Closing the Nuclear Fuel Cycle with a Simplified Minor Actinide Lanthanide Separation Process (ALSEP) and Additive Manufacturing

Expanded low-carbon baseload power production through the use of nuclear fission can be enabled by recycling long-lived actinide isotopes within the nuclear fuel cycle. This approach provides the benefits of (a) more completely utilizing the energy potential of mined uranium, (b) reducing the footprint of nuclear geological repositories, and (c) reducing the time required for the radiotoxicity of the disposed waste to decrease to the level of uranium ore from one hundred thousand years to a few hundred years. A key step in achieving this goal is the separation of long-lived isotopes of americium (Am) and curium (Cm) for recycle into fast reactors. To achieve this goal, a novel process was successfully demonstrated on a laboratory scale using a bank of 1.25-cm centrifugal contactors, fabricated by additive manufacturing, and a simulant containing the major fission product elements. Americium and Cm were separated from the lanthanides with over 99.9% completion. The sum of the impurities of the Am/Cm product stream using the simulated raffinate was found to be 3.2 × 10−3 g/L. The process performance was validated using a genuine high burnup used nuclear fuel raffinate in a batch regime. Separation factors of nearly 100 for 154Eu over 241Am were achieved. All these results indicate the process scalability to an engineering scale

Forecasting the response of Earth's surface to future climatic and land use changes: a review of methods and research needs

In the future, Earth will be warmer, precipitation events will be more extreme, global mean sea level will rise, and many arid and semiarid regions will be drier. Human modifications of landscapes will also occur at an accelerated rate as developed areas increase in size and population density. We now have gridded global forecasts, being continually improved, of the climatic and land use changes (C&LUC) that are likely to occur in the coming decades. However, besides a few exceptions, consensus forecasts do not exist for how these C&LUC will likely impact Earth-surface processes and hazards. In some cases, we have the tools to forecast the geomorphic responses to likely future C&LUC. Fully exploiting these models and utilizing these tools will require close collaboration among Earth-surface scientists and Earth-system modelers. This paper assesses the state-of-the-art tools and data that are being used or could be used to forecast changes in the state of Earth's surface as a result of likely future C&LUC. We also propose strategies for filling key knowledge gaps, emphasizing where additional basic research and/or collaboration across disciplines are necessary. The main body of the paper addresses cross-cutting issues, including the importance of nonlinear/threshold-dominated interactions among topography, vegetation, and sediment transport, as well as the importance of alternate stable states and extreme, rare events for understanding and forecasting Earth-surface response to C&LUC. Five supplements delve into different scales or process zones (global-scale assessments and fluvial, aeolian, glacial/periglacial, and coastal process zones) in detail

Learning the Rhythm of the Seasons in the Face of Global Change: Phenological Research in the 21st Century

Phenology is the study of recurring life-cycle events, of which classic examples include flowering by plants as well as animal migration. Phenological responses are increasingly relevant for addressing applied environmental issues. Yet, challenges remain with respect to spanning scales of observation, integrating observations across taxa, and modeling phenological sequences to enable ecological forecasts in light of future climate change. Recent advances that are helping to address these challenges include refined landscape-scale phenology estimates from satellite data, advanced instrument-based approaches for field measurements, and new cyber-infrastructure for archiving and distribution of products. These advances are aiding in diverse areas including modeling land-surface exchange, evaluating climate-phenology relationships, and aiding land management decisions

Forecasting the Response of Earth\u27s Surface to Future Climatic and Land Use Changes: A Review of Methods and Research Needs

In the future, Earth will be warmer, precipitation events will be more extreme, global mean sea level will rise, and many arid and semiarid regions will be drier. Human modifications of landscapes will also occur at an accelerated rate as developed areas increase in size and population density. We now have gridded global forecasts, being continually improved, of the climatic and land use changes (C&LUC) that are likely to occur in the coming decades. However, besides a few exceptions, consensus forecasts do not exist for how these C&LUC will likely impact Earth-surface processes and hazards. In some cases, we have the tools to forecast the geomorphic responses to likely future C&LUC. Fully exploiting these models and utilizing these tools will require close collaboration among Earth-surface scientists and Earth-system modelers. This paper assesses the state-of-the-art tools and data that are being used or could be used to forecast changes in the state of Earth\u27s surface as a result of likely future C&LUC. We also propose strategies for filling key knowledge gaps, emphasizing where additional basic research and/or collaboration across disciplines are necessary. The main body of the paper addresses cross-cutting issues, including the importance of nonlinear/threshold-dominated interactions among topography, vegetation, and sediment transport, as well as the importance of alternate stable states and extreme, rare events for understanding and forecasting Earth-surface response to C&LUC. Five supplements delve into different scales or process zones (global-scale assessments and fluvial, aeolian, glacial/periglacial, and coastal process zones) in detail

Fiscal Year 2012

Accurate and timely analysis of plutonium in spent nuclear fuel is critical in nuclear safeguards for detection of both protracted and rapid plutonium diversions. Gamma spectroscopy is a viable method for accurate and timely measurements of plutonium provided that the plutonium is well separated from the interfering fission and activation products present in spent nuclear fuel. Electrochemically modulated separation (EMS) is a method that has been used successfully to isolate picogram amounts of Pu from nitric acid matrices. With EMS, Pu adsorption may be turned “on” and “off” depending on the applied voltage, allowing for collection and stripping of Pu without the addition of chemical reagents. In this work, we have scaled up the EMS process to isolate microgram quantities of Pu from matrices encountered in spent nuclear fuel during reprocessing. Several challenges have been addressed including surface area limitations, radiolysis effects, electrochemical cell performance stability, and chemical interferences. After these challenges were resolved, 6 µg Pu was deposited in the electrochemical cell with approximately an 800-fold reduction of fission and activation product levels from a spent nuclear fuel sample. Modeling showed that these levels of Pu collection and interference reduction may not be sufficient for Pu detection by gamma spectroscopy. The main remaining challenges are to achieve a more complete Pu isolation and to deposit larger quantities of Pu for successful gamma analysis of Pu. If gamma analyses of Pu are successful, EMS will allow for accurate and timely on-site analysis for enhanced Pu safeguards

Structure and spectroscopy of uranyl and thorium complexes with substituted phosphine oxide ligands

Phosphine oxide ligands are important in the chemistry of the nuclear fuel cycle. We have synthesized and characterized a series of phosphine oxide ligands with polycyclic aromatic hydrocarbon (PAH) groups to enhance the spectroscopic features of uranyl, UO_2^(2+), and to make detection more efficient. Complexation of OPPh_2R, R = C_(10)H_7 (naphthyl); C_(14)H_9 (phenanthrenyl); C_(14)H_9 (anthracenyl); and C_(16)H_9 (pyrenyl), to UO_2(NO_3)_2 afforded the eight-coordinate complexes, UO_2(NO_3)_2(OPPh_2R)_2. An eleven-coordinate complex, Th(NO_3)_4[OPPh_2(C_(14)H_9)]_3, C_(14)H_9 = phenanthrenyl, was structurally characterized, and was found to be the first thorium compound isolated with three phosphine oxide ligands bound. The phosphine oxide ligands were not fluorescent but the anthracenyl-substituted ligand showed broad, red-shifted emission at approximately 50 nm relative to typical anthracene, making this ligand set a possibility for use in detection. The synthesis and spectroscopy of the uranyl and thorium complexes are presented

SERDP ER-1421 Abiotic and Biotic Mechanisms Controlling In Situ Remediation of NDMA: Final Report

This laboratory-scale project was initiated to investigate in situ abiotic/biotic mineralization of NDMA. Under iron-reducing conditions, aquifer sediments showed rapid abiotic NDMA degradation to dimethylamine (DMA), nitrate, formate, and finally, CO2. These are the first reported experiments of abiotic NDMA mineralization. The NDMA reactivity of these different iron phases showed that adsorbed ferrous iron was the dominant reactive phase that promoted NDMA reduction, and other ferrous phases present (siderite, iron sulfide, magnetite, structural ferrous iron in 2:1 clays) did not promote NDMA degradation. In contrast, oxic sediments that were biostimulated with propane promoted biomineralization of NDMA by a cometabolic monooxygenase enzyme process. Other monooxygenase enzyme processes were not stimulated with methane or toluene additions, and acetylene addition did not block mineralization. Although NDMA mineralization extent was the highest in oxic, biostimulated sediments (30 to 82%, compared to 10 to 26% for abiotic mineralization in reduced sediments), large 1-D column studies (high sediment/water ratio of aquifers) showed 5.6 times higher NDMA mineralization rates in reduced sediment (half-life 410 ± 147 h) than oxic biomineralization (half life 2293 ± 1866 h). Sequential reduced/oxic biostimulated sediment mineralization (half-life 3180 ± 1094 h) was also inefficient compared to reduced sediment. These promising laboratory-scale results for NDMA mineralization should be investigated at field scale. Future studies of NDMA remediation should focus on the comparison of this in situ abiotic NDMA mineralization (iron-reducing environments) to ex situ biomineralization, which has been shown successful in other studies

Molybdenum(VI) Coordination in Tributyl Phosphate Chloride Based System

Fundamental coordination chemistry of Mo­(VI) at its macroconcentrations in solvent extraction systems is of great importance for industrial processes that require the purification or recovery of large concentrations of Mo. The coordination of Mo­(VI) in tri-<i>n</i>-butyl phosphate (TBP) from solutions of hydrochloric acid and up to 0.3 M Mo was investigated using UV, FTIR, and ³¹P NMR spectroscopies, as well as EXAFS. From these techniques we resolved near-neighbor atoms, speciation, structural information on the coordination environment, and thermodynamic parameters affiliated with the solvent extraction of Mo­(VI) and HCl. The solvated extracted form of Mo­(VI) as MoO₂Cl₂·2TBP was identified. High extraction yield of Mo at >5 M HCl concentration is driven by replacing HCl in the organic phase by Mo. The existence of additional organic Mo adducts is also discussed with the aid of density functional theory, however no evidence of dimeric or polymeric Mo species was found to be present in TBP

Trivalent Uranium Phenylchalcogenide Complexes: Exploring the Bonding and Reactivity with CS₂ in the Tp*₂UEPh Series (E = O, S, Se, Te)

The trivalent uranium phenylchalcogenide series, Tp*₂UEPh (Tp* = hydrotris­(3,5-dimethylpyrazolyl)­borate, E = O (<b>1</b>), S (<b>2</b>), Se (<b>3</b>), Te (<b>4</b>)), has been synthesized to investigate the nature of the U–E bond. All compounds have been characterized by ¹H NMR, infrared and electronic absorption spectroscopies, and in the case of <b>4</b>, X-ray crystallography. Compound <b>4</b> was also studied by SQUID magnetometry. Computational studies establish Mulliken spin densities for the uranium centers ranging from 3.005 to 3.027 (B3LYP), consistent for uranium–chalcogenide bonds that are primarily ionic in nature, with a small covalent contribution. The reactivity of <b>2</b>–<b>4</b> toward carbon disulfide was also investigated and showed reversible CS₂ insertion into the U­(III)–E bond, forming Tp*₂U­(κ²-S₂CEPh) (E = S (<b>5</b>), Se (<b>6</b>), Te (<b>7</b>)). Compound <b>5</b> was characterized crystallographically

Trivalent Uranium Phenylchalcogenide Complexes: Exploring the Bonding and Reactivity with CS₂ in the Tp*₂UEPh Series (E = O, S, Se, Te)

The trivalent uranium phenylchalcogenide series, Tp*₂UEPh (Tp* = hydrotris­(3,5-dimethylpyrazolyl)­borate, E = O (<b>1</b>), S (<b>2</b>), Se (<b>3</b>), Te (<b>4</b>)), has been synthesized to investigate the nature of the U–E bond. All compounds have been characterized by ¹H NMR, infrared and electronic absorption spectroscopies, and in the case of <b>4</b>, X-ray crystallography. Compound <b>4</b> was also studied by SQUID magnetometry. Computational studies establish Mulliken spin densities for the uranium centers ranging from 3.005 to 3.027 (B3LYP), consistent for uranium–chalcogenide bonds that are primarily ionic in nature, with a small covalent contribution. The reactivity of <b>2</b>–<b>4</b> toward carbon disulfide was also investigated and showed reversible CS₂ insertion into the U­(III)–E bond, forming Tp*₂U­(κ²-S₂CEPh) (E = S (<b>5</b>), Se (<b>6</b>), Te (<b>7</b>)). Compound <b>5</b> was characterized crystallographically