An attempt is made of applying the shielding factor method with a coarse-group structure t o cell calculations for plate-type fast reactor assemblies. T h e 24-group collision probability calculations based on the shielding factor method derived from the basic equation is shown t o give results of practical validity f o r heterogeneity and bunching reactivities, a s proved by comparisons with 1950-group collision probability calculations and experiments in the FCA assemblies V-2 and 11-2.T h e mechanism of t h e heterogeneity effect in the two assemblies is examined in detail. Most part of the heterogeneity reactivity is found t o be due t o the flux heterogeneity effect, whereas the reactivity associated with the change of plate pattern is mostly caused by the change of the flux heterogeneity effect in the case of the assembly V-2, and by the change of the heterogeneous shielding effect in the case of the assembly 12 -2.I n comparison with experiment the calculated results on the streaming of neutrons in the entire assembly would tend t o be closer t o isotropic condition, which differs from prediction based on the anisotropic diffusion coefficients obtained in cell calculations.
An attempt is made of applying the shielding factor method with a coarse-group structure t o cell calculations for plate-type fast reactor assemblies. T h e 24-group collision probability calculations based on the shielding factor method derived from the basic equation is shown t o give results of practical validity f o r heterogeneity and bunching reactivities, a s proved by comparisons with 1950-group collision probability calculations and experiments in the FCA assemblies V-2 and 11-2.T h e mechanism of t h e heterogeneity effect in the two assemblies is examined in detail. Most part of the heterogeneity reactivity is found t o be due t o the flux heterogeneity effect, whereas the reactivity associated with the change of plate pattern is mostly caused by the change of the flux heterogeneity effect in the case of the assembly V-2, and by the change of the heterogeneous shielding effect in the case of the assembly 12 -2.I n comparison with experiment the calculated results on the streaming of neutrons in the entire assembly would tend t o be closer t o isotropic condition, which differs from prediction based on the anisotropic diffusion coefficients obtained in cell calculations.
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