Assessment of RANS and LES in predicting the flow in a 61-pin wire-wrapped bundle with a porous blockage

One of the most promising nuclear reactor designs is the Liquid-Metal Fast Reactor (LMFR). Its fuel bundle rods are separated with wire spacers that are helically wrapped around each fuel pin. Since this bundle presents a tight rod pitch to diameter ratio, accumulation of debris, cladding deformation or detachment of the wires may generate the formation of porous blockages. Understanding the coolant behavior in LMFR fuel bundles under the influence of blockages is mandatory for a complete nuclear safety evaluation. Therefore, this paper presents Computational Fluid Dynamics (CFD) results using the RANS k - epsilon Realizable and the LES models to simulate the flow of a 61-pin wire-wrapped bundle with the presence of a porous blockage that obstructed six interior subchannels. The simulated Reynolds numbers were 5,000 (transition regime) and 14,000 (turbulent regime). Results of the first and second order velocity statistics were compared with the Particle Image Velocimetry (PIV) experimental data acquired in the Thermal-Hydraulics Research Laboratory facility of Texas A&M University. The simulations results were found in reasonable agreement with the PIV data. Additional analysis of the flow structures, pressure distribution and power spectral densities were also performed to give more insight of the flow characteristics in LMFR reactors under the presence of porous blockages.