Suppressing axial oscillations of the energy distribution in a VVÉR-1000 reactor without half-length control rods

Abstract

Nonequilibrium redistribution of the concentration of {sup 135}Xe nuclei in the active zone of the VVER-1000 reactor may lead to xenon oscillations, that is, relatively powerful axial oscillations of the energy distribution, the prevention and suppression of which is one of the goals of reactor control. Xenon oscillations are described by means of the axial offset (AO); this quantity, which characterizes the nonuniformity of the energy distribution, expresses the difference in the rates of energy liberation in the upper and lower halves of the active zone as a percentage of the total rate of energy liberation. In the ascending phase of the xenon oscillations, energy liberation is redistributed from the lower to the upper half of the active zone; the offset increases. In the descending phase, conversely, energy liberation is redistributed from the upper to the lower half, and the offset decreases.