NACIE-UP: an heavy liquid metal loop for mixed convection experiments with instrumented pin bundle

Since the Lead-cooled Fast Reactor (LFR) has been conceptualized in the frame of GEN IV International Forum (GIF), ENEA is strongly involved on the HLM technology development. Currently ENEA has implemented large competencies and capabilities in the field of HLM thermal-hydraulic, coolant technology, material for high temperature applications, corrosion and material protection, heat transfer and removal, component development and testing, remote maintenance, procedure definition and coolant handling. In this frame, the NACIE-UP loop has been designed to perform mixed convection experiment with LBE. A 19-pin wire-spaced Fuel Pin bundle Simulator (FPS) is installed to measure clad temperature and heat transfer coefficients in different conditions in the different ranks of sub-channels of the MYRRHA bundle. NACIE-UP is a rectangular 2.5″-pipe loop where a difference in height H~5 m exists between the heat source (FPS) and the heat sink (Heat Exchanger, HX). This difference in height provides the pressure head Dp~rgβDT×H for the natural circulation of the Heavy Liquid Metal in the loop. A gas-lift system provides a void fraction in the riser promoting an enhanced circulation in the loop. Most of the pressure losses are located in the FPS, and the maximum mass flow rate is around 2 kg/s in natural circulation and 7 kg/s in gas-enhanced circulation. A 7 tube/shell-and-tube Heat Exchanger couples the primary LBE loop with the secondary side with water in pressure at 16 bar. The tube-in-tube technology with LBE tube side, water shell side, steel powder in the gap, and two section for low and high power, is adopted for HX. In the primary side, two prototypical Induction Flow Meters (IFM) are installed, one in the natural circulation range and another one in the enhanced circulation range. Bubble tubes with flowing Ar are adopted to measure pressure losses in the different branches of the loop. Several thermocouples monitor the loop in different points. An ancillary gas system ensures the cover gas and provides flow rate for the gas-lift system. The paper reports the description of the experiment, the proposed test matrix and description the technological solution adopted for the NACIE-UP implementation