Modeling of plasma hydrogen isotope behavior in porous materials (graphites/carbon-carbon composites)

This paper describes the physical and the theoretical fundamentals of the model TIPO (Tritium Inventory in Porous Materials) developed primarily to analyze tritium retention in graphites and porous carbon-carbon composites proposed for plasma-facing applications in next-step fusion devices. A key improvement of the model, compared with those already available in literature, consists of a better characterization of the processes in the complex bulk microstructure typical of porous graphites. The model treats both the near-surface and the bulk regions, and the main emphasis is on the mechanisms of retention beyond the implantation range such as migration of hydrogen isotopes along the interconnected pores, chemisorption on the pore surfaces, and diffusion across the graphite grains. The governing equations are formulated together with the main assumptions adopted to develop the computational algorithm. To assess its predictive capabilities and to identify the ranges of potential applicability, the model has been calibrated against fundamental experimental results and applied to make predictions of the tritium inventory in the armors of plasma-facing components of NET/ITER fusion devices. The results of these analyses are herein presented and discussed. (orig.)