Study of Heat Transfer Model of the Spiral-Fin Fuel Element

Spiral-fin fuel elements belong to the self-spacer fuel elements; they are usually arrayed in hexagonal fuel assembly and widely used in the core of the tight lattice reactor. Closely packed and helical spacer makes the heat transfer course and phenomena in the channel of the spiral-fin fuel bundle very complicated, with little literature being found in this field. The paper preliminarily studied the heat conduction through the finned can together with convection heat transfer between the fuel element and coolant. Modified fin efficiency was introduced to calculate the heat conduction; for the convention heat transfer, an imaginary channel named equivalent annulus was adopted. The geometric and physical influence of the spiral fins to the coolant in the annulus was studied. Comparing with annulus have inner surface being heated, it was found that the heated perimeter and velocity of coolant in the equivalent annulus were changed by the helical spacer, a new model correlation based on the equivalent annulus’ method was obtained by modifying the heat transfer correlation in annulus. Quantitative study was conducted for a given rods bundle, the results shows that the spiral-fins’ effect to the heat transfer is related to the change of the convection coefficient and heat conduction amount caused by the spacer, at the common condition, its impact is little.