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 availability of the siphons at elevation of -4.50 = 31,10m). Pumps of ASSGEM system are located at elevation of -3.00 m which determines that they will be affected at MWL more than +32,50 m. The only scenario is isolation of water supply systems „Zhelezni vrata” 1 and 2 as a result of the earthquake. however in this case the effect of MWL will be executed at sufficiently later phase of accident progress process (about 20 hours after the earthquake). In accordance with results of assessment of the margins at extreme meteorological conditions it is defined that due to closed and self-contained nature of the spent fuel storage system, SFP 3 and 4 and their auxiliary systems there is a high safety level in relation to external factor „Extreme winds and tornados”. 6.1.3.2.3 Unavailability of the power supply In accordance with results of assessment of margins to loss of electric power and loss of ultimate heat sink, it is defined that power supply to these systems for cooling of the fuel in SFP-3 and SFP-4 is provided from various physically separated sources (emergency diesel generators – three per unit, emergency diesel-generators of ASSGEM, mobile DG). At low value of decay heat of the fuel stored in the pools. Available time margin before the assemblies uncoverage starts is about one week for SFP-3 and more than 9 days for SFP-4 at assumption of complete loss of cooling. 6.1.3.2.4 Potential failure of measurement instrumentation Within short-term modernization program of the units analysis was done for definition of environmental parameters for equipment qualification at emergency conditions. As the first step of the qualification the sensors of emergency protection chains were replaced with qualified sensors of Emergency protection chains. For some the sensors related to safety, new location was selected, and they were moved to area which does not require qualification on extreme environmental conditions. As a result, at present all the measurement channels, related to reactor protection are qualified for correspondent seismic and environmental conditions. For conditioning of process parameter signals, precise digital equipment is used. Uninterrupted power supply units (UPS) additionally isolate power supply to these channels, by which independence is assured for the power supply to the channels. In addition to that the qualification program is executed for the remaining equipment related to safety, including test of samples of equipment for ageing, seismic and environmental conditions at loss-of-coolant accident. On the basis of results of the qualification program the remaining safety-related sensors were also replaced. To support Operator actions additional set of the computerized systems was implemented, such as: · Computerized system for supporting the operator and recording the process parameters at normal operations and in case of accident; 181/202
“Kozloduy NPP” PLC SUMMARY REPORT for Conduct of Kozloduy NPP Stress Tests · Safety-related parameters display system based on own qualified transducers (SPDS); · New digital systems for fire detection and fire annunciation allowing the operator for timely localization of fire; · Multiple additional alarms from the local boards, outside the MCR. · Failure to stationery systems for monitoring of radiation background, temperature and water level in the SFP is possible to be replenished for with portable measurement means. 6.1.3.2.5 Potential impacts from other neighbouring installations at the site The design assumes impacts from the neighbouring unit due to location of Fuel storage pools (SFP) of Units 3 and 4 in common premise of the Central Hall in the reactor compartment. The design envisions also common plant control and monitoring rooms (of both units): · dose rate control post; · control room of the reactor compartment, special water purification and process ventilation (RC CR); In case of accident at Units 5 and 6 and SFS, the personnel of Units 3 and 4 acts in accordance with NPP Emergency Response Plan. 6.1.3.3 Factors which can prevent management of accident of units 5 and 6 6.1.3.3.1 Impact on accessibility and habitability of the MCR and SCR, measures to prevent or control the situation Management of the reactor installation, control of conditions of the reactor, management and control of the process systems during normal operation modes and at emergency conditions are provided at the MCR (main control room). At the MCR, controls are located for the process safety systems, normal operation safetyrelated systems and normal operation systems. MCR is located in separate premise, in the reactor compartment building outside the containment in the “clean” area and is assigned the first category on the seismic stability. Location of the MCR is on the elevation the lower than the reactor. Design accidents related to loss of coolant do not affect the MCR. As a result of analyses of beyond design seismic impacts the civil structure of the MCR and adjacent premises maintains its integrity. At analyses of beyond design combined impacts of the earthquake and off-site flooding, the MCR also maintains its functionality. At analyses of beyond design impacts of off-site flooding, the MCR is not affected. At severe accident, the MCR may become inhabitable, if the melt penetrates through the foundation of the containment [148]. 182/202
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Summary Report for Conduct of Kozloduy NPP Stress Tests

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