(A) fast, implicit numerical scheme for subchannel geometries

Abstract

A new numerical scheme, named COMET (COmbined Mass and Momentum Equations Technique), is developed as an additional solution scheme of the COBRA-IV-I to simulate thermal-hydraulic transients in the core. The same fluid model and assumptions are used in this numerical scheme with those of the COBRA-IV-I. This method is fully implicit in time so that there are no numerical restrictions on the time step sizes. And the staggered mesh is used as the spatial scheme. There are two main parts to this numerical scheme. The first part solves the energy equations for new enthalpies and densities using the latest velocities and the other field variables. The second part solves the continuity equation and momentum equations simultaneously for all cells in each channel for velocities and pressures. The matrix equation for this solution scheme has tridiagonal matrix for each channel allowing rapid solution. Solving the continuity equation and momentum equations simultaneously ensures that the momentum flux terms do not grow without bound in the solution process. The thermal margin calculations of the bundles are performed for the steady-state and transient state by the present numerical scheme. The results of the acceptable accuracies with the reduced times are obtained.