Summary Report for Conduct of Kozloduy NPP Stress Tests

“Kozloduy NPP” PLC
SUMMARY REPORT
for Conduct of Kozloduy NPP
Stress Tests
To increase the reliability and reduce potential of total loss of power supply to OSY 400 kV,
the system is designed as double section busbar system.
To increase the reliability of Units 5 and 6 with power of 1000 MW is principle of its
connection to 400 kV side by logic “two circuit breakers for connection” has been adopted.
2.5.3.2.3 Loss of safety systems power supply
3 batteries are provided per one for the three trains of the safety systems. The batteries
operate in continuous charging mode with their charging provided from rectifiers constituting a
UPSS compound. According to [7],[8] the batteries are charged for at least 2 hours (to 3 hours for
new batteries) at maximum load (for AC voltage – in inventors). Based on the tests performed it
was identified that the batteries last over 10 hours at real load [83].
2.5.3.2.4 Loss of category II emergency power supply sources
The required inventories of fuel and oil for continuous operation of emergency sources of
category II power supply are provided as follows, [45]:
- DGS-5,6 from safety systems: general operational fuel inventory ensures continuous
operation of each DG for at least 3 days;
- DDG-5,6: 70 hours’ operation ensured;
- Diesel pumps in CPS-3,4: 24 hours’ operation of all pumps (8) simultaneously;
- DG “Emergency preparedness”: 8 hours’ continuous operation of DG at nominal load
without charging.
2.5.3.3 Loss of ultimate heat sink
Essential components service water supply system design does not provide for specific
measures to maintain cooling water supply.
In the essential components service water supply system principles of redundancy, physical
separation and independence of the trains is adopted.
For units 5 and 6 six spray pools are built. The system trains operate by a closed circuit with
water cooling in the spray pools. Each spray pool is designed to remove all the heat generated in an
accident mode of the unit and to ensure service water temperature for essential components cooling
within the range from +4°С to +33°С. in selection of the sizes of the spray pools, level change from
1.5 m ensures group A service water supply system operation without filling of the pool with wind
speed up to 2 m/s for 30 hours.
Normal and emergency makeup of the spray pools is provided. The makeup is provided
from normal electric pumps and in case of loss of external power supply from diesel pumps. The
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