TR-PIV Flow Characterization of Blockage Effects on a 61-Pin Wire-Wrapped Hexagonal Fuel Bundle

Liquid metal fast reactors often use a tightly packed triangular lattice of fuel pins that are helically wrapped with a wire spacer, enclosed in a hexagonal duct. These reactors are thought to suffer from partial or total flow blockage of coolant in various subchannel locations throughout the fuel assembly. These blockages can result from a large range of causes including debris accumulation and cladding deformation, or the combination of the two. Flow in these reactor fuel assemblies are complex, and the addition of a blockage increases that complexity as well. The effect of blockages on flow behavior in liquid metal fast breeder reactors is relatively unknown, especially experimentally, with only one recent study exploring the subject. This absence of information has motivated researchers globally to begin investigations to explore the effects of blockages on these geometries. The matched index of refraction 61-pin wire-wrapped experimental fuel bundle at Texas A&M, with the optically clear and accessible test section was designed with the express purpose of exploring flow behavior for this geometry of fuel assemblies. The experiments carried out on this facility are high-fidelity velocity and pressure measurements. High spatial and temporal-resolution particle image velocimetry measurements were conducted in this experiment to explore the flow behavior and effects of two blockage cases in a wire-wrapped bundle. Time-resolved particle image velocimetry measurements were conducted at two vertical planes in the facility, Center 2 and Exterior 1. Two blockage types were also explored, a single subchannel at Center 2, and a larger edge subchannel blockage at Exterior 1. Instantaneous velocity fields obtained from these measurements lead to the production of first and second order flow statistics such as the mean velocity, root-mean-square fluctuating velocity, and Reynolds shear stress. These experimental results provide a greater understanding of the flow behavior of a subchannel under a blockage scenario, while providing data available for validation of advanced CFD simulations using RANS or LES with unique experimental data sets. As this work continues more blockages geometries are expected to be explored, paired with friction factor experiments to examine the effect of a blockage on those parameters