[en] A three-dimensional fluid temperature fluctuation analysis was carried out using a general-purpose multi-dimensional thermohydraulics computer program AQUA to investigate the reduction measures of the fluid temperature fluctuation range. In the analysis, various conditions were chosen for the combinations of flow rate ratio β, which defined as the ratio of flow rate in a control rod assembly to that of a fuel assembly, and gap spacings between the core exit plane and the bottom of the support plate. From the analysis, it was concluded that it is effective to decrease both the flow rate ratio β and the gap spacing in order to reduce the fluid temperature fluctuation range in the core outlet region of liquid metal-cooled fast reactors. (author)