AbstractA simple yet accurate method of space-shielding cross sections in a doubly heterogeneous high-temperature gas-cooled reactor (HTGR) system using collision probabilities and rational approximations is presented. Unlike other more elaborate methods, the present method does not require point-wise cross sections that are not explicitly generated in most popular cross-section codes. Consequently, this method makes double heterogeneity space-shielding possible for cross-section codes that do not proceed via point-wise cross sections and that usually allow only for single (fuel-rod) heterogeneity cross-section space-shielding. Results of calculations based on the present method compare well with results of calculations based on more elaborate methods using pointwise cross sections. Moreover, the systematic trend of the difference between the results from the present method and those from the more elaborate methods used for comparison supports the already existent opinion that the latter methods tend to overestimate the space-shielding cross-section correction in doubly heterogeneous HTGR systems.