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 5 LOSS OF POWER SUPPLY AND LOSS OF ULTIMATE HEAT SINK In this section results are summarized of the analyses of the response and robustness of the nuclear installations at the Kozloduy NPP in case of loss of the power supply and loss of ultimate heat sink. Attention is paid to the design solutions applied to prevent occurrence of such events, and to response of the facilities at sequential degradation of the following safety functions specified in Art. 33 of [43]: · Removal of decay heat from the reactor core at specific operational conditions and accidents with maintaining reactor coolant circuit boundaries; · Removal of heat from safety systems to ultimate heat sink; · Provision of the required safety systems support functions; · Removal of decay heat from spent fuel, storage outside the reactor core, but within the boundaries of the power unit. Assessment is provided for the time period available to the operator to execute measures to prevent severe accident at various scenarios. The following nuclear facilities are subject to the analysis: · Nuclear reactors of units 5 and 6; · Fuel pool of units 5 and 6; · Fuel pool of the shut down units 3 and 4; · Storage for spent nuclear fuel. The analysis does not cover facility for spent fuel dry storage, as heat removal in it is provided on the passive principle, and as an ultimate heat sink ambient air is used. 5.1 NUCLEAR REACTORS – UNITS 5 AND 6 5.1.1 Loss of power supply 5.1.1.1 Loss of off-site power supply Operational power supply to units 5 and 6 is provided through the auxiliaries transformers, energized by the generator voltage. Standby power supply is provided from OSY-220 kV. The second standby power to the units is provided from the standby power supply busbars of the other power unit (unit 5 is powered from unit 6 and vice versa). Off-site power supply to the bank pumping stations is provided from OSY 220 kV, and the redundancy is provided from Bukyovtsy substation of 110 kV. 5.1.1.1.1 Design schemes at loss of off-site power supply, sources, capacity and operability for the emergency power supply EES. Loss of the off-site power is defined as interruption to all the connections with the NPP with 139/202
“Kozloduy NPP” PLC SUMMARY REPORT for Conduct of Kozloduy NPP Stress Tests In case of loss of off-site power supply safety-related consumers are powered from independent emergency power supply sources located at area of units 5 and 6. · Emergency DGs Each of the units 5 and 6 has three automated diesel-generators, per one for each of the safety system trains. According to section 3 and section 8 of [7] and [8], the diesel generators are class 3 by OPB-88/97 and IAEA definition for safety functions, respectively, class Е1 by IEEE, and comply with respective seismic category 1. They are located at the site level. Consumers which are supplied from emergency DGs are safety systems, SFP cooling pumps and fire-protection pumps. · Accumulator batteries Power to the first category consumers during all operational modes, including complete loss of power supply mode, is provided from the accumulator batteries. Accumulator batteries energize the I&C in the reactor compartment, primary steam-gas mixture emergency removal system, BRU- A and emergency lighting. Reliable power supply system for the bank pumping station is intended to supply power to consumers related nuclear and fire safety (emergency service water pumps, shaft pumping stations, fire-annunciation installation and fire extinguishing in BPS and their supporting systems). Dieselgenerator station in the BPS is equipped with two diesel-generator sets. There are two accumulator batteries installed in the BPS which serve to guarantee uninterrupted power supply to the most important consumers ensuring accident-free operation of facilities in the BPS shop. 5.1.1.1.2 Independency of emergency power supply and measures to prolong operational time period · Emergency DGs – At operation of two emergency DGs (one per the unit) total capacity of fuel and oil of the emergency DGs is sufficient for more than 38 days. · Accumulator battery – No need to undertake measures to prolong operational time period of the accumulator batteries. See description in par. 1.3.2.6.1. „Accumulator batteries“. · DG of the BPS – Total reserve of fuel and oil at the BPS site ensure uninterrupted operation of both DGs during 56 hours and 45 minutes. 5.1.1.2 Loss of off-site power supply and loss of emergency diesel-generators 5.1.1.2.1 Design schemes of permanently installed sources of additional emergency power supply to the site, capacity and availability for putting into operation Each of the two units has one additional independent diesel-generator with nominal power of 5.2 MW. According to the design these DGs are intended to ensure voltage to normal power supply busbars, through which – in case of loss of secondary circuit normal make-up – heated water is supplied to the SG from the deaerators, instead of cool water from the reservoirs of the secondary circuit emergency make-up system. In the same way thermal stresses in the SG tubing are 140/202
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Summary Report for Conduct of Kozloduy NPP Stress Tests

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