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 SCR (Standby control room) is intended, in case of failure to the MCR, for reliable transfer of the unit in undercritical cold condition and for maintaining the unit in that condition for unlimited time, for actuation of the safety systems and for receiving information on condition of the reactor. SCR is located at elevation of -4.20 in reactor compartment. The premise of the standby control room is assigned category I of the seismic stability. Design accidents related to loss of coolant do not affect the MCR. As a result of analyses of the beyond design seismic impacts the civil structure of the SCR and adjacent premises maintains its integrity. At analyses of beyond design combined impacts of the earthquake and off-site flooding is possible - the SCR will be flooded. At analyses of the beyond design impacts of off-site flooding it is possible that the adjacent premises of the SCR are flooded what will hinder access to the premise. 6.1.3.3.2 Feasibility and efficiency of measures for accident management in conditions of offsite hazards (earthquake, flooding) The design of Units 5 and 6 of Kozloduy NPP is robust to impacts of the off-site hazards. The reactor and the main structures of the primary circuit are located in the reinforced concrete containment, intended to localize radioactive products after accident in its own space which is qualified for seismic impacts of 0,2 g [7], [8].The main systems and components of the safety systems and these safety-related systems also are located in buildings qualified for seismic impacts 0,2g [7], [8]. Analyses of beyond design seismic impacts show that to seismic impacts 0.36 g structures with which accident management are provided, are available. At analyses of beyond design combined impacts of the earthquake and off-site flooding it is shown that safety functions are performed of units 5 and 6 with survived equipment. At analyses of beyond design impacts of the off-site flooding it is shown that systems and equipment required for performing safety functions, are not affected. Personnel of Units 5 and 6 takes measures in accordance with Emergency procedures of the units to shut down the reactor and maintain it in safe condition. In parallel with the emergency procedures of Units 5 and 6, on-site and off-site emergency response plan will be initiated according to Appendix 3.2 of [28]. 6.1.3.3.3 Unavailability of the power supply Impacts of unavailability of the power supply to Units 5 and 6 of the Kozloduy NPP were analyzed within assessment of loss of power supply and loss of ultimate heat sink. All the options were assessed of sequential loss of sources of electric power supply. Virtually availability of equipment is reduced for accident management, but the design has available sufficient standby power supply sources, actuation of which leads to restoration of the equipment required for accident management. Recovery operator actions are described in the Emergency procedures. 6.1.3.3.4 Potential failure of measurement instrumentation 183/202
“Kozloduy NPP” PLC SUMMARY REPORT for Conduct of Kozloduy NPP Stress Tests Failure to measurement instrumentation is analyzed at assessment of the earthquake, and potential failure of measurement instrumentation does not lead to loss of information due to triple redundancy of the measurement channels. The unit has available Post accident monitoring parameters system (PAMS) which is entirely seismically qualified, including the measurement channels, and these also have triple redundancy. 6.1.3.3.5 Potential impacts from other neighbouring installations at the site In case of accident at Units 3 and 4 and SFS, the personnel of Units 5 and 6 acts in accordance with NPP Emergency Response Plan. 6.1.3.4 Factors which can prevent management of accident at the SFS 6.1.3.4.1 Impact on accessibility and habitability of control room and SFS, measures to prevent or control the situation At complete drainage of SFP compartments dose rate is expecetd to reach the values requiring appropriate level of intervention. 6.1.3.4.2 Feasibility and efficiency of measures for accident management in conditions of offsite hazards (earthquake, flooding) In accordance with assessment performed for the earthquake it is defined that SFS may perform its functions for safe storage of the spent fuel at seismic acceleration within the range of 0.12 – 0.39g. Prolongation of time for safe storage of fuel in this situation depends upon the possibility of removal of construction debris and upon restoration, if it is possible, of the natural ventilation. 6.1.3.4.3 Unavailability of the power supply Analysis of the postulated initiating events due to loss of power supply to SFS shows that uncoverage of the spent fuel stored in the storage pool, is not reached. 6.1.3.4.4 Potential failure of measurement instrumentation Failure to stationery systems for monitoring of radiation background, temperature and water level in the compartments, is possible to be replenished for with portable measurement means. 6.1.3.4.5 Potential impacts from other neighbouring installations at the site In accordance with assessment performed for the earthquake it is defined that Ventilation stack - 2 possesses the required seismic safety, and at earthquake level of the RLE damage is not expected to SFS building or emergency DG building as well as difficulties to access them. In case of accident of Units 3 and 4, Units 5 and 6, the personnel of SFS acts in accordance with NPP Emergency Response Plan. 184/202
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Summary Report for Conduct of Kozloduy NPP Stress Tests

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