Numerical study of heat transfer in a distorted rod bundle

The effect of rod distortion on the flow and heat transfer in a rod (fuel) bundle similar to those in an Advanced Gas-cooled Reactor (AGR) is investigated using carefully constructed CFD models. The results are of relevance to various other engineering applications, for example heat exchangers. The distorted element contracts gradually over the first half of the element, reaching a minimum at half high then subsequently increasing back to its normal value over the second half of the element. In this paper, the results for forced convection are presented. Changes in the rod profiles divert flow to regions of less resistance, resulting in strong cross flow recirculation regions. The resultant three dimensional flow is also accompanied by large scale swirling flow around the fuel pins. The hotspot at any height coincides with the leeward side of the cross flow. It is rather surprising that the peak can temperature at the location of worst bundle distortion (i.e middle height) is actually slightly lower than that of intact fuel. The overall peak can temperature in the damaged bundle is however much higher than that in the intact fuel, and this occurs towards the top of the bundle.