ML20202C529

Requests That Encl Documents Be Placed on Docket & in PDRs for Plant

ML20202C529
Person / Time
Site:	Sequoyah
Issue date:	02/11/1998
From:	Hernan R NRC
To:	Mcknight J NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
NUDOCS 9802120271
Download: ML20202C529 (4)

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Ftoruary 11, 1998

-NOTE TO: Jim McKnightj Document Control, IRM MS 0-5-D-24 FROMi- Ron Hernan,xDRPE SUBJECT' Docketing of documents received regarding Sequoyah Nuclear Plant Please place the enclosed documents-on the docket for_Sequoyah Units 1 and 2 (Docket Nos._50-327 and 50-328) as=well as in the Public Document Rooms for Sequoyah'. ,

Thank You.

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SEuu0AHd/CEM R W Jt!STIFICATION OF OPERATING VOLTAGES USED IN CIA 910 EVALUATIOMS

%e appeonch that k used by WA la calculedas the mininuup expoeted voltage at the terminals of motor opeented valves (MOV) in GL 49 10 program is as fotbws:

If a MOV le requime to opwate la ausomatie made at onest of an design basis event, the MOV ,'k 4s tenninal vokage is evalmated to ensure that adequase voltage is available when the MOV b required to opwsw ator the S! phase A or B signal. Durlag tie time pened the 161ky othhc power supply is commervativdy assamed to instantaneously drop from its normal opersing voltage of 1651,1ky to 153kv (due to postulated worst onec transedesion eystem contingency) in conjunction with the block starting of all safety tclated loads actushd by the 11 phase A or B alsnal. As a reeuk tbc 6.9hv Shutdown Board vokage will drop to below the degraded voltage seapoint a(6456 vehs to approximately 3850 vohs. %n autrenatic ined tap changers (LTC) on the Common Station Service Transibaners (CSST) will start, afbr a 2 seoemd time delay, boosting the vokaps approaimately 1.25% each second untilthe volta 4e rooovers to within the LTC vokese range of 6997 7107 vahs. The voltage win recowr sufEoiently to reset the dageded vohnge relay S 4 M (6595 voks) wkhis 6 seconds.

For - -- *H (d n .c.r.1 operation) MOV's (such as far FCV 68 332, .333) that may aced to start and operate annt the accident starting transisat is over, the sesady eiste vohage attained due to the autommeic LTC action is utdised to ensure that adequate voltage is available.

De lowest resuhia6 vohns, on any 6.9 Shutdown Board is approaimately 6900 voks which still

{ dtN assuaws ibe 161kv oississ power source at 153ky and results la the CSST 1.TC at its maahnum boost whnge tap of 10%. %e resulting 480v Reactor MOV Board voltages reage from 477 480,7 volts which results in a mininsam terrainal voltage of 429 voks (93% of MOV rating) at any of the FCV 65-332, 333 MOV's.

The approach TVA has taken is consiseest with IEEE 741 1997, "!EEE Standard Criteria fbr the Protnotion of Class IE Power Systems and Equipment la Nuolear Power Generating Stations" Annas A, *11lustration of concepte ===adaW with degraded vehage pecesction", IEEE 741 states

.g mar, =_ ; . - ' he ev-t -*=d.._a or 52 .a the H -7: t m.a nmi power anpply vahama If analysis deternduce that the bue vokage drope into the degraded vohage relay operattag range during a snomastary voltage dip, the vokage must recover above the reset value within the time delay period ' Additionally, analvana magv eq$.ly the eftman af unhage

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,ad M switched capacitor banks, anchubag their asociated tane delays, to ensure bus voltags recovery following empoeted voltage trenaisess". WA has evaluated at marties moeors at an oNbite power supply voltage of 153ky, which in a hounding mininuun preferred power supply voltasc, and is based on Transmission System Studies (TSS) performed by Transeussion/I'lann6ng Symems, which how been conewvatively perfbemed in nooordnace with the Adlewing oriteria:

• Minimum grid vahase is -1lhi baal ou the worst case ~= hela = of gas Postulated denip basis event plus gas unrelated simultanonue ' ',, g to determine the availability, capacity, and capabihty of the offsite power sources to the nuclear units. The design basis event will always cosaist of an accident in one unit and simahaneous orderly shutdown (not unit trip) of all other units. %is is beesuse the accidest caec will always have the strictest vokaas requiromants in the plant vokage analyses (espealally on the low voltage system). De 1'ro, .. r=, e n r. m n ..m.,n ...... . . . . . ,,,m.......

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contingsney will be the ces sissle lhilure (or loss) of that part of the transmise6en rystem which gives the worst <. ass results. The selection of contingencies to be conthbred in the l TSS's are in accordance with the suklelines presented in the North Asnerican Electrio i Reliability Council (NERC) standard en Transmission Mahming. t t

e All other transmission system compancate should be opersing nonnally.  !

l I it should be noted that the 15hv assumption is wry conservative and wouhl take a pen andstina wentcanc gg, AA a. - '7 v .daia nmc d;w

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orthe ca= unit to drop to that level, g,g;-l a r; - a7 f .ao.

for a design basis svest plus a simmitaneous worst emme unnsmission systeen caeningency with a i

other ties normal /elooed, the 161kv system voltage would only drop to approximately 1.Hky.

The approach taken by TYA meets the guideliams of the OL #9 10 Action E Question 36, which I

state that " ,licaneses to use the voltage that will be pnsent at the MOV when esterminag its ability of operano under design baens conditions. This actual voltage appled to the MOV at the tims of operataos is onen less than the nominal voltage ratlag t(the MOV. Any volange less than l the nominal ratles is refbreed to se degraded voltage". For the casc of FCV.44 332, .333 the worst same calculated voltage present at tbc MOV at the thne of opastion is approximately 429 volts, which by the GL 89 10 unemsat abow, is at a degraded voltase of 429 volts which is less than l'

the MOV rating of 460 voks. The OL 8910 document does not require showing that the MOV will operses at the degunded vokage soley setpoint, but at the vokage that will be preesset et the tim of operation, whach is the method TVA used.

TVA analyses consavatively used a greatly reduced offsite power supply voltase oil 53kv (which i is only possible due to a pse<xistieg transmission contingency plus a simuhaneous transedesion contingensise all at the same tbne with an sooident in Unk 2 and an orderly shutdown of the other unit). Therefore it is mot sequked to assume additional failures inthe offsiw power alreaks, such as fhilure of tbs LTC's. It should be pointed out that, NRC lospection Report $0 327/94 28 and 30 328/94-28 in 1994 docunwnted a review wiuch found acceptable the methodology for determining the mininuun empeoted offsste vokapa. 7he only OL 89 10 guidshne is to be able to show the capability to start anotors at or below the lowest sxpected pt ftrred power supply wetage.

TVA has eeneervatively met these guidelines fbr the Gl. 89 10 MOV's.

Preparedby: G.L, Nicely 2/9/1994 kW Reviewed b  %

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