The introduction of plutonium-charged fuel elements was investigated with regard to a change in the axial power density distribution. An attempt was made to gather information regarding the influence of coolant temperature change on the local power production. The state of the reactor during the investigations was supposed to correspond to realistic operating conditions. During stretch-out operation, as a result of the reduction of the mean coolant temperature and the reactor power, the fall in coolant outlet temperature is greater than the rise in inlet temperature. Hence, the greatest coolant density change occurs at the coolant outlet. In this manner, the relative power density distribution is displaced toward the upper core half. This displacement is particularly strong in highly loaded plutonium fuel elements. During full-load operation, the control rods must be fully withdrawn to prevent deficient burnup in the upper core half. Bearing this stipulation in mind, no operating restriction is to be expected during stretch-out operation due to the recycling of plutonium. In a special experiment, the influence of turbine load changes on the axial power density distribution in a noncontrolled reactor was investigated. A power reduction at the turbine causes a rise in the mean coolant temperature of the reactor. Owing to local coolant temperature differences, the power density was found to displace toward the upper core half in a noncontrolled reactor, this being more so the case for plutonium fuel elements. The increased power production in the upper half of the fuel element increases the effectivity of the control rods. The introduction of fuel elements with recycled plutonium does not lead to the expectation of restrictions to reactor operation in this connection. The investigations cited in this report and the good agreement between the theoretical predictions and the experiments permitted the recycling of the self-bred plutonium at KWO without restrictions on the operation of the reactor.