Summary Report for Conduct of Kozloduy NPP Stress Tests

“Kozloduy NPP” PLC
SUMMARY REPORT
for Conduct of Kozloduy NPP
Stress Tests
1.6.3.1 Connections for steam and water
Connections for steam between units 3 and 4 are provided between main steam header, and
between units 4, 5 and 6 – between the main steam header of the fourth unit and the auxiliary steam
headers of units 5 and 6 (line Dcon 273 mm).
Connections for boron solutions between units 5 and 6 are provided through the pipelines of
boron solutions purification and preparation systems common for both units. Connections between
Units 3 and 4 is also by means of general systems for boron solutions purification and preparation.
Demineralised water supply between the units of the site is provided by suction pipeline
connecting respective condensate tanks, while it is possible to supply demineralised water to the
SFS from a header connecting units 4 and 6 [7].
1.6.3.2 Connections for fire ring
As mentioned in item 1.1.2.2.3 on the site of Units 3 and 4 and the site of Units 5 and 6
indoor and outdoor fire lines (ring) have been built.
Water supply to the fire lines located at the site of Units 3 and 4 are made of 8 fire pumps
and two diesel pumps. The pumps take water from conventional components service water and the
"cold" channel.
Service water supply to fire ring of units 5 and 6 is performed with water from Danube
River, through five fire pumps installed in the circulation pump stations 3 and 4. At fire in any of
the facilities, water supply for automatic fire extinguishing from internal fire protection ring
automatically starts one of the six main fire pumps, and at non-operability of all electric pumps one
of the four emergency fire diesel pumps starts.
In case of failure of the facilities for fire needs water supply from the circulation pump
stations emergency connection between fire rings of units 5 and 6 and units 3 and 4 is constructed.
The emergency connection valves are in closed position without voltage. The valves control can be
both remote and local.
1.7 SCOPE AND MAIN RESULTS OF PSA
1.7.1 Scope and main results of PSA of Units 3 and 4
For risk informed review of current design and operation aspects as well as significance of
modifications implemented on units 3 and 4 of Kozloduy NPP full-scale PSA has been performed.
Later and multiple updates of probabilistic studies were carried out and repeatedly extended in
scope, structure and methodology, so that to reflect both the current state of the plant, after
numerous upgrades, and the development of the analyses methods. The summerized results of PSA
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