Glass Property Models, Constraints, and Formulation Approaches for Vitrification of High-Level Nuclear Wastes at the US Hanford Site

Abstract

Current plans for legacy nuclear wastes stored in underground tanks at the U.S. Department of Energy's Hanford Site in Washington are that they will be separated into high-level waste and low-activity waste fractions that will be vitrified separately. Formulating optimized glass compositions that maximize the waste loading in glass is critical for successful and economical treatment and immobilization of these nuclear wastes. Glass property-composition models have been developed and applied to formulate glass compositions for various objectives for the past several decades. Property models with associated uncertainties combined with composition and property constraints have been used to develop preliminary glass formulation algorithms designed for vitrification process control and waste-form qualification at the planned waste vitrification plant. This paper provides an overview of the current status of glass property-composition models, constraints applicable to Hanford waste vitrification, and glass formulation approaches that have been developed for vitrification of hazardous and highly radioactive wastes stored at the Hanford Site.

A crucible salt saturation method for determining sulfur solubility in glass melt

“…The Hanford Waste Treatment and Immobilization Plant (WTP) is under construction, aiming to separate the wastes into high‐volume low‐activity waste (LAW) and low‐volume high‐level waste (HLW) fractions and vitrify the wastes into separate glass waste forms . Many efforts have been devoted to maximizing the waste loading in glass, which can minimize the waste glass volume and reduce mission cost …”

“…This salt segregation and accumulation can cause processing problems, such as corrosion of refractory materials, metallic components, and facilitate volatility of hazardous components such as 99 Tc during melting . In early waste glass formulation work, the sulfur limit was set conservatively at 0.44 wt% to 1 wt% SO 3 in order to avoid potential salt accumulation …”

“…The conservative sulfur limit for the WTP, used by a preliminary formulation algorithm in 2012, was ≤0.77 wt% of SO 3 ; and the target SO 3 concentrations were set significantly below this limit for the vast majority of the calculated LAW glass formulations. Employment of sulfur solubility models to formulate waste glasses would allow higher SO 3 concentrations, which would increase waste loading and decrease the total volume of glass . More data on both sulfur solubility from crucible tests and sulfur melter tolerance from scaled melter tests are needed for the successful implementation of sulfur solubility models for WTP operation.…”

Effect of chlorine and chromium on sulfur solubility in low‐activity waste glass

“…1,2 Technical challenges remain in glass formulation for economically producing durable glasses for permanent disposal. [3][4][5][6] Previous studies identified sulfur as a critical component in glass formulations because sulfur limits waste loading for many low-activity waste (LAW) glasses. [7][8][9][10][11][12] LAW is an aqueous solution containing various anions, such as NO 2 − , CO 3 2− , PO 4 3− , SO 4 2− , F − , Cl − , CrO 4 2− , and with the predominant cation Na + .…”

Melter feed viscosity during conversion to glass: Comparison between low‐activity waste and high‐level waste feeds

“…While the majority of radioactivity (~95%) is contained in the HLW, approximately 90% of the waste volume has been characterized as LAW. The waste itself, composed of 40‐60 elements, exists as water‐soluble salts and sludge …”