Investigation on heat transfer non-uniformity in rod bundle

Previous CFD investigations show strong non-uniform circumferential distribution of the wall temperature, heat flux and heat transfer coefficient on the rod surface, especially in the tight lattice bundle. This phenomenon should be considered to evaluate the peak cladding temperature, which is one of the design criteria for some Generation IV reactors such as supercritical water-cooled reactor (SCWR) and liquid-metal fast reactor (LMFR). In this paper important dimensionless numbers which affect the non-uniformity of heat transfer are identified. CFD calculations are performed to study the local heat transfer behavior of different sub-channels and the effect of these dimensionless numbers. An empirical correlation describing the heat transfer non-uniformity is proposed based on CFD data. ition, a three-dimensional fuel model with the proposed heat transfer correlation is developed and implemented into the sub-channel code COBRA-SC to calculate the distribution of local heat transfer coefficient and local cladding temperature in SCWR fuel assemblies.