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 · protocols of SSCs periodic inspections are produced. The results of SSCs inspection according to programme [82] from 30.06.2011 are provided in the completion certificate [79]. · automatic actions – emergency tripping system at an earthquake [80], item 7.2.4.2.3 [7],[8]. · automatic plant information systems is established and integrated with similar national system conducting continuous radiation monitoring within 3 km zone. · other scheduled measures to prevent, recover from and restriction of accident consequences. Following the accident in Fukushima Detailed programme was developed for review and assessment of Kozloduy NPP Co. preparedness for management and reduction of the consequences of beyond design basis accidents, external and internal impacts [84]. The results of the current work under the programme are summarized in the preliminary report [85]. According to item 2.4.2 [85] the number of portable submersible pumps in Power Generation 2 should be optimized, considering more adequate response at internal; floodings. Efficient and additional measures were proposed considering enhancement of protection at external and internal impacts (Appendix No. 1, [85]), item 2.4.2 [85]. Measures have been taken for development and updating of the emergency procedures for OSY personnel actions at earthquake, flooding, fire and explosion in departments, where needed, item 2.8.2 [85]. According to the information of item 2.9.2 [85] the emergency crew capability to perform the emergency plan and its procedures was tested realistically in an exercise for accident with earthquake and flooding. The persons responsible from the emergency activities management group according to the emergency procedure are familiarized with the procedure and properly follow it. 2.5.3 Assessment of indirect effects of the earthquake 2.5.3.1 Assessment of potential failures of SSCs not seismically qualified that can compromise heat removal to the ultimate heat sink by mechanical impact or by internal flooding Measures are provided to ensure that at destruction of elements with lower seismic class will not damage the SSCs required for nuclear installation shutdown and maintaining in safe shutdown mode. In this review general plant systems not seismically classified but important for coping with secondary post-earthquake effects are identified and analyzed. Measures taken to preserve their functionality during and after the earthquake are discussed. Within the framework of Modernization Programme [69] and [70] the following measures to prevent from seismically induced interactions have been analyzed and implemented: 75/202
“Kozloduy NPP” PLC SUMMARY REPORT for Conduct of Kozloduy NPP Stress Tests · implementation of a project to ensure free seismically induced movement of the cable channels; · implementation of a project for turbine hall reinforcement; · implementation of a project to reinforce structural elements of turbine hall over the cable channels; · coupled lines limiters have been mounted to prevent from damage to the safety systems neighbouring equipment. 2.5.3.2 Potential loss of off-site power due to destruction of the main site infrastructure After analyzing potential scenarios the following accident states that may be caused by a seismic impact lower than RLE and at RLE were defined [44]. 2.5.3.2.1 Total loss of AC power supply sources In 2006 a strategy was developed and implementation of activities started for alternative makeup of the steam generators from alternative systems at total loss AC power supply sources. The base for it is article 32, item 2, article 33, article 74 of [43]. The project was completed and in 2009 functional tests of SG alternative makeup system were conducted. The system is capable to provide makeup for the steam generators at initiating events with total loss of electric power supply of categories I and II as well as at unavailability of SG emergency makeup pumps (TX10-30D01). The system operates regardless of the standard systems of the unit using only part of the piping of one train of SG emergency makeup system. 2.5.3.2.2 Loss of OSY As the OSY is not qualified as Seismic category 1 there is potential for its failure also at a seismic impact lower than RLE. Moreover, that the national electric grid is seismically warranted by industrial standards for impacts lower than RLE and OBE. Thus, even at earthquakes lower than RLE there is potential for permanent loss of external power supply due to damage and destruction in the national power generation and power supply grid. The logics of the generator voltage of Units 5 and 6 of Kozloduy NPP are built by logic “generator – transformer ". The connection between unit and its parallel operation with the remaining units of the plant is provided at 400kV side of unit transformers. To improve the reliability generator circuit breakers are installed and transformers are connected between the circuit breaker and unit transformers. Thus auxiliary loads of the units can be powered from transformers with tripped generators. The connections between the elements of the main electric logic of the unit and deviations of transformers are made using phased capsulated bus wires 24kV. In transformers there is no switching equipment which increases the reliability. 76/202
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Summary Report for Conduct of Kozloduy NPP Stress Tests

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