Neutronic model for modal multichannel analysis of out-of-phase instability in boiling water reactor cores

neutronic model for linear multichannel analysis of out-of-phase (regional) instability in a BWR core is derived. In this model, the zero-power transfer function of a spatial-harmonic mode, the nodal component of the harmonic amplitude and the node-wise feedback coefficients for the mode appear. Applying the modal expansion technique to a transient flux, we can fonnulate the above transfer function, nodal component and feedback coefficients. When the A-mode eigenvalues, eigenfunctions and adjoint-eigenfunctions are numerically obtained by a three-dimensional calculation, these quantities can be evaluated. We derive a lumped neutronic model by the reduction of the present multichannel model. Consequently, the lumped feedback coefficients for the firstharmonic mode and the nodal component of the harmonic amplitude can be explicitly expressed