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 Each spray pool is designed to remove entire heat released from the unit during emergency mode, and to maintain inlet service water temperature for safety system consumers cooling within the range of +4 o C to +33 о С. 5.1.3.2.2 Time limitations for use of alternative heat sink and capabilities to increase the time available At initial water level in the given spray pool, correspondent to maximum, and at wind speed less than 2 m/s, the pool can operate without filling during 30 hours. At this water level in it reduces on 1.5 m. Loss due to steaming and water entrainment is 170÷175 m 3 /h. In order to fill one spray pool to minimum permissible level 2526 m 3 of water is required, and to maximum level – 7650 m 3 water. Water supply to the spray pools may be provided from: · Motor-driven pumps of service water system for cooling of normal operation system consumers, 2 per unit, each with flowrate of 1440m 3 /h. The pumps can operate at level of the cold channel above elevation 28 m. · Diesel-pumps of service water system for cooling of normal operation system consumers, 2 per unit, each with flowrate of 290 ÷ 500 m3/h. The pumps pump out virtually from the bottom of the cold channel and may use entire emergency reserve – 52264 m 3 in the intake chamber of CPS-3 and 21762 m 3 in the intake chamber of CPS-4. · The pumps in shaft pumping stations, each with flowrate of 180 m3/h. The pumps conditions: are of two groups with diverse power supply. One pump of each group may operate in each shaft pump station. Total flowrate to the spray pools is 1080 m 3 /h. in case of overflow of breaking of the state dike the shaft pump stations will be flooded and their use for water supply to the spray ponds will not be possible. Evaluation of time to exhaust of emergency volume is done considering the following · One channel of service water system for cooling of nuclear-service consumers is sufficient to remove decay heat from the reactor and SFP; · One pair of spray pools ensures cooling of per one safety system train of two units 5 and 6. Assuming that at the start of water supply to the ponds, they are empty (water was drained completely) in order to fill the pair of the ponds to minimum level at which they are operable, 2х2526 = 5052 m 3 of water is required. Time required for that is: · 53 min with motor-driven pumps of service water system; · 2 h 35 min with diesel pumps of service water system. To replenish for loss due to steaming and water entrainment in one pair of spray pools (340 – 350 m3/h), operation of one of the motor-driven pumps or one of the diesel pumps is sufficient. 149/202
“Kozloduy NPP” PLC SUMMARY REPORT for Conduct of Kozloduy NPP Stress Tests Considering emergency water reserve for CPS-3 and CPS-4 (totally 74026 m3) and volume, required to fill both spray pools to permissible minimum (provided that they were completely drained), loss due to steaming and water entrainment from all the spray pools may be replenished for during 197 hours (8.2 days). 5.1.3.3 Loss of ultimate heat sink and loss of alternative heat sink 5.1.3.3.1 Off-site actions envisioned to prevent fuel damage Required off-site actions are related with refilling of double spray pools and shall be taken 8 days after the initiating event. At this stage such actions are not envisioned in the emergency response plan. 5.1.3.3.2 Time required to recover one of the lost heat sinks or to initiate off-site actions on restoration of core cooling before fuel damage is started at different operational conditions In the following table results are summarized for robustness assessment for units 5 and 6 at loss of main ultimate heat sink and alternative heat sink. The following conditions of the units were assessed: · Power operations (for initiating event 1 and initiating event 2); · Cold condition (N=18 MW, 20 hours after shutdown), pressurized primary circuit and drained SG (for initiating event 3); · Cold condition (N=18 MW, 20 hours after shutdown), pressurized primary circuit and non-drained SG (for initiating event 4); · Cold condition (N=16.2 MW, 28 hours after shutdown), depressurized primary circuit (for initiating event 5). Outage cooldown of the primary circuit (N=12 MW, 72 hours after shutdown and N=6 MW, 18 days after shutdown) (for initiating event 6). Table 5.1-4: Assessment of time period to fuel damage at initiating events with loss of ultimate heat sink. Initiating event Option - Loss of shore and shaft pumping station Time to fuel damage 1 Loss of vacuum in the turbine condenser Reduced to initiating event 3, initiating event 4 or initiating event 5 2 Complete loss of make-up water to the SG Reduced to initiating event 3, initiating event 4 or initiating event 5 150/202
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Summary Report for Conduct of Kozloduy NPP Stress Tests

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