ML20064C598

Forwards Hydrology Engineering Summary Per Lg Hulman 780913 Request.Recommendations for Rev to SER Encl

ML20064C598
Person / Time
Site:	Sequoyah
Issue date:	10/07/1978
From:	Schrieber D CONSULTING ENGINEERING GEOLOGIST
To:	Staley G Office of Nuclear Reactor Regulation
References
CON-AT-(49-24)-1283 NUDOCS 7810230156
Download: ML20064C598 (38)

Text

{{#Wiki_filter:< s 4-i DAVID L. SCHRElBER, Ph.D., P.E. f0 ' 3d 2 CONSULTING HYDRAULIC ENGINEER [b # 32.W P.O. Box 1087 (c/o The Colony) Coeur d'Alene, Idaho 83814 TELEPHONE: (205) 667-8602 OCTOBER 7, 1978 MR. GARY STALEY, HYoR. ENGR. ^ ENGINEERING SECTioN HYOROLOGIC HM3, 0SE, NRR (P-214) U.S. NUCLEAR REGULATORY COMMIS$10N WASHINGTON, D.C. 20555 DEAR GARY: IN ACCOR0ANCE vlTH THE REQUEST OF L.G. HULMAN, DATED SEPTEMBER 13, 1975, I HAVE REVIEWED THE FILE ON SEQUOYAH UNITS 1 AND 2, INCLUDING THE APPLICANT'S LETTER OF AUGUST 11, 1978, WHICH CONTAINED RESPONSES TO RECENT STAFF HYDROLOGIC OVESTIONS. lN MY OPINION, THE APPLICANT'S RESPONSES ARE ACCEPTABLE; THEREFORE, 1 AM INCLUOlNG MY RECCMMENDATIONS. FOR PEVISION TO THE SAFETY EVALUATION REPORT (ATTACHMENT 1). MY R E C O r1 M E N D E D REVISIONS ARE B ASED ON THE APPLICANT'S RESPONSES T' STAFF CUESTIONS, NY OWN INDEPENDENT REVIEW AND CALCULATIONS, ANL STA/F MEMORANDA DATED MAY 8, 197)(ATTACHMENT 2) OCrosER 16, 1975 ' A T T A C HM EN T 3), FEBRUARY 20, 1976(ATTACHMENT 4),, AND JUNE 23, 1.77( A T T A C HM E N T 5). NOTE THAT I HevE-INSERTED fiY RECOM-MENDED REVISIOUS(ATTACHl1ENT 1) ON THE CRIGINAL ENCLOSURE TO ATTACHMENT 2. PLEASE NOTE THAT MY NRC CONTRACT NO. FOR NRR WORK IS AT-(49-24)- 1275. THE CONTRACT NO. STATED IN L.G. HULMAN'S LETTER OF SEP-TEMBER 13,1975, AT-(45-24)-1283, 15 MY NRC CONTRACT No. FOR NMSS WORK. IF YOU HAVE OUESTIONS REGARDauG MY RECOMMENDED REVISIONS TO THE SEQUOYAH SAFETY EVALUATION REPORT, PLEASE CALL ME. SINCERELY, 1 ffj Md ' v ' <.fc' 6f D Avi o L. ScHR El e ER, PH.O., P.E. CCNSULTING HYORAU61C ENGINEER ENCLOSURES: AS STATEo CC W 0 ENCL: W. 31 VINS L. HULMAN H. SILVER h \\ g t o 3blu A x

se Athicfmen} L 'DR A F T REvtsC D HYDROLOGIC ENGINEERING SU'04ARY~ SEQUOYAH NUCLEAR PLANT, UNITS 1/2 DOCKET NOS. 50-327/328 2.4 Hydrologic Engineering

2.4.1 Hydrologic Description The plant site is comprised of about 525 acres on a peninisula on the western shore of Chickamauga Leke at Tennessee River Mile (TRM) 484.5.

Plant Frade is elevation 705 feet above mean sea level datum (feet MSL). The plant has been designed to be safely shut down in the event that floods occur which exceed plant grade. The drainage area of the Tennessee River above the plant site is about 20,650 square miles. -At ChickamauFa Dam,13.5 miles downstream, the drainage area is about 20,790 square miles. Rainfall occurs relatively evenly throughout the year and averages about 51 inches per year (in/yr) above Chickamauga Dam. Snowfall on the watershed above the plant averages about 14 in/yr. There are two general typ?s of major flood-producing storms in the Tennessee River Basin -- the cool-season winter-type storm and the warm-season hurricane-type storm. Historically, most floods at the plant site have been produced by winter-type storms occurring from January through earlf April. Mater surface elevations on Chickamauga Lake at.the plant site are controlled by Chickamauga Dam. At normal full pool, the water surface elevation is 6S2.5 feet MSL, and the water surface area of the lake is about 35,400 acres. The corresponding volume of water impounded by Chickamauga Dam is about 628,000 acre fect. The lake is about 3000 feet ~ ~

T r, . vide at the plant site with depths ranging to 50 feet at normal full pool elevation. 20 Upstream from the plant there are major reservoirs in the TVA system and 6 major dams owned by the Aluminum Conpany of America (ALC0A). Flood control with emphasis on protection for the City of Chattanooga, 20 miles downstream from the plant site, is a primo purpose of the TVA water control system. Above the plant site, flood control ir provided i r largely by-19-tributary reservoirs and two main river reservoirs, Watts Bar and Fort Loudoun. Average daily streamf, low discharges from Chickamauga Dam repre'sen*. approximate streamflow rates at the plant site. Houever, upstream releases fron Watts Bar Dam can also affect streamflow rates at the plant site. Furthermore, instantaneous flows at the plant site may vary considerably from daily averages, depending upon turbine operations at Watts Bar and Chickamauga Dams. Periods of several hours may occur when there are 4 no releases from either dam, and periods of upstream flow in Chickamauga, r Lake can occur following rapid turbine shutdown at Chickamauga Dam. 2 Since the closure of Chickamauga Dam in 1940, the average daily stream-flow rate at the plant site has been about 32,800 cubic feet per second (cfs). The maximun daily discharge was 219,000 cfs on March 18, 1973, and the minimum daily discharge was 700 cfs on November 1, 1953. Water velocities in the river channel at the plant site'averar,e about 0.6 feet per second (fps) during normal winter conditions and about 0.3 fps. during the summer months. r , - -, r y o--m w,-,,, r .e --gu n

e . Cooling water for both the Condenser Circulating Water (CCW) system and safety-related systems for Unit 1 operation, before the startup of Unit 2, will be provided by once-through flow takea from the river upstream of the plant. Water will flow from the river under a skimmer wall into an intake channel and CCW intake pumping station forebay ' prior to entering the plant. Two natural draf t (main) cooling towers and a permanent safety-related Emergency Raw Cooling Water (ERCW) intake pumping station will be completed prior to startup of Unit 2. The ERCW intake pumping station will be located of fshore in the permanent lake at the skitser wall, and it will be capable of taking suction from the river channel,,even in the event that the downstream dam, Chickamauga, f ails.' ~' Prior to Unit 2 operation, the heated cooling water will be discharged through a 1500-foot embayment (holding pond) and diffuser discharge ' system into the lake. Upon startup of Unit 2, the CCW system may be operated in any of the three following modes:

1. ono -through mode, as described above;

2. helper mode, in which the heated water is passed through the main cooling towers prior to downstream release through the holding pond and diffuser pipes; or

3. closed-cycle mode, in which the heated water is returned from the main cooling towers to the CCW pumping station forebay.

~ During operation of Unit 1 before the completion of the permanent ERCW pumping station, Auxiliary ERCW (AERCW) mechanical draf t cooling toucts and pumps will be used in the event that floods occur which exceed plant

i; - . grade and/or in the event that the downstream dan is lost. For the flood condition, the AERCW pumps and cooling towers will be used to For recycle and cool water for the necessary safety-related systems. the postulated condit. ion considering the loss of the dovastream dam, the temporary (prior to Unit 2 operation) ERCW system will function in a ince-th:ough mode until the CCW intake pumping station forebay (the forebay) is isolated from the lake. Upon occurrence of the latter, the AERC'1 closed-cycle mode will begin. After the main cooling towers and permanen't EP,CW intake pumping station are put into service, the AERCW and the temporary ERCW systems will be decommissioned. The CCW discharge sf. stem dif fuser pipes emanate from the holdup ' P -Ict pond and are located +11i:hly ur m _ - ~whc k -{ 14441t; Oc Guso:rislt Ill olo y Dis /r tei (D' D) l (S"O 2:cc a n:c' s in Chickamauga Lake at TPO! 483.6. Relocation ofgt4+=- rn er tu /c r g r intake, which supplief water to over 2000 people, was required at the g The CP licensing stage prior to Isauance of an Operating License. applicant has conducted a groundwater investigation study and ph---lM S -te replacM the StrD river intake with wells. As stated in Amenc' ment &37' -flic a c l/s ede /c c uiccl deui %S*mo!as nu flue'stsf cf to the FSAR,,on: veil capele c r prchcieg e c c r 1. " -i !an--geHen+-e4 4I,c r>4,d en iI,e Mhee si de o (c'Im haina v ga. L a ie a f dep/fs f rilli.g ;Merwey-ee-C.;l) ' - ': _ _ n ic ; st cd, cr a -vater cr dey //> e A'n a Do lo m i se hina fait. Th a k[ccat e a hac' up u 11.90-/CC fe e l /77 "nuc e s, t h e app li e we-4.es-cot-.yet--sukka+dh-D lC 8 SYC/ ll'r2 [CrictSeuja [ lx)? / l l7 d(< m l t"& SC _c v n u*e se 'e7 e + e,. _ _. .mm. m Sh a Ic fo rn to ren, a biel, u n dc r li e s th e j,4-n f by a +ra ce elysis tccr pr vieca :+ee creuccc-the cerc:ta, :he ;ua,. cr c( -fl> c kol FdollGet $~cc T'/ cit E. 'f: // o [ll11 S SGR) mmc lf rc. fs/ cit shcsc re: b, c: ci;m vcy.a. Thi M m c,:: Ec rcrin d - c n cl C ri c /(c. oy a v g( l, p /ce. 7/tus, th e re. w r N be no qWecf' pr4er tc lice;,-i.g, ad thc scplacc-ent cf-the 5'O river ints' u +4 on ll1 e p f'ct n f b>y lmi c "7 fY: a7 !ll e Sc hic /VS, O r t/i,C e V 2Xfct, 1 t tonf o r' tc c;g ict e ic .c .ng te ~ct the " cr'! tir ,\\ p n

, Af ter the SUD rivmr ineskc is.cplaccd ';y wc!13 ~The nearest present 3 downstream public surface water user is the City of Chattanooga, which has a river intake located about 18.3 river miles from the plant discharge diffuser pipes. A future river watmr supply intake is planned by the East Side Utility District (ESUD) to be located about - nine river miles below the plant site in the k'olf tever Creek enhayment of Chickamauga Lake. The nearest industrial users of surface water for human consumption are located about 10.6 river miles downstream from the plant discharbe diffuser pipes. The ESUD is the nearest major public user of groundwater, which is obtained by wells loc'ated about 7 miles from the plant site. In addition, there are about 100 snall-yield domestic wells within a 2-mile radius of the plant. The applicant estimates that the total domestic groundwater withdrawal within tre 2-mile radius is ahbut 50,000 gallons per day (gpd). Most of these wells obtain water from the Knox Dolomite formation, which is the regional groundwater ~ ' source for eastern Tennessee. 2.4.2 Flood Potential Continuouc river discharge records dating frem 1874 are availabic for the Tennessee River at Chattanooga about 20 miles downstream from the plant site. Flood flows and corresponding river stages (levels) at the plant site have been altered by TVA's reservoir system beginning in 1936 with the closure of Norris Dam and reaching the present level of control in 1952 with the closure of 11oone Dam. The maximum known flood that occurred prior to regulation (March 1867) reached an estimated elevation

. 690:5 feet MSL (450,000 cfs) at the plant site. Under present day regulation, the largest flood occurred on March 18, 1973, and reached elevation 687.0 feet MSL (219,000 cis) at the plant site. The Probable Maximum Flood (PMF) stillwater (excluding windwave effects) is 72 2. 6 level for the plant 710.5 fc(t MSL.. css estirated by thc splicent ed 3 eeeepud b;. un during -the C" mic-. Such a flood would result from the occurrence of the Probable Maximura Precipitation (PPP) on the Tennessee River drainage basin above the plant site. During such an event, the flood crest at the plant could be augmented by the failure of the earthen embankments at Vatts Bar Dam upstream and diminished by the failure of the'Udtthen embankments at Chickamauga Dam downstream. 370 The estimated PMF discharge at the plant site would be 1,+ M,000 cfs. 775. +/- The estimated r:aximum water surface elevation in the lake, -721.3 feet MSL, results from a postulated 45 miles per hour (mph) overwater wind wave activity coincident with the PMF stillwater level. The corresponding ximug water icvel (Design Basis Flood (DBF)n cred rio c twc/es >,H arr dj leveli at the plant including c,.= weet MSL ct s it s e c. TAtc fan in() sD m / -6c +u ee s a ora r7 va.s runup etteR s, is esticated to be 72 .e.,feet MSL at the diesel generator Q1, d A E tiCQwg2n unt er n d cay,,re, -fe:w E buiDWuclMeKrM%1N1?1?="sT&^WR%f%"*d bN'N&* rE cc,r s e m 4 w e. ~74 e PMF, as well as other lesser rainfall floods, could exceed plant grade, 3 7 705 feet MSL, and will necesr.itate plant shutdown. Energency operation requirements and technical specifications are described in Section 2.4.5 ~ of this SER. 20 Since there are 9-major dams above the plant site, the applicant examined these dams individually and in groups to determine if arbitrarily

. assumed seismic failures coincident with river flooding would create critical water levels at the plant. The applicant examined two postulated' combinations of natural events acceptable to us:

1. a one-half Safe Shutdown Earthquake (SSE), as defined in Section 2.5 of this SER, coincident with a on.e-half PMF; and

2. an SSE coincident with a 25-year flood.

Neither of the above conditions were estimated to result in water levels at the plant site greater than that created by the PMF.

However, one combination of events, dam failures assumed from a critically one-half ca e - hs If } h e j'Mi~

centered SSE coincident with a 25 ycar fic-d, could cause the simultaneous A 4 Fcniana Uc'*n ch the / Ale Icir ic.ssec h%c.r etnd HoWa ssee, Bh c Rike, r f ailure ofrNoceis, Chcrckce, end-Ocuglac "" ced the dinnWeent rf the auid A pa ls cliset Denns s>1 1h e Hiwa sse e Rwc r-Test Loudcun gate-heistr The resulting maximuct stillwater elevation 7/0.9 in the lake at the plant was estimated to reach-M9d feet MSL. 712. fc Wind caused setup could raise this water level to elevation M +r4 feet-FGL. Wind wave runup on plant safety-related buildings could reach vi5.e (vevh / tc.t // in 5 A a //ow w/a f ed. Fwe elevation 714.7 feet MSL T h other assumed seismic dam failure - e 3 flood combinations with coincident wind wave activity were ectinated to also possibly cause water levels that' exceed plant grade, 705 feet MSL. ^ As described in Section 2.4.5 of this SER, plant shutdown will be initiated n tste upon notice that any one of-he-upstream da=s (Norris. Cherokee, Douglas, Fe n s.-na, d' u s: e c s APah 'h a, Bh c 6 d 6.> 9 or Tellico) has failed seismically. In the absence of Fort Loudoun,g communications for S hours after an earthquake, shutdown will be initiated, as discussed in Section 2.4.5. Site drainage to the Tennessee River has been provided to accommodate + 4 h

8-runoff from precipitation as severe as a local PMP. Structures that house safety-related facilities are protected from such local flooding by the slope of the plant yard; the local PMF will not reach or exceed the critical floor elevation, 706 feet MSL. ,Tta applicant conservatively neglected precipitation losses in estimating the local PMF level. At our request, the applicant assumed all underground drains to be clogged and all surface drains to be full in analytically testing the adequacy of the site drainage system. A peak local PMF discharge rate of 14 in/hr (equal to the maximum hourly rainfall' rate) from the outlet of each drainage area was used. With all drains clogged, the plant y' aid perimeter road and railroad embankments control site drainage outflow. Standard backwater methods were used to estimate the corresponding water levels at plant buildings, assuming a flat plant yard slope. Resulting water levels were estimated to be less than 705.5 feet MSL. We have reviewed the applicant's analysic of the adequacy of the site drainage system, and we find it conservative [ and acceptable. i I We also asked the applicant to evaluate the ability of the site l drainage system to function properly during the period of time between i startup of Unit 1 and startup of Unit 2. The applicant stated that the plant would not flood from a local PMP during this period of time, since grading essential to the site drainage system will be complete j prior to startup of Unit 1. w I

. We required the applicant to demonstrate that no flooding of safety-related structures can occur in the event of precipitation as severe as a local PMP coincident with clogged roof' drains and scuppers. The applicant demonstrated to our satisfaction that water buildup under such conditions would be less than the allowable depth of water the roofs of safety-related structures can withstand. 2.4.3 Lou Water Considerations The applicant's expected minimum average daily river flow rate past the plant site is 5,000 cfs. This estimate is based upon a low flow frequency analysis conducted for the period of record since January 1942. Since then, low flow ~ ~ 'a t the site have been regulated by TVA dams. Recorded average daily flows at the plant site have been less than 5000 cfs only 0.2 percent of the time. We requested the applicant to compare the estimated minimum water level at the plact site, elevation 673 feet MSL (occurring in the winter flood season as a result of special preflood reservoir drawdown), with a minimum flow rate, level, and frequency of occurrence resulting from the rost severe drought considered reasonably possible in the region,to evaluate the dependability of safety-related water supply. The most severe historical drought in the Tennessee Valley region occurred in 1925. The _ minimum average daily flow at the plant site during tiiis drought was 3,200 cfs: the applicant's frequency studies indicated that this flow rate had a probability of 10-2 of occurring in any given year. The same studies indicated that a daily flow rate of 1,300 cfs at the plant site would have a probability of 10-7 of occurring in any given year.

u a .c-The corresponding lake level would be about elevation 675 feet MSL. The plant can operate normally during low water conditions down to elevation 668 feet MSL, the level at which the CCW pumps must be assumed to-cease operation. This elevation is three feet above the elevation, 665 feet MSL, where the intake forebay would lose access to the river. "We have reviewed the applicant's low water analyses, and conclude that an adequate water supply for safety systems should be available. Prior to two-unit operation, and in the unlikely event of the lor.s of the downstream dam, the Seismic Category I intake forebay pool (also designed to withstand. erosion and sedimentation effects of a PMF) will ~ provide in excess of 2.5 million gallons storage capacity, of which 2.2 million gallons will be available for supplying makeup water to the closed-cycle AERCW system. This is enough makeup water for about 6 days, assuming severe environmental conditions in conjunction with a loss of Coolant Accident (LOCA) and a loss of the downstream dam. Four portable forebay makeup water pumps will be deployed, as soon as any radiation levels permit and prier to total dep3ctien of the forehay ,- pool, to supp1v makeup water from the river. These pumps, which will be stored onsite above the DBF elevation and protected against the SSE, can supp1y water at a combined rate of 2100 gpm. The forebay makeup requirement under such postulated conditions does not exceed 300 gpm. i In the event of the loss of the downstream dam, as a result of a severe flood (not the preceding case, in which a scismic event also is postulated I 7:- ' ' l

to cause a LOCA), the forebay portable makeup system will be. deployed immediately following isolation between the river and the forebay, and the system is to be operational within three days. The permanent ERCW pumping station is to'be functional upon 2-unit-operation. Since this seismic Category I structure will have direct communication with the river for all water levels Gncluding any loss of downstream dam) and is above the PMF level, the ERCW system for 2-unit operation will' be capable of functioning in an open cooling-cycle mode for all anticipated river conditions. Therefore, makeup by portable means to the CCW intake forebay will not be necessary, nor will there be-a need for dependence upon the AERCW system. We requested.the applicant to provide an analysis of the river water level and flow rate at the plant site resulting from the less of the downstream dam coincident with a drought of historical severity. 'The lowest average daily flow of record 3,200 cfs, occurred prior to reservoir regulation, and thus represents-the minimum flow of historical severity that could j be expected to be available after a loss of the downstream dam. The water surface elevation corresponding to this flow rate is greater than 10 feet above the elevation (665 feet !!SL) where the forebay loses connection with the river. Only 300 gpm (less than 1 cfs) is needed for r the UHS to perform adequately (closed-cycle mode) prior to 2-unit operation, and less than 50 cfs is required for the UHS to perform adequately (open-l cycle mode) during 2-unit operation. Therefore, we conclude that the proposed UHS systems will be capable of perforciing adequately during all creaible i l l i ( l

1 , low river flow conditions. i 2.4.4 Croundwater An outcropping of the Conasauga Shale, a poor water bearing formatioc, i underlies the plant. A trace of the Kingston Fault, located about

• 2000 feet northwest of the plant, separates hydraulically the Conasauga Shale outcropping from a wide belt of the Knox Dolomite formation.

The latter is the major water bearing formation of eastern Tennessee. Because the Knox Dolomite is essentially hydraulically separated from the Conasaaga Shale, offsite pumping, including future development, should have little ef fect upon the groundwater table in the Conasauga Shale at the plant." ~ ' I Small openings along fractures and bedding planes contain the groundwater in the Conasauga Shale. In the Knox Dolomite, however. groundwater I occurs in solutionally enlarged openings formed along fractures and bedding planes and in locally thick cherty clay overburden. The applicant does not intend to use groundwater at the plant. Local offsite groundwater use was described above in Section 2.4.1. i I l l Recharge to the groundwater system (Conasauga Shalc) at the plant site 1 is from local precipitation. Discharge from the system is towards the northeast and southwest into Chickamauga Lake. i l P k l l

x , Ariour request, the applicant provided conservative estimates of the perceability and porosity of the Conasauga Shale, the hydraulic gradient, \\ and an acceptable estimate of groundwater travel time from the plant to the nearest downgradient surface water body, Chickamauga Lake. There are no downgradient wells between the plant and Chickamauga Lake, for which the nearest downgradient location is about 1000 feet northeast of the plant. We accept as conservative the applicant's estimate of about 300 days for groundwater to move along this pathway in the event of a postulated accidental liquid radwaste release to the groundwater system. We have conservatively estimated that a groundwater dilution factor of about 2.8 would 'be' applicable to the postulated accidental release prior to entry into Chickamauga Lake. Upon e 'ry and initial nixing with 4 lake water, we estimate that a dilution f actor of 9.8 x 10 is appropriate. The total dilution factor applicable at the nearest present downstream surface water user, SUD water intake (to be removed prior to 5 fuel loading), is 9.8 x 10, Even though the potential for accidental contamination of the groundwater system is extremely low, the applicant plans to monitor radioactivity levels and groundwater levels in 5 observation wells in the plant area throughout the plant lifetime. Denn,r Ba su Fhe d leve Is The applicant has chosen.: 2t.~ ci c. t ica. 722.5 fcc: .Ch, for designing 3 safety-related structures against static and dynamic water forces.

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4 . We find this to be conservative in regard to the design basis groundwater level. i 2.4.5 Hydrological 1v Related Technical Specifications k The applicant nas provided an emergency flood protection plan, designed to minimize the impact of floods exceeding plant grade on safety-related facilities, and a corresponding technical specification outlining the action to be taken to prevent any flood caused accidents. Tbc applicant's flood protection plan includes procedures for predicting rainfall floods, arrangements to warn of upstream seismically induced dam failure floods, i and lead times available and types of action to be taken to meet i safety-related requirements for both sources of flooding. The applicant's warning scheme for both types of floods is to be divided into two stages. Stage I will allow preparation steps and some damage, but will withhold major economic damage until Stage II warnin assures a flood above plant grade. o ] Reservoir levels for large rainfall floods can be predicted well in 27 advance by the applicant. The applicant estimates that a minimum ofiG-hours, divided into the two warning stages, will be availabic between the tine a.' preflood preparation order is issued and the time the flood waters exceed plant grade. A minimum 10-hour Stage I will begin upon prediction that IT ' ~ flood producing conditions might develop. A minimum as-hour Stage II will be based on a confirmed estimate that conditions will produce a flood above plant. grade. F Seismically induced !ailure of upstream dams can result-in flood surges that exceed plat 'rade. However, such surges do not have a water-level potential as great as thc rainfall-induced PMF water IcVel. A i

. 27 minimum of ibb hours, divided into the two warning stages, is estimated by the applicant to be availabic to prepare the plant for such floodir:g. The applicant defines " flood mode" operation as the means by which the plant will be safely maintained during the time when flood waters exceed plant grade, elevation 705 feet MSL, and during the succeeding time period until recovery is accomplished. Plant 'oling requirements during flood mode operation will be met by the ERCW System, unless flood mode operation is necessary prior to operation of the permanent ERCW pumping station. If the latt'er is necessary, the AERCtJ, System will provide closed-cycle water circulation to meet plant cooling requirements. Water supply by both these systens is discussed in greater detail above in Sections 2.4.1 and 2.4.3. The applicant proposes one kind of warning scheme for rainfall floods and another type of warning scheme for seismically induced dam failure floods. For rainfall floods, the first stage (Stage I) of shutdown will ~ begin when sufficient ralnfall occurs to yIcid a projected 697.0 plant site water level of 607.~. feet MSL in O e winter months (October 1 70.1 ' through April 15) and 494-feet MSL in the summer months (April 16 through September 30). These water levels assure that any additional rain will 27 not produce water levels in excess of 703 feet MSL in less than sf-hours. The latter level provides a nargin (requested by us) so that waves resulting from high winds cannot disrupt flood protection preparation.

. Stage I will be held until either Stage II begins, or until the applicant determines that floodwaters will not exceed elevation 703 feet MSL at the plant. Stage II shutdown will begin only when enough aJditional rain 103 has fallen to yield water levels in excess of F&Fre feet MSLg(vinter), er -?O1 feet :0L-(seer)r The applicant estimates that required shutdown 2+ 3-procedures will take no longer than 33-hours, which allows a Jr hour contingency margin. Mon e As stated in Section 2.4.2 abov,e, the failure of f4ve upstream dans (Norris, (Fc,danc, Haus ss e e. Apais citsat, BL e ti a oge e,4 h e y g,,9 jy y Cherokee, Douglas,FortLoudoun)g'Er Tellico) n varying conbinations can produce floods over plant grade. Stage I shutdown vill be scarted upon notification that an;+,one of those da.ns has f ailed, and will continue until it has been determined that critical combinations do not exist. At our request, the applicant committed to initiating Stage II shutdown if communications are lost, or if there is no certainty that critical corbinations do not exist in such situations. Three corrunication networks are available to the applicant:

1. the applicant's own microwave network; 9,

2. the applicant's own powerline carrier system; and

3. the Bell System.

We have reviewed the applicant's proposed emergency flood protection plan and corresponding plant shutdown technical specification. We find both acceptable from a hydrologic engineering standpoint. Technical specifications for plant shutdown to minimize the possibility of an I i

_ = _.. o 4 17 ~ accident resulting from hydrologically associated phenomena other than floods are not necessary, since such phenomena should have inconsequential effects upon safety-related facilities. 4 2.4.6 Conclusions Wa conclude that adequate flood design bases have been'provided and implemented, including an adequate emergency flood protection plan and corresponding plant shutdown technical specification. k'e niso conclude that an adequate water supply can be assured for safety related purposes, 5 and that plant operation and the remainder of plant construction will not adversely affect, or be affected by, local and regional groundwater fs+ hermes, we supplics.3 4:cwcvcr, us cac. nc:-conclude,that plant operation yill not s a v-ia ce 4)a lcr or cycund adversely affect, or be affected by,3 water userspntil the s"/HCt. f/l e has rep 41ced the Sava nah forsciscacir.gerreplacir.i%5mt?cs applicant a l nits fic.al plans g with we //s /cca 4 cc Utility District river water intake for sur r aicu r.d appre w ~rr norificas+ o f 1he p /a n f. -cuch rc:ccc:'un e.culd bc c + <d,,e rcqui mw w-uecacing, prior :c-fuc! ler. ding.- ,e** 4

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gulune,d a ~ UNITED STATES NUCLEAR HEGULATORY COMMISSION W ASHIN G T Cff. D. C. 20555 UAY g ' 1375 i V. A. Moore, Assistant Director for Light Water Reactors, Group 2, DRL HYDROLOGIC ENGINEERT :G SU:0!ARY (SER) PLANT NA"E: Sequoyah Nuclear Plant, Units 1/2 LICE!! SING STAGE: OL DOCKET NU:!3ER: 50-327/323 RESPONSIBLE BRANCH: UTR 2-2 REQUESTED CO:!PLETION DATE: April 9, 1975 (Target) April 30, 1975 (Estimated) APPLICANTS RESPONSE DATE NECESSARY FOR NEXT ACTIO:: PIR NED ON PROJECT: As soon as possible DESCRIPTION OF RESP 0:;SE: Amendment to FSAP to resolve open iten REVIEW STATUS: Hydrologic Engineering Section (SAB) - Complete, except for resolution of open item Enclosed is the Hydrelof,ic Engineerit.g Su= ary, prepared by D. L. Schreiber and L. G. Hulcan, for your use in preparing the Safety Evaluation Report. There is one open item concerning the relocation of the Savannah Utility District river unter intake. Fir,al plans for the relocation cust be submitted for our review and approval, and we recortmend that the relocation be cortpletcd as a requirement for licensing prior to fuel loading. M Harold R. Denton, Assistant Director for Site Safety. l Division of Techt.ical Reviev Office of Nuclear Reactor Regulation i I

Enclosure:

l As stated cc: v/o enclosure A. Giacbusso W. Mcdonald J. Panzarella cc: v/ enclosure l S.-Hanauer K. Kniel F. Schreeder H. Silver SS Branch Chiefs R. Klecker V. Benaroya D. Eisenhut J. Collins S. Varga A. Kenneke g Schreiber OTIO4 gd5,N,e, 5 s f e

e O A M,e -li n ' e " f ~' M s. UNITLis StATLS NUCLEAR HCGULATORY C O *."M I SSI ON W ASif 8N G ton. D. C. 20555 00T 10 1375 Voss A. Moore, Assistant Director for Light Water Reactors, Group 2, RL REVISED I!;PUT FOR SER PLA!TT NAME: Sequoyah Nuclear Plant, Units 1/2 LICENSING STAGE: OL DOCKET NUICER: 50-327/328 MILESTONE No.: 24-32 .lESPONSIBLE BRANCll: LWR 2-2 REQUESTED COMPLETION DATE: October 20, 1975 APPLICA!;TS RESPONSE DATE NECESSARY FOR !; EXT ACTION PLANNED 0:; PROJECT: N/A DESCRIPTION OF RESPONSE: N/A REVIEW STATUS: Ilydrologic Engineering Section (SAB) - Complete Enclosed are revisions to our SE2 transmitted Pay 8,1975, which resolve the open item concerning the relocation of the Savannah Utility District river water intake. The applicant corrnitted in A:nendmen t 37 to the FSAR to replace the intake with wells, and to abandon and dismantle the intake by March 31, 1976. This is acceptable providing confirmation is received and approved prior to fuel leading scheduled for March 1977. [j,'. Y, i/ ( ct m.~---- [r'~HaroldR.Denton,AssistantDirector ~ for Site Safety Division of Technical Review Office of Nuclear Reactor Regulation

Enclosure:

As stated cc w/o enc 1: R. Boyd W. Mcdonald J. Panzarella cc w/ encl: S. -Hanauer R. Heineman H. Denton D. Crutchfield SS Branch Chiefs J. Collins K. Kniel H. Silver R. Klecker D. Eisenhut S. Varga M. Williams D. ScLreiber ~*~ * .m e .m.e- .n .--on-

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grade and/or in the event that the downstrenn dan in lost. For the the AEnci? pumps and cooling towers will be used to flood condition, y recycle and cool water for the necessary safety-related systems. For 1 l the postulated condit inn considerint; the loss of the downstreau dam, the I tenporary (prior to Unit 2 operation) ERCU system vi)) function in a I .cnce-through rode u M il the CCU intake pur. ping station forebay (the forebay) is it.olated f rom the lahc. Upon occurrence of the latter, the AEP.CU cloned-cycle mode u111 begin. Af ter the train cooling touers and permanent ERCU intake purplug station are put into service, the AERCU and the tcrporary E!!CU nyntens vill he decommissioned. The CCU discharge Efbten dif fuser pipes enannte from the holdup pond and are located slightly upst$ cam fror the Scrann h Utility District (SUD) va cr intake in Chickanauga Lake at TRM 483.6. Relocation of this intake, uhich supplier unter to over 2003 people, uan required at the .. CP licensing stage prior to issuance of an Operating Licr v e. The-applicant has conducted a groundwater investigation study and plana 37 to replace the SUD river intake with weuc, t.2 st at ed in Amend: cat 44-the wells are located about 4.5 miles northeast of the plant to the FSAR, +n t ll-wWe of predtv. T ' 3r 1 0 -ill les f'allorM on the other side of Chickamauga Lake at depths of 90-100 feet in the Knox weter-i +-r-sey-(r pO-MMu - 3 ces t c m', c*t4-d r-1-1-14en :. - t4ww-te Dolomite fornation. This formation is hydraulically separated from the --loeftte 3-he' up c-11 Weer7-the-eppi i e r i W-e.+yet+*br4+ml-f or Conasauga Shale for ation, which underlies the plant, by a trace of the Kingsten .wr---r+v.4 +r-nJ-a t-Pr*MI M **# E " C ^f then c!?n, uw 4n' r Fault (-S c 0 Section 2.4.4 of this SER) and Chickamauga Lake. Thus, there will ~ -e nMy+A-1.smeed tLth t-ew eba++-t hew 44 eet%>-+be-p?+snt-+ f be no effect on the plant by punping from these wells, or vice versa. The .tumi4*g-4 m huc ulia, ar-v4w -ve roa,---TM r l' .m st ' e  ? Applicant com.itted in Amendeent 37 to the FSAR to abandon and distantle -p riWe-16-e.Mtry;---+h 31, m4++e--etH-c(-t-he-A14br i -. is '. m ' %4 mP-h tne SUD intake by barc 1970, and to conffrm the removal as soon as k,- be-e(@t-ed-t r-lo -to-felaMne--twost--41e '"' ;xA Lon - possible after completion. This is acceptable providing confirmation is I. eeived and approved prior to fuel loadings scheduled for ILrch 1977.

p. ;.; --

. ' '. **I.j 'j{2y. _ 17 - ?! accident resulting from hydrologically associated phenomena other than ~ f1ceds are not necessary, since souch phenomena r.hould have inconsequential effects upon safety-related facilitics. p 2.4.6 Conclusions Un conclude that adequata flood design bancs have been 'provided and ir:ple=ented, including an adequate emergency flood protection plan and corresponding plant shutdown technical specification. We also conclude that an adeq'uate water supply can be assured for safety related purposes, and that plant operation and the remainder of plant construction will not adversely affect, or be affected by, local and regional groundwater Furthermore, we supplies. -ilowser,:e en we conclude that plant operation will not surface water or groundwater users, adversely effect, or be af fected by, -water-usem*wi4-tle ] (. since the applicant plans to replace --e M44 wet--subutt<.-f4nni pl:~ Sor-r+1oMa-or-r+phciaa-the Savannah wit. wells by P. arch 31, 1976. 5 Uti)ity District river unter intake fe-our---ref = nnd approwd,- Ue will confirra the relocation -Suels<4eeat ton-r4xwM-be--c+mp' e t ed, m"4 r e-~ far-licen4 r- -- a 8 prior to fuel loading scheduled for March 1977. e l i ~ l i l ~ (L. l

k C 61CV1 f d.* U*diTED STATES [ {( y,jh..,;y )g *,j ,.( NUCLE AR REGULATORY s.T. MISSION V. ASwiNGToN, C C 20 % 3 .n,..u.:. i %, vy/ .u Dochet Un. 50-327 and 50-328 W. P. Gamill, Assistant Director for Site Technology, SSEA R. C. DeYoucg, Assistant Director for Light Water Reactors, Division of Project Management DOCbME"TATION OF TELEpFONE C0!.TERSATION ON FEBRUARY 13, 1975, WITH TVA REGARDING SEQUOYAH NUCLEAR PLA!:T { On February 13,197/c A. Cardone (CSB), D. Schreiber (H'!B), H. Silver (LUR 2), and 1 participatcJ in a Conference Telephouc Call with the applicant regarding their recent analyses of flood wavta rewlting from potentini dam failures, seismically induced. In the FS*.P., the applicant presented a screening analysis of such dam failures occurring in con.bination with floods resulting f rom precipitation. This analysis hac recently been refined for the Hiwassee River Uributary to the Tennensee River) as a result of preparir:; an FSAR for tite Watts Ear Nuclear Plant. The analysis presented in the Se:.".r.h FSAR consisted of arbitrarily ascu,Ing that the six Jargest dans in the 111wassee River Basin and Fontana Dam on the Little Tennesace River failed sinultaneously fro r. a sci:aic event ir ;nbinatina with one-half the Probable Maxitum Flood (PHF). Neither basic fL od routing technic es nor t.nsteady flow analyses were used to roitte the resulting flood wave u m the Hiuansee River. Instead, an " upper lind.t failure wave hydrograph" us.. impesed froa the Hiuassee River at its mouth in Chickarauga Reservoir on the Tennessee River. Unsteady flou nethods were then used to carry the flood downstream to the Sequoyah Plant Site. This anilysis did not rasult in the critical potential scismically induced da.. iailure flood at the plant site. l The applicant reported in the telephone call that his recent (not yet docurented) unsteaJy flow analysis of the saw arbitrarily assumed, sinul-tetneous dan failures resulted in the rest critical dam failure flood wave l at the Sequoyah site. In fact, t';e applicant indicated that under such con-ditions, suf ficient carr.ing tire ould not he av. ilable to shutdown th : ' plant. I Thus, the applicant i nads to conduct a refined seisnic study to locate the , earthquake epicen;cr that vould produce the most d,nace at tha various dccs (rather than arbitrarily assuning complete failures). A detailed unsteady flow analysis would then be used to determine the resulting flood wave at the Sequayah site. l l

The applicaat indicated that the above nnalyses vould require frou 3-6 mont1:s to co. plete am! dodet. Our revi':u of tmch analy.4es will take froe 6-8 weche. Tim n, it was enac ieded thot thia topic could be carried t as an op.:n itc in C e SER and reavived prior to fuel loadin; (currently scheduled for Mar '.197 3 ). As a result of the ate.T, D. L. Schreiber has revised our 1:ydrologic Enginecting input to th; SER. See letter from !!. Dentoa to V. Itoore dated 1:ay 8,1975, and October 16, 1975. These changes are noted in the enclosure. cTo>m*,I-<\\ L. r. L. d.,.Ilult.' ant Ch'ie f ....s. liydrology and Meteorology Branch Division of Site Safety and Environmental Analysis

Enclosure:

As stated cc w/ enc 1: H. Denton R. Eoyd D. !!uller M. Ernst V. Moore R. Vollmer D. Crutchfield SSI:A Eranch Chiefs ST Section Leaders E. Knic1 H. Silver D. Schreiber 9 e aw h

s. I s RWISED IIYDROLOGIC ENCINI:l:RIt,G INPUT FOR SAFETY EVALUATION REPORT SEQUOYAll NUCLEAlt PLANT UNITS 1 AND 2 DOCKET NOS. 50-327 AND 328 February 1976 O e e map s ++*e-mee

~ p- .,,h assuaed seisnic failures coincident uith river flooding would create critical vatier hv.D at the plaut. T h" v ei l i c a n'. c..4ned t..o p os t ula t e d cc.r.5 ? na t i'. ns of nT: ural cuntn acent. ale to us:

1. a one-half Safe Shutdown Earth-{uate (SST.), as defined in Section 2.5 of thin SER, coincident with a one-half P:fF; and

2. an SSE coincident with a 25-year. flood.

/,9 pr^3 ente' P t : T . *J p r i o.- t.' Tahr.m y 1976, neither of the above conditions vere esticated to result in water Icvels at the plant cite greater than that created by the PMF. lloweve r, one combination of eventn, den failurcs asau.'l frcm a critically centered SSE coin {1d at with a 23-year fload, could cause the simultaneous failure of ::orrin, C arokee, and Pau31:.n do"i an] the dianblenent of the 1 Tort Loudora gate beist. The resulting maxir.:um stillwater elevation in the lake at the plant was entin sted to reach 709.7 feet IISL. Wind caused setup could raine this uater level to elevation 711.2 feet MSL. L'ind uave runup on plant rafety-rclated buildings, could reach el evation 7.14. 7 f eet ::SL. Three other assuced seismic dan f ailure - flood conbinatiens with coincident vind uava activity were esti:.ned to also possibly cause water levels that exceed plant grade, 705 feet MSL. l As described in Section 2.4.5 of thit SEn, plant shutdnun will be initiated t l l , upon notice that any one of fi/e upstream dans (t:orr.;, Cherckee, tougica, f Tort Loudaun, or Tellico) has failed seisnically. In the absence of cornunication: for C hourn af ter an earthc.uake, shutdcun vill be..,itiated, l ce discussed in Section 2.4.5. l l rh e l l i

- 7a - The appihant reported to the sta!' in February 1976 that a recent unsteady flow a.@esi-c.f an event asset.nl com.prir,ed (if the c.onplete sinultaneou.s faib m o ~ the ni> Jargest da'r t he !!iwa,:re 1:1ver an f oa Tontana Dan on tlw Lit tle Tenn :st.ee River combinad with a one-half P;E results in the rost critical dan failure flood at the plant. The applicant plans to subtit for staff review prior to September 1976, a more refined an.11ysis, including a seismic study of the area, structural stability analyses for these dans, and an unsteady flow analysis.

Thus, this issue cust remain open and must be resolved prior to fuel loading.

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c .'i.te dr 13.,ge a e,,. IPtee Riv, UU fren Preefpftagg3 e 3 ',. 83fety re'ated e- " Sever C O a ccor..huda t e e as ,4 5 : t :. a 10 g-p,,,* M OPd cs a '. n the pla,e - Prot':c ted frop* Struttures the h of I"UT ., g,, the lo ouse elev ttoa, n, _.,, I cat fj Odia a ca) by the 7pr e.,..,,,r, i r c;. teed the

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-cal DPPlitant coanervativel.. the local p;77 ICVel-drains to ba At ou request testing the cloL'Ced and a^iz ",urf th - s tir.a tin", ade;uacy of ace drains t 'UC"r'ed all underRr I c.ad IUCharr.c the site draLnage y r.t t e or 14 in/hr (equal Y yr a the to the outlet of each drai naxww, y clo33ed, the plant 7 ,Se area v^S rate) cn d-e Iith all drains r;Ite draina.,,,- outfl

Imate the Standard backwate i road embankment ov-co77,__

s r 'U# 1 c~u i, n',ing u ter Jev 13 'e ~ d"~ W re flat pinnt ya7g cy 4 n used to e c, less tha Rc W n 705.5 f eet ;;37 ult 1"a w ter lev %%m a ej", the adequacy of ,' ha v e review d 00timated the Lite d e th to be and acceptah1c, YSIO Of d ** find it conse

rvatyy, e also aske-' the cpp3

,,_t ainage ~. to sys t e~~' "e e*DIuhte the c, e'uact! abiyytY *', the U tit.. of 1: nit 1 Properly durin~.* t1 -*U *l cite a,a Plant vo ~ ,',a,. ud of Unit tir-e hetucea uli! not 9

ryg_,

e grading; c33cn,,., fro.7 a loca; p;9 w M ated the. t during','y:", M,od ' tO to to,e "e4 e .~ Ota-'tud Of {'ni ra t nn..g of ef_, g y 21ct? J m

o 37 - ~ accident r e s n '. t i :-- fro 1 hydrolo;;icall:. aweiat< d phenc:. ::na other th in floedr. are na: :R C .Wy, Fir.Ce Such phrr' i'M 4huuld h"VJ In c o.Y:c q u' t!al of fcct s upon sa f ety-: e late d fac il it ins. 2.4.6 Conclusione. 1.'e cannot conclude that adequate flood design bases have beca provided and inpler.,ented, inc3nding an adequate cuerucury flood protection plan and corresponding plant shutdrivn technical specification, until we resolve the open item ref,arding potential sett,mically induced dam failures coln-cident with a one-half PMP. We can conclude that an adequate uater supply is availnble for t.afety related purposen, and that plant operation cnd the re-nainder of plant construction ufil not adversely affect, or be affected by, local and regionni groundwater supp]les. Furthermore, we conclude that plant operation will not adversely effect, or be affected by, surface water or groundwater users, since the applicant plans to replace the Savannah Utility 1)istrict river wat er intake with valls by March 31, 1976. We will confirm the relocation prior to fuel loading scheduled for March 1977. t 1 W

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UNITf o i?AT*3 fiUCLE A T4 REGUL ATCHY COWISSIO*. ~ye '.CJJ i e, w.af: a o c. ass

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Q ~'Ql:;?- Jk's 2 3 *g.77 s,, ....+ ':CiORANDL*M FOR: S. A. *.'arga, Chief, Lisht Uater Reactors Branch #4, DPM FROM: L. G. Hulman, Chief, Hydrology-Meteorology Branch, DSE

SUBJECT:

REVISD hTDR0 LOGIC ESGINEERING SER INPUT - SEQUOYAH Enclosed are changes prepared by D. L. Schreiber to our SER input (see remos dated S/8/75,10/16/75, and 2/20/76) necessitated by the receipt of Amend.:ent 46 to the FSAR (revised flood analysis).

• ih es e changes will allow publication of the SER; however, because a detailed review is necessary, this open item will nct be co=pletely resolved t ntil publication of Supplement N3. 1 to the SER.

This plan of action was discussed and agreed to by H. Silver, LPM. b"fli 6T._ s _.b ~v.. ?f 1.. G. Hulmaa, Chi Hydrology-Meteorology Branch Division of Site Safety and Environmental Analysis Office of Nitelear Reactor Regulation

Enclosure:

As stated cc w/o encl: H. Denton R. Boyd D. Muller R. DeYoung cc w/ enc 1: W. Ga nill H. Silver D. Vassallo L. Heller C. Stepp R. Hof=anr. F. Miraglia T. Cardone . - F. J. Williams ,,D. Schreiber 6 4

e TtCVISED !{YDROLOGIC E iGINEERING INPUT FOR SAFETY EVALUATION P2 PORT SEQUOYAH NUCLEAR PLAST UNITS 1 PID 2 DOC 1:ET 505. 50-327/328 JUNE 19 77 i 1 l s t t

. s - 7a - ?2plcce the previous page 7a (2/20/76) with the follesteg: The applicant reparted to the staf f in February 1976 that a revised dam f ailure flooding analysis was b*ing prepared. This analysis was received by the staf f in June 1977 (Amendment 46), and includes a ~ r.eismic study of the area, structural stability naalyses for the affected dams, and an unsteady flow analysis. According to the applicant's revised analyses, the highest flood level at the plant f eca seismic dam f ailure and flood conbinations would be elevation 710.2 trom simultaneous failure of Fontana Dam on the Little Tennessee River and the Hiwassee, Blue Ridge, and Apalachia Dams on the Hiwassee River during a one-half SSE coincident with one-half the PriF. Wind caused setup could raise this water level to elevation 711.9. Wind wave runup on plant safety-related buildings could reach eleva ion 7L5.4 feet MSL. This is 10.4 feet above plant grade, 705 c feet MSL, but it is 7.1 below the design basis flood level, 722.5 feet MSL (including wins caused setup and wave runup). Two other seismic das failure co=binations with coincident floods could cause water elevations above plant grade. Coincident wind waves would cross plant grade in three other events. As a result of revising the das failure flood analysis, the applicant also revised appropriate plant shutdown procedures. As described in Section 2.4.5 of this SER, plant shutdown will be initiated upon notice that any cne of nine upstre m dass (Norris, Cherokee, Douglas, Fort Lo adoun, fontana, Hivessee, Apalachia, Blue Ridge, and Tellico) has failed seismically.

.e e - 7h - k'e have completed a preliminary review of the applicant's revised dam failure flood analyses and changes in the flood protection plan, and they appear reasonable. '4e are currently naking our own detailed analysis, the results of which will be reported in a Supplement to this SER. G 6

. _. _.. _ - =. ,e ~. t Ue find thic to be conservative in regard to the design basis groundwater level. I 2.4.5 HydrologicaJly Related Technical Specifications The applicant nas provided an energency flood protection plan, designed to minimize the icpact of floods exceeding plant grade on safety-related facilitia., and a corresponding technical specification outlining the action to be taken to prevent any flood caused accidents. The applicant's flood protection plan includes procedures for predicting rainfall floods, arrange =ents to warn of upstream seismically induced das failure floods, J and lead tires available and types of action to be taken to meet safety-related requirements for both sources'of flooding. The applicant's ~' j varnIng scheme for both types of floods is to be divided into tuo stages. Stage I will allow preparation steps and some damage, but will withhold najor economic damage until Stage II warning assures a flood above plant grade. Reservoir levels for large rainf all floods can be predicted well is advance by the applicant. The applicant es,timates that a minimum of 27 hours, j divided into the two warning stages, will be available between the time a preflood preparation order is issued and the time the flood waters exceed f plant grade. A cinicum 10-hour Stage I will begin upon prediction that flood pr:ducing conditions might develop. A minimem 17-hour Stage II will be based on a confirmed esticate that conditions vill preduce a flood above plant grade. Seismically induced failure of upstream dams can result in flood surges that ex:eed plant grade. Eoweve, sach surges do not have a va:ce level potential as great as the rainfall-induced PM? water level. A s. v ~,

...~ -.. 4 =* ^ nIni=u., of 27 hours, divild b:to th.: two warning ;tr,es, is eutier:ed by s the applicant to be availabl.: to preparc the plant for such flooding. The applicant defines " flood mode" cpers: ion as the means by t hich the plant vill be uaf ely ru.iac.1.ted duriu ne time.%n flood waters exceed plant grade, elevation.705 feet MSL, and during the succeeding time period J I until recovary is acconplished. Plant cooling requirenents during flood rode operation vill be met by the E2C*! System, unless flood code operation is necessary prior to If the latt'er is operation of the permanent ERC'J pu:nping station. the /ERCB, System uill provide closed-cycle water circe:Lation i necess,ary, to meet plant cooling requirements. Unter supply by both these systees is discussed in y,reater detail above in Sections 2./..I and 2.4.3. proposes one kind of warning schene for rainf all floods The applicant and another type of warning scheme for seismically induced dass failure (Sta3e I) of shutdown vill ficods. For rainfall floods, the first stage l begin when sufficient rainfall occurs to yield a projected plant site water level of 700 0 feet MSL in the vinter conths (October 1 through April 15) and 703 feet MSL in the sumer =onths (April 16 through Septe=ber 30). These uater levels assure that any additional rain will not produce water levels in excess of 703 feet MSL in less than 27 hours. The latter level provides a margin (requested by us) so that waves resulti. ; from high Ands cannot disrupt flood protection preparation. i l ~ 8 6 8 j -. -., - - -,- -_-.,_.~..,.. ,.-..,~, . _., -. ~. -. ~.}}