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 2.4.3 Evaluation of indirect effects of the earthquake 2.4.3.1 Evaluation of potential failures of non seismically qualified SSCs that may compromise heat removal to the ultimate heat sink through mechanical interaction or through internal floodings The analyses of condition of ventilation reinforced concrete chimney of the auxiliary building 2 demonstrate proper robustness [61], but if scenarios with earthquake events with a level over RLE are reviewed and analysed then falling of a part of the chimney is possible. According to the analysis performed [44] it is evaluated that at falling of one third part of the length of the ventilation chimney (50 m from its top), the debris will not affect the additional system for SG emergency makeup (ASSGEM) of unit 4 and CPS-2, but will fall on the AB (its south-east part) and radioactive contamination can hinder personnel access to some areas (e.g. ASSGEM building). 2.4.3.2 Potential loss of off-site power due to destruction of the main site infrastructure At loss of off-site power backup power is supplied to the SFP cooldown pumps from ASSGEM sections. Thus SFP condom pumps power supply is ensured both from the system dieselgenerator and emergency diesel-generators of ASSGEM. If conservative scenario is considered where events occur due to an earthquake causing simultaneous occurrence of an accident in the nuclear installation of Power Generation 2 and nuclear installation in Power Generation 1 and the need of using MDG in two places, it becomes clear that availability of at least two MDGs is required. 2.4.3.3 Loss of ultimate heat sink Essential components service water supply system ensures cooling water supply to the heat exchangers for SFP cooldown and the backup supply is ensured by fire pump station 2, by means of two headers, notched into the service water head pipelines. According to the safety analysis of SFP [55] it is possible to connect additional alternative systems for the pool flooding and cooldown that can replenish for sufficiently large flow-rate maintaining the level in the SFP for the time of elimination of the leakage or for the time for the fuel movement into the reactor. An underwater protective barrier (overflow) is constructed before the section – “end curve 8” for restriction of overflow of the Danube water outside the advance chamber of CPS 2 back to the cold channel. The scenario to cope with the consequences of loss of ultimate heat sink includes Additional system for SG emergency cooldown. If there is loss of BPS, for SG, with the standard systems components maintained (primary and secondary circuits) water inventories enclosed in the advance chambers of CPS-2 and between it and the advance chamber of CPS-1 and underwater barrier at end curve 8 are used. 69/202
“Kozloduy NPP” PLC SUMMARY REPORT for Conduct of Kozloduy NPP Stress Tests An emergency pump station directly before BPS-2 and 3 was built. The emergency pump station ensures independent water supply from the advance chamber of BPS-2 and 3 to cold channel after end curve 8. If due to some reason the spray pool function fails, for nuclear installation cooling ASSGEM-3,4 systems are used whose inventory tanks have backup power supply besides fire water and artesian wells water in the site. 2.5 PROVISIONS MADE FOR PROTECTION AT RLE OF UNITS 5 AND 6 The actual state and the operability of the equipment has been identified based on the review of the elements (components) seismic qualification and the method for performance of the seismic qualification of SSCs of seismic category 1 [44]. 2.5.1 Systems, structures and components (SSCs), required for bringing and maintaining of units 5 and 6 in safe shutdown mode Based on the SSEL existing in the plant SSCs required for nuclear facility shutdown and maintaining in safe condition that need to remain operable during and after earthquake have been identified. The analyses performed [44] are focused mainly on the reactor installation at power operation and specifically on the limits for ensuring integrity of the second protective barrier – fuel elements cladding. The stress tests for SFP cover respective structures at operations with SNF (the most adverse operational states allowable by the technical specifications), again considering the fuel elements cladding integrity. The elements seismic qualification has been reviewed having established the current status and operability of the equipment. All buildings and facilities related to the unit nuclear safety have been analyzed in the framework of Modernization Programme of Units 5 and 6, according to the new requirements for seismic stability. 2.5.1.1 Buildings Seismic stability of all safety related buildings and structures has been reviewed in the framework of modernization programme of Units 5 and 6 for site specific impact. Seismic qualification of the main civil structures of Units 5 and 6, Seismic category 1, has been performed as follows: · Reactor building; · SFP-5,6; · Diesel-generator stations including underground tanks; · Auxiliary building. Liquid radioactive waste storage; 70/202
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Summary Report for Conduct of Kozloduy NPP Stress Tests

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