Improvement and Assessment of Stiffness Confinement Method with Pseudo Absorption - 14186

A refined Stiffness Confinement Method (SCM) is formulated within the framework of the coarse mesh finite difference (CMFD) formulation for multigroup three-dimensional reactor kinetics calculations. By introducing flux factorization involving the amplitude and shape functions and by assuming an exponential variation of the solutions with time varying frequencies, a dynamic eigenvalue problem is derived that contains pseudo absorption terms consisting of the amplitude frequency and node-dependent shape frequencies. The algorithm for searching for the amplitude frequency that makes the dynamic eigenvalue unity is developed in a systematic way along with the methods for determining the shape and precursor frequencies. The overall nodal calculation flow within the CMFD framework to incorporate thermal feedback as well as the changes in dynamic frequencies is introduced. The performance of the refined SCM is assessed by comparing the solution accuracy and computing times for the NEACRP control rod ejection benchmark problems with those of the Crank-Nicholson with Exponential Transform method. (authors)