Experimental campaign on the HLM loop NACIE-UP with instrumented wire-spaced fuel pin simulator

Abstract This work reports post-processed data of the experimental campaign carried out in the HLM-operated NACIE-UP facility in the framework of the HORIZON2020 SESAME project. NACIE-UP is a rectangular loop, where the two vertical pipes, which work as riser and downcomer, are 8 m long and the two horizontal pipes are 2.4 m long. A prototypical MYRRHA-like wire-spaced fuel pin bundle simulator (FPS) is installed in the bottom part of the riser, whereas a shell and tubes heat exchanger (HX) is placed 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. A typical PLOFA test is presented in this paper, from the three fundamental tests performed. Temperatures showed a coherent behaviour with a sharp decrease due to the power decrease from about 100 kW to 10 kW followed by local maximum due to the gas-lift stop. The time trend of the main thermal-hydraulic parameters during the transient are illustrated in detail: among the others, there is the curve of the primary coolant flow rate, measured by a prototypical thermal flow meter. 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. Nusselt numbers in the fully developed section exhibited values close to the Kazimi-Carelli correlation and a similar trend. On the initial and final steady states, a statistical analysis was carried out to determine average overall and local values, and the associated uncertainties. The error propagation theory was applied for the derived quantities. Lots of data, both integral and local, were produced and published; the aim is that this information can be used to qualify STH codes, verify CFD codes and coupled STH/CFD methods for HLM systems.