Optimal control of axial xenon oscillation in PWR based on on-line data processing of axial offsets

In a large pressurized water reactor (PWR), xenon oscillations can occur due to the variation of xenon distribution in the reactor. Horizontal and axial modes of oscillation are known. The former is of less concern because of its convergence but the latter can be divergent. Sometimes xenon oscillations are intentionally introduced to obtain recalibration data for the nuclear instrumentation system and in this case oscillations must be eliminated after the data acquisition as soon as possible. Many studies and experiments have been made on control of xenon oscillations, and this problem was solved clearly from the theoretical points of view on the reactor physics and control. However it is found that fine control is required within actual plant constraints to apply the principles and control laws to be indicated from the previous studies. From this point of view a new method has been developed for providing clear operating instructions to the reactor operator. Here, the new method is based on online data processing of axial offsets and the validity of the method has been evaluated through numerical simulations. Then the method has been applied to the experiments in actual PWRs and it has also been proved to be quite effective. (author)