Effect of Fuel Depletion
During operation of a reactor the amount of fissile material contained in the fuel assembly constantly decreases, therefore the assembly kinf constantly decreases. During fuel depletion the decrease of the assembly kinf will be greatest where the power is greatest. The differences in kinf between fresh fuel assemblies and high-burnup assemblies decreases. Therefore during cycle depletion, this process will cause the power to shift away from regions with highest kinf. This process also depends on the use of burnable absorbers, which disrupt the first assumption about the constantly decreasing assembly kinf.