Summary Report for Conduct of Kozloduy NPP Stress Tests

“Kozloduy NPP” PLC
SUMMARY REPORT
for Conduct of Kozloduy NPP
Stress Tests
3.2 ENSURING THE PLANT PROTECTION AGAINST MWL
3.2.1 SSCs required for bringing and maintaining of the units in safe shutdown state most
threatened at MWL
3.2.1.1 Units 3 and 4s of Kozloduy NPP
3.2.1.1.1 Major SSCs
The list of SSCs of safety systems and safety related systems includes equipment failure to
which may lead to failure to perform the following fundamental safety functions:
· Residual heat removal from the spent fuel pool during and after an accident;
· Limiting radioactive releases into the environment.
According to the current license for operation of Units 3 and 4 in state "E" spent nuclear fuel
is stored in the near reactor pool. In accident states related to non-replenishable leakage from the
spent fuel pool, according to the applicable documents [58],[59], the fuel can be moved to reactor to
ensure its reliable cooling with available systems in the secondary circuit. At definition of systems
critical for ensuring safety this requires considering both possible locations for spent fuel storage.
3.2.1.1.2 Protective measures to maintain cooling water supply
The spent fuel pool cooling system is a two-train system with: pool cooling pumps, heat
exchangers, service water and electric power supply. At MWL loss of spent fuel pool cooling
system is not anticipated.
Essential component service water system is the main source of cooling water. The pool
cooling heat exchangers are always connected for service water. The nominal temperature of the
water in the pool is maintained by starting and tripping of the pool cooldown pumps. Cooling water
removal at all cooling logics will be by normal drain headers.
For redundancy of spent fuel cooling in the spent fuel pool to the pressure collectors for
essential components service water two independent headers are mounted for additional cooling
water from fire protection system-2.
At inoperable cooldown system, the cooldown is provided by other methods (filling and
draining) or by maintaining SFP temperature below 65 0 С through non-design cooling logics
(following procedures developed).
3.2.1.1.3 Protective measures to maintain emergency power supply
At MWL loss of emergency power supply sources located in Diesel-generator station – 2 is
not anticipated.
It should be noted that backup power supply of the pumps for the pools cooling is provided
from ASSGEM sections. Thus, at loss of off-site power pumps power supply is ensured both from
system diesel-generators and from emergency diesel-generators of ASSGEM.
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