Causes of Non-Stationary Vibrations of a Moving Reflector Shaft of the IBR-2 Research Reactor

This article is devoted to an investigation of the reasons for the growth in the axial vibrations of the shaft of a movable reflector of the IBR-2 research reactor, which are repeated at the start of each cycle of operation. After the passage of some time, the axial vibrations of the shaft and the housing stabilized and the device returned to its normal state of operation. The vibrational state of the shaft, the front support, and the blade of the main modulator of reactivity, which are situated near the core, was of practical interest. A finite-element model of the reflector was developed and a thermophysical calculation was performed. Based on the results, the temporal instability of temperature fields was analyzed before a stationary state arose. A dynamic strength calculation confirmed that the reflector’s performance, taking into account the appearance of non-stationary temperature fields, is preserved and the requirements for cyclic strength are met.