A model to simulate tritium behaviour after a release into a confined ventilated volume has been developed. The model assumes that for the investigated cases, tritium behaviour can be characterized by solving the dynamic equations of motion (the compressible Navier-Stokes equations) coupled with the classical k-[variant epsilon] turbulence model to simulate the ventilation in the room and mass diffusion for tritium spreading. The GASFLOW-II fluid dynamics field code, developed through a Los Alamos National Laboratory (LANL) - Forschungszentrum Karlsruhe co-operation, was used as the computational tool to solve the equations that describe the processes. The numerical results have been validated with experimental data collected on the experimental facility (Caisson) at the Tritium Process Laboratory (TPL) Japan. Additionally an investigation of the influence of the obstacles to the tritium distribution inside the Caisson is presented.