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 Potential to reach 1% 0,1% 0,01% Water level 29,93 m 30,87 m 31,73 m The Updated Safety Analysis Report [7] confirmed maximum water levels in natural modes: Potential to reach 1% 0,1% 0,01% Water level 30,58 m 31,47 m 32,23 m In a study of Energoproekt for “Reassessment of maximum flooding” Part I, December 1991, and Part II, March 1993, maximum water levels in case of postulated destruction of the water supply system "Iron Gate" 1 and 2 are set out. Considering overflow and destruction of dikes and accumulation of the high wave from flooded plains the maximum level is 31,43 m, with 0,80 m lower than the design 32,23 m. In 2010 a survey was conducted in conjunction with the design of Belene NPP to determine the hydrologic and hydraulic characteristics of the Danube River [106]. According to the survey the maximum water level in the Kozloduy NPP in the course of catastrophic wave caused by the destruction of this water supply system "Iron Gate" is 32,53 m. This MWL is reached 28 hours and 20 minutes after the anticipated destruction of the water supply system "Iron Gates 1" and will last approximately 2 hours. In all postulated cases involving extreme increase in the level of the Danube River the elevation of MWL at flooding is lower than elevation 0.00 of the site, which confirms the definition of the plant site “NON-FLOODING”. 3.1.2.1.2 Definition of MWL due to rupture of the dam of lake "Shishmanov shaft" The flooding of the plant site due to rupture of the dam of "Shishmanov shaft” has been studied. As a result of this study in the destruction of the wall with present water quantity of 2 885 600m3 it can be calculated that the water level will not exceed elevation 25.50 and will not jeopardise the plant safety. In the theoretical assumption that the volume of the impoundment is limited to the maximum extent possible (8,1.106 m3), actually effective volume is 6 990 000 m3 (dead volume - 1 110 000m3). In case of release of this quantity of water from the dam it is anticipated that the main damage from flooding will be caused rather to the town of Kozloduy. The flooding of the plain northwest of Kozloduy NPP assessed under an expert review will not exceed elevation of 29.00, i.e. this water level is not a direct danger to the plant with the elevation 35.00. The only possible variant is to disable shaft pumps stations in a short time. 3.1.2.1.3 Definition of MWL from tributary valley “Marichin Valog” 103/202
“Kozloduy NPP” PLC SUMMARY REPORT for Conduct of Kozloduy NPP Stress Tests Another potential source of flooding of the plant site is the tributary valley “Marichin Valog”. It is preceded with a small tributary of the Danube River with non-constant water swelling. In the late 70-s, near the spray pools an erosive gully with a depth of 5m passed, which was subsequently corrected and filled. This action has eliminated the possibility of flooding of the plant site from this source. 3.1.2.1.4 Definition of MWL from slope water from location “Marishkin Dol” To ensure smooth passing of high water quantities from the slope waters around "Marishkin Dol", the slope waters to the west of Kozloduy NPP site and water from irrigation channel M-1 (sized to have a throughput of 3,20m 3 /s) at overflow or leakage of its siphons, a drainage channel was built to the west of the plant site with section 9.00m2. The construction of this channel ensured elimination of ravine generation and flooding hazard at Kozloduy NPP site from the aforementioned sources. 3.1.2.2 Methodology used for assessment of design basis flooding As methodology for definition of the MWL the methodology of the study provided in report [106] is adopted. The report discusses tracing of the movement and the overlaying of catastrophic waves caused by destruction of dams in lower Danube. The most important is the first scenario considered, assuming sequential destruction of the existing water supply system “Iron Gates” 1 and 2. In this scenario, catastrophic wave is overlaid on the basic quantity Q0 = 10 000 m3/s. This destruction logic aims to obtain the maximum possible parameters of the wave resulting from overlaying of two waves. The resulting maximum water level in the Kozloduy NPP is 32,53 m. It would be reached 28 hours and 20 minutes after the assumed destruction of water supply system "Iron Gates 1" and will last approximately 2 hours. It is 30 cm higher than the design MWL under natural conditions, but is 2,47 m below the site elevation 0.00. 3.1.2.2.1 Influence of heavy rainfalls The rain downstream Danube River over the Kozloduy NPP is involved in the statistical determination of natural MWL and should not be added to it again. Otherwise, however, there is a question in the calculations for the flow of catastrophic wave caused by destruction of water supply system "Iron Gates 1". The rain from the plane around Kozloduy NPP and the river bank can be involved in raising the water level around the site. Precipitations with probability p = 0.01% and catastrophic wave from destruction on the walls of the "Iron Gates" are independent events and the likekihood of simultaneous occurrence is negligibly low and should not be overlapped. Assuming also precipitation probability 0.01%, the probability to occur simultaneously is 0.01 x 0.01 = 0.0001%. This probability is unacceptably small for nuclear power plants. Therefore, it is more realistic to assume an additional increase in water level due to rainfall with greater probability, e.g. approximately p = 1%. In this sense, at the 104/202
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Summary Report for Conduct of Kozloduy NPP Stress Tests

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