Experiment design to assess the inter-wrapper heat transfer in LMFR

Highlights: • LBE experiment designed to assess heat transfer through inter-wrapper flow in LMFR. • CFD studies show negligible influence of up-stream instrumentation in test-section. • CFD analyses are performed to determine most suitable location for instrumentation. • Measurement data will be used for CFD validation. - Abstract: The inter-wrapper flow (IWF) between fuel assemblies in an LMFR plays an important role in the reduction of the peak cladding temperature in abnormal scenarios, such as blockages or flow reductions. This paper focusses on the heat transfer through the IWF in a geometry which is representative for the MYRRHA reactor under design by SCK• CEN in Belgium. To this purpose an LBE experiment is designed in the Karlsruhe Lead LAboratory (KALLA) at KIT in Germany. Three 7-pin wire-wrapped rod bundles, creating a rotating flow representative for a MYRRHA wire-wrapped fuel assembly, and the adjacent inter-wrapper region form the experimental setup. The thickness of the wrapper and the region for the inter-wrapper flow have the same dimensions as selected for MYRRHA. The instrumentation is designed such that the temperatures and heat fluxes can be measured and used to validate Computational Fluid Dynamics (CFD) models for the inter-wrapper flow. This validation will allow CFD models to be applied in full core models for liquid metal cooled reactors. This paper concerns the experiment design and the supporting CFD calculations. The influence of the equipment upstream of the test section is assessed to determine the domain size and boundary conditions required for the code validation simulations. The selected domain and boundary conditions are subsequently applied in simulations to determine the most suitable locations for the instrumentation to measure the most interesting phenomena of the heat transfer through the inter-wrapper region and to be suitable for CFD validation.