A simple “first principles” model has been developed to establish the level of activation product transport through ITER confinement barriers in both wet (steam) and dry (air) accident scenarios. The model accounts for steam condensation (wet scenarios only), aerosol agglomeration, gravitational settling, and leakage. Parametric studies have been performed for a range of aerosol particle sizes and mass densities expected by activation product mobilization. Recommended aerosol confinement release fractions for both wet and dry scenarios have been developed.