ML17256B084

Discusses SEP Topics II-3.B, Flooding Potential, II-3.B.1, II-3.C & III-3.C & NRC Conclusion That Util Should Provide Protection from Flooding of Deer Creek.Nus Corp Std Project Flood Peak Analysis Concludes Site Adequately Protected

ML17256B084
Person / Time
Site:	Ginna
Issue date:	06/25/1982
From:	Maier J ROCHESTER GAS & ELECTRIC CORP.
To:	Crutchfield D Office of Nuclear Reactor Regulation
References
RTR-NUREG-0821, RTR-NUREG-821, TASK-02-03.B, TASK-02-03.C, TASK-03-03.C, TASK-2-3.B, TASK-2-3.C, TASK-3-3.C, TASK-RR NUDOCS 8207010066
Download: ML17256B084 (34)

Text

REGULATORY

'FORMATION DISTRIBUTION SY

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AOCE'SSION NBR:8207010066 DOC ~ DATE: 82/06/25 NOTARIZED:

NO DOCKET FACIL:50-244 Robert Emmet Ginna Nuclear Planti Uni;t ii Rochester G

05000244 AUTH BYNAME AUTHOR AFFILIATION MAIERiJ ~ E ~

Rochester Gas 8 Electric Corp'EC IP ~ NAME RECIPIENT AFFILIATION ORUTCHF IELDi D ~

Operating Reactors Branch 5

SUBJECT:

Discusses SEP Topics II 3', "Flooding Potentia II-3' 8 III 3', 8, NRC conclusion -that util sho protection from flooding of Deer Creek

~ NUS Corp flood peak analysis concludes site adequately p

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ROCHESTER GAS AND ELECTRIC CORPORATtON

~ 89 EAST AVENUE, ROCHESTER, N.Y. 14649 JOHN E. MAILER VlCO PlRsldont TCLCPHORC

• RCA COOC 7IC 546.2700 June 25, 1982 Director of Nuclear Reactor Regulation Attention:

Mr. Dennis M. Crutchfield, Chief Operating Reactors Branch No.

5 U.S. Nuclear Regulatory Commission Washington, D.C.

20555

Subject:

SEP Topics IX-3.B, II-3.B.1, II-3.C, III-3.C, "Flooding Potential Deer Creek" R.

E. Ginna Nuclear Power Plant Docket No. 50-244

Dear Mr. Crutchfield:

RG6E submitted a report entitled "Ginna Station Design Basis Flooding Study" by letter dated August 18, 1981.

Xn that report, RGSE concluded that. the Deer Creek channel is capable of carrying a 12-inch in 24 hour2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> rainfall event, with an associated Deer Creek peak flow of,13,700 cfs, without exceeding a flood level of 270 ft msl (plant grade).

The estimated return period of this

event, in excess of tens of thousands of years, was deemed sufficiently great, by RGRE that no additional measures were considered to be required to prevent site flooding.

The NRC responded, by letter dated April 26, 1982 and the attached Technical Evaluation Report "Hydrological Considerations" by Franklin Research Center.

In that report, the NRC estimated

that, based on the peak floods resulting from the maximum rainfall that has occurred historically in the general vicinity of the Ginna site, a peak flood resulting in a flow of approximately 30%

of the capacity of the Deer Creek channel could be expected to occur, with a recurrence interval of several hundreds of years.

It should be noted that this result is comparable to the estimate made in RGSE's report of August 18, 1981.

The April 26 NRC letter also noted that the Standard Project Flood (SPF) peak discharge for Deer Creek is estimated to be about 15,000 cfs.

In the NRC's draft Integrated Plant Safety Assessment Report (NUREG-0821), published May 27,

1982, Section 4.5, the NRC concludes that RGEE should provide protection from flooding of Deer Creek to the levels produced by the Standard Project Flood plus one foot.

Xn response to this recommendation, RGSE contracted with NUS to perform an SPF analysis for the Ginna site, to determine what type of protection would be required.

8>07010066 800g00 PDR'ADQCK 05000244,

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ROCHESTER GAS AND ELECTRIC CORP.

DATE June 25, 1982 Mr. Dennis M. Crutchfield SHEET NO.

The results of the NUS study (provided as Attachment

1) demonstrate

that, using site-specific information regarding site conditions, rather than the conservative estimates used in the FRC report, the SPF would be contained by the Deer Creek channel, with almost one foot of margin (see Table 2 of Attachment 1).

No site flooding would result.

There is additional margin to flooding already incorporated at the site.

Curbs and dams in and around the screenhouse and diesel generator

rooms, which are at grade elevation 253 ft msl, provide protection to at least 15 inches above grade (this was noted in the NRC's Safety Evaluation Report).

No additional margin is considered warranted at, the Auxiliary Building, which is at grade elevation 270 ft. msl.

Thus, no additional protection for plant safety-related equipment is required relative to Deer Creek flooding.

RG6E has also estimated the recurrence interval for the Standard Project Flood, and concluded that it would be in excess of tens of thousands of years.

Thus, because of the small likelihood of the occurrence of an

SPF, and the additional margin above grade provided at lower site elevations, RG6E concludes that the Ginna site is adequately protected from flooding due to Deer Creek, and that all concerns regarding this subject should now be alleviated.

Very truly yours, Jo E.

Maier

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Attachment 1

GINNA STATION STANDARD PROJECT FLOODING STUDY I

STUDY PURPOSE Franklin Research Center (PRC) prepared a report

( ) for the Nucgqar Regulatory Commission (NRC) commenting on an earlier NUS study

<~> of design basis flooding for Rochester Gas

& Electric Corporations Ginna Station.

The station is..located. along, Lake Ontario in, the. Deer Creek Watershed as shown in Figure l. 'Ihe major thrust of FRC's report was that flood return periods greater than about 588 years can not be predicted very accurately with the limited time period of available data (a point also brought out in the NUS report).

FRC presents a Standard Project Flood (SPF) which represents "flood discharges that may be expected from the most severe combination of meteorologic and hydrologic conditions that are considered reasonably charac-teristic of the geographical region, involved, excluding extremely rare com-binations."(

)

They determined an SPF of 15,888 cfs based on certain assum-ptions and parameter selection.

They do not present the accompanying water elevations although they indicate that the plant will be flooded by any flow greater than 12,888 cfs.

This report presents our best estimates of the SPF, the corresponding water surface elevations, and its probability of occurrence.

Quantitative and qualitative comparisons between these results and those of the FRC report are also included.

STANDARD PROJECT STORN (SPS)

The SPS index rainfall was obtained from Figure 2 (Plate 2 of Ref.

3) for the Ginna Station environs as 9.5 inches.

Figure 3 (Plate 9 of Ref.

3) relates this index rainfall to the area of the drainage basin and the storm duration in order to obtain an SPS inde~ rainfall ratio which, for the Deer Creek drainage area of 13.9 sq.

mi.

<~) and the minimum indicated duration, 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />, is 116K However, in order to be both consistent with the FRC report and conservative a value of 118% was chosen.

Therefore, the 24-hour SPS for the Ginna Station is 11.2 inches (9.5 X 1.18).

Figure 4 (Plate 18 of Ref.

3) gives the time distribution of the 24-hour rainfall in consecutive 6-hour intervals.

Applying this distribution to the Ginna Station SPS of 11.2 inches results in rainfall of 8.51, 1.41, 8.42, and 8.86 inches for the four 6-hour periods of the SPS.

The maximum 6 hour6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br /> rainfall of 8.42 inches is further broken down, using Figure 5 (Plate ll of Ref.

3), into consecutive hourly rainfall depths of.8.84, 1.81, 1.26, 3.28, 1.18, and 8.93 inches.

STANDARD PROJECT FLOOD (SPF)

'Ihe HEC-1 computer code

(, ) was used to calculate the flow of the SPF from the 4

above described SPS.

The Soil Conservation Service dimensionless unit hydro-graph option, which is designed for small ungaged watersheds such as Deer

Creek, was used to estimate the discharge.

The antecedent moisture condition (ANC) of the soil was chosen for this study as condition II, "an average of the conditions which have preceded the occurrence of the myimum annual flood on numerous watersheds."<5>

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'I I ~ ~ ~ P ~ ~ 40 30 20 STANOARO PRO JECT STORM STUOIES SPS DEPTH-AREA-DURATION RELATIONSHIPS SY 24-HOUR STORM INCREMENTS I ' ~ I ~ I I 'i ~ ~ IO 0 ~ ~ ~ ~ I ~ ~ ~ ~ ~ I I ~ ~ I ~ ~ ~ ~ I ~ j ~ I ~ ~ ~ ~ ~ ~ ~ ~ ~ I I I ~ I ~ ~ ~ I ~ t I~ ~ ~ ~ ~ ~ I ~ ~ I ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ I ~ ~ I' ~ ~ ~ I ~ ~ I I ~ I ~ 'I' '! I ~ I I' ~ ~ 7 ~ ~ 7 ~ ~ I I ~ ~ ~ ~ ~ ~ ~ I ~ I I ~ ~ ~ I ~ ~ I ~ ~ 'I ~ I I I ~ 20 ~ I ~ I ~ 'P ~ ~ 120 ~ ~ l40 SPS INC7EX RAINFALL RATIO IIN PERCENT) ll6 0 70/$ ISI CIViL. wORKS ENGINEER BULLETIN 52" 5 PLATE NO 9 Figure 3. Standard Project Storm Depth-Area-Duration Relationships ~ ~ /J I IIIOf4 AlIII'.L W IIICIC4 fUKCMTlCt Of t + NXR $f$ 1l<IIf@II III t(O 4 oe KIIIOO on e 440 IO 40 T$ $ 0 I ~ ~ 1 80t 8$ FIG. Ib) TTPICAL ARRANGEMENT OF 4-HOUR RAINFALL OUANTITIE5 IN 5P5 IO IS. I4 I~ I~ IS LI IO9 4$ 4 t0 I40 44$ t ~ It0 44$ KI Its 4t ~ ~J I4$ 40$ SI ISt $4$ $ 4 t0$ $44 IOI tl0 SII IO ~ 0 4tO Cl 4$ 0 St <<0 tot ~ S IC$ 7$ $ I$ ~ ~ 0 $ 4 t$ ~ O II4 IS I I$ ~ 00 t 4 ~ ~ IO It IO I4 I4 tQ $II$ 4IOC1 AtuIfKL IN NCt44, IIIAK) 5 P 5 E4-HOUR PRECIPITATION OVER Sl Ml ot PERCENT IN 4-HOUR PERIO05 FIG. 4) TASULATION OF OATA FIIOM FIG 4) STANDARD PRhlKGT STORM STINIES IfENERALIZED ESTIMATES TlME DISTRIBUTION OF 24-HOUR SPS RAINFAlL Figure 4. Time Distribution of 24-hour Stan<lard project Storm Rainfall t 1 ~ ~T DEPARTMENT QF 'THE ARMY ~ ORPS F N IN TINE DISTRIBUTION OF MAPMUN 6 HOUR SPS RAXNFALL Period (Sub-Division of 6-.Hour ",eriod) eeoc 6&ours na a on 3~pours 2<<Hours 1-Hour T e Distr ution of Ha um &our SPS Rainfa "xnressed in hkrcont of Total 6-Hour Rairi&11 2nd 3rd 4th 5th 6th 33 6T 53 10 38 TOTAL 'IIIOA< The "selected unit rainfall duration,e tR ia detenained approximately free the synthetic unit hydregraph equationi tr e tp YZ in reich "tp" ie the lag titae free midpoint of unit rainfall durat5.oa>. t, to peak of unit hydrograph~ in houra, (See page lip Engineering Manual for Ci<1 4rke, Part CXIV - Hydrologic and Hydraulic Analyeee, Chapter 5- .Flood~drograph Analyeee and Coaputatione) ~ The follcnting'ouaded~ff valuee are to be ueed in the above tablet If t exceeds 16, use Q e 6 If t is between 12 and 16use t - 3 P If t ia between 6 and 12, uee Q g 2 If t ie betwen 4 and 6, use Q 1 P ~'r i I 4'C5 CIVIL WORKS ENGINEER 9ULLE IN 52-8 PLATE NQ. I I Figure 5. Time Distribution of Maximum 6-hour Standard Project Storm Rainfall p ~ 4, c I t .= soil group, land use, and ANC, the time distribution of the SPF discharge was determined. This distribution is portrayed in Figure 6, from which the peak SPF discharge is seen to be 13,892 cfs. SPF WATER SURFACE ELEVATIONS Qe site cross-sections shown in Figure 7 were used by the HEC-2 computer code ( ) to calculate the water surface elevation during the period of peak dis-charge. The Nanning's Coefficients, which describe the "roughness" of the channel bed and bank and the shape of the channel were determined from direct observation, with specific values chosen for different reaches of the creek.( ) Other coefficients, which describe transitions between ~caches and the bridge loss coefficients were described in detail previously.( ) Columns 1 and 2 of Table 1 show the water elevation vs. feet above the creek mouth. The section at the Culvert Bridge is at elevation 269.3, which is 8.7 feet below plant grade (278 feet). Columns 1 and 2 of Table 2 show the water elevations at the Culvert Bridge (representative of the maximum site water elevation) for various flows. It is seen that a flow of 14,888 cfs results in a surface elevation approximating that of plant grade. The FRC report( ) discusses the flood probabilities and notes that an assumption of stationarity (no significant change in the interactions of the natural forcegJ is required in order to extrapolate the precipitation return period curve < ) beyond 588 years. This is, of course, true if the probability distribution over the long term is required. In our case we are not interested in the return'period per se, but instead in the frequency of occurrence within the lifetime of the. plant (expressed as probability per year). Over such a time frame, the assumption of stationarity is quite good. Accordingly, an extrapolation of available probability i,nformation, although imprecise by the nature of extrapolation, gives a qualitative interpretation to the precipitation frequency. Based on the probability of occurrence of various 24-hour precipitation

events, as shown in Figure 8( ), the probabjlity that an 11.2 inch rainfall will occur in a given year is less than 18 (for such a small value, the probability of occurrence over the plant lifetime is equivalent to the annual probability multiplied by the lifetime in years).

'CONPARISON WITH FRC ANALYSIS Aside from the above discussion of probabilities, a number of differences exist between the analysis of this report and that of FRC.( ) First among these is the FRC choice of a 6-hour storm for the SPS, rather than the 24-hour storm. They declare that, "the peak flow almost certainly will be higher for a 6-hour storm that produces 6 inches of runoff than for a 24-hour storm that produces 12 inches." This declaration does not account for the time distribu-tion of the 24-hour storm. In fact, inspection of Figure 4 reveals that the maximum 6-hour period within the 12-inch runoff 24-hour storm produces 8~7 inches of runoff, 45% more than the 6-inch runoff 6-hour storm. HEC-1 ( ) was ~ ~ 1 1 CD ~Z 2 3 CC TOTAL RAIN R 11.20 INCHES LOSSES R1.87 INCHES EXCESS RAIN R9.33 INCHES 13 12 PEAK DISCHARGE % 13,092 CFS TIME TO PEAK R18.5 HOURS 10 9 CA CD eDa 8 llJ 7 CD 6 0 0 2 4 6 8 10'2 14 16 18 20 22 24 26 28 30 32 TIME (HOURS) Figure 6. SPF Hydrograph \\' l P 14 lf ~~a A ~ ll glL I Oataaa0 lf fl < ca c ~ ~ a<ca ~<a ~ ~ < 'OQ )%lb: ~ c<I ~ ~<a I00 Ma ~ ~lx I I aa I tp< 0act Icac O<<aaaa I 0aet 100 0 II0 Iaat I~ Itaah to %Ktlcaa 5<ctlcac Data Iccaa ttpo Iacpa 0actlcac Data fceca Sccvay 1010 IIttIS IOIAGC gULV&fIOIDCP J~.' 'II<na I~ I ctw Ihc'<I 1010 Ma I~ 10 II10 LOVVLINIIX:L~b I00 ~.<% ~ I ~<a I~ ~ <<~ II<a 0< ioo CLEFT 4 a 2 1 0 Figure 7. l.ocation of Cross-sections Used for Backwater Calculations ~ V I I' 12 11 10 24-HOUR RAINFALL WxOZ 5 4' <<C fL 6-HOUR RAINFALL 0 6 10 20 SO 2 8 8 8 2 8 8 8 2 8 8 8 2 8 8 8 2 8 8 8 10'0$ 10'ECURRENCE INTERVAL-YEARS 10'0'01 0 1 8 6 8, . 7 8 9 10 11 12 13 18 18 18 17 REOUCED VARIATE-Y l Figure 8. Return Periods for 6-and 24-hour Rainfall s ~ ~ used to quantify this comparison. It was found that the peak discharges for the 6-inch 6-hour storm (CN=188, implying all precipitation is'runoff) and the 12-inch 24-hour storm (CN=188) were 9,914 and 14,688 cfs, respectively. FRC chose a 9-inch 6-hour storm as the SPS. We are not quite sure how this value was obtained, the 6-hour storm not being explicitly given in the docu-ment describing Standard Project Floods.( ) We do note that the probability of this storm is equivalent to the 11.2-inch 24-hour storm, as shown in Figure 8 (derived from information in reference 7). (This equivalence gives further credence to the efficacy of extrapolating the probability of occurrence.) Using all of the parameters and methodology described previously in this

report, the peak discharge for the 6-hour SPS (9 inches) was calculated

=as 12,895 cfs. This value is comparable to the 13,892 cfs peak discharge for the 24-hour SPS (11.2 inches). Another major difference between these reports is FRC's choice of antecedent moisture condition III. Such a condition occurs, "when heavy rainfall or light rainfall 'and low temperatures have occurred during the 5 days previous to the given storm, and the soil is nearly saturated."( ) Although AMC III is certainly more conservative than AMC II, (average case for annual floods) its utilization with the SPS is questionable, having the effect of making a low probability event even more improbable. This decrease in probability can't be strictly quantified; nevertheless a factor of 18 seems reasonable (this is the approximate decrease corresponding to an increase in precipitation equivalent to the increase in runoff from the SPS for a change from AMC II to AMC III). The effect of the AMC choice is illustrated by considering the SPF with AMC II (CN=85), AMC III (CN=94), and total precipitation runoff (CN=188), resulting in peak discharges of 13,892, 13,914, and 14,112 cfs, respectively. A further difference between the analyses is the FRC choice of constant over-bank and channel Manning's Coefficients for the entire creek length. This contrasts wiQ the varying coefficients used in this report, and described elsewhere, (~> which are based on direct observations of the basin. It is of note that no mention of FRC's modeling of the reach transitions and bridge constrictions is given. Assuming that they considered the'se effects in the same way as we, and using the SPF and cross-sections of our study, the effect of the change in Manning's Coefficients is an increase in water surface eleva-tion at the Culvert Bridge of approximately six inches, as shown in Table 2. The compound effect of the differences between the two analyses is illustrated in Table l. Using FRC's SPF of 15,888 cfs (this contrasts with our calcula-tion using FRC's parameters of 14,248 cfs) with their Manning's Coefficients results in water elevations approximately 1 1/2 feet higher in the area of the Culvert Bridge then would be the case with our SPF and Manning's Coefficients. FRC does not show water surface elevations for any flood other than their "limiting flood" (12,888 cfs). Based on our modelling efforts, their eleva-tions are too high. In fact, the elevations corresponding to FRC's SPF and Manning's Coefficients calculated by us were equivalent to the limiting flood elevations indicated in the FRC report. This may be due either to a mislabel-ling of their profile (i.e., their limiting flood may be their SPF) or a different characterization of land'urface elevations. REFERENCES l. J.S. Scherrer et al, H drolo ical Considerations Rochester Gas and Electric Cor

ration, R.E. Ginna Nuclear Power Plant, Technical Evaluation Report, Franklin Research Center, Philadelphia, PA, April 27, 1982.

2. NUS Corporation, Ginna Station Desi n Basis Floodin Stud For Rochester Gas and Electric Cor ration, Rockville, MD, August 1981. 3. Corps of Engineers,Standard Pro ect Flood Determinations, EM 1118-2-1411 (Revised March 1965), Washington, D.C., March 26, 1962. 4. Corps of Engineers, HEC-1 Flood H dro ra h Packa e Users Manual, Davis, CA, September 1981. h 5. Desi n of Small Dams, U.S. Department of Interior, Bureau of Reclamation, Water Resources Technical Publication, Washington, D.C., 1977. 6. Corps of Engineers, HEC-2 Water Surface Profiles Users Manual, Davis, CA, January 1981. 7. D.M. Hershfield, Rainfall Fr uenc Atlas of the United States for Durations From 38 Minutes to 24 Hours and Return Periods From 1 to 188 Years, Technical Paper 48, U.S. Weather

Bureau, Washington, D.C.,

May 1961. e. ~ Conclusions The FRC analysis choices for antecedent moisture condition and Manning's Coefficients are less realistic than those chosen for this analysis. Further-more, it appears that the FRC calculation of limiting flood (12,888 cfs) water elevations is either incorrect or mislabelled. For these reasons, it is our belief that'he results presented in this report are a more appropriate indi-cation of flood flows and corresponding water elevations than are the results presented by PRC. It is our conclusion that the Standard Project Flood, using Standard U.S. Army Corps of Engineers methods, will not result in flooding of the Ginna Station. E 4 ~ 4 TABLE 1 WATER SURFACE ELEVATIONS PROFILE FOR SPF Water Elevation (ft) Section Number {ft above mouth) 478 588 688 788 868 888 988 928 1128 1428 1828 2288 2288 2388 2328* 2488 2628 SPF (13,892 CFS) 256. 9 259. 3 263. 1 266. 3 266. 3 266. 5 266. 6 266. 6 266. 8 266. 8 266. 9 266. 3 266. 1 269. 1 269.2 269.3 269.3 269.3 269.5 FRC SPF (15'88 CFS) 'ith FRC Manning's Coefficient 257.9 268.2 264.8 267.8 267.7 267.9 268.8 268. 8 268. 2 26S. 3 268. 3 267. 6 267. 8 278. 6 278. 7 278. 8 278. 9 278. 8 278. 9

• Section at Culvert Bridge Note:

Both sets of elevations are results of NUS calculations. ~ ~ l F J WATER ELEVATIONS AT CULVERT BRIDGE VS. DISCHARGE Peak Discharge (CFS) Water Elevation (ft) at Culvert Bridge Present Report FRC Manning Coefficient Manning Coefficient 18,888 11,888 12,888 13,888 14,888 15,888 16,888 267.4 268. 8 268. 7 269. 3 269.9 278.4 271.8 267.9 268. 6 269. 2 269. 8 278. 3 278. 9 271. 4 Note: Both sets of elevations are results of NUS calculations..