Durability of glasses from Pacific Northwest Laboratory Composition Variability Study-II (CVS-II) (original) (raw)
Related papers
Nuclear waste glass Product Consistency Test (PCT), Version 3. 0
1990
Liquid high-level nuclear waste will be immobilized at the Savannah River Site (SRS) by vitrification in borosilicate glass. The glass will be produced in the Defense Waste ' Processing Facility (DWPF), poured into stainless steel canisters, and eventually disposed of in a geologic • repository. In order to comply with the Waste Acceptance Preliminary Specifications (WAPS), the durability of the glass needs to be measured during production to assure its long term stability and radionuclide release properties. A durability test, designated the Product Consistency Test (PCT), was developed for DWPF glass in order to meet the WAPS requirements. The response of the PCT procedure was based on extensive testing with glasses of widely different compositions. The PCT was determined to be very reproducible, to yield reliable results rapidly, and to be easily performed in shielded cell facilities with radioactive samples. Version 5.0 of the PCT procedure is attached. This draft version will be submitted to ASTM subcommittee C26.13 on Repository Waste Package Materials Testing in January 1992.
Forty years of durability assessment of nuclear waste glass by standard methods
npj Materials Degradation
Standard methods to assess the durability of vitrified radioactive waste were first developed in the 1980’s and, over the last 40 years, have evolved to yield a range of responses depending on experimental conditions and glass composition. Mechanistic understanding of glass dissolution has progressed in parallel, enhancing our interpretation of the data acquired. With the implementation of subsurface disposal for vitrified radioactive waste drawing closer, it is timely to review the available standard methodologies and reflect upon their relative advantages, limitations, and how the data obtained can be interpreted to support the post-closure safety case for radioactive waste disposal.
2016
Mechanistic models can be applied to composition regions outside of the regions for which they were developed. The DWPF mechanistic models allow more flexibility for process control than empirical models which are (1) restricted to the compositional region over which they were developed and (2) require glass formulations near the center of a pre-qualified glass composition region instead of in regions where waste loading can be maximized. ƒ Glasses not exhibiting amorphous phase separation and not crystallized, i.e. the types of glasses used in the THERMO™ durability models. SRNL-STI-2016-00372 Revision 0 3 Equation 1 process control composition control dissolution rate control performance control acceptable performance The linkages expressed in Equation 1 are appropriate for HLW waste glasses because the radionuclides are incorporated within the glass structure and are released congruently as the glass dissolves. In general, for any waste form, it must be established that control of performance in a laboratory test predicts acceptable control of performance in a disposal system based on performance testing and modeling. The Waste Acceptance System Requirement Document (WASRD) states that the durability and phase stability of vitrified HLW must be assessed [ 28 ], while geologic repository modeling requires the "maximum radionuclide release." These are tied together by the linking relationships shown above, i.e. that process and composition control translates into acceptable performance. The "product quality constraint" on the HLW glass requires that the waste form producer demonstrate control of the waste form production by comparing production samples or process control information, separately or in combination to the Environmental Assessment (EA) benchmark glass [ 29 , 30 ] using the Product Consistency Test (PCT also known as ASTM C1285) [31] or equivalent. For waste form acceptance ƒ , the mean concentrations of lithium, sodium, and boron in the leachate, after normalization for the concentrations in the glass, shall be 2σ less than those of the EA benchmark glass. For borosilicate glass dissolution, the rate of release of a radionuclide from the waste form is proportional to both the dissolution rate of the waste form and the relative abundance of the radionuclide in the waste form.[32] Thus for borosilicate glass, 99 Tc is the radionuclide released at the fastest rate (137 Cs is released at a somewhat slower rate). However, extensive testing [ 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43] has demonstrated that 99 Tc is released congruently at the same rate as Na, Li and B for homogeneous glasses. § This enables the Na, Li, and B to be measured in a glass durability test such as ASTM C1285 and be equated to the "maximum radionuclide release." The Na, Li and B are not sequestered in precipitates that participate in surface alteration reactions and are also not solubility limited. In vitreous waste forms, the molecular structure controls dissolution (contaminant release) by establishing the distribution of ion exchange sites, hydrolysis sites, and the access of water to those sites.[44,45] Thus the DWPF durability model, THERMO [19,20], estimates the relative durability of silicate and borosilicate glasses based on their compositions. THERMO calculates the thermodynamic driving force of each glass component to hydrate based on the mechanistic role of that component during dissolution, e.g. ion exchange, matrix dissolution, accelerated matrix dissolution, surface layer formation, and/or oxidative dissolution. The overall tendency of a given glass to hydrate is expressed as a preliminary glass dissolution estimator, i.e. the change in the free energy of hydration of a glass (∆G p) based solely on its composition expressed as ∆G i for each "i" different silicate and oxide component in the glass. ƒ The following is a quote from ASTM C1285. "The most important elements to be analyzed in the PCT leachate are those that best represent the extent of dissolution of the glass waste form. For example, elements that are not sequestered in alteration phases that participate in surface alteration reactions, and are also not solubility limited, are good indicators of glass waste form durability. Extensive testing of any glass waste form must be performed in order to determine what elements represent the extent of dissolution of the glass waste form. This bounds the extent of dissolution of the radioactive constituents. For example, in high level borosilicate waste glass, Tc 99 , present at ~4.1 × 10-4 weight % in the waste form, has been shown to be released congruently (stoichiometrically) with boron, lithium, and sodium." Therefore, for borosilicate glass waste forms, the leachates are routinely analyzed for boron, lithium, and sodium if these elements are present at > 1 mass % in the glass. Additional mechanistic information about high level borosilicate waste glass durability is gained by analyzing for other elements present in the glass, i.e. Si." § Na and Li can precipitate in long term ASTM C1285B testing as zeolitic phases but not in short term ASTM C1285A testing. B does not precipitate in either long or short term testing. * * 0.00-1.67 [19,20] ZrO 2 0.00-1.80 [19,20] Nb 2 O 5 Validation this study [27] *These are REDOX active species and the oxidation states of the species are predicted at the REDOX range over which DWPF processes.[19,20] ‡During development of THERMO, it was determined that a minimum of 3 wt% Al 2 O 3 was necessary in high Fe 2 O 3 containing and high Na 2 O containing glasses to avoid phase separation [51]. This is consistent with the known miscibility gap in the Al 2 O 3-Fe 2 O 3-Na 2 O-SiO 2 quaternary system that defines the crystallization of basalt [51]. ξ From the Waste Form Compliance Plan (WCP) glass ranges [52]. § A ∆G i term exists in THERMO™ and 7-day PCT data exist to assess the ∆G i terms but such validations of the terms have not been performed. Since 1995, when THERMO™ was developed, partial molar free energies have been developed for HfO 2 and NpO 2 .[53] Additionally, two potential partial molar free energy were developed for Nb 2 O 5 .[27] While these partial free energies have been developed, they have not been assessed against the existing validation data for glasses high in HfO 2 , NpO 2 , and other species noted in Table 2 as yet. The Nb 2 O 5 partial free energy will be validated in this study. Note that Ag° and Au° are not oxides at the DWPF REDOX range and are not included in Table 2. They are metallic, and/or melt insoluble phases that do not have partial molar free energies associated with them in THERMO™. Free energy is used rather than enthalpy because chemical durability is a chemical process, and the reaction progress is related to the free energy rather than the enthalpy of the overall reaction. The more negative the ∆G p, the more readily the reaction will occur. The less negative the ∆G p, the less readily the reaction will occur. HLW Glass for PCCS Modeling Sum Oxides = 100±5 wt% Yes No Exclude from Modeling Fe 2+ /ΣFe ≤ 0.33 No Yes Inhomogeneous visible crystallization or P 2 O 5 ≥2.25 wt% or B 2 O 3 ≥14.0 wt% or Al 2 O 3 ≤2.99 wt% Yes Yes No No Durability Predictable TiO 2 <2 wt% ΣR 2 O ≤ 19.3 wt% Al 2 O 3 ≥3.00 wt% or Al 2 O 3 ≥4.00 wt% where R=Cs, Na, K and Li for TiO 2 ≥2 wt% Al 2 O 3 ≥4.00 wt% Model Data Revision 0 Revision 0 Exhibit B3. Measurements of the Solution Standard by Analytical Block.
Compositional Effects on the Long-Term Durability of Nuclear Waste Glasses: A Statistical Approach
MRS Proceedings, 2004
As a result of the development of a reference glass formulation for the immobilization of West-Valley nuclear waste, a large number of glass compositions have been tested under a variety of leaching conditions for extended durations. In this work, data from the standard PCT leaching procedure (deionized water, 90°C, S/V = 2000 m -1 ) are evaluated for a subset of 98 of these glasses, for which the alteration times extend up to fifteen years. Analysis of the leachate data over this extended period has led to a classification of the glass compositions according to their PCT behavior, as characterized by the boron release in solution, the decrease in the rate of alteration, or the occurrence of a resumption of alteration. Three types of behavior are associated with a normalized mass loss of boron after 100 days of around 1, 2, or 5 g m -2 respectively, and a ratio of the rate of alteration at 7 days to the rate at 1000 days of about 30. A fourth type is characterized by a much larger decrease between the rates at 7 and 1000 days with a ratio exceeding 120. Four further categories are associated with late-stage resumption of glass alteration. A statistical analysis of the data has been used to model the leachate data as a function of glass composition. The effects of seven major elements (Si, B, Al, Li, Na, K, Fe) on the longterm glass durability have been studied. As a result of this analysis, the different types of leaching behaviors can be predicted with a good reliability from the composition of the pristine glass.
MRS Proceedings, 2006
ABSTRACTThis paper reviews the main conclusions of two European Commission funded projects, GLASTAB and GLAMOR, on the durability of HLW glass in geological disposal, and the remaining uncertainties. The progress in GLASTAB relates to the characterization of the alteration layer, the modeling of glass dissolution, the interaction of glass with near field materials, the behaviour of radionuclides, and the calculation of HLW glass dissolution as part of geological disposal. The GLAMOR programme was focused on the decrease of the glass dissolution rate upon achieving silica saturation in solution. Two conclusions from this programme are the importance of the residual rate measured beyond silica saturation and the need to reduce the uncertainties in model parameters. The overall conclusion from the two projects is that strong progress has been achieved on basic dissolution mechanisms and interaction with disposal environments - HLW glass will act as a good barrier to the release of radi...
1993
some discussions, terminology, and references may not be current due to developments during the intervening 19 months. Further, the results themselves have been superseded by results from the second ~tage of the study (CVS-II). The purpose in publishing the report at this time is to provide a publicly referencable account of the CVS-I study, because of its importance in laying the foundation for CVS-II .