An analysis of the selective mass transfer of alloys exposed to flowing sodium

A mathematical analysis of the behaviour of alloys in flowing sodium is presented for describing the time dependent concentration of all metallic components in both the alloy and the sodium at any point in a sodium loop. Two simplified solutions are presented for the behaviour of a single component in the alloy, one assuming the concentration in the sodium is constant and the other assuming that it is linearly proportional to the surface concentration. The solutions apply either bulk corrosion of bulk deposition. It is shown that whether the component is enhanced or depleted at the alloy surface depends upon the values of two parameters which depend on the concentration and saturation concentration of the sodium, the mass transfer coefficient, and the recession velocity. Finally expressions are derived for the asymptotic concentration profile of a species in austenitic steel with a ferrite surface layer. (author)