Summary Report for Conduct of Kozloduy NPP Stress Tests

“Kozloduy NPP” PLC
SUMMARY REPORT
for Conduct of Kozloduy NPP
Stress Tests
3 EXTERNAL FLOODINGS
3.1 DESIGN BASIS
The Bulgarian legislation in accordance with Section II, Article 29, paragraph 3 of
"Regulations for ensuring nuclear safety of nuclear power plants" provides the following wording
of requirement for external flooding:
"For the site of Kozloduy nuclear power plant the maximum water level and duration of
possible flooding in case of rainfall, intense snow melting, high water level in the reservoir,
blocking of the river from ice, avalanche and landslide shall be determined; for KNPP site the
features of maximum possible flood in the river spills with frequency 10-4 events per year is
assessed in combination with the tide and waves caused by wind. According to [134] that all
nuclear power plants located on sites where flooding is possible shall withstand the design MWL.
The most appropriate design solution is the elevation of the plant and the safety related components
above the MWL.
3.1.1 Floodings against which the plant is designed
The sources of potential external floodings are maximum possible natural water levels of
Danube River, destruction of the walls of water supply system “Iron gates”, accident on
“Shishmanov Val”, slope waters from location “Marishkin Dol”, waters from tributary valley
“Marichin Valog” and durative heavy rains in the plant site.
3.1.2 Current reassessments of MWL
3.1.2.1 Characteristics of the MWL reassessed
In determining the maximum possible water level of Danube River both natural extreme
water levels and water levels at the rupture of the two water supply systems "Iron Gate" 1 and 2 are
considered. Separately, the impact of intense local rainfall, water retention due to ice drift and the
formation of waves when water enters the valley is also considered.
Below options of potential flooding of the plant site, caused by potential rupture of the dam
of lake "Shishmanov shaft", the slope water from "Marishkin Dol" or water from tributary valley
“Marichini Valog” are also considered.
3.1.2.1.1 Definition of MWL due to increase of Danube River level
The design of the plant and three new studies relating to the determination and revaluation
of the maximum water level (MWL), which can be reached at the plant site are discussed. For level
0,00 at the plant site elevation 35.00 of Baltic altitude system was adopted.
Initially, the maximum water levels of Danube River have been set in detailed design
(Volume "Hydrology", 1972, and Volume "НОПТУ", May ,1975) at Kozloduy NPP water intake
facilities at 687 km of:
102/202