Method for operating a nuclear reactor to accommodate load follow while

Abstract

This invention provides a method of operating a nuclear reactor having a negative reactivity moderator temperature coefficient with the object of maintaining a uniform and symmetric Xenon distribution above and below substantially the center of the core over a substantial axial length of the core during normal reactor operation including load follow. In one embodiment variations in the Xenon distribution are controlled by maintaining a substantially symmetric axial power distribution. The axial offset, which is employed as an indication of the axial power distribution, is maintained substantially equal to a target value, which is modified periodically to account for core burnup. A neutron absorbing element within the core coolant, or moderator, is employed to assist control of reactivity changes associated with changes in power, with the full-length control rods mainly employed to adjust variations in the axial power distribution while the part-length rodsremain completely withdrawn from the fuel region of the core. Rapid changes in reactivity are implemented, to accommodate corresponding changes in load, by a controlled reduction of the core coolant temperature. Thus, active core coolant temperature control is employed to control the reactivity of the core during load follow operation and effectively increase the spinning reserve capability of a power plant without altering the axial power distribution.