Evaluation of standard durability tests towards the qualification process for the glass-zeolite ceramic waste form Page: 4 of 10
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absorb any remaining free salt and are hot isostatically pressed with glass to produce a glass-
bonded zeolite, termed the "ceramic" waste form. Because the salt with the accumulated fission
products is associated with the first stream in the processing of irradiated fuel and may contain
transuranic elements, it is considered a high-level waste. This report focuses on the development
and evaluation of tests for acceptance of the ceramic waste form.
The development of a technical basis for acceptance of a waste form into the DOE Civilian
Radioactive Waste Management System must follow the guidelines presented in the Waste
Acceptance System Requirements Document (WASRD, DOE/RW-0351, 1996) for spent nuclear
fuel and high-level waste and in the Waste Acceptance Product Specifications (EM-WAPS, 1993)
for borosilicate glass [3]. As outlined in the WAPS, the WASRD defines the "borosilicate glass"
produced by programs directed from the DOE Office of Environmental Management as a standard
high-level waste form. The WASRD specifications define the physical characteristics and
consistency required for a waste form. These include chemical composition (elemental and oxide);
crystalline phase projections; waste form production control demonstration through a comparison
of the waste form with the environmental assessment benchmark (EA) glass (by a product
consistency test); structural and compositional phase stability; and hazardous waste accountability.
To be accepted into the DOE Civilian Radioactive Waste Management System, the ceramic
waste form must be reviewed and deemed "acceptable" with the identification and development of
the appropriate qualification methods and criteria. As an initial step in this process, the present
work evaluates the utility of standard durability tests for providing the information needed to
qualify the ceramic waste form [3]. The Materials Characterization Center Test #1 (MCC-1,
"American Society for Testing and Materials" [ASTM] method C1220-92), Product Consistency
Test (PCT) [4], and Vapor Hydration Test (VHT) [5] will be the focus of these initial
investigations because of their widespread use in testing borosilicate glass, the ASTM approval of
the PCT and MCC-1 test, and their use in qualification of borosilicate glass (e.g., PCT). A broad
range of potential repository conditions were incorporated into the testing procedures to determine
the bounding parameters appropriate for the corrosion testing of the ceramic waste form and its
behavior under accelerated conditions. The effects of pH, leachant composition, sample surface-
area-to-leachant-volume ratios, and test temperature on the results from durability tests with the
ceramic waste form are discussed. Scanning electron microscopy with electron dispersive
spectroscopy, analytical electron microscopy, and X-ray diffraction were used to provide
background information about morphology, composition, structure, bonding, and alteration phase
formation of both the ceramic waste form and the precursor material of zeolite, blended with
simulated waste salt (salt-loaded zeolite).
EXPERIMENTAL
The ceramic waste form group of the electrometallurgical treatment program provided the
samples used in these experiments. Equal amounts by weight of salt-loaded zeolite and glass were
mixed together in an industrial mill, packed into 304 stainless steel canisters, and hot isostatically
pressed to produce the ceramic waste form [7]. The zeolite and glass were uniformly distributed
throughout the sample for dimensions greater than 100 jm. Compositional analyses from electron
dispersive spectroscopy agreed reasonably well with the values calculated from the initial
components of the zeolite and glass mixture (Table I). Electron beam stability of the zeolite during
analytical electron microscopy indicated a low intrinsic water content in the ceramic waste form.
To minimize pretest leaching, all sample cutting and polishing was performed without the use of
any aqueous lubricants. Isopropyl alcohol was used to clean residual polishing material from the
specimens. Except for the omission of aqueous lubricants, ASTM protocols were followed in the
preparation of samples and in performing the durability tests [ASTM C1220-92, 4, 5].
Table I. Elemental compositions of the salt-loaded zeolite and ceramic waste form.
elements Li B Na A Si Cl K Ca Y Sr Cs Ba La Ce Nd O
LZ,Wt% 1.36 12.9115.0 15.6 12.9 5.49 0.01 0.06 0.63 0.21 0.13 0.24 0.39 35.1
WF, Wt% 0.68 2.46 5.43 9.42 22.1 6.46 3.00 4.27 0.01 0.04 0.32 0.11 0.06 0.12 0.19 45.3
SLZ: Salt-loaded zeolite 4A. CWF: Ceramic waste form.
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Simpson, L.J. & Wronkiewicz, D.J. Evaluation of standard durability tests towards the qualification process for the glass-zeolite ceramic waste form, report, December 31, 1996; Illinois. (https://digital.library.unt.edu/ark:/67531/metadc680492/m1/4/: accessed March 28, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.