A Strategy to Assess Performance of Selected Low-Activity Waste Forms in an Integrated Disposal Facility

Abstract

Low-activity tank wastes will be generated during cleanup of high-level radioactive tank wastes on the Hanford site. The low-activity tank waste will be among the largest volumes of radioactive waste within the U.S. Department of Energy (DOE) complex and is one of the largest inventories of long-lived radionuclides planned for disposal in a low-level waste facility. The Department of Energy's Office of River Protection is evaluating several options for immobilization of low-activity tank wastes for eventual disposal in a shallow subsurface facility at the Hanford Site. A significant portion of the waste will be converted into low-activity waste (LAW) glass with a conventional Joule-heated ceramic melter. In addition, three supplemental treatment processes are presently under consideration by the DOE to treat wastes in selected tanks with the goal of accelerating the overall cleanup mission at the Hanford site. These are: 1) bulk vitrification (BV), 2) cementation or the cast stone (CS) process, and 3) steam reformation (SR). The DOE is expected to select by October 2003 one or more of these supplemental treatment technologies for more detailed evaluation. As part of the selection process, a preliminary risk assessment is being performed to evaluate the impacts of the disposal facility on public health and environmental resources.The same computational framework used to conduct the 2001 ILAW performance assessment will be used for all three waste forms. Cast stone will be modeled with a diffusion-advection transport model and bulk vitrified glass and steam reformed LAW will be modeled with a reactive chemical transport simulator. Modeling waste form performance requires the determination of a number of wasteform specific input parameters. The required input parameters for BV and SR waste forms are derived from a mechanistic model that describes the effect of solution chemistry on contaminant release rates. The single-pass flow-through test is the principal method used to obtain these input parameters, supplemented by product consistency test measurements and physical property measurements. The diffusiveadvective transport model for cast stone requires measurements of effective diffusion coefficients and hydraulic properties.

Sorption and transport behavior of radionuclides in the proposed low-level radioactive waste disposal facility at the Hanford site, Washington

“…The high-activity fraction will be vitrified and is planned to be disposed at the proposed federal geological waste disposal facility at Yucca Mt., Nevada; the low-activity immobilized fraction will also be vitrified (some may also be immobilized in other processes [2]) and will be disposed in a near-surface Integrated Disposal Facility (IDF) located at the 200 East Area on the Hanford Site [2].…”

Laboratory Testing of Bulk Vitrified and Steam Reformed Low-Activity Waste Forms to Support A Preliminary Risk Assessment for an Integrated Disposal Facility

“…The purpose of this report is to document the results from laboratory testing that was conducted to support a preliminary risk assessment for two waste forms that are being considered for supplemental treatment Hanford low-activity tank waste: glass produced by a bulk vitrification (BV) process, and a polycrystalline ceramic produced by a steam reformation (SR) process. The laboratory testing information presented in this document represents the execution of a testing strategy that was outlined previously by McGrail et al (2003a). To limit duplication, only very limited background information is provided in this report.…”

“…To limit duplication, only very limited background information is provided in this report. The reader should refer to the prior strategy report (MCGRAIL et al, 2003a) for details on the background and rationale for the testing program described here.…”

Integrated Disposal Facility FY 2012 Glass Testing Summary Report

“…These kinetic rate equations assume that 1) the dependence of dissolution and precipitation rates on departure from equilibrium are based on arguments and assumptions of Transition State Theory (TST) and 2) the driving force for the transformation of unstable to stable silicate materials is governed principally by the magnitude of displacement from thermodynamic equilibrium. This technical strategy (McGrail et al 1998, Mann et al 2001, McGrail et al 2001, McGrail et al 2003 requires the use of a reactive chemical transport code (e.g., Subsurface Transport Over Reactive Multiphases [STORM]) that integrates the results obtained from bench-scale laboratory test methods and from long-term accelerated weathering tests to simulate and model glass weathering. For the IDF PA program, data collection has been focused on measuring and quantifying the effects of environmentally relevant and sensitive parameters (e.g., effect of pH, temperature, and solution composition) that are needed to simulate and model, with a high level of confidence, the long-term behavior of glass.…”

“…Computer models are essential for this purpose because effects on groundwater resources must be projected out 10,000 years and longer. Details on the recommended technical strategy for developing this source term have been published (McGrail et al 2003) and have undergone review by an international panel of experts.…”