The Department of Energy Office of Environmental Management (DOE/EM) plans to conduct the Plutonium Disposition Project at the Savannah River Site (SRS) in Aiken, SC, to disposition excess weapons-usable plutonium. A plutonium glass waste form is a leading candidate for immobilization of the plutonium for subsequent disposition in a geologic repository. The objectives of this present task were to fabricate plutonium-loaded lanthanide borosilicate (LaBS) Frit B glass and perform testing to provide near-term data that will increase confidence that LaBS glass product is suitable for disposal in the proposed Federal Repository. Specifically, testing was conducted in an effort to provide data to Yucca Mountain Project (YMP) personnel for use in performance assessment calculations. Plutonium containing LaBS glass with the Frit B composition with a 9.5 wt% PuO 2 loading was prepared for testing. Glass was prepared to support glass durability testing via the ASTM Product Consistency Testing (PCT) at Savannah River National Laboratory (SRNL). The glass was characterized with X-ray diffraction (XRD) and scanning electron microscopy coupled with energy dispersive spectroscopy (SEM/EDS) prior to performance testing. This characterization revealed some crystalline PuO 2 inclusions with disk-like morphology present in the asfabricated, quench-cooled glass. A series of PCTs was conducted at SRNL with varying exposed surface area and test durations. Filtered leachates from these tests were analyzed to determine the dissolved concentrations of key elements. The leachate solutions were also ultrafiltered to quantify colloid formation. Leached solids from select PCTs were examined in an attempt to evaluate the Pu and neutron absorber release behavior from the glass and to investigate formation of alteration phases on the glass surface. A series of PCTs was conducted at 90°C in ASTM Type 1 water to compare the Pu LaBS Frit B glass durability to current requirements for High Level Waste (HLW) glass in a geologic repository. The PCT (7-day static test with powdered glass) results on the Pu-containing LaBS Frit B glass at SA/V of ≈ 2000 m -1 showed that the glass was very durable with an average normalized elemental release value for boron of 0.013 g/m 2 . This boron release value is ≈ 640X lower than normalized boron release from current Environmental Assessment (EA) glass used for repository acceptance. The PCT-B (7, 14, 28 and 56-day, static test with powdered glass)

Revision 0iii EXECUTIVE SUMMARYThe Department of Energy Office of Environmental Management (DOE/EM) plans to conduct the Plutonium Disposition Project at the Savannah River Site (SRS) to disposition excess weapons-usable plutonium. A plutonium glass waste form is a leading candidate for immobilization of the plutonium for subsequent disposition in a geologic repository. A reference glass composition (Lanthanide Borosilicate (La 2 O 3 -B 2 O 3 -SiO 2 (LaBS)) -Frit B) was developed and testing with the LaBS Frit B composition is underway to provide data to support the Yucca Mountain License Application process. The objective of this task was to investigate alternative frit compositions and/or processing conditions that may improve the performance of the reference Frit B -LaBS glass in the repository. The current LaBS Frit B composition was used as the baseline for alternative glass formulation development efforts. A review of the literature and past high actinide concentration glass development efforts was conducted to formulate candidate compositions for testing. Glass science principles were also utilized to determine candidate frit components that may meet task objectives. Additionally, glass processing methods (e.g. slow cooling or induced heat treatment) were investigated as potential means to improve the glass durability and/or minimize fissile material and neutron absorber separation. Based on these analyses, a series of candidate surrogate glasses were fabricated and analyzed. One composition was then selected for fabrication with PuO 2 and subsequently analyzed.A phase equilibrium approach, developed from the assessment of previous high lanthanide glass formulations, was used to recommend modifications to the SRNL Frit B composition. A specific recommendation to increase Ln 2 O 3 a content with concurrent reduction of Al 2 O 3 and SiO 2 content proved to be successful in improving the melting behavior and component solubility of the glass. This change moved the formulation from a compositional region of potential glass-in-glass phase separation toward a region near a low melting eutectic trough. The resulting LaBS Frit X composition was fabricated and tested.The chemical durability of the LaBS Frit X glass was shown to be equivalent to the reference Frit B composition as measured by the Product Consistency Test (PCT). The Frit X composition demonstrated improved component solubility in surrogate and plutonium testing. This composition also exhibited improved devitrification behavior that could translate to lower glass processing temperatures and minimize any negative impacts on glass pouring.Testing with the LaBS Frit X composition also indicated the potential to intentionally precipitate a PuO 2 -HfO 2 solid solution phase. This could result in a means to dramatically improve the plutonium leach performance in the repository by the formation of a highly insoluble phase with an inherent neutron absorber. Preliminary testing indicated that glass heat treatment could be used to intentionally form this phase...

This report provides the results of the Waste Isolation Pilot Plant (WIPP) technical assessment led by the Savannah River National Laboratory and conducted by a team of experts in pertinent disciplines from SRNL and

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The reaction of silicon‐based ceramics with 2% Cl2/Ar and 1% Cl2/1% to 20% O2/Ar at 950 °C was studied with thermogravimetric analysis and high‐pressure mass spectrometry. Pure Si, SiO2, several types of SiC, and Si3N4 were examined. The primary corrosion products were SiCl4(g) and SiO2(s) with smaller amounts of volatile silicon oxychlorides. The reactions appear to occur by chlorine penetration of the SiO2 layer, and gas‐phase diffusion of the silicon chlorides away from the sample appears to be rate limiting. Pure SiO2 shows very little reaction with Cl2. SiC with excess Si is more reactive than the other materials with Cl2, whereas SiC with excess carbon is more reactive than the other materials with Cl2/O2. Si3N4 shows very little reaction with Cl2. These diferences are explained on the basis of thermodynamic and microstructural factors.