A RESONANCE CALCULATION METHOD BASED ON THE MULTI- TERMS RATIONAL APPROXIMATION FOR GENERAL GEOMETRY WITH GRAY RESONANCE ABSORBERS

摘要

A new resonance calculation scheme based on the multi-terms rational approximation is developed and its outline is presented in this paper. On the present method, coefficients appeared in the expression of escape probability can be evaluated including the gray resonance absorption effect. Neutron fluxes are calculated by one group fixed source transport calculations with the method of characteristics for different macroscopic total cross sections of resonance materials. Then multi-terms coefficients of the escape probability are evaluated by fitting the results of the previous transport calculations on the wide range of the optical length. The present method can be used for general geometry and the escape probability is accurately reproduced both for black and gray absorbers. On the traditional resonance calculations based on the equivalence principle, the blackness assumption has been applied both for the single and multi-terms rational approximations, so the present method is an enhanced approach for considering the resonance self-shielding effect. Verifications of the present method are carried out in some simple benchmark problems. As a result, the theoretical validity of the present method is numerically confirmed. The present method has been implemented in the next generation lattice physics code GALAXY of Mitsubishi Heavy Industries, Ltd..