Summary Report for Conduct of Kozloduy NPP Stress Tests

“Kozloduy NPP” PLC
SUMMARY REPORT
for Conduct of Kozloduy NPP
Stress Tests
2.4.3 Evaluation of indirect effects of the earthquake
2.4.3.1 Evaluation of potential failures of non seismically qualified SSCs that may
compromise heat removal to the ultimate heat sink through mechanical interaction or
through internal floodings
The analyses of condition of ventilation reinforced concrete chimney of the auxiliary
building 2 demonstrate proper robustness [61], but if scenarios with earthquake events with a level
over RLE are reviewed and analysed then falling of a part of the chimney is possible. According to
the analysis performed [44] it is evaluated that at falling of one third part of the length of the
ventilation chimney (50 m from its top), the debris will not affect the additional system for SG
emergency makeup (ASSGEM) of unit 4 and CPS-2, but will fall on the AB (its south-east part)
and radioactive contamination can hinder personnel access to some areas (e.g. ASSGEM building).
2.4.3.2 Potential loss of off-site power due to destruction of the main site infrastructure
At loss of off-site power backup power is supplied to the SFP cooldown pumps from
ASSGEM sections. Thus SFP condom pumps power supply is ensured both from the system dieselgenerator
and emergency diesel-generators of ASSGEM.
If conservative scenario is considered where events occur due to an earthquake causing
simultaneous occurrence of an accident in the nuclear installation of Power Generation 2 and
nuclear installation in Power Generation 1 and the need of using MDG in two places, it becomes
clear that availability of at least two MDGs is required.
2.4.3.3 Loss of ultimate heat sink
Essential components service water supply system ensures cooling water supply to the heat
exchangers for SFP cooldown and the backup supply is ensured by fire pump station 2, by means of
two headers, notched into the service water head pipelines.
According to the safety analysis of SFP [55] it is possible to connect additional alternative
systems for the pool flooding and cooldown that can replenish for sufficiently large flow-rate
maintaining the level in the SFP for the time of elimination of the leakage or for the time for the
fuel movement into the reactor.
An underwater protective barrier (overflow) is constructed before the section – “end curve
8” for restriction of overflow of the Danube water outside the advance chamber of CPS 2 back to
the cold channel. The scenario to cope with the consequences of loss of ultimate heat sink includes
Additional system for SG emergency cooldown.
If there is loss of BPS, for SG, with the standard systems components maintained (primary
and secondary circuits) water inventories enclosed in the advance chambers of CPS-2 and between
it and the advance chamber of CPS-1 and underwater barrier at end curve 8 are used.
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