The Ceramic Waste Form Process at Idaho National Laboratory

The treatment of spent nuclear fuel for disposition using an electrometallurgical technique results in two high-level waste forms: a ceramic waste form (CWF) and a metal waste form. Reactive metal fuel constituents, including all of the transuranic metals and the majority of the fission products, remain in the salt as chlorides and are processed into the CWF. The solidified salt is containerized and transferred to the CWF process, where it is ground in an argon atmosphere. Zeolite 4A is dried in a mechanically fluidized dryer to ~0.1 wt% moisture and ground to a particle-size range of 45 to 250 m. The salt and zeolite are mixed in a V-mixer and heated to 500°C for ~18 h to occlude the salt into the structure of the zeolite. The salt-loaded zeolite is cooled, mixed with borosilicate glass frit, and transferred to a crucible, which is placed in a furnace and heated to 925°C. During this process, known as pressureless consolidation, the zeolite is converted to the final sodalite form and the glass thoroughly encapsulates the sodalite, producing a dense, leach-resistant final waste form. During the last several years, changes have occurred to the process, including particle size of input materials and conversion from hot isostatic pressing to pressureless consolidation. This paper is intended to provide the current status of the CWF process, focusing on the adaptation to pressureless consolidation. Discussions include impacts of particle size on final waste form and the pressureless consolidation cycle. A model is presented that shows the heating and cooling cycles and the effect of radioactive decay heat on the amount of fission products that can be incorporated into the CWF.