Tritium transport model at breeder unit level for HCLL breeding blanket

The Helium-Cooled Lithium Lead (HCLL) breeding blanket is one of the European blanket designs proposed for DEMO reactor. A tritium transport model is fundamental for the correct assessment of both design and safety, in order to guarantee tritium self-su ffi ciency and to characterize tritium concentrations, inventories and losses. The present 2D transport model takes into account a single breeder unit located in the outboard equatorial module of the HCLL breeding blanket, which is one of the most loaded modules in normal operating conditions. A multi- physics approach has been adopted considering several physics phenomena, providing for buoyancy e ff ect, temperature fi elds, tritium generation rate and velocity pro fi le of lead-lithium and coolant. The transport has been modelled considering advection-di ff usion of tritium into the lead-lithium eutectic alloy, transfer of tritium from the liquid interface towards the steel (adsorption/desorption), di ff usion of tritium inside the steel, transfer of tritium from the steel towards the coolant (recombination/desorption), advection-di ff usion of diatomic tri- tium into the coolant. Tritium concentrations, inventories and losses have been derived under the above spe- ci fi ed phenomena. In particular, the e ff ect of buoyancy forces on the tritium transport has been implemented and compared with the condition without buoyancy