Liquid high-level nuclear waste at the Savannah River Site (SRS) will be immobilized by vitrification in borosilicate glass. The glass will be produced and poured into stainless steel canisters in the Defense Waste Processing Facility (DWPF). Other waste form producers, such as West Valley Nuclear Services (WVNS) and the Hanford Waste Vitrification Project (HWVP), will also immobilize high-level radioactive waste in borosilicate glass. The canistered waste will be stored temporarily at each facility for eventual permanent disposal in a geologic repository. The Department of Energy has defined a set of requirements for the canistered waste forms, the Waste Acceptance Preliminary Specifications (WAPS). The current Waste Acceptance Preliminary Specification (WAPS) 1.3, the product consistency specification, requires the waste form producers to demonstrate control of the consistency of the final waste form using a crushed glass durability test, the Product Consistency Test (PC'T). In order to be acceptable, a waste glass must be more durable during PC'I' analysis than the waste glass identified in the DWPF Environmental Assessment (EA). In order to supply ali the waste form producers with the same standard benchmark glass, 1000 pounds of the EA glass was fabricated. The chemical analyses and characterization of the benchmark EA glass are reported. This material is now available to act as a durability, analytic, and/or redox Standard Reference Material (SRM) for ali waste form producers.

The durability of natural glasses on geological time scales and ancient glasses for thousands of years is well documented. The necessity to predict the durability of high level nuclear waste (HLW) glasses on extended time scales has led to various thermodynamic and kinetic approaches. Advances in the measurement of medium range order (MRO) in glasses has led to the understanding that the molecular structure of a glass, and thus the glass composition, controls the glass durability by establishing the distribution of ion exchange sites, hydrolysis sites, and the access of water to those sites. During the early stages of glass dissolution, a "gel" layer resembling a membrane forms through which ions exchange between the glass and the leachant. The hydrated gel layer exhibits acid/base properties which are manifested as the pH dependence of the thickness and nature of the gel layer. The gel layer ages into clay or zeolite minerals by Ostwald ripening. Zeolite mineral assemblages (higher pH and Al 3+ rich glasses) may cause the dissolution rate to increase which is undesirable for long-term performance of glass in the environment. Thermodynamic and structural approaches to the prediction of glass durability are compared versus Ostwald ripening.

High Cr 2 O 3 containing Monofrax TM K-3 is a robust refractory that is used in the fiberglass industry and used in radioactive waste glass melters worldwide. Monofrax TM K-3 is tolerant of transition metal oxides but contains highly reduced solid solutions of spinels, that is, (Mg,Fe 2+ )(Al,Cr) 2 O 3 . Conversely, many of the waste feeds being processed are highly oxidizing. The K-3 refractory corrosion was tested in sealed crucibles starting with slurried melter feed instead of prereacted glass called for by ASTM C621. Testing the refractory coupon during the feed-to-glass conversion exposes the refractory to the oxidizing and reducing species being released during vitrification, for example, NO 3 À , NO 2 À , CO 2 , CO, O 2 . Corrosion rates measured in highly oxidizing (high nitrate) feeds § were~1.8-2.8 times higher than those determined using prereacted glass or reduced feeds. ¶ Confirmatory corrosion rates were measured on Monofrax TM K-3 coupons immersed in oxidizing feed in a 1/100th-scale HLW pilot-scale melter. Corrosion is heterogeneous or incongruent as Ni and Fe in the waste glass exchange with Mg and Al in the refractory. An insoluble NiFe 2 O 4 spinel corrosion product is formed that can build up a protective layer along the refractory walls or spall and settle to the melter floor depending on melt pool convection/agitation.

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