Study on Heat Transfer Characteristics of 2×2 Helical Cruciform Fuel Assembly Under Non-Uniform Heat Source

Abstract Helical cruciform fuel, due to its unique geometric shape, affects heat transfer, thereby improving the power level and safety margin of existing pressurized water reactors. This article establishes a unidirectional neutron thermal coupling calculation method for the complex geometric cross-section of helical cruciform fuel to study its flow and heat transfer characteristics under non-uniform heat sources. Based on the Monte-Carlo particle transport encoding OpenMC, the fission power distribution of the two-dimensional cross-section of a helical cruciform fuel rod were studied, and we used this as a non-uniform heat source for calculation of flow and heat transfer of 2 × 2 fuel assembly. The neutron calculation results show that the fission energy is concentrated at the fuel petal convexity, and the radial power factor peak fluctuates around 1.3. The flow heat transfer calculation results show that the temperature and heat flux at the petal convexity of the fuel rod cladding outer are lower than those at the petal concavity due to the longer heat conduction path; the swirling flow in the coolant channel enhances the heat transfer on both sides of the petal convexity, and flattens the heat flow distribution at the petal convexity, resulting in a smaller heat flow peak here. The trend about distribution of heat flow and wall temperature on the outer surface of the cladding under non-uniform heat source is basically the same as that under uniform heat source, with a relative deviation of 2.38% for temperature and 18.32% for heat flow. The influence of large heat flux deviation on the local thermal design of fuel cannot be ignored, and it is necessary to further optimize the coupling method and accurately the actual deviation value.