Summary Report for Conduct of Kozloduy NPP Stress Tests

“Kozloduy NPP” PLC
SUMMARY REPORT
for Conduct of Kozloduy NPP
Stress Tests
availability of the siphons at elevation of -4.50 = 31,10m). Pumps of ASSGEM system are located
at elevation of -3.00 m which determines that they will be affected at MWL more than +32,50 m.
The only scenario is isolation of water supply systems „Zhelezni vrata” 1 and 2 as a result of
the earthquake. however in this case the effect of MWL will be executed at sufficiently later phase
of accident progress process (about 20 hours after the earthquake).
In accordance with results of assessment of the margins at extreme meteorological
conditions it is defined that due to closed and self-contained nature of the spent fuel storage system,
SFP 3 and 4 and their auxiliary systems there is a high safety level in relation to external factor
„Extreme winds and tornados”.
6.1.3.2.3 Unavailability of the power supply
In accordance with results of assessment of margins to loss of electric power and loss of
ultimate heat sink, it is defined that power supply to these systems for cooling of the fuel in SFP-3
and SFP-4 is provided from various physically separated sources (emergency diesel generators –
three per unit, emergency diesel-generators of ASSGEM, mobile DG). At low value of decay heat
of the fuel stored in the pools. Available time margin before the assemblies uncoverage starts is
about one week for SFP-3 and more than 9 days for SFP-4 at assumption of complete loss of
cooling.
6.1.3.2.4 Potential failure of measurement instrumentation
Within short-term modernization program of the units analysis was done for definition of
environmental parameters for equipment qualification at emergency conditions. As the first step of
the qualification the sensors of emergency protection chains were replaced with qualified sensors of
Emergency protection chains. For some the sensors related to safety, new location was selected, and
they were moved to area which does not require qualification on extreme environmental conditions.
As a result, at present all the measurement channels, related to reactor protection are
qualified for correspondent seismic and environmental conditions. For conditioning of process
parameter signals, precise digital equipment is used. Uninterrupted power supply units (UPS)
additionally isolate power supply to these channels, by which independence is assured for the power
supply to the channels.
In addition to that the qualification program is executed for the remaining equipment related
to safety, including test of samples of equipment for ageing, seismic and environmental conditions
at loss-of-coolant accident. On the basis of results of the qualification program the remaining
safety-related sensors were also replaced.
To support Operator actions additional set of the computerized systems was implemented,
such as:
· Computerized system for supporting the operator and recording the process
parameters at normal operations and in case of accident;
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