancformer Operation) Gri:1 Voltan ?or ;l LC A (Prior to Lant ES Cenernent: Sta tim.) Post I CC.\\ 232 E7 h2CV hlly hob VE" ini; 10 the volta;e le el after all FS cceronents have cLurted. LOiV i; needed fer starti g ec ; nent:, hovever, co ponents trill safe]y cparate at a much lover > cite;c (363 velts). An can be seen fr r t'as chart, the voltage availabla fcr start.n; thn last safety-related etaperants (hll V) exceeds th'e voltage requirel f'>r starting these component.= (LC7 V). Also, the voltage available af ter all safety-reinted conranents rre stcrted (LOh V) is far in excess of the .citace needed to keep those component; oparating (363 V). I t. in hoped that thase Inn., tem ccrrect ive actions can be implemented within the next six weer.L. o. n. ul ts o f t-i: 0 t'c :tbove n.enLionc.1 leadn up:n the de-enerci-c tion wil' bo a n d.o:w.t. Le rm.u-tion of r':it p: ter cc nc. 21 tag a a-. <" a x i ca t e t y '; '. (1aic.. ill be accenplished aut 'iaot', by the CC , J. - due to t h-t: :p L-

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e,a ;0.C0 vs.t.s A d e.? _4./ 3 J.c, %.. .,s4 3.-- o.. ,o.. seg.cga..A. e. .1_s. c.1, sea bu.s cuw-s -..>..... u. e . w - u. 1 _ a e.,.' _. s.ia.a. 2.. n; swi chges: breaka:s. The 230 'ci subs:stion is con =ec:cd :o the exis:ing P.e :cpcli:an Ediscu Ccupan7 c.w... t o Le a.a i e. .....c... by .w ee c ,.,,,.s, ..c w.4 .._. _< s 3 4 n..0 c/. a..s _4 s s.4,,,, .....s .4 tevn Junction en a d:uble ci'cui: tewer. P.iddleteen Junction, loca:ad 1..i =11es f c= ttree P.ile Island, is a =ajor substa: ice in the ?cnnsylvania-New Jersey- -~.73a-A._.,..,. ca. _,..,.. ' - h. ". O 'c. t a.. s _' 3 - ' c...'.*. e.- -. ~. e.-..c.. a ".o-.4 -^ er, .e.... w.s42a_< , a; a c t..w . o... _.. t 3.3.,..,2, a .5.:. C 0 'd. 1 u _.. a _3 -.., eaa.. 3 a... ..2 c e a ad by ".Ae. a-, ' 't a.' a. ~ a. a.. > L.'.'.. C - < a.v.. o. 3a 3 <,- s. a. _<.,, -.. A r a A: a u..,,...,.., s.,,. e.-. < e.<,..,,.... c. s. t. e.. 0.... s u.., s. 2 4_ -.... 4.- w. ..., c00,.i substatica, :o which :he cu:put of Uni: 2's genera:or is delivered and f : .r., au _a.a. . u.. r., c..,u...: m...z -._ es. -.a -.n,c.ag z, o.e.,...g aO. --,... -

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buta then :he 5. The line to Jack. follows an entirely differen ^- lines : o. '.dletown June:1:n. The lines ara in physical pro:.ici*.y :o cach other in the sta:ica swicchyard. Never:heless, the scene:rj of the : vers ::'..cs 31: ult:neous s::ucturni da:a;c unlikely. The cavi-rennental design of the :: vers =akes 1: unlikaly tha: they could be:h fail fro: a co: on envirennental cause. An enviren=ca::1 effac: severa encugh to ever: urn ene ::ver into the other uculd al cs: cer:: inly have ft s: resulted in 1::: cf offsita pcuer. c. The Middletown June ion subs:ation is only 1.3 niles away, thus reducing line exposure. d. Ar. autotransforce: tie is providad to tie :he 500 kv substa:ica, in:o which Uni: 2's generato: dischar;cs 1:s cutpu, and the 230 kv sub-station froc which Unit 2's auxiliaries ob:ain thel: power. Loss of the tie will not shut down :he uni:'s au cilia:1es. e. The breaker-and-a-half switching a ange: cat in the 230 kv cubs:a: ion includes :vo full capacity main buse:. Pri=ary and bachup relaying has been provided for cach circuit alca; vi:h circuit brush:: ftilure backup switching. These provisions per=i: the following: 1. Any circuit can be swi::hed under sor=al or fault cenditions wi:hou: lass of ex:ernal pcuur sources. 2. Any si:gle circuit b:2aker can be isola:ed for =aintenen:c r vi:hou~ interrupting the pcuer or prote::1on to any circuit. 3. Short circuit of c single main bus will be isol..ted tichout incarrupting sc vice :o any outgoin; lina er to the plan: for cora than 6 cycles. .w . e _-.a 3... 4, . c.., i, s s ...e ..__ b.,,........t_i .m .o_4_,.a .,c. S.n. -. c.4.... <. .we.... .s o..-. a.w' b.v d.i - -.....'.. c <. s.". o a d,i a - a_... c.'..-".<.- t..ril.

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. d.d a. loss of one circuit and one auxiliary transf ormer until 1: is isolated by disecanect switchcs. 6. Circuit p ccection w.51.' be innu cd f:ca failu:2 to the prir2ry protective relaying by beckup : claying. T. ~cch bre;ker has duni trip coilu, cne supplici frc: a prinary and ana frc: a ';ackup source. Both of these cources are electrically independent. Alth0 ugh these circuit: are act phy51cally separated, each ;cuer source has . c..., u> s_.. .eu <..3-s- f. Transient stability studies for the bulk pcrer transmissio., cyste.m h2ve been perfarned ac discussed in. 6.2.0 'Jith the une protective fer* r?;, the pubability of le:s of '. ra ' "x.: on e ::'.;.-c e ...e _oog .,.w 3 i n. :,., u.,. 4.,. n,. e.tc.....

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g. y nore of the re=2ining sour:c: cf en;ite power c: d iscuu nel ' n F. 3.1.

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g SEP 6 1978 MEF. TING SliMARY acket File NRC PDR Local PDR TIC NRR Reading LWR #4 File E. Case R. Foyd D. Vassallo J. Stol: R. Baer 0. Parr

5. Varga L. Crocker D.

Crutchfield F. Williams R. Mattson R. DeYoung Proj ect Manager: II. Silver Attorney, ELD M. Service IE (3) ACRS (16) L. Dreher S. Rubenstein NRC

Participants:

R. Tedesco 17 Rosa F. Ashe R. Fitzpatrick J. Calvo

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