Summary Report for Conduct of Kozloduy NPP Stress Tests

“Kozloduy NPP” PLC
SUMMARY REPORT
for Conduct of Kozloduy NPP
Stress Tests
Using the system as well as all other systems supplying boron solution to the primary circuit
heat removal from the primary circuit can be performed by feed-and-bleed procedure. The procedure
involves removal of the coolant from the primary circuit through leak (if any) or by opening primary
circuit valve to the containment and replenishment of resulting leak by means of these systems. The
removed steam-water mixture is liquefied by spray system, falls to the bottom of the containment
and into the boron solution emergency makeup tank (EMT). From EMT coolant is cooled through
heat-exchangers of essential components service water system, i.e. the heat is removed to the
alternative ultimate heat sink – the atmosphere, and by means of systems listed above, it goes back
to the primary circuit.
Emergency core cooling system – passive part.
Passive part of ECCS is a protective system (section 12 from [7],[8]) and is a part of the
safety systems designed for flooding of the core at large loss of coolant accident when the primary
circuit pressure drops below 5.9 MPa (60 kgf/cm 2 ).
The boron concentration in the hydro accumulators is 16 g/kg and ensures sub-criticality in
the reactor core. The system is designed so that the boron acid solution volume in three hydro
accumulators (out of four installed) to be sufficient at occurrence of double-ended break of the main
circulation line, for core cooldown before startup of primary circuit normal and emergency
cooldown pumps.
1.3.2.2.3 Availability of heat removal logics and measures to extend the systems operability
The equipment and pipelines of all active safety systems are physically separated and
protected against external events, which ensures impossibility of common cause failure of two or
more channels simultaneously. Service water supply system channels are spatially separated. Thus
the systems are capable of performing their functions considering single failure.
Electric power supply sources and inventories of working media and cooling water ensure
autonomy of safety for not less than 72 hours.
1.3.2.2.4 Heat removal systems AC and DC power supply
Electric power supply to the active components for each channel of the safety systems is
ensured for uninterruptible power supply І and ІІ category.
The equipment that cannot be de-energized for time over 20 ms is powered from I category
power supply, i.e. from the batteries. For Units 5 and 6 it is proved that one battery of safety system
train can bear full load for over 10 hours.
The capacity of the fuel storage tank of each emergency diesel-generator is 100 m 3 and
allows for 72 hours operation at full load, i.e. ensures power supply of the II category for at least 72
hours.
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