Analysis of tritium permeation in the steam generators of the SEAFP/SEAL fusion power reactor

The key uncertainty in estimating tritium permeation from fusion reactor cooling system components is the permeability coefficient, which is strongly dependent on the component material, pressure, temperature, chemistry, etc. Published tritium permeability values, for typical cooling system materials, range at least six orders of magnitude, resulting in estimates of tritium permeation carrying a large degree of uncertainty. In this work, both theoretical and empirical approaches are used for estimating tritium permeation and environmental releases for the water cooled SEAFP reactor. The steam generators are the major source of tritium permeation from the primary coolant. The theoretical model is based on the thermodynamic equilibria and the mass transfer phenomena at steady state conditions. A calculation code, from the theoretical model, allowed us to describe the behavior of the system under the main operating conditions. A parametric analysis has been carried out by varying the hydrogen concentration. The beneficial effect of oxide layers in reducing the permeation of hydrogen isotopes through steam generator tube materials has been observed experimentally by others, and is modeled here by a permeation reduction factor (PRF). The oxide layer effect has also been observed in operating steam generators, as demonstrated in the analysis based on CANDU operating experience. Such experience, which covers the range of conditions of the water cooled SEAFP reactor, has been used to estimate tritium permeability for the SEAFP steam generators. Hence, the use of measured data from CANDU plants has reduced the range of uncertainty in tritium permeability to approximately one order of magnitude. It has also permitted a meaningful estimate of tritium permeation to be performed. The best estimate is ∼16 Ci year-1 per steam generator. (orig.)