The thermomigration of biphase vapor-liquid droplets in solids

Abstract

The thermomigration of biphase vapor-liquid droplets was studied in KCl as a function of droplet size and the relative proportions of gas and liquid phases in the droplets. Droplets containing more than 10 vol. % of gas migrated down thermal gradients toward lower temperatures in contrast to the usual thermomigration behavior of simple gas or liquid inclusions up thermal gradients in solids. By considering viscous gas flow, vapor diffusion, liquid diffusion, evaporation and condensation and liquid currents driven by surface tension gradients, the observed thermomigration behavior of biphase vapor-liquid droplets can be adequately explained. The results of this and previous investigations were applied to the thermomigration problems associated with the proposed storage of highly radioactive waste products in abandoned salt mines. The thermomigration of naturally occurring brine droplets in a salt formation up thermal gradients generated by the vigorous self heating of these nuclear wastes is shown to be capable of causing an undesirable inflow of water into the nuclear waste crypts. In addition, the thermomigration of contaminated vapor-liquid droplets created on the salt crypt walls in a direction away from the crypt may lead to a modest dispersal of radioactive wastes in the salt formation. Droplet migration along the gravitational field or along the weak natural thermal gradient of the earth would be prevented by the trapping of droplets on grain boundaries in the salt. Thus, the escape of radioactivity to the outside environment is unlikely even on a geological time scale.