Summary Report for Conduct of Kozloduy NPP Stress Tests

“Kozloduy NPP” PLC
SUMMARY REPORT
for Conduct of Kozloduy NPP
Stress Tests
supply boric acid solution through the primary circuit makeup and blowdown system and need for
attenuation of reactor at primary circuit high pressure (9-18 MPa).
Intermediate pressure emergency boron injection system.
The system is designed for emergency injection of emergency boric acid solution to the
primary circuit with concentration of 40 g/kg in case of loss of off-site power or in case of failure to
supply boric acid solution through the primary circuit makeup and blowdown system and need for
attenuation of reactor at primary circuit intermediate pressure (below 11 MPa).
1.3.2.1.2 Systems ensuring core criticality with the reactor depressurized
With the reactor depressurized and presence of fuel in the core before and after refuelling
criticality of the core is provided the control rods in fuel and the boric acid solution solution with
concentration ≥ 16 g/kg circulating in the primary circuit and emergency and normal cooling
system. Material balance of the coolant can be maintained by boron solution from primary circuit
emergency makeup tank (EMT).
During refuelling the material balance of the entire system consisting of fuel storage pool,
reactor, primary circuit and emergency and normal cooldown system is maintained with boric acid
solution with concentration ≥16 g/kg through SFP water filter purification system or reactor building
boron containing water system.
The fuel sub-criticality during all stages of refuelling outage measures is ensured by taking
measures to prevent from penetration of clean condensate to the reactor circuit and SFP and to carry
out automatic and manual physical and chemical monitoring of the coolant content.
1.3.2.1.3 Systems ensuring fuel storage pool sub-criticality
The spent fuel sub-criticality for at least 5% in SFP is ensured through: reliable remoting of
the cells for storage during the entire period of operation of the SFP; use of homogenous absorber on
the water of SFP with boric acid solution with concentration 16 g/kg; use of effective fixed
heterogenuous absorbers that do not lose their properties in the process of operation. The cells for
assemblies are designed from borated stainless steel. The absorbing capacity (at burnup of 10 B and
wall depth reduction due to the corrosion) of the racks cells is preserved during the entire service
life.
Maintaining the level and water chemistry of the SFP is ensured by SFP water purification
system. At fuel storage the level is maintained at height +28.8 m with total volume of 585 m 3 . In
refuelling mode SFP is connected to the refuelling shaft and the water level is maintained at the
height of +36.2 m which requires additional water inventory (about 1400 m 3 ) ensured by SFP water
purification system.
1.3.2.2 Reactor Heat Removal to the Ultimate Heat Sink
1.3.2.2.1 Heat removal logics
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