Protection against external events

PROTECTION AGAINST EXTERNAL EVENTS

The design criteria for the structures, systems and components important for safety take into account the characteristics of the most severe natural phenomena that are historically inherent to the Belene site, the relevant combinations of normal and natural phenomenon conditions, as well as the significance of safety functions to be implemented.

Building structures and equipment falling within this category (category I) are calculated to withstand the following specific natural impacts:

Extreme wind and snow loads, temperature loads, and other extreme weather loads with a likelihood of occurrence - once in 10,000 years;
Maximum Design Basis Earthquake (MDBE) with a likelihood once in 10,000 years;
Loads from flying objects during extreme environmental impacts;
Flooding of the site with likelihood once in every 10,000 years.

In calculating building structures, impacts of extreme loads are considered together with the operational loads. A special case is postulated when calculating the containment and the elements ensuring its functions - simultaneous impact of MDBE (SL-2) and design basis accident.

Structures of buildings and facilities of category I are calculated to withstand the loads, resulting from external technogenic impacts, including air shock wave, flying objects, falling of an aircraft.

The fall of a military aircraft is considered for a design basis impact from an airplane crash. Design takes account also of the impact of the crash of a large commercial aircraft.

Building structures of I category of seismic resistance are verified for seismic impact exceeding MDBE by 40%.

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