In the framework of BWR stability analysis based on reduced order models (ROM) with (spatial) mode kinetic models one of the key task's is the calculation of the mode-coupling feedback reactivities ρ_mn(t) (m,n=0,1,... number of the spatial modes). This type of dynamical reactivity is a result of the expansion of the neutron group fluxes (or power) in a series of suitable spatial modes (so called λ-modes or ω-modes. In the current paper the feedback reactivity calculation of the mode kinetic model of an extended and modified ROM will be shortly discussed.