On Coherent Structures, Flow-Induced Vibrations, and Migratory Flow: In Liquid Metal Nuclear Reactors

Flows in rod bundles are common to many industrial applications such as heat exchangers or some types of nuclear reactors. The core of many classes of nuclear reactors can be easily sketched as a bundle of rods, the fuel pins, inmmersed in an axial ow of coolant that removes the heat produced by the fission reaction. Coupling this geometry to an...

Investigation of the gap vortex street in densely packed tube arrays in axial flow using CFD and experiments

Axial flow in tube bundles with small pitch-to-diameter ratio, a geometry encountered in nuclear reactor cores and heat exchangers, often displays periodic fluctuations. A significant velocity discrepancy between the inter-cylinder gap and subchannel center originates from the difference in through-flow area, feeding an instability. As it is...

Fluid-structure interaction of a 7-rods bundle: Benchmarking numerical simulations with experimental data

Fluid flows through rod bundles are observed in many nuclear applications, such as in the core of Gen IV liquid metal fast breeder nuclear reactors (LMFBR). One of the main features of this configuration is the appearance of flow fluctuations in the rod gaps due to the velocity difference in the sub-channels between the rods. On one side,...

Understanding migratory flow caused by helicoid wire spacers in rod bundles: An experimental and theoretical study

The core of a Liquid Metal Fast Breeder Reactor (LMFBR) consists of cylindrical fuel rods that are wrapped by a helicoidally-wound wire spacer to enhance mixing and to prevent damage by fretting. It is known that the liquid metal close to the rod is forced to follow the wires, and that liquid metal further away from the rod crosses the wires ...

Vibrations in a 7-rod bundle subject to axial flow: Simulations and experiments

Being able to quantify mechanical vibrations is of key importance for the safety of nuclear power plants, as they are able to induce damage. In this work, numerical simulations are used to compute water flow and vibration in a densely packed bundle of 7 rods, mimicking an experimental setup. This flow configuration is chosen to resemble the...

Experimental investigation on the influence of gap vortex streets on fluid-structure interactions in hexagonal bundle geometries

Gap vortex streets characterise many industrial applications involving rod bundle flows, such as heat exchangers and nuclear reactors. These structures, known as gap vortex streets, may excite the structural components of the bundle to resonance, leading to fretting and fatigue. This work aims to measure these coherent structures and the...

Towards validated prediction with RANS CFD of flow and heat transport in a wire-wrap fuel assembly

Liquid metal fast reactors (LMFRs) are foreseen to play an important role in the future of nuclear energy, thanks to their increased fuel utilization and safety features profiting from the optimal heat transfer performance of the metallic coolants. Accurate thermal-hydraulic analysis of their fuel assemblies, typically employed with wire...

LDA measurements of coherent flow structures and cross-flow across the gap of a compound channel with two half-rods

The enhancement of heat transfer from fuel rods to coolant of a Liquid Metal Fast Reactor (LMFR) decreases the fuel temperature and, thus, improves the safety margin of the reactor. One of the mechanisms that increases heat transfer consists of large coherent structures that can occur across the gap between adjacent rods. This work...