ALFRED Protected Loss of Flow Accident Experiment in CIRCE Facility

Lead cooled Fast Reactors (LFR) are one of the most promising nuclear technologies, able to meet the goals set out by the Generation IV International Forum (GIF) and playing an important role in the international context. ALFRED (Advanced Lead-cooled Fast Reactor European Demonstrator) is the European Technology Demonstration Reactor for the LFR technology and aims to bridge the gap between the research and development effort and the industrial deployment. Fostering ALFRED CONstruction, an international consortium under the leadership of Ansaldo Nucleare with ENEA (IT) and ICN (Ro), is pursuing the re-design of the European Technology Demonstration Reactor in addition to the definition of an R&D and licensing roadmap. Fostering ALFRED CONstruction gathers European organizations who share the objective of making ALFRED the prototype of a viable competitive LFR commercial unit in the small modular reactors segment, by 2035-2040. Among these organizations, CIRTEN (IT) and SRS (IT) takes part as Supporting Organization to Fostering ALFRED CONstruction to enhance the R&D activities devoted to ALFRED. In this frame an R&D activity has been carried out at the ENEA Brasimone Research Center, aiming at investigating the thermal-hydraulic behaviour of an innovative Steam Generator (SG) based on a double wall bayonet tubes concept. For this purpose, a dedicated Test Section (TS) named HERO (Heavy liquid mEtal pRessurized water cOoled tubes) has been developed and installed in the pool-type integral effect facility, LBE (Lead-Bismuth Eutectic) cooled, named CIRCE (CIRcolazione Eutettico). The HERO steam generator is a mock-up (full length and scaled in volume) which represents the ALFRED Steam Generator (SG), and it consists of seven double wall bayonet tubes. In this configuration, the CIRCE-HERO facility has been involved in a set of experimental tests in the framework of the HORIZON2020 SESAME (Simulations and Experiments for the Safety Assessment of MEtal cooled reactors) European project. An integral test experiment has been designed and realized to reproduce a Protected Loss of Flow Accident (PLOFA) occurring with the facility operated in nominal steady-state conditions for both primary and secondary side. The transient test is obtained reducing the thermal power supplied by the Fuel Pin Simulator (FPS), accordingly to a characteristic heat decay curve, while the loss of the primary pump is simulated by the reduction of the argon injection in the primary loop. The loss of the heat sink is simulated reducing the HERO feedwater in the secondary loop, simulating the activation of the decay heat removal system. The aim of the paper is to discuss the main results achieved from the performed experimental test, investigating on the thermal-hydraulic performances of the HERO SG in operating conditions and characterizing the system behaviour during this reference accidental scenario, using all obtained data to assess the RELAP5-3D© system code for Heavy Liquid Metal (HLM) reactors focused on the ALFRED design. The paper summarizes the post-test activity performed for the experimental test, respecting the main trend for all thermal-hydraulics phenomena analysed and highlighting a good agreement between simulations and experiment for all the primary circuit physical quantities monitored. (author)