STUDY OF XENON POWER FLUCTUATIONS IN WWER-1000 REACTORS IN ONE-DIMENSIONAL AXIAL GEOMETRY

Abstract

The article uses the adiabatic modelling method for slow transient processes in nuclear reactors. The essence of this method is that the spatial component of the neutron flux density is determined by the solution of static equations of neutron transport. And the time dependence is reduced to the change of parameters (neutron interaction cross-section) of neutron transport equations accordingly to the change of ¹³⁵Xe, 149Sm concentrations.

In this work, we propose to use a unidimensional (axial) model in the two-group diffusion approximation to investigate xenon transients. As a result, the effect of delayed neutrons in this case may be overlooked. All neutrons are assumed to be instantaneous because the lifetime of both instantaneous and delayed neutrons is much shorter compared to the characteristic time of the xenon transition process. The diffusion equation is based on a balance equation in which the generation, absorption, and leakage of neutrons per unit core volume determine the rate of change in neutron density over time. The differential equations used to calculate the spatio-temporal behavior of the neutron field in the core volume are calculated numerically, by finite-difference method, and analytically. The neutron-physical constants of each axial layer are determined by averaging, taking into account the number and types of fuel assemblies in accordance with the loading of the core in question. The fuel assembly type constants are preliminarily calculated using spectral codes.

As a result of the work, an algorithm for the physical calculation of the WWER 1000 reactor in one-dimensional axial geometry was obtained, the validation of the developed program was carried out, a number of transient calculations were carried out and a variety of xenon transient optimizations were proposed.