Effective diffusivity and solubility of gaseous tritium in selected microporous thermal insulation materials

• Microtherm - an insulator proposed for ancillary systems of ITER has been analysed. • Microtherm is an anisotropic microporous ceramic reinforced with fibres with cracks on the surface. • Microtherm interactions with tritium were assessed experimentally with a permeation system. • Results show that effective diffusion and solubility are mostly governed by materials porosity. Permeation, effective diffusivity and solubility experiments of tritium in thermal insulation materials proposed for ITER is vital for assessing the conditions required for the operation of the Test Blanket System, including its maintenance. With these results, simulation models can be prepared to predict tritium migration behaviour and therefore, air in the estimation of tritium inventory within the concerned components, and the concerned outgassing rates. This paper looks at three different grades of microporous thermal insulation material, which have been tested for the behaviour of tritium in the form of HT. Effective diffusion coefficients, activation energy and effective solubility has been assess together with characterization of the material. An effective diffusion coefficient, which involves gas transport through structure defects, has been evaluated based on Fick's law. Effective diffusivity results are obtained in the range of 1 to 5 × 10 –1 cm 2 /s and the results show no significant difference between the three grades analysed. Effective diffusivity was found to be significantly larger than in other silica-based materials, which can be explained by structural defects observed using SEM. Calculations show that the material's solubility is mostly dominated by its porosity.