CFD investigation of effect of helical wire-wrap parameters on the thermal hydraulic performance of 217 fuel pin bundle

Based on detailed parametric study, it is found that the transverse flow induced by wire-wrap increases if the helical pitch is reduced. As a consequence of this, the friction factor and the Nusselt number increase with reduction in helical pitch. When the wire diameter is reduced, the pin bundle becomes tighter with high resistance for transverse flow. As a result of the reduced cross flow, the friction factor as well as Nusselt number decrease when wire diameter is reduced. Based on the computational data, suitable correlations have been derived for estimation of Nusselt number in 217 pin fuel bundle for a range of practical interest in fast reactor core design. It is also seen that the clad temperature decreases with decrease in helical pitch and increase in wire diameter due to increase in the transverse flow and associated enhancement in heat transfer coefficient. It is seen that the sodium temperature difference between the central sub-channels in the various rows of pin bundle and the peripheral sub-channels at the same hexagonal face is lower for shorter helical pitch and larger helical wire diameter which is attributed to the enhanced heat exchange due to higher cross flow in these cases.