11.79. Separation of uranium from the fission products can be accom­plished by volatilization since nearly all of the fluorides of the latter ele­ments vaporize at higher temperatures than uranium hexafluoride. Ura­nium may therefore be recovered from a mixture of fluorides by distillation at a relatively low temperature. If plutonium is present, difficulties arise because of the chemical reactivity of plutonium hexafluroide, but sepa­ration of plutonium from uranium can be accomplished by a more com­plicated volatilization process.

11.80. In reprocessing fast-reactor fuels, the complete removal of fission products may not be necessary since their effect on the neutron economy is much less in a fast-neutron spectrum than it is in a thermal spectrum. In these circumstances pyrochemical (or pyrometallurgical) processes are of interest. Among the procedures which has been proposed are high — temperature chemical methods involving molten salts and molten-metal refining by oxidation and volatilization. None of these processes have yet achieved commercial status and so will not be considered further. However, pyrochemical processes offer advantages over the Purex process from the weapons proliferation viewpoint since there is only partial removal of the fission products.