Abstract
Fuel assemblies’ deformation is an industrial issue that has been first reported in the 90’s. This phenomenon has originally been pointed out for being the explanation of IRI (incomplete rod cluster insertion). Recently, fuel assembly bowing has regained attention for its impact over several core’s management issues, including core neutronics.
When deformation occurs, it tends to alter bypasses geometry around the affected fuel assembly. The water gaps’ thicknesses along the assembly’s height does not match the nominal value anymore. As a result, spacer grids can get closer of farther to the surrounding ones. The redistribution between the bypasses and the grid is then involved, depending on the bypasses’ thicknesses and the grid geometry. This unfolding effect entails differences in pressure laterally along a grid, which thus brings about a lateral hydraulic force exerting on the grid.
The following paper presents a method to esteem this redistribution thanks to an hydraulic network. Hydraulic resistances can be set up according to the bypass thickness. As a result, both pressure and volumetric flow rates can be calculated to further estimate lateral forces.
The approach has been validated with both CFD simulations and an experimental mock-up.