NODAL NEUTRON KINETICS MODEL-BASED ON NONLINEAR ITERATION PROCEDURE FOR LWR ANALYSIS

A 3-dimensional neuron kinetics model based on the analytical nodal me thod and nonlinear iteration procedure is developed for Light Water Re actor (LWR) transient calculations. The solution procedure is decouple d on a local solution of the nodal equations for two-node problems and global iterations of the coarse-mesh finite-difference method. An ort hogonality of the basic functions used for the neutron flux expansion results in an efficient algorithm of the solution of the nodal equatio ns for the two-node problem. The initial system of 8G nodal equations is reduced to a set of G and 2G equations, where G is a number of neut ron energy groups. A fully implicit scheme with an analytical treatmen t of the delayed neutron precursors equations is used for time integra tion. An adaptive time-step size control procedure based on the time-s tep doubling technique is applied. The described numerical methods are implemented into the computer code SKETCH-N. The 3D LWR Langenbuch-Ma ures-Werner (LMW) operational transient and 2D and 3D Boiling Water Re actor (BWR) LRA super-prompt-critical benchmark problems are calculate d in order to verify the code. A comparison of the computed results wi th the solutions obtained by the other nodal computer codes demonstrat e fidelity and efficiency of the SKETCH-N code. (C) 1998 Elsevier Scie nce Ltd.