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.