Flow characteristics within an interior subchannel of a 61-pin wire-wrapped hexagonal rod bundle with a porous blockage

Abstract

Potential accumulation of undesirable debris in a subchannel of a Liquid Metal Fast Reactor (LMFR) hexagonal fuel bundle presents accident conditions, which are crucial to investigate. Very limited experimental research persists in literature to understand the fluid dynamics effects of partially blocked subchannels, due to the presence of porous blockages. It is imperative to comprehend flow regime-dependent fluid response in the vicinity of porous blockages, to predict and counter abnormal conditions in an LMFR rod assembly. The presented experimental research investigates flow-field characteristics in a 61-pin wire-wrapped rod assembly with a three-dimensional (3D) printed porous blockage medium in an interior subchannel, at Reynolds numbers (Re) of 350, 5,000, and 14,000. Time-resolved velocimetry measurements were acquired yielding first- and second-order Reynolds decomposition flow statistics - revealing important fluid responses upstream and downstream of the porous blockage. Profiles of velocities, velocity fluctuations, Reynolds stresses, and vorticities uncovered the downstream blockage perturbation effects. Spatial cross-correlations of the velocity fluctuations displayed eddie structure elongations and quantified eddie integral scale lengths. A time-frequency analysis of the velocity fluctuations further detailed the mechanisms of flow instabilities via power spectral analysis. Application of a one-dimensional continuous wavelet transform revealed complex Re-dependent flow and characterized the temporal turbulence occurrences - caused by the trailing edge effects of the porous blockage. This research provides unique and novel experimental analyses on flow regime-dependent fluid physics due to a porous blockage medium and provides data sets vital for computational model benchmarking and development, towards the enhancement of LMFR rod bundle designs.