Long-term performance assessment (PA) models are used to assess contaminant and radionuclide transport from the integrated disposal facility (IDF), ensuring the safe disposal of immobilized low-activity waste (ILAW) glass wasteforms at the Hanford Site. Laboratory data is collected for various ILAW glass compositions to determine parameters to populate a rate model of glass dissolution that is used in the PA modelling efforts. To validate the laboratory inputs to the long-term dissolution models, a field demonstration is being performed at the Hanford field lysimeter test facility (FLTF) using glass and cementitious wasteforms.<br/><br/>Borosilicate glass dissolution reportedly occurs through pH-dependent mechanisms. Primarily, glass dissolution occurs through the hydrolysis of the Si-O bonds within the glass network (or other network formers). In the PA rate model, the dissolution rate is controlled by the [Si] in the near-field solution. The soon-to-be initialized lysimeter experiment at the FLTF will replicate the disposal scenario where the contact solution will be equilibrated with the surrounding backfill soil. One candidate configuration for an individual FLTF test cell (not yet planned for actual disposal in the IDF) stores cementitious-based material above glass waste material, and investigates how cementitious material affects the near-field solution and glass dissolution. Our objective is to quantify the effects of cement-contacted groundwater on glass dissolution in laboratory experiments to help design this potential cementitious/glass lysimeter configuration predict long-term glass dissolution in environments containing cementitious-based materials.<br/><br/>Single-pass flow-through (SPFT) experiments were carried out to determine the dissolution behavior of ILAW glass ORLEC28 in a wide range of pH (8-12) and temperature (25°C, 40°C, 70°C) to establish baseline dissolution behavior. The SPFT method keeps the glass in dilute conditions, allowing determination of the dissolution behavior without precipitation or solution effects. The contact solution composition was then varied to mimic the equilibrated groundwater and presence of cementitious material.

Single-pass flow-through studies of simulated Hanford low-activity waste glass in varying pH, temperature, and presence of cement-contacted groundwater

2019 Fall National Meeting

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