Summary Report for Conduct of Kozloduy NPP Stress Tests

“Kozloduy NPP” PLC
SUMMARY REPORT
for Conduct of Kozloduy NPP
Stress Tests
· unit 6: The function will be used according to the design bases, i.e. all the system
trains will be available as they will not be affected by the earthquake. Due to the flooding of
ShPS, inventories in the spray ponds guarantee 90 hours’ performance of the function at
stage by stage switching of the available trains.
Obviously, for Unit 5 of Kozloduy NPP appropriate solutions shall be found for filling of
spray ponds and/or using inventories from water of the first train of the safety systems.
Reactor. Cold state
In this condition the heat is removed from the fuel by operation of emergency and normal
cooldown system by the line for scheduled or maintenance cooldown. The ultimate heat sink is the
spray pools.
When considering the scenario with combination of beyond design basis earthquake with
beyond design basis flooding, the functionality of either operating systems (emergency and normal
cooldown system or essential components service water supply system) does not depend on the
water level, i.e. performance of the safety functions is fully determined by the earthquake impact.
Therefore, for this condition scenario with combination of beyond design basis earthquake
with beyond design basis flooding is not considered as the earthquake effect has been defined under
[44].
SFP
SFP fuel heat removal is provided by joint operation of the SFP cooldown system or
essential components service water supply system.
When considering scenario with combination of beyond design basis earthquake with
beyond design basis flooding, the functionality of either operating systems (SFP cooldown or
essential components service water supply system) does not depend on the water level, i.e. here also
performance of the safety functions is fully determined by the earthquake impact.
Therefore, for this condition scenario with combination of beyond design basis earthquake
with beyond design basis flooding is not considered as the effect of the external events has been
defined under [44].
2.10.3.4 Measures to enhance robustness of Units 5 and 6
After the completed analyses for units 5 and 6 of Kozloduy NPP it is recommended to
perform study of capabilities for alternative residual heat removal after failure of essential
components service water supply system. In this proposal consideration is given to possible use of
ASSGEM system which is available in Kozloduy NPP site.
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