Tritium transport model at breeder unit level for WCLL breeding blanket

In a fusion power demonstration plant (DEMO), the development of a tritium transport model is mandatory in order to correctly predict the tritium concentration inside the liquid metal, the permeated flux through the structural materials and into the coolant, playing a fundamental role in guaranteeing tritium self-sufficiency in the fusion reactor and safety both for the workers and for the external environment. In the present work, a multi-physics 3D tritium transport model has been assessed for a single breeder unit located in the outboard equatorial module of the Water-Cooled Lithium Lead (WCLL) breeding blanket of DEMO, adopting an approach that permits to have a modelling tool able to be adaptive within certain margins to changes in operating parameters and geometry. The transport has been modelled considering advection-diffusion of tritium into the lead-lithium eutectic alloy, transfer of tritium from the liquid interface towards the steel (adsorption/desorption), diffusion of tritium inside the steel, transfer of tritium from the steel towards the coolant (recombination/dissociation), advection-diffusion of diatomic tritium into the coolant. The effect of buoyancy forces, which arise due to temperature variation, has been also considered. Under the above-specified phenomena, tritium concentrations, inventories and losses have been derived.