HLM fuel pin bundle experiments in the CIRCE pool facility

Since Lead-cooled Fast Reactor (LFR) has been conceptualized in the frame of GEN IV International Forum (GIF), great interest is focused on the developing and testing new technologies related to HLM nuclear reactors. In this frame the Integral Circulation Experiment (ICE) test section has been installed into the CIRCE pool facility and suitable experiments have been carried out aiming to deeply investigate heat transfer phenomena in grid spaced fuel pin bundle providing experimental data in support of European fast reactor development. In particular the fuel pin bundle simulator (FPS) has been conceived with a thermal power of about 1 MW and a linear power up to 25kW/m, relevant values for a LMFR. It consist of 37 fuel pins (electrically simulated) placed on a hexagonal lattice with a pitch to diameter ratio of 1.8. The FPS has been deeply instrumented by several thermocouples. In particular two sections of the FPS have been instrumented to monitor the heat transfer coefficient along the bundle as well as the cladding temperature in different rank of sub-channels. Nusselt number in the sub-channels was therefore calculated as function of the Peclet number and obtained results were compared to Nusselt numbers computed from correlations available in Heavy Liquid Metals (HLM) literature. A full characterization of the FPS has been experimentally achieved both under forced and natural circulation (Pe~500÷3000), and the main results gained during the run are reported into the paper.