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UNITED STATES NUCLEAR REGULATORY COMMISSION 1,
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WASHINGTON, D. C. 20555 hL APR 16 994 4lb Docket Nos. 50- C / O MEMORANDUM FOR: Ashok C. Thadanf, Chief Reliability and Risk Assessment Branch, DST FROM:
William P. Gammill, Chief i
Meteorology and Effluent Treatment Branch, DSI
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SUBJECT:
TORNADO AND HIGH WIND FREQUENCIES AT GRAND GULF NUCLEAR STATION (TAC NO. 54222)
In response to your request of April 11, 1984, the following analysis of.__
probabilistic analysis of winds is provided for your use in the determination of the frequency of station blackout events at Grand Gulf.
A probability distribution _ of high_ winds without tornadoes was-taken--from Simiu, et al,1979 (" Extreme Wind Speeds of 129 Stations in the Contiguous United States," NBS Building Science Series 118). This distribution is based on analysis of 29 years of annual fastest mile wind data (i.e., one.
fastest mile-ofwind-per year) from-Jackson, MS. The distribution includes winds resulting from hurricanes.
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For tornadoes, a probability distribution of tornado winds was calculated using the combined methodologies of WASH-1300 and of Thom 1963 (" Tornado
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Probabilities',"a Mon. Wea. Rev., pp. 730-736). This distribution is based on 28 years of gornado data within a one degree latitude-longitude " square" (area = 4030 mi ) centered on the Grand Gulf sit the probability of-a torngdo strike is u.9 x 10 g. Bgsed on these data, - --
yr-and the magnitude of a tornado at the 10-7 yr-probability level is 360 mph.
The expected value exceedance probability distributions of non-tornado and -
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tornado winds are shown in the enclosure.
These distributions show that j
tornado winds produce higher sgeeds than non-tornado winds at probability levels less than about 6 x 10- y r
and that non-tornado winds are most
-j important at higher probability levels.__ _ _ _
.j It should be noted that station blackout events can occur as a result of other meteorological phenomena such as lightning, ice storms and snow load.
Therefore, we recommend that these phenomena be considered if loss of offsite power is a factor related to station blackout events. Also, higher i
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probability (i.e.,
> 10-2
~1) wind events may need to be considered if yr fastest mile winds less than 70 mph can cause loss of offsite power. If requested, we can supply this information within about a two week time frame, This evaluation was performed by E. Markee, Meteorology Section.
If you e
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have any questions about this evaluation, please contact Mr. Markee on extension 27635.
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0 William P. Gammill, Chief Meteorology and Effluent Treatment Banch Division of Systems Integration
Enclosure:
As stated cc:
R. Mattson D. Muller F. Rowsome R. Capra A. Spano D. Houston I. Spickler E. Markee 4
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