Axial offset as a measure of stability of a light-water nuclear reactor at daily maneuver by power

Requirements for the power operation while maneuvering are high reliability and power security, which depend on the reactor stability during the transition from one power level to another. A quantitative measure of the stability of the reactor is an axial offset. Dual-zone reactor model allows to control the change of neutron-physical and technological parameters in height of WWER-1000. Identified boron control model differs from the known one by the monotonously boric acid input into the coolant. It is shown that the temperature change at the inlet of the reactor core causes uncontrolled disturbance which affects the axial offset and, consequently, the reactor stability. To ensure the reactor stability a compromise-combined method of regulation was suggested, which differs from the known ones by that the coolant temperature at the reactor core inlet is maintained constant by changing the steam pressure in the steam generator due to changes in the position of the turbine control valves. An advanced system of power control unit was developed and was based on the method of regulation. A feature of the system is the method of coolant temperature control, which allowed to develop a program of power changes in WWER-1000 with a constant inlet water temperature, characterized by minimal damage to the shell with minimal movement of the regulating group of control rods. A comparison of the proposed regulation program with one that currently used in power control unit was done.