System-level hydraulic modelling of the PbLi loop for the Breeding Blanket of a tokamak

The breeding blanket (BB) is a key part of future fusion reactors. Its purposes are: 1) absorbing the energy from neutrons produced in the plasma by the fusion nuclear reactions between deuterium and tritium (D-T), 2) breeding further tritium fuel and 3) shielding other radiation-susceptible components. The Water-Cooled Lithium-Lead (WCLL) is one of the candidate design options for the European DEMO nuclear fusion reactor. The current design is based on pressurized water as coolant, liquid lithium-lead (PbLi) as breeder-multiplier and EUROFER as structural material. However, this design is in a pre-conceptual phase and it is important to analyze with numerical models the behavior of the system from the different points of view, e.g. neutronics, thermal-mechanics and thermal-hydraulics. In view of the relatively large electrical conductivity of the liquid metal used as breedermultiplier, the flow regime in the PbLi loop are strongly susceptible to magnetic field and this causes the onset of a magneto-hydrodynamic (MHD) flow. The magnetic field in a fusion reactor is principally composed by a toroidal and a poloidal component which changes based on the position within the reactor. In general, for an electro-conductive fluid that flows under a magnetic field, the pressure drop is the sum of ordinary-hydrodynamic (OHD) pressure drop (\Delta p_OHD) and magneto-hydrodynamic pressure drop (\Delta p_MHD). For high value of magnetic field, it possible to consider only the MHD case in which the overall pressure drop can be split into the distributed (\Delta p_2D) and concentrated losses (\Delta p_3D). With respect to the OHD case, the MHD pressure drops have different correlations based on the geometry of the channel, orientation of the magnetic field, cross section variation and presence of obstacles. The aim of this work is to develop a 1-D model through the Modelica language for the PbLi loop, to characterize the pressure drop inside the BB region. In this study, the 2018 WCLL design of the PbLi loop is considered. First, the correlations for each type of pressure loss are implemented with the Modelica language and are compared and validated with the available experimental results. Then, all the components of the PbLi loops are modeled according to the different types of pressure losses (\Delta p_2D and/or \Delta p_3D), taking into account the corresponding geometry, fluid properties and magnetic field parameters. Finally, the model is applied both for the OB and the IB loops in nominal operation and in two possible transients.