ML20202D168
| ML20202D168 | |
| Person / Time | |
|---|---|
| Site: | Sequoyah  |
| Issue date: | 02/11/1998 |
| From: | Calvo J NRC (Affiliation Not Assigned) |
| To: | Wessman R NRC (Affiliation Not Assigned) |
| Shared Package | |
| ML20202D161 | List: |
| References | |
| GL-98-10, NUDOCS 9802170007 | |
| Download: ML20202D168 (8) | |
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UNITED STATES 4
5 NUCLEAR REGULATORY COMMISSION w as m w o w, e.c. asses esa i
j Tebruni 11. 1998 i
L MEMORANDUM TO:
Richard H. Wessman, Chief i
j Mechanical Engineering Branch Division of Engneering l
j FROM:
Jose A. Calvo, Chief
/
Electrical Engineering tragh Division of Engineering
SUBJECT:
MOV TERMINAL VOLTAGE ISSUE PER OL 8910 PROGRAM
'" SEQUOYAH NUCLEAR PLANT During recent inspection activities to close out NRC review of the motor opera 1
i program at Sequoyah Nuclear Plant per OL 8910, the NRC inspector notlood that the licen i
(MCC) for PORV Block Valves (FCV48 332, 373). assumed steady j
the voltage that might be calculated using the guidance provided in GL j
i justification of the operating voltages used in its OL 8910
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- conference calls with the licensee on this lasus. On January 30,1998, the licensee p i
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justification of the operating voltages used in GL 8910 evaluations which was su 1
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revised by the licensee on February 10,1998, (see attachment ).
The licensee stated that if an MOV is required to operate in automatic mode at the ons design basis accident, the MOV terminal voNage is evaluated to ensure that ad i
available when the MOV is required to operate after the safety irjection is actuated. During this time the 161 kV offsite power supply is conserva(SI) phase A or B sign l
tively assumed to instantaneously drop from its normal operating voltage of 16511 kV to 153 kV (assu case transmission system contingency) in corSunction with the block load starting of all -
l safety related loads actuated by the.81 phase A or 8 signal. As a result, the 6.9 kV shutd 4
board voNage will drop below the degraded voNage set point of 6456 volts to appr 5850 voNs The licensee confirmed in a conference call on February 10,1998, that the M required to o perate in automatic mode at the onset of a design basis accident, were i
point of 6456 volts. We find that the licensee's approach is
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f The licensee stated that for non socident (manuel-normal operation) MOVs (such as the steady state voltage attained due to the automatic i
ensure that adequate voNage is available. However, the GL 6910, Supplement 6 recommends that the licensee use the d* graded grid relay set point as the starting point for determ i
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Richard H. Wessman 2-(.
4 minimum vohage at the motor terminals for oc motors. Wa have reviewed the licensee's i
l Justification of ueing higher voNage at the distribution buses. On the basis of our review, we find j
that the justification provided by the licensee for non accident MOVs (manual normal operation) j is acceptable based on the following:
I 1)
The automatic LTCs are provided on each low voltage windings of the C88Ts. The taps will start after two seconds time delay and boost the voNage to approximately 1.26% each second until the voNage recovers within the LTC vonage range of 89g7 7107 vehs. The loss of one LTC willimpact only one train of one unit. The loss of one LTC can be treated similarly as loss of degraded vohage relay protection j
en a single division.
2) 161kV offsite power supply is maintained at 18511 kV (refer to Procedure SWYD.18, Rev.15). The control room operator checks the 161kV offsite system 3
i voltage every shift and maintains the log. This procedure directs to comply with LCO 3.8.1.1, Action d (modes 1,2, 3,4) or LCO 3.8.1.2 (modes 5 and 6), if the offsite power system la not acceptable or the system cannot be brought within an i
acceptable range without exceeding the Unit 2 MVAR limn.
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3)
The unit's main generator does not trip until after 30 seconds into 81 phase A or 5 4
event at which time its share of the voltage support to the local grid is lost. The instantaneous drop of 161 kV system with 81 phase A or B event is therefore conservative telstive to operation of automatic MOV which will actuate at the l
beginning of the event.
L, We conclude that the licensee's approach for determining the operating voNage for ha safety-related MOVs is acceptable.
Attachment:
As stated 1
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'.1 i flr Richard H. Wessman 2
February 11, 1998 1
minimum voltage at the motor terminals for oc motors. We have toviewed the licensee's.
i justification of using higher voHage at the distribution buses. On the basis of our review, we find that the justification provided by the licensee for non socident MOVs (manual normal operation) t is acceptable based on the following:
1)
The automatic LTCs are provided on each low voNape windings of the C88Ts. The laps will start after two seconds time delay and boost the voNage to approximately 1.26% each second until the voNage recovers within the LTC vonage range of 6997 7107 volts. The loss of one LTC willimpact only one train of one unN. The 4
'i loss of one LTC can be treated similarly as loss of degraded voNage relay protection on a single division.
I 2) 161kV offsite power supply is maintained at 16511 kV (refer to Procedure SWYD.18, Rev.15). The control room operator checks the 161kV offsite system i
voltage every shift and maintains the log. This procedure directs to comply with LCO 3.8.1.1, Action d offshe power system is(modes 1,2,3,4) or LCO 3.8.1.2 (modes 5 and 6), if th not acceptable or the system cannot be brought within an acceptable range without exceeding the Unit 2 MVAR limit.
3)
The unit's main generator does not trip until afle'r 30 seconds into 81 phase A or B event at which time he share of the vohage support to the local grid is lost. The instantaneous drop of 161 kV system with 81 phase A or B event is therefore conservative relative to operation of automatic MOV which will actuate at the beginning of the event.
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We conclude that the licensee's approach for determining the operating voltage for hs safety related MOVs is acceptable.
Attachment:
As stated DISTRIBUTION:
GLains:
File Center /NUDOC8 JStrosnider EELB R/F RHeman T8carborough JLazevnick EGirard i
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JUSTIFICA110N OF OPERATING VOLTAGES USED Di GAAS 10 EVALVATEDNS 1
h appreneh that is used by TVA la enlemledag tbs miabuh empened vehage at the tenminals of j
suseer eyessted valves (WOY) in GL 9910 pnyons is as Astews:
If a MOV le required to opernes in anaemesis mods et eenst of an desip basin event,6a MOV
,f es terminst witnes is evelased to ename that adequese vahage is avaGable when es MOV is reguired es spwete aner the SI phase A er 3 eipal. Dmier, tis time period the 161W afties j
newer supply is meanervaively eseamed to insesnianaeusly drop from its normal operaslag vnhage et les 2,1ky se 133hv (ilme as postalsted wesst enae transmin'en symem seeingsmaA in i
enquasden whh the blesk starties of all saAsty velated leads 6cmetod by the 11 phase A er 3 algaat. As a resak Ibs 6.eky Sheldown Board vohage *01 dsp to below the dagaded vehage j
eeapoint of 6456 vehs to gh-ty $830 voks. W nunmatic Inad int changers (LTQ an the Canunna Smaios Servies Tmashneers (CSET) w!!! sort, afbr a 2 eseand time delay, beesties the voltage appromhne!aly 1.as% enah seemed untilthe vnksse resenre en witWe the LTC veienes i
range of 6997 7107 voks. The vahage wGi ronever afEsiently to reset 6e dayeded vehnse relay (6595 voks)wkhin 6 anseeds.
lr nood to start and operate sent the accidset starting transisat is ever, the sesady.emte vehaps ensiaed du es the automaals LTC metien is meilland to easwo that adegaans witage is avaanble.
l 5,9 k N k
h lowest resuhias vehage en sur 6.9 Shutdown Snard is apprenimanaly 4900 veks which mill j
assenes the 161ky othhs power sewee at 133ky and resuhs la the CSST LTC et les =-1--
beest vehage top et 10%. The sesuking 400v Esaster MOV 3eard vahases map tesu 477 480.7 velts which resale in a salainnun tesminal vokage of 429 voks (93% of MOV sting) a any of te l
The approach TVA has taken is sensisteet with IIII 741 1p97, "!EEE Standard Crhena ihr ths Pietaedom of Class 15 power Systems and Equipranat la Nuclear Power Ox. A Stations" Amasc A, *1119stration of asnospes aseeeisted with degraded vehage preesction". lEBE 741 mans
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power eupply sahama If analyels dotarmlace that the bus whnge drops into the doyaded velenge relay opersnas range during a isomestary voltage dip, the vohage mum #scover above tbs reest value within the time delay period. Na=aHy, ~Ma"nh==tda ehe :Sa af = "
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switched esparJtor banks, including their asseclami ihne dahiys, to ensure bus voltage eseevery fellowing sepneed vehage transiaans".1VA has enlueted at startles meters at an eShas power supply vehage of 153ky, which in a houndergs ininismun preAirred pewar supply witage, and is based on Transmission System Studies (TSS) perfwmed by Transmisioevrianairig systems, m%h haw been eenservenively perfumed is asserdance with the Adlewing eriesria:
Mlalanun yid vehage is m=8 based ou sks worst <ase enmbination ofma postulated denly baals ewet plus ans unreleasd simuhansene emotinpney to determin the availability, unpacity, and espability of the ofikite power sources to the nuclear unks. M desip basis ennt will always eenalet of an accident la one wait and sienshaneous orderly shutdown (pet unit trip) of all other units. This is bossuse the accidset enso wC1 always have the strimest voltage requiremane in the plant vohnge analyses (espedally on the low voltage systent). M i
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eastingssey WR1 he flee eat ab'$lt hihert (or less) of M put af es tressadesion systes which gim en mn e seews. Th innenism er :-t "e te k aa ald-ed la es TS$'s are la assardenes wi6 the guldsimair prinsmad in the Nort Asneriaan Eisserie Raushaity Commeil (NERC) senadard en Tmannisales Phtmies.
An aest % syns= me,imum shead be apuehg ansany.
k should be acted &st 6e 133ky assuspelan is wry senserveelve had weald tab a M
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,.i... i "- hanw in thh M a w vasasass transenisalan avslarn asedinaariry alnian erderly shutdess of the other anit to drap 13 that laval.
For a design basis evest pie a shankansnes weret enes unassinion symem samningsasy wish all 6&ar ties mannal/dened, the 161ky sysw whngs would only drop to n 11 - ; I A%v.
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1 The approach sken by TVA meses the pidelius etthe OL 3910 Astlen E Questies H, which state that " lla==naes to use k veliase that wulbc prisant atthe MOV when detsmdaing la ability of operets unde design 4 asis osadhinas. This acual vokage appued as she MoV at the tisw of operation is ones last 6am the nemlaal volage ruung of the MOV. Any vehage less than the wenimal ratteg '.s shrved en an e'eraded gehass". For the case of FCY48 332 331 the worst mas palcunstad voltage presem at the MOV at the thse of operstien is app: cl-
-"y 429 vehn, whis by the oL 8910 statement eben, is at a degraded volage of 429 veks which is nons than
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the Mov rasing of 460 wks. The OL sp.10 dounset does am nesin s6mv6ng em es MoV wat ey=== at es dost s did v.h ee pier papeist, but m es vokas, that wat be pr.een a the eine of operenas, which is the r:thed TVA weed.
TVA analyses someervatively used a smetty reduced ofNes power supply vehese erissky (oblah is only posible due to a pn<uistieg transmissian -4ency plus a simuhaseous transmission eastinstasies all at se same than with an asuiden In Unk 2 and an orderly shatdove of abs star uhit). Therefore k is not sagsked to assene addidonal faums in the oHbiw power airentes, such as hilum etths LTC's. A should be polnied out est NRC laspection Raport $0 32WG4 38 and 30 328/9448 in 1994 doeweeded a eoview wWeb bund acespoble ths & ' 'O Sur daarmlalag es minimum saposted admite vreings, The ody CT,8910 guideline is to be able to eew es anpabaity i. mart maan a er below. the lowest aspected profurred power supply schase.
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JUSTIFICATION OF OFfJLATING VOLTAGE 5 USED IN GLep.10 EVALUATIONS The apprensh est is emed by TVA la salentating es wenimes exposted vokses at du tsunients of i
meest apesated valves (MOV) in OL 69 10 stegram is as huows:
Ita Mov le mtwind se epomne in u _A mede at aussi etna deelen bads evear, es Mov -
sannimal vehaps is evelessed to ensure est adageses voMage is ownable when to MOV is tegelred to epsress mAur 6e il phans A er 3 elpal Dudng 61s time persed the 141ky eGisste power supply is esaserwelvdy assumed to lastustaneoudy drop Aom he monant operating voltags of 165 d.lky to 133kv (ilus to puutuissed worst case transsnission system oestlegancy) In ooquasden w6di the bleek seerdag of all sahty relsend leads assusand by the $1 phase A or B alcant As a sonelt the 6.9kv Shutdomst Board vohap will drop to below the degraded vokass l
esipsint of 64H vehs to ;;r '- ^ 'j Se$0 eles. Thereders the MOV's respired se operses la I,p automsde made at the enset of a design basis accident were conservatively evalusied wish the 6.9hv Itheimen Board vokage below the degraded voltage estpoint of 64S6 voks *!he autemesis lead esp shangers (LTC) on the Casunsa 9tesion Servies Treandbanerv (CSST) wn! seert, a$er a 2 neene sinne esey, Mens su wines appromisusely 1.2s% sash sossed unsit se vehaes removers to within the LTC vehags reago of 6997 7107 volts. The vokage will recover samoisalty so resst to dageded vehny relay (6598 vehs) wishin 6 sensads.
Per non eenident (manuel eormal operation) M0V's (sueh as for PCV44432,.333) er other leads that may need to start and operase sher the transient is owr, tbs steady etans vokees ensimed l
due w the nuesmusic LTC action is utnised to ensure that adsgeme vehese is available. The lowest resulting vokses on say 6.9 thatdown somed is ;;: '
-'y 6900 vohs whiok still assumes the 161kv omhe power sourse at isskv and seedie in the C85T LTC et its smaalensa boost vokage top of 10%. The sesultleg 400v Remoeur MOV Board vohages range Aum 477 480.7 vehs whidi venidts la a minimum terminal alongs of 429 veks (93% of MOV reting) et say of the FCV48-332, 333 MOV's.
The apprees6 TVA has taken is condssent with IEEE 741 1997, '15BE Sundard Crheria hr the Proeserion of Class IB Power Systems and Equipment in Nocisar power Osseresing Stations" Annew A."Illustredenofunnespes ud wi6 degraded vahay protestion". IEEE 741 states aihn " "avinmarr
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=2 - 'ra pomar mante unhaas. If naalysis deinnaises that the bus voltop drops imo the degraded voltage relay germeing remes dwing a momensury vehnes dip, ths vehese nest remover above the reest value widde the tbne deley pweed, Additionally, aanbets.may canalder the af!Was of vakage
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3 % g. _, =._ m _ __ _ gg switched espeester beads, includies their assneintal time delays, to casure bus vokage recovery ibuowins esposeed vohaps trenaisses". TVA has evaluated att starting motors as an omke pour supply vehage et l$ sky, whidt is a bounding minbnwa preoured power supply vokses, and is based on Transmission sysism studies (Tss) performed by Transmission /rianoing systens, whish how besa senserweinty pwommed ia momennoc wie 6. hit. wing erkerta:
Minimen arid vehese is enablished based un the worst-case rT% of est patuimed design buis veest plus gas innslated simultaneous uniinseey to deseausue the avedability, espamty, and espsbility #the offsite power sources to the muelser units. The essign basis mest wtB always semmist of an ocident la one unit and simuhaseous ordedy shutdown (not v,v,,,d swi ri.n n
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CO*d *W OA unit trip) of all other unho nis is becaese the accidest case will always have the strictest to.tmee rwomiremsats in the plead vohnge analyses (esponiaDy on the low vokage symem). The
- --^;ny will be the one eingic bilurs (or loss) of that part of to tesnomission system which gives the worst case resehs. %e selection of contingenctee to be considered in the T55's are in aceerdance with the guidelinee presented in the North American Electric Relisbeity Council (NBRC) standard on Transmisalon Planning, All othu unneminales eystem eenyoneuse abound be operating sauntly.
It thould be Isoled that the IS3ky assumption is very conservativt nad wotild take a preslating a--=v alus a " hde event h1 Unit 2 A a el=>h*'mous worst saat e-r - -
'n nic. eantir.u.ev slus an sJelv shutdm. of the other unit to drop to thm levet For a design beels event plus a simuhaneous worst case transmission system contingency with all other ties normaWie+ed.11e 161ky sysunn vdtage would only drop to appreedmately 1SSky.
De approach taken by TVA ineste ilw guidelines of the OL 89 10 Action E Question 36, which state that "..liornwee la usc the volinec that will be preeant at thw MOV when doicrmining its ablihy of operato under design basis conditione. %is actual vohage applied to the MOV.et the time of operation is onen tees thae the nominal vukese ratios of the MOV. Amy vokase less thac the nominal rating le referred to as degraded wltage". For the case of PCV 68 332,.333 the wntst ones coloulated witage parecot at the MOV at tlw tims of operation is approximately 429 vohs, eloh by the OL 8910 statement above, is at a degraded witage of 429 wits dich is less than the MOV eating of 460 volts, he OL 6910 document does not regare ebewing that the MOV will operate at the dogmded voltage relay acept; int, but at the vohage that will be passent at the time of operation, whleh is the method WA used.
WA analyses conserweivdy used a senasty reduced esehe past supply voltage of 153ky (which le only possib)e due to a preediting transmission untmemry plus a simultaneous transmission cundasenoles all at the same time with an accident in Unit 2 and an orderly shutdown of the other unit), werefbe, it is not e. quired to assume additional failures in tlw of! bite power aircuits, such as iniluiu of the LTC's. It should be pointed out that. NRC 1rupaction Report 50 327/94 28 and 50 328/9414 in 1994 documented a nview eAich found acceptable the methodology for determinmg the mininuam espected oHbite vehnee, ne only GL 1910 guideline is to be able to show the capabilley to start rnotors at or below the lowort expected pteferred power supply voltase.
WA has conservatinly met theco guidelines kr the GL 8910 MOV's.
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Picpared by. O.L.Nioely 2/12/199g Reviewed by: SN TOTR P.03
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