CIRCE experimental report

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 CIRCE pool facility has been refurbished to host a suitable test section able to thermal-hydraulically simulate the primary system of a HLM cooled pool reactor.In particular a fuel pin bundle simulator (FPS) has been installed in the CIRCE pool. It has been conceived with a thermal power of about 1 MW and a linear power up to 25 kW/m, relevant values for a LMFR. It consist of 37 fuel pins (electrically simulated) placed on a hexagonal lattice.The LBE, heated by the FPS, flows up through the riser, reaching the Heat Exchanger (HX) inlet though a gas separator placed in the tank upper zone. The primary fluid circulation occurs employing a gas lift system which injects Argon from a nozzle connected to the riser entrance, enhancing the LBE flow. The heat exchanger represents the heat sink of the system and it is designed to have a thermal duty of about 800 kW; it consists of 91 double-wall bayonet tubes (with helium gap) fed by low pressure boiling water. Finally the decay heat removal system (DHR), designed to remove 40 kW and uncoupled from the main flow path. It consists of a bayonet element in which the air is injected from the top, flows downward through the inner tube and then flows upward through the annular region, where heat is removed from primary LBE side. The bayonet element is placed into a suitable shell thermally insulated from the external pool. LBE enters into the shell from the top and flows downwards in a counter flow heat exchanger configuration. The experimental campaign was designed to study the PLOHS+LOF accident, with decay heat removed by the DHR-system. This paper reports the experimental data as well as a preliminary analysis and discussion of the results, focusing on the most relevant tests of the campaign, namely Test IV Temperatures along the three sections of the FPS were reported and the Nusselt number in the FPS sub-channels was investigated . Moreover, the void fraction in the riser was computed and the riser inlet and outlet average temperatures were discussed. Concerning the HX, temperature measurements in the sub-channels were presented, as well as temperatures at the inlet and outlet sections. For the DHR-system, temperatures at the entrance and exit section were analyzed both for the primary lead bismuth eutectic (LBE) circuit and for the secondary air side, estimating the thermal power removed by DHR under the formulated accidental scenario. Finally system codes thermal hydraulics analyses performed adopting the RELAP5/Mod3.3 are presented. A comparison with the data obtained from preliminary experimental tests is presented.