Design and Assessment of the New CIRCE-THETIS Facility for the Development of Heavy Liquid Metal Cooled Fast Reactors

Within the roadmap for the technological development of Generation IV reactors, the HORIZON2020 European Union–funded Partitioning And Transmuter Research Initiative in a Collaborative Innovation Action (PATRICIA) project was launched to support innovative solutions for the development of the Multi-purpose hYbrid Research Reactor for High-tech Applications (MYRRHA) accelerator-driven system concept and lead fast reactor technologies in general. The ENEA contributes to the project by involving the experimental infrastructures of the Brasimone Research Center (Italy). In particular, a large-scale pool-type facility named CIRColazione Eutettico (CIRCE), using lead-bismuth eutectic as the primary coolant and pressurized water as the secondary fluid, is under refurbishment with the implementation of a novel test section (TS) named Thermal-hydraulic HElical Tubes Innovative System (THETIS) to be installed in the CIRCE main vessel. The new TS will include a vertical mechanical pump for primary coolant circulation and a new prototypical helical coil steam generator (HCSG). This steam generator concept turns out to be very promising for nuclear power plants since the helical geometry is very compact and it assures high power removed, taking up a minimum amount of space. Accordingly, with the aims of the project, the experimental tests in CIRCE-THETIS will focus on (1) investigating the thermal-hydraulic behavior of the system in steady-state operation (forced circulation regime) during operational and accidental transients (postulated scenarios) and in a natural circulation regime considering as heat sink the HCSG (acting as a decay heat removal system) and the reactor vessel auxiliary cooling system in stand-alone or coupled operation and (2) characterizing the performance of the HCSG. The present work presents the layout of the CIRCE-THETIS facility at the end of the final design phase, describing in detail the main components of the TS, along with the instrumentation installed. Focus will be given to the HCSG mock-up, for which pretest analyses using the system thermal-hydraulic code RELAP5/Mod3.3 and a computational fluid dynamics code have been carried out to support the design of the component and to evaluate its thermal-hydraulic performance under the operative conditions foreseen during the experiments.