Patent Number: 045487847
Section: summary

The present invention relates to a nuclear reactor power control system, and more particularly to a system for automatically controlling a power level of a nuclear reactor. In a prior art control system for a power distribution or a power level such as that disclosed in Japanese Patent Application Laid-Open No. 46594/78, signals from power detectors uniformly distributed in a nuclear reactor are summed and averaged and the averaged signal is fed back to automatic power control rods to control the power. In such a nuclear reactor which uses such a power control system, when a safety rod or a power control rod is inserted during the operation by reason of drop of a control rod or another, the power of the nuclear reactor is abruptly reduced and then the power recovers as a result of the withdrawal of the automatic power control rod by the action of the power control system. When the above power control takes place, the power is raised by the automatic power control rods over the entire area of the reactor so that the power distribution exhibits a large distortion such that the area at which the insertion accident of the safety rod or the control rod has taken place shows a low power distribution while the other areas show a high power distribution. As a result, thermal limitations such as maximum linear heat generating rate and minimum critical heat flux ratio may exceed design limitations for the high power area and fuel may become molten and fail. It is an object of the present invention to provide a power control system which can assure safe operation of a nuclear reactor even when the power is reduced by an accident or improper operation. According to a feature of the present invention, a nuclear reactor power control system is provided with a withdrawal protection function to prevent the movement of the automatic power control rod by the power control system when the power is reduced below a predetermined level by some reason. The inventor of the present invention considered that the insertion of the safety rods or the power control rods into the nuclear reactor when the accident or the improper operation takes place results in a local reduction of the power level due to one to several safety rods or control rods, the increase of the power by the withdrawal of the control rods is improper and that it is proper to stop the automatic power control movement when the power is reduced with a remarkable unbalance in the power distribution. According to the present invention, even if the control rods or the safety rods drop into the nuclear reactor during the operation of the nuclear reactor, the rise of the reactor power level which prevents the integrity of fuel is avoided, and a highly safe nuclear reactor is provided.