ML20002C023

Tornado & Straight Wind Hazard Probability for Haddam Neck Nuclear Power Reactor Site,Ct

ML20002C023
Person / Time
Site:	Haddam Neck File:Connecticut Yankee Atomic Power Co icon.png
Issue date:	05/31/1980
From:	Macdonald J TEXAS TECH UNIV., LUBBOCK, TX
To:
Shared Package
ML20002C017	List: ML20002C016 ML20002C023
References
CON-NRC-04-76-345, CON-NRC-4-76-345, TASK-02-02.A, TASK-2-2.A, TASK-RR NUDOCS 8101070586
Download: ML20002C023 (23)

Text

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ENCLOSURE 2 TORNADO AND STRAIG-T WIND HAZARD PROBABILITY for HADDAM NECK NUCLEAR POWER REACTOR SITE CONNEG1 CUT by James R. Mcdonald, P.E.

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nstitute for Disaster lesearca l

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~EXAS TEC-Us VETSI Y

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1 TORNADO AND STRAIGHT WIND HAZARD PROBABILITY for HADDAM NECK NUCLEAR POWER REACTOR SITE, CONNECTICUT by James R. Mcdonald, P.E.

Prepared for U.S. Nuclear Regulatory Commission Site Safety Research Branch Division of Reactor Safety Research May', 1980' i

Institute for Disaster Research Texas Tech University Lubbock, Texas l

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FOREWORD Hazard probability assessment for tornadoes and other extreme winds at the Haddam Neck nuclear power reactor site are presented herein at the request of Robert F. Abbey, Jr., Site Safety Research Branch, Division of Reactor Safety Research, U.S. Nuclear Regulatory Comission. The work is supported under NRC Contract NRC-04-76-345.

Principal Investigator and Project Manager for the Institute for Disaster Research is James R.

Mcdonald, P.E.

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INTRODUCTION The objective of this report is to assess tornado and straight wind probability hazards at the Haddam Neck nuclear power reactor site. The hazard probability analyses are developed using storm records from the geographical region surrounding the site, Ninety-five percent confidence limits on the probabilities are presented to give an indication of the accuracy of the expected hazard probabilities.

The final hazard probability model is presented graphically in Figure 6.

Windspeeds corresporcing to selected probability values are summarized in Table 8.

The basic data used in the calculations are presented in this report.

Cerivation of the tornado hazard assessment-methodology, the rationale and assumptions are given in Mcdonald (1980).

Use of the Type I extreme value distribution function for straight wind t

hazard assessment is well documented in Simiu and Scanlan (1978).

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LOCAL AND GLOBAL REGIONS FOR HADOAM NECK 2

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II. TORNADO HAZARD PROBABILITY ASSESSMENT A.

METHODOLOGY The tornado hazard model developed by the Institute for Disaster Research (IDR) accounts for gradations of damage across the tornado path width and along its length (Mcdonald,1980). There are four basic steps involved in the methodology:

(1) Determination of an area-intensity relationship in a global region surrounding the site of interest.

(2) Determf aation of an occurrence-intensity relaticnship in a local region surrounding the site.

(3) Calculation of the probabilities of a point within the local region experiencing windspeeds in some windspeed interval.

(4) Detennination of the probability of windspeeds in the local region exceeding the interval values.

B.

CALCULATIONS 1.

Site Haddam Neck Nuclear Power Reactor Site 2.

Coordinates Latitude 41 28' 56" N

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Longitude 72 29' 57" W 3.

Area-Intensity Relationshio t

Global Region Latitude 39 to 44 N 0

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Longitude 70 to 76 W Data DAPPLE Tornado Data Tape UT1678 (Fujita, et al., 1979)

Period of Record s

1971 - 1978 3

k See Figure 'l for definition of the global region. The region is selected to be as large as possible and still give reasonably homoge-nous conditions for tornado formation. The relatively short period of record is used because the data are more comolete and accurate than that collected prior to 1971, especially with regard to tornado damage path characteristics. The area-intensity matrix is shown in Table 1.

It gives the number of tornadoes in each corresponding area-intensity classification.

From this information, the mean damage path area per F-scale c*n be obtained.

TABLE 1 AREA-INTENSITY MATRIX Number of Tornadoes

• Area Mean Area Interval F0 F1 F2 F3 F4 F5 (so mi) 0 4

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Mean Damage Path Area Per F-Scale i

F0 F1 F2 F3 F4 F5 Mean Area, sq mi 0.0220 0.0'07 0.4337 0.1158 3.160 Median Windspeed, mph 56 92.5 135 182 233.5 289.5 4

J Area-Intensity' Function Linear regression analysis of the above area-intensity data, based on a long-log plot, yields the following functional relationship:

Log (Area) = 2.95 Log V - 6.889 (1)

The coefficient of determination is r = 0.897 Area-Intensity Relationship The expected mean area is obtained from Equation (1) above.

Upper and lower bou'nd confidence limits are calculated at the 95 percent level. These values arr shown in Table 2.

Figure 2 shows a plot of the area-intensity relationship.

TABLE.2 AREA-INTENSITY RELATIONSHIP WITH 95 PERCENT CONFIDENCE LIMITS F0 F1 F2 F3 F4 F5 Expected Mean c

area, ag,.sq mi 0.0187 0.0824 0.2516 0.6079 1.2687 2.3933 Lcwer limit aj, sq mi 0.0079 0.0349 0.1063 0.2542 0.5239 0.9744 Upper limit a$,

sq mi 0.045 0.194 0.596 1.454 3.072 5.878 Median F-scale Windspeed, mph 56 92.5 135 182 233.5 289.5 i

4.

Occurrence-Intensity Relationshio Local Region 0

Latitude 40 to 43 0

0 Longitude 71 to 74 Area = 32,220 - 11,660 i

= 20,560 sq mi An area of 11,660 sq mi is deducted from the local region because of s

the ocean. There are, of course, no tornadoes recorded over water.

See Figure 1 for definition of local region and its relationship to the site.

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AREA-INTENSITY RELATIONSHIP FOR HADDAM NECK t

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Data DAPPLE Tornado Data Tape UT1678 (Fujita, et al.,1979)

Period of Record 1950 to 1978 The records used do not necessarily include every tornado that has occurred in the local region.

For one reason or another, some tornadoes go unreported. Because the population density of the local region is fairly high (greater than 200 persons per so mi, USNRC,1979) and because the terrain is such that identifiable paths can be seen should a tornado touch down (damage to structures, trees, fences, or power lines), the number of unrecorted tornadoes in the region is likely to be less than ten percent. The number of reported tornadoes in the local region is shown in Table 3.

TABLE 3

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NUMBER OF TORNADOES IN THE LOCAL REGION F0 F1 F2 F3 Fa F5 Numcer of Tornadoes 38 98 49 9

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Cumulative Number 196 158 60 11 2

1 Lower Bound F-Scale Windspeed, mph 40 73 113 158 207 261

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Occurrence-Intensity Function The function used is obtained by performing a linear regression analysis using the F0 and F1 tornadoes and another linear regression analysis using the F2 to F5 tornadoes.

The one F5 tornado in the records is the Worcester tornado of 1953.

It creates problems with the occurrence-intensity relationship because it overloads the func-4 tion towards the more intense tornado side. Because an F5 tornado is a rare event, and because the period of record is only 29 years, the one event will tend to overemchasize the more intense tornadoes.

For this reason, a rationale judgment is made to treat the F5 tornado as if it is F4 in defining the occurrence intensity function. Over t

a longer period of record, a larger number of less intense tornadoes will occur so that if the regression analysis were performed at some time in the future, the net result would be essentially the same as the one performed today using the F5 tornado as an F4.

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Linear regression analysis of the data in Table 3 on a semi-log plot gives the following functional relationships:

y = (254.51)10-0.00284x (x < 88 mph) y = (3487.55)10-0.0157x (x g 88 mph) where y is the cumulative number of tornadoes with windspeeds greater than or equal to x.

Occurrence-Intensity Relationship j

The expected number of tornadoes in the 29 year period is obtained from the occurrence-intensity function (Equation 2). Upper and lower r

bound confidence limits are also obtained at the 95 percent level.

These values are then divided by the period of record (29 years) to obtain the number of tornadoes per year for each F-scale classifica-tion A, wnich is the needed occurrence-intensity relationship required for thd hazard orobability assessment. Table 4 lists the values used in the probability calculation.

Figure 3 shows a plot of the occurrence-e intensity relationship.

TABLE 4 OCCURRENCE-INTENSITY RELATIONSHIP c

WITH 95 PERCENT CONFIDENCE LIMITS F0 F1 F2 F3 F4 F5 Expected number of tornadoes in inter-val,6 38.00 93.41 47.08 9.55 1.68. 0.278 t

4 Lower limit 6 27.15 85.69 35.36 3.65 Upper limit 6 48.85 113.12 58.81 15.45 4.21 1.31

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Expected number of 1.31 3.43 1.62 0.33 0.06 0.010 tornadoes per year 19 Lower limit 1

.93 2.95 1.22 0.13 9

Upper limit A 1.68 3.90 2.03 0.53 0.15.045 j

5.

Tornado Hazard Probability The tornado hazard probability calculations are performed e computer, although they can easily be done by hand. The expected hazard probabilities are obtained by using the expected area-intensity

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relationship (a4) and the expected occurrence-intensity relationshio (A ).

Upper and lower limits of hazard probability are obtained by 4

using the upper and lower limit 1 's and a 's respectively. The 4

4 computer printouts for these calculations are contained in Aapendix A.

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OCCURRENCE-INTE.4SITY 1ELATIONSHIP FOR HADDAM NECK L

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TABLE 5 TORNADO HAZARD PROBABILITIES WITH 95 PERCENT CONFIDENCE LIMITS Mean Hazard Tornado Windsneeds, moh Recurrence Probability Expected Lower Upper Interval Per Year Value Limit Limit r-10,000 1.0 x 10-4 39 10 81 100,000 1.0 x 10-5 120 74 170 1,000,000 1.0 x 10-6 184 140 239 10,000,000 1.0 x 10-7 245 203 314 e

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III. STRAIGHT WIND HAZARD ASSESSMENT A.

METHODOLOGY A set of annual extrece fastest mile windspeeds are used to fit a cumulative probability distribution function in order to obtain the straight wind hazard probabilities. The Type I extreme value function generally fits the data well.

In view of the studies by Simiu and Filliben (1975),

the Type I distribution function is used in lieu of the Type II that was used previously (ANSI,1972). A detailed description of the methodology is given in Simiu and Scanlan (1978).

B.

CALCULATIONS Annual extreme fastest-mile windspeed data are not available at the power plant site. The closest weather station with the needed data is New Haven, Connecticut, which is located twenty-five miles southwest of the site (See Figure 1). Terrain and meteorological conditions are such that the data should be representative of wind conditions at the site.

The data are taken from weather records from the Environmental Data Service, National Climatic Center, Asheville, North Carolina, and covers the eighty-year period 1888 to 1968. The set of annual extreme fastest mile windspeeds for New Haven, Connecticut is given in Table 6.

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The windspeeds have been adjusted to a standard anemometer height of 10 m.

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A type : extreme value distribution function is fit to the data.

The expected windspeeds for various mean recurrence intervals along with 95 percent confidence limits are given in Table 7.

1 12

TABLE 6 ANN 1JAL EXTREME FASTEST-MILE WINDSPEEDS AT NEW HAVEN, CONNECTICUT Windspeed Windspeed Year moh Year moh 1888 46 1928 35 1889 33 1929 38 1890 41 1930 29 1891 32 1931 27 1892

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1924 38 1964 43 1925 38 1965 42 1926 37 1966 48 1927 40 1967 44 1968 54 Mean Windspeed:

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TABLE 7 STRAIGHT WINO HAZARD PROSABILITIES WITH 95 PERCENT CONFIDENCE LIMITS Mean Expected Upper Lower Recurrence Hazard Fastest-Mile Limit Limit Interval Probability Windsoeed, mph moh moh 10 1.0 x 10~l 46 48 43 20 5.0 x 10~2 49 52 45 50 2.0 x 10~2 53 58 49 100 1.0 x 10-2 56 62 51 200 5.0 x 10~3 60 66 54 500 2.0 x 10-3 64 71 57 1,000 1.0 x 10-3 67 75 60 10,000 1.0 x 10-4 78 88 68 100,000 1.0 x 10-5 89 1 01 76 1,000,000 1.0 x 10-6 99 114 84 The straight wind hazard probabilities along with the 95 percent

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confidence limits are presented in Figure 5.

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STRAIGHT WIND HAZARD PROBABILITIES WITH 95 PERCENT CONFIDENCE LIMITS t

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IV. WINDSPEED HAZARD PROBABILITY MODEL Windspeed hazard probability, which includes both tornadoes and straight winds, is the probability of a point within some defined geographical region experiencing windspeeds greater than or equal to some threshold value in one year. Tornado hazard probabilities are the same at any point within the defined local region. The Type I extreme value distribution function obtained from data collected at New Haven, Connecticut is used for the straight wind probability hazard assessment at the Haddam Neck reactor site.

Thus, in effect, New Haven and the reactor site are contained in a ccmon local region.

Tornado windspeeds are referenced to 30 ft above ground level (approx-imately 10 m) and are the maximum horizontal windspeeds. According to Fujita (1971), F-scale windspeeds are fastest-one-quarter mile winds.

t However, because of the translational speed of a tornado, winds acting on a structure may be of considerably shorter duration. Because tornado windspeeds are based en appearance of dcmage, they are considered to be effective velocities, which include effects of gust, structure size and structure frequency.

For design purposes, the gust response factor for tornada winds may be taken as unity.

The straight winds are fastest-mile windspeeds which have a variable time. duration, depending on the magnitude of the windsoeeds. Values are normalized to a 10 m anemometer height.

For design purposes, gust rescanse t

factors greater than unity are appropriate (See ANSI A58.1,1972).

The tornado and straight wind models are combined in Figure 6 to obtain the final windspeed model.

For design or evaluation purposes, one needs to know the type of storm that controls the criteria. For windspeeds less than 85 mph, the straight wind model governs.

For windspeeds greater than 16

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85 mph, the tornado model governs.

In the case of a tornado, the atmospheric pressure change and missiles must be taken into account in addition to the wind effects.

Because of this, the union of the two events (tornado and straight winds) is not of particular interest. Table 3 summarizes the final windsoeed hazard probabilities.

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TORNADO AND STRAIGHT WIND HAZARD PROBABILITY MODEL FOR HADDAM NECK POWER REACTOR SITE, CDNNECTICUT 18

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TABLE 8

SUMMARY

OF WINDSPEED HAZARD PROBABILITIES FOR HADDAM NECX Mean Excected Recurrence Hazarc Windspeed Interval Probability moh Tyoe of Storm 10 1.0 x 10-l 46 Straight Wind 100 1.0 x 10-2 56 Straight Wind 1,000 1.0 x 10-3 67 Straight Wind 10,000 1.0 x 10-4' 78 Straight Wind 100,000 1.0 x 10-5 120 Tornado 1,000,000 1.0 x 10-6 184 Tornado 10,000,000 1.0 x 10-7 245 Tornado

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REFERENCES 1.

ANSI, 1972:

"Suilding Code Requirements for Minimum Cesign Loads in Buildings and Other Structures," AS8.1, American National Standards Institute, Inc., *!ew York, New York.

2.

Fujita, T. T.,1971: " Proposed Characteri:ation of Tornadoes and Hurricanes by Area and Intensity," SMRP No. 91, The University of Chicago, Chicago, Illinois.

3.

Fujita, T. T., Tecson, J. J., and Abbey, R. F.,1979:

" Statistics of U. S. Tornadoes Based on the DAPPLE Tornado Tape," lith Conference on Severe Local Storms, Kansas City, Missouri, October 2-5, 1979, published by American Meteorological Society, Boston, Massachusetts.

4 Mcdonald, J. R.,1980:

"A Methodology for Tornado Hazard Assessment,"

Institute for Disaster Research, Texas Tech University, Lubbock, Texas.

5.

Simiu, E. and Scanlan, R. H.,1978: Wind Effects on Structures, John Wiley and Sons, New York, New York.

6.

Simiu, E. and Filliben, J. J.,.1975: " Statistical Analysis of Extreme Winds," Technical Note No. 868,, National Bureau of Standards, Washington, D. C.

7.

U. S. Nuclear Regulatory Commission,1979: Demographic Statistics Pertaining to Nuclear Pcwer Reactor Sites, NUREG-0348, Office of Nuclear Reactor Regulation, Washington, D. C.

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