Summary Report for Conduct of Kozloduy NPP Stress Tests

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“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 29/202
“Kozloduy NPP” PLC SUMMARY REPORT for Conduct of Kozloduy NPP Stress Tests The heat removal logics can be divided mainly into two types: · Heat removal to the ultimate heat sink – River Danube; · Heat removal to the ultimate heat sink – the atmosphere. Main ultimate heat sink from the reactor to units 5 and 6 is provided by water of Danube River. At loss of the main ultimate heat sink systems are provided to remove heat to the alternative ultimate heat sink which is the atmosphere. Heat removal to the main ultimate heat sink is ensured from circulating water system where heat is transferred through turbine condenser by cooling of the steam entering supplied to it to the circulating water which in turn returns to River Danube (Figure 1.3-1). This process is used both during unit operation and with the turbine tripped at primary circuit temperature approximately to 120°C. In case of loss of main ultimate heat sink – River Danube – ultimate heat sink – the atmosphere – can be used. This can be done through heat removal from the steam generators to the atmosphere by means of steam dump through the BRU-A. In this case the steam generators can be supplied from feedwater or emergency makeup water system. At primary circuit temperature decrease below 120°C, the only way of cooldown remains the socalled water-water cooldown which in turn uses the atmosphere as the ultimate heat sink. Reactor heat removal is done through emergency and normal core cooling system to essential components service water supply system which circulates by closed circuit and transfers heat from the reactor to the atmosphere through spray ponds (Figure 1.3-2). . 30/202
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Summary Report for Conduct of Kozloduy NPP Stress Tests

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