Modeling fuel assembly distortion in light water reactors using bison

In this paper, bowing of a pressurized water reactor fuel assembly as a result of spatially asymmetric power profiles is analyzed using a beam representation of the 3D fuel assembly. Past studies on this topic have focused on the mechanical deformation of the fuel assembly with simplistic modeling of the fuel rod elongation, which is the major factor driving the fuel assembly bowing. In this study, the beam representations of individual fuel rods and guide tubes are coupled to corresponding 2D axisymmetric models, simulated using the Bison code, to capture all the intrinsic mechanisms that cause elongation of the fuel rod or guide tube. This study shows that both the magnitude as well the shape of fuel assembly bow changes significantly with variations in the spatial power profile and the fuel rod - spacer grid contact conditions.