２次元増倍系における空間高次モードの計算

Abstract

The improved power method in the higher-harmonic eigenvalue calculation of nuclear plant thermal-hydraulic dynamics was applied to the λ- and ωp-eigenvalue problems of thermal and fast reactor systems to obtain the two-dimensional, few-energy-group higher-harmonic eigenvalues and eigenfunctions. As a result, the efficiency of the method was confirmed in the large-scale neutron diffusion problems consisting of the variables amounting to tens of thousands, and the interesting spatial patterns of the eigenfunction were obtained.Even though a harmonic order may be lower, the discrepancy between λ- and ωp-eigen-functions, which are usually assumed to be approximately identical, is significant in a thermal system with low-absorbing region (e.g. reflector). In the higher ωp-harmonics of the system, zero loci of the eigenfunctions depend on neutron energy groups. Therefore, the particular attention should be paid to placements and energy-response of detectors in the kinetic experiments.