Thermo-fluid dynamic transients in the NACIE-UP facility

Highlights: • Experimental data on heavy liquid metal flow in the NACIE-UP loop were presented. • Integral and local thermal behaviour of the MYRRHA-like Fuel Bundle Simulator. • Local data show thermal development in the test section. • Mass flow transition case in the experimental loop NACIE-UP presented in details. - Abstract: This work reports data of the experimental campaign in the NACIE-UP facility in the framework of the SESAME H2020 project. NACIE-UP is an HLM cooled rectangular loop with two vertical pipes, about 8 m long, acting as riser and downcomer and two horizontal branches 2.4 m long. A prototypical MYRRHA-19 pin bundle is installed in the bottom part of the riser, while a shell and tube Heat Exchanger is located in the upper part of the downcomer. The difference in height between the centre of the heating section and the centre of the heat exchanger is about 5.5 m and is essential for the establishment of the natural circulation regime inside the loop. The heating section is highly instrumented with thermocouples and provide a local characterization of fluid flow and heat transfer in the bundle. In the present paper typical transients are discussed, including gas-lift transition, power transition and PLOFA conditions, while the gas-lift transition case is here detailed. In this case, temperatures showed coherent behaviour with a sharp increase due to the gas-lift variation followed by a local minimum. The thermo-fluid dynamic behaviour of the loop during the transient is illustrated and discussed in the paper. Temperatures in different position of the loop and mass flow rate are measured. A prototypical thermal flow meter is used to monitor the mass flow rate. In the FPS, the developing thermal field was experimentally proved, with larger radial differences in the temperature distribution at the outlet monitored sections with respect to the inlet monitored one. Time-dependent behaviour in the different flow conditions is shown in the paper. On the initial and final steady states, a statistical analysis was carried out to determine the average, overall and local values and the associated experimental uncertainties. The error propagation theory was applied for the derived quantities. A database, including both integral and local data, was produced and published. The main aim of the experimental data is the validation of STH codes and the verification of CFD codes and coupled STH/CFD methods for HLM systems.