bluuebunny/crossref_metadata_2025_split huggingface dataset:
7-Years Leaching Tests of NPP Vitrified Radioactive Waste
Authors: Barinov A. S. , Ojovan M. I. , Ojovan N. V. 
Published: April 2011

AbstractLong term tests of vitrified intermediate level waste from nuclear power plants were performed in a shallow ground repository as well as on an open testing area. Borosilicate glasses were tested. Radionuclide leaching differs significantly in natural conditions in contrast to laboratory behaviour. Average leaching factors were obtained for open area tests as well as for repository tests. These factors should be used for long term predictions since they take into account the real character of leaching.
Modelling Glass Dissolution with a Monte Carlo Technique
Authors: Aertsens Marc , Iseghem Pierre Van 
Published: April 2011

AbstractWe present a Monte Carlo simulation method for modelling glass dissolution in aqueous solutions. This simulation method is consistent with transition state theory, and therefore also with the glass dissolution rate law, used for instance in the Grambow model. The simulation method allows to add dynamics (kinetics) to the existing thermodynamic models for glass dissolution. Using this method, it is possible to model non stoichiometric dissolution of the glass.Besides, we introduce a simple, first version of a model in which we use the simulation method. In this model, we approximate the glass by a lattice. We assume that the glass contains two components: a network former and a network modifier. Bonds between two network formers are assumed to be much stronger than any other bond in the system. We observe that above a threshold value for the concentration of network modifiers, the glass dissolves fast. No surface layer develops and the dissolution rate is constant (linear stoichiometric dissolution). Below this threshold, the glass is more durable and surface layers are formed. As time goes on, the thickness of the surface layers grows. The dissolution of the glass is not stoichiometric. This behaviour agrees with experimental results.
A Melting Route to Synroc for Hanford HLW Immobilization
Authors: Vance E. R. , Day R. A. , Carter M. L. , Jostsons A. 
Published: April 2011

AbstractFor the HLW fractions of certain Hanford tank wastes, wasteforms consisting mainly of crystalline Synroc phases in an aluminosilicate matrix can be formed by melting at 1350–1450°C in a neutral atmosphere, with waste loadings of up to 70 wt%, depending on the waste composition. The leachability of all measured elements in 7-day PCT tests was <0.1 g/m2/d at 90°C in the best materials.
Options and Choices in the Disposition of Excess Weapon Plutonium
Authors: Garwin R. L. 
Published: April 2011

AbstractMore than 50 tons of weapon-related plutonium (WPu) is expected to become excess andavailable for disposition by the year 2003 in Russia and a similar amount in the United States.Per two reports from the Committee on International Security and Arms Control of the NationalAcademy of Sciences (1994 1 and 1995 2), the hazard of theft and incorporation into nuclearweapons impels us to guard this Pu carefully and as soon as possible to transform it into a formless accessible for use in nuclear weapons. To this end, CISAC adopted the “Spent FuelStandard” for the disposed WPu, which, if met, renders the WPu no greater hazard per kg thanthe much larger amount of reactor Pu in the form of spent fuel, since CISAC finds that separatedRPu can be used for nuclear weapons with little additional difficulty beyond that posed byseparated WPu. Many disposition routes can be eliminated on the basis of cost or other metric.The two principal survivors (of about equal cost and difficulty for the United States) are thepartial burning of WPu as MOX and the direct vitrification of WPu (as oxide) with high-level‘defense wastes’. Both these approaches should be pursued urgently, with experiments toqualify the processes, until one is selected on the basis of hard evidence. Either approach wouldcost about $1 B, within a factor two, to dispose of 50 tons of excess WPu. The CISAC analysiswill be presented, with comments on utility of RPu in weapons, on the DOE PlutoniumDisposition Study, and on ‘explosive criticality’ in the repository.
Ceramic Waste Form for Residues from Molten Salt Oxidation of Mixed Wastes
Authors: Konynenburg Richard A. Van , Hopper Robert W. , Rard Joseph A. , Ryerson Frederick J. , Phinney Douglas L. , Hutcheon Ian D. , Curtis Paul G. 
Published: April 2011

AbstractA ceramic waste form based on Synroc-D is under development for the incorporation of the mineral residues from molten salt oxidation treatment of mixed low-level wastes. Samples containing as many as 32 chemical elements have been fabricated, characterized, and leach-tested. Universal Treatment Standards have been satisfied for all regulated elements except two (lead and vanadium). Efforts are underway to further improve chemical durability.
Synthesis of Zircon for Immobilization of Actinides
Authors: Burakov B. E. , Anderson E. B. , Rovsha V. S. , Ushakov S. V. , Ewing R. C. , Lutze W. , Weber W. J. 
Published: April 2011

AbstractA new method of synthesis for actinide-doped zircon is presented based on studies of zircons formed by crystallization from the reactor core melt generated in the course of the accident at the Chernobyl Nuclear Power Plant. These zircons have compositions in the range (Zr0.94, U0.06)SiO4to (Zr0.9, U0.1)SiO4. Hot-pressing of oxides was studied to make Zr-based waste forms. The results demonstrate the efficacy of using metallic zirconium in synthesizing high-actinide zircons. In the event of deviations from zircon's ideal stoichiometry, ZrO2forms, which is also an effective host phase for actinide elements. Waste streams high in zirconium and actinides could be converted into Zr-based waste forms. The adaptation and modification of the mixed-oxide reactor fuel (MOX) production process is proposed as a process for the production of (Zr,Pu)SiO4, a durable waste form for excess weapons plutonium.
Effect of Conjoint Additions of Rare Earth Element Oxides on the Phase Stability of Zirconia
Authors: Maddrell Ewan R. 
Published: April 2011

AbstractThe ability of the cubic phase of zirconia to accommodate in solid solution the oxides of rare earth elements with differing cationic radii has been investigated. Mixed oxide phase assemblages were prepared by hydrolysing zirconium butoxide with solutions of rare earth element nitrates followed by drying, calcining and sintering. The resulting products were characterised by X-ray diffraction and energy dispersive spectroscopy. The cubic zirconia phase can accept into solid solution the larger, non-cubic stabilising, rare earth element ions such as lanthanum in the presence of the cubic stabilising oxides of yttrium and samarium. As the proportion of the larger rare earth element ions is increased the formation of pyrochlore type compounds is favoured.
Aeschynite and Euxenite Structure-Types as Host Phases for Rare-Earths and Actinides from HLW
Authors: Gong W. L. , Ewing R. C. , Wang L. M. , Xie H. S. 
Published: April 2011

AbstractAeschynite and euxenite structure-types are proposed as host phases for rare earth elements and actinides. Aeschynite and euxenite structure types are represented by the general formula: (REE,Y,Th,U,Ca)(Ti,Nb,Ta)2O6. In both structure-types, a variety of large cations such as rareearths and actinides can be accommodated in the tunnels of connected holes in aeschynite or the interlayer space in euxenite. The waste loadings (rare-earths and actinides) in aeschynite and euxenite are at least 40 wt. % based on chemical compositions of naturally occurring aeschynite and euxenite.The sol-gel method has been successfully used to prepare aeschynite and euxenite as preferred crystalline ceramics. The aged gels and finally calcined products have been characterized by infrared and Raman spectroscopy, differential thermal analysis, and X-ray diffraction analysis. The fabrication technology of aeschynite and euxenite type ceramics is feasible by using hot-pressing as a final processing stage. The mechanistic processes of aeschynite and euxenite formation by the sol-gel method as described as REE(OH)3 · Nb(OH)5·Ti(OH)4 coprecipitation; the polymerization of Nb and Ti hydroxides to form isolated (Nb,Ti)2O10 di-octahedra through oxygen and hydroxyl bridges accompanied by a dehydration reaction; welding together of isolated “pieces” of (Nb,Ti) 2010 to form longer (Nb,Ti)2O10 di-octahedral chains; REE being connected to the dioctahedral chains through oxygen and hydroxyl bridges; and to gradually form small threedimensional nucleates of aeschynite and euxenite. Critical data from the literature on radiation effects and secondary alteration are reviewed as a part of the evaluation of the long-term performance of these phases.
Excess Pu Disposition in Zirconolite-Rich synroc
Authors: Vance E. R. , Jostsons A. , Day R. A. , Ball C. J. , Begg B. D. , Angel P. J. 
Published: April 2011

AbstractThe design philosophy of a zirconolite-rich Synroc variant, hot-pressed at 1200°C/20 MPa, for immobilizing excess weapons Pu is summarized. Phase analysis of Synroc variants containing different (nominated) proportions of zirconolite, Pu and Gd is presented. The presence of hollandite allows the incorporation of radioactive Cs to reduce diversion risks. The influence of chloride impurities on Synroc properties was studied to bear on the usage of encapsulated 137CSCI for this purpose. The maximum incorporation of the neutron poisons Gd and Hf in solid solution in zirconolite from XRD/SEM is 0.5–0.7 and 1.0 formula units respectively, with the value for Gd depending on the charge compensation scheme employed. The use of deep boreholes for disposal would promote the self-annealing of radiation damage from α-decays. The production of zirconolite-rich Synroc ceramics via fired PuO2 or a liquid Pu/microsphere precursor is also discussed. The choice of processing atmosphere for a zirconolite-rich ceramic containing Pu is oxidizing to neutral for Pu-only and Pu + Cs immobilization options, and reducing for a Pu + fission product option
Leachability of Nd, U, Th, and Sr from Cements in a CO2 Free Atmosphere
Authors: Serne R. J. , Rai D. , Martin P. F. , Felmy A. R. , Rao L. , Ueta S. 
Published: April 2011

AbstractTo determine the leachability and concentration-controlling solids for nuclides contained in solidified low-level nuclear wastes, cement doped with neodymium, uranium, thorium and strontium was prepared and cured in a CO2-free atmosphere. Leaching tests were conducted by equilibrating aliquots of the crushed doped cement with CO2-free deionized water at pcH+ values ranging from 7.5 to 12.5 in an effort to determine if solubility constraints could be used to predict leachable concentrations of Nd (an analog of trivalent actinides), U, Th, and Sr. Steady state concentrations of Nd, U, Th and Sr were attained within a few days. The observed Nd concentrations continually decreased with the increase in pcH+ from about 7.5 to 9.0, and were at detection limit at pcH+ values > 9.0. The comparison of these results with thermodynamic data suggests that Nd(OH)3(am) is the controlling solid phase. The observed U concentrations decreased by two orders of magnitude with a unit increase in pcH+ in the range of 7.5 to 9.0 and were at the detection limit at pcH+ > 9.0. From the multitude of U(VI) solids that can form under the test conditions, the data suggest that CaUO4 is the likely controlling solid. The concentration of Th was at the detection limit over the entire pcH+ range covered. Based on previous work, ThO2(am) is likely to be the controlling solid. In the absence of CO2, no solubility-controlling solid was found for Sr.
The Effect of Water Vapor on the Corrosion of Carbon Steel at 65°c
Authors: Gdowski Gregory E. , Estill John C. 
Published: April 2011

AbstractAISI 1020 carbon steel was exposed to air at various relative humidities at 65°C. A “critical relative humidity” (CRH) of 75–85% was determined. The CRH is the transitional relative humidity where oxidation/corrosion changes from dry oxidation to aqueous film electrochemical corrosion. Short term testing suggests that aqueous film electrochemical corrosion results in the formation of an inner oxide of Fe3O4, and an outer oxide of a powdery Fe2O3 and/or Fe2O3·xH2O.
Long-Term Thermal Stability of Alloy 825 as a High-Level Nuclear Waste Container Material
Authors: Dunn D. S. , Pan Y.-M. , Cragnolino G. A. , Sridhar N. 
Published: April 2011

AbstractThe thermal exposure of Fe-Cr-Ni-Mo materials to certain temperature regimes often results in the formation of grain boundary carbides and the associated depletion of alloying elements. This phenomenon, termed sensitization, is frequently the result of welding processes or in service exposure to elevated temperatures. In this investigation, alloy 825, a candidate high-level nuclear waste (HLW) container material, was thermally exposed to temperatures in the range of 550 to 800 °C for periods of up to 1,000 hr. Sensitization of the material was evaluated by corrosion tests and grain boundary analyses using an analytical electron microscope. The sensitized microstructure was found to contain M23C6-type carbides as well as a Cr-depleted region in the vicinity of the grain boundaries. The degree of sensitization was correlated to the extent of Cr depletion in the grain boundary region.
Effect of [HCO3-+CO32−[ on Corrosion Crevice Repassivation Potential of Carbon Steel in Simulated Bentonite Environment
Authors: Fukuda Takanori , Akashi Masatsune 
Published: April 2011

AbstractIn order to evaluate the localized corrosion susceptibility of carbon steel in water containing bentonite, the critical pH for depassivation, pHd, the critical potential for crevice corrosion, ERCREV, and the free corrosion potential, Esp, were determined in simulated aqueous solutions of 1 to 100 mmol/L [HCO3- - CO32−], 1 to 1000 mmo!/L [NaCI], and pH of 7 to 12. The Following results were obtained; 1)ER, CREV. increases with increasing [HCO3− CO32−] concentration. The relationship can be described as a function of the ratio of [CI-I HCO3−- CO32−], 2)The Esp increases with increasing pH in the passive region, and 3)ThepHd shows [HCO3− - CO32−] concentration dependency. This paper also discusses the relationship between critical initiation potential for crevice corrosion of carbon steel, [CI-], and [HCO3− CO32−] anion. The crevice corrosion that occurs on passivated metals and alloys is characterized by determinable critical initiation potential that can be induced in a potential range nobler than its critical potential.
Coprecipitation of Sr, Ni and U with CaCO3: An Experimental Study
Authors: Carlsson Torbjörn , Aalto Hannu 
Published: April 2011

AbstractAt the Finnish candidate sites for a nuclear waste repository, calcite (CaCO3) is a common fracture mineral that may participate in coprecipitation processes. The objective of this preliminary work was to study the coprecipitation of the trace elements Sr, Ni, and U with CaCO3 under controlled conditions. The experiments were made in a titration vessel at room temperature under pure N2 or a 0.1 % CO 2/N2 mixture. The water phase contained CaCl2 (0.01M) and NaCl (0.05 M) to which trace amounts of Ni2+, Sr2+ and UO22+ were initially added. CaCO3 was precipitated by the addition of Na2CO3 and the use of CaCO3 seed crystals. When about 10−4 mol of precipitate had formed, the solution and solid phases were analysed with ICPMS. The results seem to indicate that Ni coprecipitated with CaCO3 under the experimental conditions, while U did not. In the case of Sr, further data are needed in order to make any conclusions from the experiments.
Durabilities and Microstructures of Radioactive Glasses for Immobilization of Excess Actinides at the Savannah River Site
Authors: Bibler N. E. , Ramsey W. G. , Meaker T. F. , Pareizs J. M. 
Published: April 2011

AbstractThis paper presents results of an investigation of the microstructures and durabilities of glasses for immobilization of excess Pu, Am, and Cm at the Savannah River Site (SRS). The glasses investigated had compositions based on commercial lanthanide glasses developed in the 1930's. All the glasses were prepared remotely in shielded cells and the analyses performed using instruments in radio hoods or benches. Durabilities were measured using the ASTM C-1285 standard leach test (PCT). Results for three glasses are presented. Two glasses contained 15 and 7 wt.% Pu, respectively. The third glass contained Am and Cm. The 15 wt% Pu glass was not completely amorphous and contained crystals of undissolved PuO2 and as well as dissolved PuO2. The 7 wt% Pu glass was completely amorphous. The Am/Cm glass contained <1 wt% actinides and was homogenous. The PCT tests for the Pu glasses indicated that B and Ba were leached congruently. Sm and Pu were leached at slower rates. In some cases release rates for specific Ba, Sm, and Pu isotopes were measured by analyzing the leachates by mass spectroscopy. For the Am-Cm glass release rates for B and Ba were equal indicating congruent dissolution. All three glasses were 25 to 50 times more durable than the borosilicate glasses developed at SRS for immobilization of the fission product HLW resulting from reprocessing operations at SRS.
Preparation of Titanium Hexacyanoferrate Microspheres (Diameter <70 μm) by Water Extraction Variant of Sol-Gel Process and its Application to Sorption of 137Cs from Nuclear Reactor Cooling Water
Authors: Deptula A. , Chmielewski A. G. , Lada W. , Olczak T. 
Published: April 2011

AbstractTitanium hexacyanoferrate microspheres (diameter <70km) were obtained in the following steps: (1) extraction of chlorides from an aqueous solution of TiCl4 with long chain amine -Primene JMT- in paraffin diluent (the resulting sol has the concentration 320 g TiO2/dm3 and the mole ratio Cl-: Ti4+ = 1.83); (2) blending of titania sol with an aqueous solution of K4 Fe(CN)6. 3H2O (280 g/dm3) in order to obtain final sols with Fe(CN)64-: Ti4+ mole ratio of 0.05 - 0.1; (3) formation of multicomponent sol emulsion in 2-ethylhexanol-1 containing I vol. % of Ethomen S/15 (EH), (4) gelation of emulsion drops by extraction of water with partially dehydrated EH; (5) filtration and washing with acetone; (6) drying at 140°C using a special procedure elaborated on the basis of TG and DTA studies.The final product is insoluble in water and exhibits high sorption efficiency of 137 Cs.
Natural Analog Support for Unsaturated Transport Modeling Using Data from the Akrotiri Archaeological Site
Authors: Murphy William M. , Pearcy English C. 
Published: April 2011

AbstractA review of the natural analog study at the Akrotiri archaeological site is provided with regard to its use in support of long-term predictive modeling of chemical transport. Evidence for a plume of contaminants was collected using samples taken from the area under the location where artifacts were buried in silicic tuff for 3600 years. A transport model was developed using site characterization data, but no data for the plume. Qualitative data from the field support the model result that flux of metals from the artifacts was small. However, transient transport characteristics and the role of notable system heterogeneities and complexities were not fully represented by the model. The Akrotiri natural analog study indicates that long term releases and transport may be limited in an unsaturated repository site, but releases may be strongly affected by unknown processes or processes that are neglected in simplified models.
Uranium-Series Ages of Secondary Uranium Minerals with Applications to the Long-Term Evolution of Spent Nuclear Fuel
Authors: Finch R. J. , Suksi J. , Rasilainen K. , Ewing R. C. 
Published: April 2011

AbstractUranium-series activity ratios for U(VI) minerals from the Shinkolobwe mine in southern Zaire indicate that these minerals have not experienced significant preferential loss of uranium since their formation more than 100,000 years ago. The minerals examined include rutherfordine, UO2CO3, schoepite, [(UO2)8O2(OH)12]·12H2O, becquerelite, Ca[(UO2)6O4(OH)6]·8H2O, and uranophane, Ca[(UO2)2(SiO3OH)2]·5H2O. No correlation between mineral species and mineral age was evident. The oxidative dissolution of primary uraninite (UO2+x) has maintained ground waters supersaturated with respect to all of the secondary U(VI) minerals, providing an inexhaustible source of dissolved U6+ for mineral formation and growth. As long as uraninite persists in an oxidizing environment, the assemblage of secondary U(VI) phases is determined by local ground water chemistry (including transitory changes), but not necessarily a unidirectional reaction path towards equilibrium with U(VI) minerals of lower solubility. Thus the Shinkolobwe mine displays a complex assemblage of U(VI) minerals that reflects variations in the availability of dissolved elements besides U. Similarly, for a geologic repository exposed to oxidizing waters, the assemblage of corrosion products that will form during the corrosion of spent UO2 fuel is likely to be as complex as mineral assemblages found in natural uranium deposits under similar conditions.
Natural Occurrence and Stability of Pyrochlore in Carbonatites, Related Hydrothermal Systems, and Weathering Environments
Authors: Lumpkin Gregory R. , Mariano Anthony N. 
Published: April 2011

AbstractStoichiometric and non-stoichiometric (defect) pyrochlores crystallize during the magmatic and late magmatic-hydrothermal phases of carbonatite emplacement (T > 450–550 °C, P < 2 kb). Defect pyrochlores can also form at low temperatures in laterite horizons during weathering. After crystallization, pyrochlore is subject to alteration by hydrothermal fluids (T ∼ 550-200°C) and ground water. Alteration occurs primarily by ion exchange of low valence A-site cations together with O, F, and OH ions. The high valence cations Th and U are generally immobile; however, we have documented one example of hydrothermal alteration involving loss of U together with cation exchange at the B-site in samples from Mountain Pass, California. During laterite accumulation, the cation exchange rate of pyrochlore greatly exceeds the rate of matrix dissolution. The exceptional durability of pyrochlore in natural environments is related to the stability of the B-site framework cations. In carbonatites, defect pyrochlores may contain significant amounts of Si (up to 7.6 wt% SiO2) which is negatively correlated with Nb.
Postglacial Matrix Diffusion in a Boulder Sample
Authors: Rasilainen K. , Suksi J. , Hellmuth K.-H. , Lindberg A. , Kulmala S. 
Published: April 2011

AbstractA boulder sample was studied for its unusual U content. Analyses of U-series nuclides within the rock matrix perpendicular to an assumed fracture face show abrupt pulse-like concentration distributions with very low concentrations of U daughters. Both Th-230/U-234 and Pa-231/U-235 activity ratios are low, indicating recent U accumulation into the rock. Matrix diffusion is tested as a possible cause for the experimental observations. We assume that the diffusion process was triggered and controlled by rock expansion, strong mixing of different water types and rapid land uplift at the end phase of the last glaciation.