Summary Report for Conduct of Kozloduy NPP Stress Tests

“Kozloduy NPP” PLC
SUMMARY REPORT
for Conduct of Kozloduy NPP
Stress Tests
4 EXTREME METEOROLOGICAL IMPACTS
4.1 ACTUAL ASSESSMENT OF METEOROLOGICAL PHENOMENA USED
AS DESIGN BASIS FOR THE SITE CONSTRUCTION
To assess the climate characteristics of the region around Kozloduy NPP in the design basis
data from the meteo-stations in Lom, Oryahovo Buzovets and data for the period from 1916 to 1977
were used. For this assessment data for 1969-2010 from the meteorological monitoring system for
Kozloduy NPP site are used.
The estimates of meteorological phenomena in the vicinity of Kozloduy NPP for the past 11
years confirm the trends in climate change described in the fourth report of the Intergovernmental
Panel on Climate Change (IPCC).
4.1.1 Extreme winds and sand spouts (tornado)
Dominating for Kozloduy NPP are the west winds, followed in frequency by east and northwest
winds.
At probability P=1% (once per 100 years) the maximum velocity of wind in Kozloduy NPP
and Oryahovo are respectively 37-42 m/s. Dominating are west winds with wind frequency 34.9-
35.5 % at winds 4.2-5.6 m/s.
At probability Р = 0.01% (probability once per 10000 years) the calculated wind velocity is
45 m/s, which is accepted as extreme, at application of the estimated impacts on the civil structures
and facilities ensuring nuclear and radiation safety.
According to the analysis of National Institut of Meteorology and Hydrology of Bulgarian
Academy of Science performed in 2009 the characteristics of 16 sand-spouts observed during the
period from 1986 to 2009 and evaluated for the zone with the radius of 178 km around Kozloduy
NPP are: maximum velocity - 332 km/h(92,2 m/s); wind speed - 263 km/h(73,1 m/s); motion speed
- 69 km/h(19,2 m/s); radius corresponding to the maximum wind speed air flow 45.7 m; probability
of sand spout occurrence with the above characteristics in the area of 12 500 km2 around Kozloduy
NPP is 6.3×10-7 for 1 year and with speed over 332 km/h – 1.26×10-8 for 1 year.
The probability of wind spout over the given section of area 100 000 km 2 during one year is
estimated at 5,05х10 -6 .
The maximum wind speed 92,2 m/s will lead to pressure on the structures of 5,2 kN/m 2 .
4.1.2 Humidity and freezing
The average annual humidity is 78%. With specific combination of temperature, humidity
and wind speed, the probability of icing and freezing increases. The most likely combinations
temperature-wind-humidity necessary to determine the combined ice and wind loading on the
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