Abstract
Ukrainian nuclear power plants (NPPs) generate approximately 55 % of all the country’s electricity production in the basic mode. The Ukrainian energy system faces power shortage for load-following mode (LFM). Hence, operation of Ukrainian NPPs in LFM is advisable. The second stage of LFM pilot operation has been completed at Khmelnitsky NPP Unit 2 to date.
 Following the above, the research of LFM implementation key aspects at Ukrainian NPPs is urgent and relevant. One of the key aspects is the definition of the appropriate mode for reactor power change in LFM for common type of the Ukrainian reactors (WWER-1000/V-320).
 Power density field and thermal power in WWER-1000 are controlled by means of boron control and control rods. The paper provides investigation of the standard power change modes and power density field control in accordance with the safety requirements in the context of the boric acid volume used to decrease the power level, the axial offset stability, maximum values of the power peaking factor and fuel utilization performance (parameters).
 The computer data of the parameters are obtained in SE «NNEGC «Energoatom» during neutron-physical calculations of WWER-1000 cores by means of the «BIPR-7A» program, that uses a mathematical model of WWER reactors. The calculation was conducted for three modes:
 Mode 1: CRs of group 10 and boron control. The mode is being operated for LFM in Ukraine. Group 10 and boric acid/distillate water (BC) are used for power change and power density field control.
 Mode 2: Only CRs of group 10. Only group 10 is used for power change and power density field control.
 Mode 3: Only CRs of groups 10, 9 and 8. All the A-algorithm control groups are used for power change and power density field control.
 Compensation of the slow reactivity variations due to the xenon poisoning and fuel burn up before/after power change was provided by boric acid for all modes.
 The research define the appropriate mode in the context of the parameters.
 The research determine the advantages and drawbacks of the considered modes in the context of the parameters, as well as ways to improve the power density field control and power change system of WWER-1000 core.
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