Summary Report for Conduct of Kozloduy NPP Stress Tests

“Kozloduy NPP” PLC
SUMMARY REPORT
for Conduct of Kozloduy NPP
Stress Tests
· implementation of a project to ensure free seismically induced movement of the
cable channels;
· implementation of a project for turbine hall reinforcement;
· implementation of a project to reinforce structural elements of turbine hall over the
cable channels;
· coupled lines limiters have been mounted to prevent from damage to the safety
systems neighbouring equipment.
2.5.3.2 Potential loss of off-site power due to destruction of the main site infrastructure
After analyzing potential scenarios the following accident states that may be caused by a
seismic impact lower than RLE and at RLE were defined [44].
2.5.3.2.1 Total loss of AC power supply sources
In 2006 a strategy was developed and implementation of activities started for alternative
makeup of the steam generators from alternative systems at total loss AC power supply sources.
The base for it is article 32, item 2, article 33, article 74 of [43].
The project was completed and in 2009 functional tests of SG alternative makeup system
were conducted. The system is capable to provide makeup for the steam generators at initiating
events with total loss of electric power supply of categories I and II as well as at unavailability of
SG emergency makeup pumps (TX10-30D01). The system operates regardless of the standard
systems of the unit using only part of the piping of one train of SG emergency makeup system.
2.5.3.2.2 Loss of OSY
As the OSY is not qualified as Seismic category 1 there is potential for its failure also at a
seismic impact lower than RLE. Moreover, that the national electric grid is seismically warranted
by industrial standards for impacts lower than RLE and OBE. Thus, even at earthquakes lower than
RLE there is potential for permanent loss of external power supply due to damage and destruction
in the national power generation and power supply grid.
The logics of the generator voltage of Units 5 and 6 of Kozloduy NPP are built by logic
“generator – transformer ". The connection between unit and its parallel operation with the
remaining units of the plant is provided at 400kV side of unit transformers. To improve the
reliability generator circuit breakers are installed and transformers are connected between the circuit
breaker and unit transformers.
Thus auxiliary loads of the units can be powered from transformers with tripped generators.
The connections between the elements of the main electric logic of the unit and deviations of
transformers are made using phased capsulated bus wires 24kV. In transformers there is no
switching equipment which increases the reliability.
76/202