Since 2021, the scientific group of a new neutron source has been conducting thermophysical calculations of the reactor core of pulsed reactors. It was suggested that the deformation of the fuel assemblies is the cause of the oscillatory instability of the IBR-2M reactor. In order to confirm this hypothesis, the group conducted a series of numerical and analytical calculations of the thermophysical processes occurring in the pulsed reactor and affecting its dynamics. A theoretical (numerical-analytical) IBR-2M power feedback was calculated.