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 prevented. These DGs can be used also for removal of reactor decay heat as well as in case of failure to the three emergency DGs. Additional DGs are in hot standby mode. Additional DG is located in the container of platform of 1m above the site and according [7]and [8] refer to class 4 by OPB-88/97 and respective seismic category 2. Total fuel and oil reserve of additional DGs ensure uninterrupted operation of each of them for more than 4 days 5.1.1.2.2 Capacity of the batteries, operational time period and capabilities to recharge the batteries No possibility is envisioned to recharge the accumulator batteries of the safety system from additional or mobile DG. Their charging is provided from emergency DG of the related safety train of the SS. Common-plant accumulator battery and that of the computer-based informational system can be charged from additional diesel generator. Full description of accumulator battery description is provided in par. 1.3.2.6.1. „Accumulator batteries“. 5.1.1.2.3 Time to reaching severe accident in the specified conditions. Threshold values in plant behaviour The following conditions of the units were assessed: · Power operations; · Cold condition (N=18 MW, 20 hours after shutdown), pressurized primary circuit and drained SG; · Cold condition (N=18 MW, 20 hours after shutdown), pressurized primary circuit and non-drained SG; · Cold condition (N=16.2 MW, 28 hours after shutdown), depressurized primary circuit; · Outage cooldown of the primary circuit (N=12 MW, 72 hours after shutdown and N=6 MW, about 18 days after shutdown). Operator actions aimed at prolongation of the time period before fuel damage occurs are specified for each of the modes considered in the analyses Table 5.1-1: Assessment of time period to fuel damage at loss of normal and standby power supply and failure to emergency DGs. Time to fuel Option damage (h:min) 1 Power operations (Considered: actuation of MDG and use of water reserve in the tanks of SG emergency make-up system) 115:45 (4.8 days) 141/202
“Kozloduy NPP” PLC SUMMARY REPORT for Conduct of Kozloduy NPP Stress Tests Option 2 Shut down reactor, planned cooldown at pressurized primary circuit and drained SG (Considered: drainage of three hydro accumulators) 3 Shut down reactor, planned cooldown at pressurized primary circuit and non-drained SG (Considered: drainage of three hydro accumulators, make-up of SG from high pressure deaerator, chemically demineralised water system tanks and SG emergency make-up system tanks) 4 Shut down reactor, planned cooldown at depressurized primary circuit (Considered: drainage of three hydro accumulators) Time to fuel damage (h:min) 16:44 More than 3 days and 19 hours 19:45 5 Shut down reactor, outage cooldown (Considered: drainage of three hydro accumulators) 3 days after shutdown 25:51 18 days after shutdown 50:12 The first threshold is discharge of the accumulator batteries (about 10 hours after complete loss of AC sources). As a result the shift personnel losses information on unit parameters. Before that the valves required for accident management shall be positioned (safety valves of the pressurize, BRU-A, steam/gas mixture emergency removal line, etc.). However, discharge of the accumulator batteries does not terminate the started processes of heat removal (motor-driven pumps will maintain their position). The second threshold is water exhaust in chemically demineralised water tanks (at pump make-up of SG auxiliary make-up system) and in the tanks of SG emergency make-up system (at make-up using SG EMS). At power operations exhaust of the three SG emergency make-up system tanks, of high pressure deaerator water reserve and chemically demineralised water tank is expected after more than 3 days. The third threshold is exhaust of fuel oil reserve for additional and mobile DG. Fuel oil reserve for additional DG is sufficient for more than 4 days, and for MDG – for 60 hours. Oil reserves for both DGs are sufficient for this period of time. If emergency DGs are inoperable, oil and fuel intended for these can be used on the operating DGs, with which their operation is ensured for more than 30 days. 142/202
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Summary Report for Conduct of Kozloduy NPP Stress Tests

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