Vitrification Process for Idaho HLW Calcine - 18433
The majority of the liquid wastes produced from reprocessing of several types of spent nuclear fuel at the Department of energy's (DOE) Idaho site have been volume reduced by calcination. The resulting ∼155,600 ft{sup 3} of calcined waste is stored in 43 shielded stainless steel bins, which have a 500-year design life. The calcined material is both a high-level waste and a RCRA hazardous waste, which complicates treatment and disposal options. In addition to a potential direct disposal option, treatment options that have been considered include steam reforming, hot isostatic pressing (HIP), and vitrification. This paper describes testing and evaluation of a vitrification option for the calcine. Vitrification to produce a borosilicate glass has the advantage that it is the only treatment that provides a waste form that meets the current HLW repository waste acceptance criteria. It is therefore the lowest risk option in terms of regulatory and legislative concerns. The present work addressed several key questions: (i) Calcine waste loadings in glass, which determine the number of HLW canisters produced and the required glass production rate (throughput) for the system design; (ii) Melt rate per unit glass pool surface area of the melter, which determines the sizing of the vitrification system; and (iii) The ability to meet waste form acceptance requirements (PCT and TCLP) while achieving reasonable waste loadings. These are issues of fundamental importance to the sizing estimates for the unit operations and overall flow-sheet and they, therefore, directly impact the cost and schedule estimates. Fully compliant, high-waste-loading glasses were developed for two of the four Idaho calcine wastes. The results demonstrate that waste loadings of 35 wt% waste oxides are achievable for the two alumina calcines and about 30 wt% is achievable for the two zirconia calcines. Testing of these formulations in a joule-heated ceramic melter showed glass production rates of over 5000 kg/(m2/d) for the Alumina calcine and over 8500 kg/(m{sup 2}/d) for the Zirconium-Na Blend calcine. These extremely high production rates translate directly into smaller system size and shorter mission duration and, therefore, reduced costs. Based on these results, a preliminary design for the full-scale vitrification system was developed. The system consists of waste receipt, vitrification, off-gas treatment, and canister sealing and decontamination equipment. The calcine is blended with the appropriate glass forming chemicals (or glass frit) and fed to the melter as a solid stream. The melter has a glass pool surface area of about 2.5 m{sup 2} and is equipped with a bubbling system to increase processing rates. Glass production rates of about 6 metric tons per day are projected. The vitrification system would be installed into the existing Idaho Waste Treatment Unit Facility (IWTU) so that no new facilities are required to house the treatment system, thus greatly reducing overall cost, duration, and risk. The system would be designed to treat all of the calcine waste within a period of 12 years at an operating efficiency of 80%, producing a total of about 8500 canisters each weighing two metric tons. (authors)