Summary Report for Conduct of Kozloduy NPP Stress Tests

“Kozloduy NPP” PLC
SUMMARY REPORT
for Conduct of Kozloduy NPP
Stress Tests
2.10.4 Evaluation of safety margins against earthquake for SFS
The SFS margin is at least 0,16g or 80% considering RLE (PGA=0.2 g), i.e. SFS can bear
without fuel damage at an earthquake by 1,8 times greater than the RLE re-evaluated and valid as
per 30.06.2011.
2.10.4.1 Assessment of the seismic impact leading to severe fuel damage.
Based on the analysis performed in [44] it can be concluded that with the restrictions placed
in [45] SFS can perform the functions for safe storage of the spent fuel up to seismic impact in the
range of 0.36 – 0.39 g, after which collapse of the main support structure occurs and the capability
of the building for natural ventilation of the pool cooling fails. Extension of the time for safe storage
of the fuel in this situation depends on the possibility for cleaning the construction debris and
recovery, if possible, the natural ventilation.
2.10.4.2 Evaluation of the seismic with loss of SFS integrity
According to the approach applied in analysis [44] seismic accelerations at which it is
accepted that the structure integrity fails and it cannot ensure natural air circulation required for the
fuel damage were defined. The following values are obtained:
· destructive acceleration for columns by row D (190/50 cm) – 0.39 g;
· destructive acceleration for columns by row (60/50 cm) – 0.44 g.
Therefore, in the below part of the considered range of seismic acceleration destruction of
the main support columns of SFS and falling of roof and the cranes over the pools cover can be
anticipated. This may potentially lead to damage to the shells storing the fuel and to damage of the
reinforced concrete structure of the pools coupled with significant leaks in the damaged sections.
2.10.4.3 Scenario with beyond design basis earthquake followed by the beyond design basis
flooding
According to the results of [89], there are no SSCs that will be affected by the MWL.
Therefore, for this nuclear installation scenario with combination of beyond design basis earthquake
and beyond design basis flooding as the effect of external events is defined in the framework of
[63].
2.10.4.4 Measures to enhance robustness of SFS
With regard to SFS measures to increase robustness are not proposed as its margin is fully
dependent on the capacity of the civil structure.
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