NEUTRONIC MODEL FOR MODAL MULTICHANNEL ANALYSIS OF OUT-OF-PHASE INSTABILITY IN BOILING WATER-REACTOR CORES

A neutronic model for linear multichannel analysis of out-of-phase (re gional) instability in a BWR-core is derived. In this model, the zero- power transfer function of a spatial-harmonic mode, the nodal componen t of the harmonic amplitude and the node-wise feedback coefficients fo r the mode appear. Applying the modal expansion technique to a transie nt flux, we can formulate the above transfer function, nodal component and feedback coefficients. When the lambda-mode eigenvalues, eigenfun ctions 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 first-ha rmonic mode and the nodal component of the harmonic amplitude can be e xplicitly expressed. Copyright (C) 1996 Elsevier Science Ltd.