Summary Report for Conduct of Kozloduy NPP Stress Tests

“Kozloduy NPP” PLC
SUMMARY REPORT
for Conduct of Kozloduy NPP
Stress Tests
facilities are: a temperature between 0ºC to -4ºC, wind speed between 0 and 3 to 5 m/s and relative
humidity along Danube River between 95 and 100%.
With data from meteorological monitoring system in the last four years a combination of
such conditions was not observed in the region of Kozloduy, which is mainly due to lower levels of
humidity. The risk of icing conditions on the basis of the last 11 years has averaged 2% annually.
This means that freezing is relatively rare.
4.1.3 Extreme precipitations
The annual rainfall in the region is about 518-558 mm and is one of the lowest in the
country, due to rainfall "shadow" of the Southern Carpathians in the ocean incursions from the
west. It is unevenly distributed throughout the year. In autumn rainfall is about 130 mm, which
represents 23-25% of the annual amount. In winter rainfall is about 110-120 mm (20-23%), in the
spring - 135-150 mm (24-29%), and in summer 145-150 mm (26-29%) [7], [8].
In some years a number of days with precipitation can reach 4-5 days. Heavy rains with high
intensity are of short duration. Maximum 24 hours for Kozloduy are 86 ÷ 87 mm [7], [8].
4.1.4 Lightning
ZEUS lightning recording system has been in operation for several years and the data it
receives for the field with coordinates 0 – 32 0 Е and 31 – 46 0 N which includes the territory of
Bulgaria shows that the number of recorded lightning over land is more significant from April to
September as compared to the other months of the year. For Kozloduy territory within a radius of
about 50 km for the summer months June, July and August of 2005 and 2006 around 3000-4000
lightning were recorded. Considering that the average three-month period in the world is over 5000,
it can be estimated that the number of lightning in the area of Kozloduy NPP is below average
statistical values [140].
4.1.5 Extreme snowfalls
Snow in the region is volatile and with relatively shallow depth due to the fact that stable
snow cover is typical of regions with average January temperatures below -3 º C. There is no
characteristic period of the calendar year in which snow cover is regularly formed [139].
The average annual snow cover height does not exceed 20 cm. Of the greatest recurrence of
24-30% is the height of 11-20 cm. Considered in decades, in winter months snow cover height for
not more than 3-4 days is about 5 cm. This allows for excluding the possibility for the water
reserves in the snow cover in the region of Kozloduy to be involved in possible flooding even
during sudden warming [139].
Height of snow cover of 70-80 cm has a low recurrence - only 3% (1 to 2 days, based on the
past data for 1977). This value is considered extreme.
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