The pool-type experimental facility CIRColazione Eutettico (CIRCE) has been built by ENEA in support to the development of liquid-metal fast reactors. A computational fluid dynamics (CFD) model of the new test section, called the Thermal-hydraulic HElical Tubes Innovative System or THETIS, is being built, and is described along with the pretest numerical results. The pretest study analysis supports the dimensioning of the experimental setup and provides a sound but still not complete basis for the experimental transients. Appropriate thermal boundary conditions for the steady state are implemented. These conditions are found to be not suitable for thermal transients, hence the necessary compliance is analyzed and defined, requiring additional preliminary experimental tests. The main novelty in the refurbishment of the CIRCE is the installation of an innovative helical coil steam generator (HCSG). The realization of its numerical counterpart is challenging; therefore, a specific CFD model of the HCSG has been developed separately from the global model. Its preliminary results are described and discussed.