High-level nuclear waste produced from fuel reprocessing operations at the Savannah River Site (SRS) requires pretreatment to remove Pu. This paper provides a summary of data acquired to measure the performance of MST to remove strontium and actinides from simulated waste solutions. These tests evaluated the influence of ionic strength, temperature, solution composition and the oxidation state of plutonium.

Although the current baseline Hanford flowsheet for immobilizing low-activity waste (LAW) assumes borosilicate-based glass, opportunities exist to improve or change this baseline to reduce the current schedule and cost requirements of accomplishing the mission of site cleanup. Development of an alternative glass-forming system can lead to this goal of cost and schedule reduction through enhanced waste loading and higher plant throughput. The purpose of this project is to investigate the ironphosphate glass system as an alternative for immobilizing Hanford LAW. Previous studies on the iron phosphate glass systems and their potential advantages for immobilizing Hanford LAW have been reviewed and technical uncertainties and data required before implementing this technology have been presented. A team of researchers and engineers from the MO-SCI Corporation, the Pacific Northwest National Laboratory, the Savannah River Technology Center, and the University of Missouri at Rolla has performed a series of tests to address some of the open questions about the potential use of iron phosphate glass for immobilizing Hanford LAW. The results of this team effort are summarized along with recommendations regarding the further laboratory study needs. Additional longer-term testing requirements for implementing the iron phosphate glass-based immobilization process at Hanford are also presented.

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Radioactive high level waste (HLW) at the Savannah River Site (SRS) has successfully been vitrified into borosilicate glass in the DWPF since 1996. Vitrification requires stringent product/process (P/P) constraints since the glass cannot be reworked once it has been poured into ten foot tall by two foot diameter canisters. A unique "feed forward" statistical process control (SPC) was developed for this control rather than relying on statistical quality control (SQC). In SPC, the feed composition to the DWPF melter is controlled prior to vitrification. In SQC, the glass product would be sampled after it is vitrified. Individual glass property-composition models form the basis for the "feed forward" SPC. The models transform constraints on the melt and glass properties into constraints on the feed composition going to the melter in order to determine, at the 95% confidence level, that the feed will be processable and that the durability of the resulting waste form will be acceptable to a geologic repository.The DWPF SPC system is known as the Product Composition Control System (PCCS). One of the process models within PCCS is known as the Thermodynamic Hydration Energy Reaction MOdel (THERMO™), which was developed in 1995 and utilizes data from the short term (7-day) durability test given in the ASTM standard C1285A. The DWPF durability model is based on a free energy of hydration function calculated from the molar glass compositions. An individual component free energy, ∆G i , exists for each oxide in a HLW glass and the ∆G i 's are weighted by the molar concentration of each oxide in the glass. This gives an overall preliminary hydration free energy, ∆G p , for a given glass, which is predictive and independent of any leachate solution pH impacts. The less negative the ∆G p the more durable the glass; the more negative the ∆G p the less durable the glass.The DWPF PCCS models are parsimonious in that the oxide terms in each model are only those which are necessary and sufficient to describe the glass property of interest. This approach excludes composition terms that are unnecessary to the implementation of the DWPF flowsheets, and helps to minimize the sources of error in the PCCS models. These parsimonious models have successfully operated the DWPF vitrification process over the last 20 years.

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