CFD SIMULATIONS TO DETERMINE THE EFFECTS OF DEFORMATIONS ON LIQUID METAL COOLED WIRE WRAPPED FUEL ASSEMBLIES

摘要

Over the course of their lifespan, wire-wrapped liquid metal fast reactor (LMFR) fuel bundles deform due to tension of the pre-stressed wires, contact pressure between clad and adjacent rods' wires, thermal and irradiation clad creep, irradiation-caused swelling and fuel burnup. This deformation is geometrically complex, because it is the result of multiple effects, most of which do not arise until after burnup. This deformation affects both the axial flow areas and the crossflow mass fluxes, which have an effect on the subchannel outlet temperatures - a limiting parameter in many LMFRs. This paper aims to identify and quantify the effects of deformations on the heat transport in LMFR fuel assemblies. To achieve this, a 19-pin and a 127-pin hexagonal wire-wrapped fuel bundles are simulated in nominal and deformed geometries, using deformations of varying fidelity. A thorough CAD deformation algorithm is developed and presented; this algorithm generates a realistic solid model of a deformed LMFR fuel bundle, with a deformation shape similar to shapes observed experimentally. This algorithm is applied to the 19-pin bundle. The results of the simulations of the 19-pin bundle, together with its CAD deformation algorithm, are used to develop a methodology that core designers could use to quantify the hot channel penalty factors due to bundle deformation with a set of CAD and CFD codes. The CFD-based hot subchannel deformation penalty factor quantification methodology was tested by applying it to the 19-pin bundle experiment. For this benchmark, the penalty factor was evaluated to be 5.8%. Additional results presented in the paper include a study of the effects of deformations on the outlet fluid temperatures in both the 19-pin and the 127-pin assemblies.