Summary Report for Conduct of Kozloduy NPP Stress Tests

“Kozloduy NPP” PLC
SUMMARY REPORT
for Conduct of Kozloduy NPP
Stress Tests
6.1.3.5 Factors which can prevent management of accident at the DSFS
6.1.3.5.1 Impact on accessibility and habitability of DSFS, measures to prevent or control the
situation
At studies performed within the analysis of the earthquake it is defined that for the container
blocked with debris which might result from extreme off-site initiating events, such as the
earthquake, maximum temperature of the container will increase.
For 100% blocking with debris results of calculations at conservative assumptions show that
maximum temperature of the shell may be exceeded correspondingly only after more than 2 days.
Considering the structure of the roof cover, it is required to expect realistic level of заравяне
surely below 50%. This will increase available time for counter measures to more than 7 days. Even
for this the worst case of accident scenario with loss of heat removal there is sufficient time
available for taking adequate countermeasures, i.e. to remove debris and to restore the natural
ventilation.
6.1.3.5.2 Feasibility and efficiency of measures for accident management in conditions of offsite
hazards (earthquake, flooding)
DSFS will perform its functions of safe storage of the spent fuel at seismic acceleration of
about 0.31 g. Prolongation of time for safe storage of fuel in this situation depends upon the
possibility of removal of construction debris and upon restoration, if it is possible of the natural
ventilation. This is seen from the analysis performed for the earthquake.
6.1.3.5.3 Unavailability of the power supply
Scenario of complete loss of power supply is not relevant to safety of DSFS. Due to
availability of the passive system to remove heat of the radioactive decay, safety operational mode
of the storage structure is not dependent upon power supply. This is seen from the analysis
performed for loss of power supply and loss of ultimate heat sink.
6.1.3.5.4 Potential failure of measurement instrumentation
Failure to stationery systems for monitoring of radiation background and temperatures in
container storage hall, is possible to be replenished for with portable measurement means.
6.1.3.5.5 Potential impacts from other neighbouring installations at the site
In case of accident of Units 3 and 4, Units 5 and 6 and wet SFS, the personnel of SFS acts in
accordance with NPP Emergency Response Plan.
6.1.4 Measures which may be envisioned to improve capabilities for accident management
6.1.4.1 Measures for Units 3 and 4
Measures to enhance robustness of Units 3 and 4s of Kozloduy NPP resulted from the
analysis of combination of beyond design basis earthquake and flooding:
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