Summary Report for Conduct of Kozloduy NPP Stress Tests

“Kozloduy NPP” PLC
SUMMARY REPORT
for Conduct of Kozloduy NPP
Stress Tests
3.4.1.3.2.1 Rooms with drain pumps near the first and second staircase at reactor
compartment clean zone of units 5 and 6
In the reactor compartment of Units 5 and 6 premises of drain pumps to the first and second
staircase at elevation of -4,20 m are examined as it was found that rainwater and domestic sewage is
released from the building of the reactor department by these premises to the respective shafts
outside the reactor compartment.
Domestic and rainwater sewage enters vertically into the room and exits through the general
penetration. The pipes are steel, and their connections are welded. The lowest elevation of the sewer
pipe is 33.20, which is 0,27 m higher than the designated MWL. At reaching such a height of water
due to external flooding influx of water into reactor compartment through the sewage network is not
expected.
Engineering evaluation of leakage at rupture of pipes of domestic sewage in the room to the
first staircase (made of cast iron pipes and sealing of connections between pieces of lead калчища)
and the room to the second staircase (made of PVC pipes) has been performed. Based on the results
of the calculations the level of flooding from 0,32 m for premises of elevation -4,20 m is defined.
From the value obtained from water level at elevation -4,20 m at flooding from water retention of
domestic sewage it can be seen that:
· There is a margin of 38 cm to flooding of windings of the electric motors of the
pumps for the steam generators emergency makeup (the latter are located on the concrete
base with height from floor of 70 cm according to data from [36]);
· There is a margin of 8 cm to flooding of emergency control room. The room has a
threshold with height of 40 cm and does not have drain opening to the drain system. The
flooding of the room starts after increase of the water level above 40 cm.
It should be noted that for recovery of normal operational conditions after MWL an operable
drain system will be required.
3.4.1.3.2.2 Cable channels between the reactor compartment of units 5 and 6 and the
emergency diesel-generator stations
The cable channels connecting the diesel generator stations and reactor compartment of
units 5 and 6 are composed of trough elements with trapezoidal cross-section. The routes for all
cable channels are placed at elevation 31.00. Connections between the elements constituting the
cable channels are not watertight and in the presence of water above elevation 31.00, in the area
around them smooth entry of water inside the cable channels is expected. The compromising of the
cables, at flooding of the cable channels will depend on the state of their insulation.
Penetrations connecting cable channel to the reactor compartment and diesel generator
stations are repaired under the modernization programme and are seismic-resistant and waterproof.
Influx of water through these penetrations is nor expected.
3.4.1.4 Summary of safety margins at external flooding
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