[en] A short summary is given of our studies on the major factors that affect the chemical durability of nuclear waste glasses. These factors include glass composition, solution composition, SA/V (ratio of glass surface area to the volume of solution), radiation, and colloidal formation. These investigations have enabled us to gain a better understanding of the chemical durability of nuclear waste glasses and to accumulate.a data base for modeling the long-term durability of waste glass, which will be used in the risk assessment of nuclear waste disposal. This knowledge gained also enhances our ability to formulate optimal waste glass compositions

[en] A comparison of glass reactivity between radioactive sludge based and simulated nuclear waste glasses has been made through long-term testing of both glass types for SRL 165, SRL 131, and SRL 200 frit compositions. The data demonstrate that for time periods through 280 days, differences in elemental release to solution up to 400% are observed. However, in general, differences in glass reactivity as measured by the release of boron, lithium, and sodium are less than a factor of two. The differences in reactivity are not large enough to alter the order of glass durability for the different compositions or to change the controlling glass dissolution mechanism. A radiation effect exists, mainly in the influence on the leachate pH, which in turn affects the glass reaction mechanism and rate. The differences in reactivity between fully radioactive and the simulated glasses can be reasonably explained if the controlling reaction mechanism is accounted for. Those differences are glass composition and leaching mechanism dependent. Lithium is found to have the highest elemental release in an ion-exchange dominated glass reaction process, while lithium has a lower release than boron and sodium in a matrix dissolution dominated process, where boron and sodium are usually among the most concentrated solution species

[en] The US Department of Energy (DOE) and nuclear utilities have large quantities of low-level and mixed wastes that must be treated to meet repository performance requirements, which are likely to become even more stringent. The DOE is developing cost-effective vitrification methods for producing durable waste forms. However, vitrification processes for high-level wastes are not applicable to commercial low-level wastes containing large quantities of metals and small amounts of fluxes. New vitrified waste formulations are needed that are durable when buried in surface repositories

[en] This paper explains the technology developed to produce Self-Assembled Mercaptan on Mesoporous Silica (SAMMS) for mercury removal from aqueous wastewater and from organic wastes. The characteristics of SAMMS materials, including physical characteristics and mercury loading, and its application for mercury removal and stabilization are discussed. Binding kinetics and binding speciations are reported. Preliminary cost estimates are provided for producing SAMMS materials and for mercury removal from wastewater. The characteristics of SAMMS in mercury separation were studied at PNNL using simulated aqueous tank wastes and actual tritiated pump oil wastes from Savannah River Site; preliminary results are outlined. 47 refs., 16 figs., 16 tabs

[en] The Mixed Waste Focus Area has declared mercury removal and stabilization as the first and fourth priorities among 30 prioritized deficiencies. Resource Conservation and Recovery Act (RCRA) metal and mercury removal has also been identified as a high priority at DOE sites such as Albuquerque, Idaho Falls, Oak Ridge, Hanford, Rocky Flats, and Savannah River. Under this task, a proprietary new technology, Self-Assembled Monolayers on Mesoporous Supports (SAMMS), for RCRA metal ion removal from aqueous wastewater and mercury removal from organic wastes such as vacuum pump oils is being developed at Pacific Northwest National Laboratory (PNNL). The six key features of the SAMMS technology are (1) large surface area (>900 m²/g) of the mesoporous oxides (SiO₂, ZrO₂, TiO₂) ensures high capacity for metal loading (more than 1 g Hg/g SAMMS); (2) molecular recognition of the interfacial functional groups ensures the high affinity and selectivity for heavy metals without interference from other abundant cations (such as calcium and iron) in wastewater; (3) suitability for removal of mercury from both aqueous wastes and organic wastes; (4) the Hg-laden SAMMS not only pass TCLP tests, but also have good long-term durability as a waste form because the covalent binding between mercury and SAMMS has good resistance to ion exchange, oxidation, and hydrolysis; (5) the uniform and small pore size (2 to 40 nm) of the mesoporous silica prevents bacteria (>2000 nm) from solubilizing the bound mercury; and (6) SAMMS can also be used for RCRA metal removal from gaseous mercury waste, sludge, sediment, and soil

[en] Magic-angle spinning nuclear magnetic resonance (MAS-NMR) has been used to determine the fraction of four-coordinate Al and B in a series of Na₂O-B₂O₃-SiO₂, Na₂O-CaO-B₂O₃-SiO₂, and Na₂O-Al₂O₃-B₂O₃-SiO₂ glasses. It was found that Al occurs nearly exclusively (>98%) as tetrahedral network-forming sites. The fraction of B that obtained tetrahedral coordination, determined by MAS-NMR, was found to be correlated to the nominal concentrations of Na, B, Ca, and Al in the glasses studied. For glass compositions containing both sodium and calcium it was shown that Na⁺ is the predominant contributor to the charge-compensation of BO₂-tetrahedral units. Based on these results, the authors obtained a description of the effect of composition and Na₂O incorporation on the structure of these glasses, which can be used to enhance current and future structural modeling approaches to predicting glass chemical durability

[en] The behavior of radioactive sludge-based and simulated nuclear waste glasses has been compared by long-term testing of radioactive and simulated compositions of Savannah River Laboratory 165, 131, and 200 glasses. Static tests at glass surface area-to-solution volume (SA/V) ratios of 340 and 2000 m^-1 up to 720 days show little difference in reactivity between radioactive and simulated waste glasses. The same leach trends are observed for both glass types. The differences in reactivity at an SA/V of 2000 m^-1 or below are not large enough to alter the order of glass durability for the different compositions nor to change the controlling glass dissolution processes. The small differences in reactivity between fully radioactive and simulated glasses can reasonably be explained if the controlling reaction process and leachate pH values are accounted for. However, at an SA/V of 20,000 m^-1, the simulated nuclear waste glass, 200S, leaches faster than the corresponding radioactive glass by a factor of 40 within 1 yr. The accelerated reaction with the simulated glass 200S is associated with the formation of crystalline phases such as clinoptilolite (or K-feldspar), and a pH excursion. The radiation field generated by the fully radioactive glass reduces the solution pH, which, in turn, may retard the onset of the increased reaction rate. This result suggests that the fully radioactive nuclear waste glass 200R may be substantially more durable than the simulated 200S glass if the lower pH in the 200R leachate can be sustained. Meaningful comparison tests between radioactive and simulated nuclear waste glasses should include long-term and high SA/V tests

[en] A glass durability model, structural bond strength (SBS) model was developed to correlate glass durability with its composition. This model assumes that the strengths of the bonds between cations and oxygens and the structural roles of the individual elements in the glass arc the predominant factors controlling the composition dependence of the chemical durability of glasses. The structural roles of oxides in glass are classified as network formers, network breakers, and intermediates. The structural roles of the oxides depend upon glass composition and the redox state of oxides. Al₂O₃, ZrO₂, Fe₂O₃, and B₂O₃ are assigned as network formers only when there are sufficient alkalis to bind with these oxides. CaO can also improve durability by sharing non-bridging oxygen with alkalis, relieving SiO₂ from alkalis. The percolation phenomenon in glass is also taken into account. The SBS model is applied to correlate the 7-day product consistency test durability of 42 low-level waste glasses with their composition with an R² of 0.87, which is better than 0.81 obtained with an eight-coefficient empirical first-order mixture model on the same data set

[en] Ti-50.6 at.% Ni shape memory alloy specimens were irradiated under the austenite state (parent phase) using a tandem accelerator by 18 MeV protons with doses of 1.53 x 10¹³ and 1.53 x 10¹⁴ H⁺/cm². The microstructure and phase transformation of the specimens before and after irradiation were examined by transmission electron microscopy (TEM) and differential scanning calorimetry (DSC). After the irradiation the parent phase (austenite) was stabilized. R-phase transformation start temperature and the reverse martensitic transformation finish temperature decreased with the increasing proton fluence. They decreased about 13 K and 6 K at a dose of 1.53 x 10¹⁴ H⁺/cm², respectively. The reverse martensitic transformation start temperature and R-phase transformation finish temperature were not affected by the proton irradiation. There is no observable change in the microstructure after irradiation for the low atom displacement probability. The variation of the transformation temperature was assigned to the local stress fields and change in the ordering degree of lattice generated by proton irradiation

[en] The different composition Zr-Sn-Nb alloy specimens were irradiated using a tandem accelerator by 18 MeV proton at room temperature to injection capacity of 1.5 x 10¹⁴ cm^-2 at 1 mm depth. It was observed that resistance ratio was increased by proton irradiation. The increasing point defects by proton irradiation were thought to be major reason of this phenomenon. TEM observation showed that microstructure was not changed by proton irradiation