A helium-gas-cooled fast reactor with coated-particle-type fuel is being examined as a candidate of commercialized fast reactors at Japan Nuclear Cycle Development Institute. As one of characteristics of this reactor design, coolant passes through coated particle fuel regions of fuel assemblies “laterally” to reduce pressure loss. From the viewpoint of coolability and structure integrity of the fuel assembly, it should be confirmed that the coolant keeps flowing through the fuel regions laterally and uniformly to remove heat from the fuel particles properly under various operating conditions. In this study, two kinds of numerical simulations were carried out: A whole fuel assembly simulation using a multi-dimensional thermal-hydraulic analysis code AQUA and a local detailed simulation using a commercial computational fluid dynamics code FLUENT. From these results, thermal hydraulic characteristics in the fuel region were clarified and coolability was confirmed for several operating modes as rated operation, decay heat removal operation and depressurization accident.

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