Apatite- and Monazite-Bearing Glass-Crystal Composites for the Immobilization of Low-Level Nuclear and Hazardous Wastes

This study demonstrates that glass-crystal composite waste forms can be produced from waste streams containing high proportions of phosphorus, transition metals, and/or halides. The crystalline phases produced in crucible-scale melts include apatite, monazite, spinels, and a Zr-Si-Fe-Ti phase. These phases readily incorporated radionuclide and toxic metals into their crystal structures, while corrosion tests have demonstrated that glass-crystal composites can be up to 300-fold more durable than simulated high-level nuclear waste glasses, such as SRL 202U

The Effect of Soluble Salts on the Corrosion Process in Sandstone

Studies of failed engineering structures have found that soluble salts can cause extensive breakdown to sandstone and cement. The mechanism for this failure is postulated to result from crystal growth pressures as evaporate minerals crystallize in the pores. This postulated mechanism. however, is inconsistent with the thermodynamic theory as crystal precipitation and growth should occur in the most energetically favorable setting. We will test this hypothesis by examining the corrosion behavior of sandstone when it is constantly submerged in saline solutions (without crystal formation). A number of tests will be performed in order to observe the effect of saline solutions on sandstone matrix dissolution. The tests are performed on Jacobsville sandstone that was acquired from a construction site in Marquette, Michigan. A synthetic sea water, brine solution and deionized water will be used. Samples are placed in closed container containing one of the solutions. Samples are undergoing tests at room temperature, 90°C, and 200 °C. Degraded samples will be periodically examined in order to see the effects of salt corrosion and/or crystallization

Geochemical Assessment Of Mineral Sequestration Of Carbon Dioxide In The Midcontinent Rift

This Study Examines The Potential Of Midcontinent Rift Rocks To Facilitate Long-Term CO2 Sequestration By Providing The Necessary Ca And Mg For Carbonate Mineralization. Surface Samples Were Collected From The Oronto And Bayfield-Jacobsville Groups Around Lake Superior And Used For Petrography And X-Ray Diffraction To Determine Their Mineral Composition. Also, X-Ray Fluorescence Was Also Used To Assess Their Bulk Chemical Composition. The Samples Were Then Exposed To CO2 And Deionized Water In Teflon-Lined Vessels At 90°C, And The Resulting Leachate Fluids Were Analyzed For The Cation Released During The Testing. SEM Microscopy Was Used To Examine The Samples For Potential Mineralization Of Carbonate Minerals. The Oronto Group Sediments Consist Primarily Of Feldspathic To Feldspathic Lithic Arenites With A Chlorite-Dominated Matrix, And The Primary Porosity Is Blocked By Calcite And Hematite Cement. The Bayfield–Jacobsville Sequences Are Porous Quartz Arenites To Feldspathic Quartz Arenites That Do Not Contain Significant Accumulation Of Ca-, Mg-, And Fe-Bearing Minerals. The Leachate Fluids Obtained From Oronto Group Samples Exhibit A Maximum Ca Release Rate (5.2 X 10−4 Mole/cm2.day), Indicating Rapid Calcite Cement Dissolution And Increased Porosity And Permeability. SEM/EDS Microanalysis Revealed Areas Where Pore-Filling Calcite Was Preferentially Dissolved. Longer-Term Rock-Water Reactions Resulted In Induced Carbonate Mineralization, As Evidenced By Calcite Crystals Observed In A Sample Reacted For 102 Days. © 2024 Society Of Chemical Industry And John Wiley & Sons, Ltd

Sophomore and Junior Recital: Viola Trio

Kemp Recital HallApril 19, 2014Saturday Evening7:30 p.m

Alpha and gamma radiation effects on air-water systems at high gas/liquid ratios

Radiolysis tests were conducted on air-water systems to examine the effects of radiation on liquid phase chemistry under high gas/liquid volume (G/L) ratios that are characteristic of an unsaturated nuclear waste repository setting. Test parameters included temperatures of 25, 90, and 200{degrees}C; gamma vs. alpha radiation; dose rates of {approximately}3500 and 50,000 rad/h; and G/L ratios of 10 and 100. Formate, oxalate, and total organic carbon contents increased during irradiation of the air-water systems in gamma and alpha tests at low-dose rate ({approximately}3500 rad/h). Increases in organic components were not observed for tests run at 200{degrees}C or high-dose rates (50,000 rad/h). In the tests where increases in organics occurred, the formate and oxalate were preferentially enriched in solutions that were rinsed from the test vessel walls. Nitrate (NO{sub 3}{sup {minus}}) is the dominant anion produced during the radiolysis reactions. Significant nitrite (NO{sub 2}{sup {minus}}) also occurs in some high-dose rate tests, with the reduced form of nitrogen possibly resulting from reactions with the test vessels. These results indicate that nitrogen acids are being produced and concentrated in the limited quantities of solution present in the tests. Nitrate + nitrite production varied inversely with temperature, with the lowest quantities being detected for the higher temperature tests. The G(NO{sub 3}{sup {minus}} + NO{sub 2}{sup {minus}}) values for the 25, 90, and 200{degrees}C experiments with gamma radiation are 3.2 {+-} 0.7, 1.3 {+-} 1.0, and 0.4 {+-} 0.3, respectively. Thus, the elevated temperatures expected early in the life of a repository may counteract pH decreases resulting from nitrogen acid production. Little variation was observed in G values as a function of dose rate or gas/liquid ratio

Incorporation of Cerium and Neodymium in a Uranyl Hydroxide Solid

The migration behavior of radionuclides in a nuclear-waste repository will be influenced, in part, by their equilibrium solubilities in the presence of radionuclide-bearing solids and/or adsorption affinities as trace components onto the surfaces of solid host phases. Uranium phases that precipitate on the surface of altered spent nuclear fuel may thus influence the mobility of radionuclides released in the near-field environment, since by proximity, these will be the first phases that the radionuclides encounter following their release from the spent fuel matrix. We have evaluated the potential for incorporating radionuclides into crystalline compounds by precipitating uranyl phases from aqueous solutions containing dissolved rare earth elements (REE; 2.1 ppm Ce4+, 4.6 ppm Ce4+, or 286 ppm Nd3+). Rare earth elements serve both as monitors for evaluating the potential behavior of REE radionuclides and as surrogate elements for the actinides (e.g., Ce4+ and Nd3+ for Pu4+ and Am3+, respectively). Although the crystalline compound that formed in the present set of experiments has not been positively identified, x-ray diffraction profiles suggest the presence of a uranyl hydroxide (UO2(OH)2) as the principal reaction product. An analysis of the crystalline products indicates a progressive decrease in concentration of cerium; from 26, to 20, and finally 11 ppm for crystals produced in 7-, 35-, and 190-day tests, respectively (Kd = 14, 11, 3, respectively). Results with neodymium display a similar trend, with concentrations in the solid decreasing from 1240 to 922 ppm between 7 and 35 days of reaction (Kd = 14 and 11, respectively). The decreasing concentration of REEs in the uranyl crystals can be correlated with both a coarsening in crystal size and a decrease in the concentration of dissolved uranium over time. Thus, REE incorporation in the crystalline solids decreases in conjunction with a decrease in the ratio of surface area/volume of the crystals, a decrease in the rate of crystal growth as uranium concentrations are lowered, or both. These data also suggest that adsorption of REE (and by analogy, actinides) onto crystal surfaces and subsequent trapping by crystal overgrowth processes may play key roles in the limiting the mobility of radionuclides in a nuclear waste repository

Dendritic position is a major determinant of presynaptic strength

Different regulatory principles influence synaptic coupling between neurons, including positional principles. In dendrites of pyramidal neurons, postsynaptic sensitivity depends on synapse location, with distal synapses having the highest gain. In this paper, we investigate whether similar rules exist for presynaptic terminals in mixed networks of pyramidal and dentate gyrus (DG) neurons. Unexpectedly, distal synapses had the lowest staining intensities for vesicular proteins vGlut, vGAT, Synaptotagmin, and VAMP and for many nonvesicular proteins, including Bassoon, Munc18, and Syntaxin. Concomitantly, distal synapses displayed less vesicle release upon stimulation. This dependence of presynaptic strength on dendritic position persisted after chronically blocking action potential firing and postsynaptic receptors but was markedly reduced on DG dendrites compared with pyramidal dendrites. These data reveal a novel rule, independent of neuronal activity, which regulates presynaptic strength according to dendritic position, with the strongest terminals closest to the soma. This gradient is opposite to postsynaptic gradients observed in pyramidal dendrites, and different cell types apply this rule to a different extent

Grain boundary corrosion and alteration phase formation during the oxidative dissolution of UO{sub 2} pellets

Alteration behavior of UO{sub 2} pellets following reaction under unsaturated drip-test conditions at 90 C for up to 10 years was examined by solid phase and leachate analyses. Sample reactions were characterized by preferential dissolution of grain boundaries between the original press-sintered UO{sub 2} granules comprising the samples, development of a polygonal network of open channels along the intergrain boundaries, and spallation of surface granules that had undergone severe grain boundary corrosion. The development of a dense mat of alteration phases after 2 years of reaction trapped loose granules, resulting in reduced rates of particulate U release. The paragenetic sequence of alteration phases that formed on the present samples was similar to that observed in surficial weathering zones of natural uraninite (UO{sub 2}) deposits, with alkali and alkaline earth uranyl silicates representing the long-term solubility-limiting phases for U in both systems

Plutonium Silicate Alteration Phases Produced by Aqueous Corrosion of Borosilicate Glass

Borosilicate glasses loaded with {approx}10 wt % plutonium were found to produce plutonium-silicate alteration phases upon aqueous corrosion under a range of conditions. The phases observed were generally rich in lanthanide (Ln) elements and were related to the lanthanide orthosilicate phases of the monoclinic Ln{sub 2}SiO{sub 5} type. The composition of the phases was variable regarding [Ln]/[Pu] ratio, depending upon type of corrosion test and on the location within the alteration layer. The formation of these phases likely has implications for the incorporation of plutonium into silicate alteration phases during corrosion of titanate ceramics, high-level waste glasses, and spent nuclear fuel

Apatite- and Monazite-Bearing Glass-Crystal Composites for the Immobilization of Low-level Nuclear and Hazardous Wastes

This study demonstrates that glass-crystal composite waste forms can be produced from waste streams containing high proportions of phosphorus, transition metals, and/or halides. The crystalline phases produced in crucible-scale melts include apatite, monazite, spinels, and a Zr-Si-Fe-Ti phase. These phases readily incorporated radionuclide and toxic metals into their crystal structures, while corrosion tests have demonstrated that glass-crystal composites can be up to 300-fold more durable than simulated high-level nuclear waste glasses, such as SRL 202U