THERMOCHEMISTRY OF CRYSTALLINE AND AMORPHOUS PHASES RELATED TO RADIOACTIVE WASTE

摘要

The incorporation of actinides and radioactive fission products into solid glassy and ceramic materials is crucial to their containment. This paper focuses on thermodynamic aspects of such materials. Vitrification (placing radionuclides into a borosilicate, aluminosilicate, phosphate, or other glassy matrix prepared by melting) results in a predominantly glassy log of material whose durability is governed both by its intrinsic thermodynamic properties and by the environment in which it sits. Because actinides have a profound influence in modifying and disrupting the molecular-level structure of a glass, a tutorial on glass structure and thermodynamics is presented which culminates with an assessment of what is known about the thermochemistry, phase separation, and crystallization of lanthanide- and actinide-containing glasses.rnSynroc, a crystalline waste form, consists of host phases (perovskite, zirconolite, pyrochlore) which incorporate actinides easily and stably. Zircon has been proposed as a host for weapons plutonium. The thermodynamics of these families of related phases is reviewed, with emphasis on systematic trends which can be used to estimate the energetics of actinide incorporation.rnCrystalline and glassy waste forms will be subjected to moderately intense alpha, beta, and gamma irradiation as the radionuclides decay over hundreds of thousands of years. The energetics of radiation damage in crystals and glasses is reviewed.rnNuclear accidents may release actinides and fission products. The thermochemistry of compounds of Cs, Ba, Sr with bivalent, tetravalent, and hexavalent ions of lanthanides, actinides, silicon, titanium and zirconium, relevant to the fate of such release, is reviewed.