bluuebunny/crossref_metadata_2025_split huggingface dataset:
Dissolution Behaviour of UO2 in Anoxic Conditions. Comparison of Ca-bentonite and Boom Clay
Authors: Mennecart Thierry , Cachoir Christelle , Lemmens Karel 
Published: October 2011

AbstractA general concept for the disposal of spent fuel in clay formations is based on the multibarrier principle. In such concept, the barriers for radionuclides released into the environment are the clay host rock, the backfill, the canister overpack and the fuel itself. The innermost barrier is the dissolution of UO2 matrix, which is the main component of spent fuel. However the dissolution of UO2 upon groundwater contact depends strongly on the (geo)chemical constraints prevailing in the repository. In order to determine in how far the clay properties influence the dissolution of spent fuel, two different kinds of clay were considered: Ca-bentonite which presents an initial oxidizing environment, and Boom Clay which is characterized by its strong reducing capacity. The experiments were carried out with depleted UO2 in presence of either compacted dry Ca-bentonite with Boom Clay groundwater or compacted dry Boom Clay with Boom Clay groundwater. The leach tests were performed at 25°C in anoxic atmosphere (glove box under 0.4%CO2/99.6%Ar) for 2 years. The U concentrations were sampled during these 2 years, once every 6 months and the amount of U was determined in the clay after 2 years in order to determine the dissolution rate. After 2 years, an unexpected uranium concentration was found 50 times higher in the system Boom Clay with Boom Clay water (2.10-7 mol/L) than in the system Ca-bentonite with Boom Clay water (4.10-9 mol/L), maybe resulting from a larger colloidal fraction in the system Boom Clay with Boom Clay water. Final results are expected to allow the comparison of the U retention capacity of Ca- bentonite and Boom Clay in anoxic conditions with the U retention of Boom Clay found in reducing conditions.
Alteration of Coffinite (USiO4) Under Reducing and Oxidizing Conditions
Authors: Deditius Artur Piotr , Utsunomiya Satoshi , Ewing Rodney C. 
Published: October 2011

AbstractSamples of natural coffinite (USiO4·nH2O) from Grants uranium region, New Mexico were investigated in order to understand the alteration process of coffinite under reducing and oxidizing conditions. Alteration of the primary coffinite under reducing conditions was promoted by organic acids and as a result secondary coffinite precipitated. Subsequently oxidizing fluids altered the coffinite, and (Na,K)-boltwoodite and jáchymovite precipitated with no rare earth elements. Based on the charge balance calculation we suggest that the amount of U6+ in the coffinite is less than 0.2 [apfu] and U6+ is accommodated in the structure via substitution: U4+ + Si4+ ⇔ U6+ + 2(OH)-. The high and variable analysis total of electron microprobe indicates that H2O is not an essential component in coffinite structure. The U-Pb ages of coffinite formation vary from 36.6-0 Ma suggesting that the coffinite has precipitated continuously in this period and organic matter can preserve reducing conditions even when oxidizing conditions dominate.
Hydrothermal Phase Relations Among Uranyl Minerals at the Nopal I Analog Site
Authors: Murphy William M. 
Published: October 2011

AbstractUranyl mineral paragenesis at Nopal I is an analog of spent fuel alteration at Yucca Mountain. Petrographic studies suggest a variety of possible hydrothermal conditions for uranium mineralization at Nopal I. Calculated equilibrium phase relations among uranyl minerals show uranophane stability over a broad range of realistic conditions and indicate that uranyl mineral variety is a consequence of chemical potential heterogeneity.
Influence of Temperature on the Corrosion of Uranium Dioxide Nuclear Fuel
Authors: Broczkowski Michael E. , Noel Jamie J. , Shoesmith David W. 
Published: October 2011

AbstractThe anodic dissolution of UO2has been studied at 60°C and the results compared to previous observations at 22°C. The rate of oxidation / dissolution was determined electrochemically at constant potentials in the range -500 mV to 500 mV (vs. SCE). The composition of the electrochemically oxidized surface was determined by X-Ray Photoelectron Spectroscopy (XPS). The onset of oxidation (UO2→ UO2+x) occurred at approximately the same potential (-400 mV) at both temperatures. However, the conversion of UV to UVI, and hence to soluble UO22+, was accelerated by temperature. This acceleration of dissolution caused the development of acidity at localized sites on the fuel surface at lower (less oxidizing) potentials (≥ 100 mV) at 60°C than at 22°C (≥ 350 mV).
New Perspectives for the Spent Nuclear Fuel Radionuclides Release Model in a Deep Geological Repository
Authors: Poinssot Christophe , FERRY Cécile , POULESQUEN Arnaud 
Published: October 2011

AbstractSpent Nuclear Fuel (SNF) source terms are used to define the release rate of radionuclides (RN) in a direct disposal and to assess the performance of this waste form. They classically distinguish between two contributions: (i) the Instant Release Fraction (IRF) of RN which are directly leached when water contacts the fuel, (ii) the slow and long term release of RN which are embedded within the fuel matrix. Recent experimental results bring significant input in our understanding and assessment of both contributions. However, they have not yet been integrated in the definition of the SNF source term. This paper will present the impact on the RN source term of the latest results on the SNF long term evolution and the key remaining scientific issues.
Uranium Sequestration by Aluminum Phosphate Minerals in Unsaturated Soils
Authors: Jerden James L 
Published: October 2011

AbstractA mineralogical and geochemical study of soils developed from the unmined Coles Hill uranium deposit (Virginia) was undertaken to determine how phosphorous influences the speciation of uranium in an oxidizing soil/saprolite system typical of the eastern US. This paper presents mineralogical and geochemical results that identify and quantify the processes by which uranium has been sequestered in these soils. It was found that uranium is not leached from the saturated soil zone (saprolites) overlying the deposit due to the formation of a sparingly soluble uranyl phosphate mineral of the meta-autunite group. The concentration of uranium in the saprolites is approximately 1000 mg uranium per kg of saprolite. It was also found that a significant amount of uranium was retained in the unsaturated soil zone overlying uranium-rich saprolites. The uranium concentration in the unsaturated soils is approximately 200 mg uranium per kg of soil (20 times higher than uranium concentrations in similar soils adjacent to the deposit). Mineralogical evidence indicates that uranium in this zone is sequestered by a barium-strontium-calcium aluminum phosphate mineral of the crandallite group (gorceixite). This mineral is intimately inter-grown with iron and manganese oxides that also contain uranium. The amount of uranium associated with both the aluminum phosphates (as much as 1.4 weight percent) has been measured by electron microprobe microanalyses and the geochemical conditions under which these minerals formed has been studied using thermodynamic reaction path modeling. The geochemical data and modeling results suggests the meta-autunite group minerals present in the saprolites overlying the deposit are unstable in the unsaturated zone soils overlying the deposit due to a decrease in soil pH (down to a pH of 4.5) at depths less than 5 meters below the surface. Mineralogical observations suggest that, once exposed to the unsaturated environment, the meta-autunite group minerals react to form U(VI)-bearing aluminum phosphates.
Study of the Susceptibility of Oxygen-Free Phosphorous Doped Copper to Corrosion in Simulated Groundwater in the Presence of Chloride and Sulfide
Authors: Escobar Ivan , Lamas Claudia , Werme Lars , Oversby Virginia 
Published: October 2011

AbstractCopper of the quality oxygen free and high conductivity, doped with phosphorus (Cu OFP) has been chosen as the material for the fabrication of high level nuclear waste containers in Sweden. This material will be the corrosion barrier for spent fuel in the environment of a deep geological repository. It is planned that the service life of this container will be 100,000 years. During this time water with high concentration of chloride ions might come in contact with the copper surface. If pH conditions are appropriate, this might cause pitting corrosion. This work reports a study of the susceptibility of Cu OFP to corrosion when chloride ions are present, both deionized water (DW) and in standard synthetic underground water (SUW). The techniques used were electrochemical methods such as corrosion potential evolution and Tafel curves. In addition, this system was studied with Electrochemical Impedance Spectroscopy (EIS). We also used characterization techniques such as Scanning Electronic Microscopy (SEM), Energy Disperse Spectroscopy (EDS) . The main conclusions are that copper is more susceptible to corrosion at high chloride ion concentration. Additionally, when the chloride concentration is low, it is possible to form copper chloride crystals, but at the highest concentration, copper chloride complexes are formed, leaving the copper surface without deposits. When the chloride concentration is low (<0.1 M) the corrosion process is mainly controlled by diffusion, while at higher concentrations (0.1M to 1M) corrosion is controlled by transport processes. At low concentration of sulfide ( <3*10-5M), copper corrosion in the presence of chloride is controlled by diffusional processes.
Salt Fog Testing Iron-Based Amorphous Alloys
Authors: Rebak Raul B. , Aprigliano Louis F. , Day S. Daniel , Farmer Joseph C. 
Published: October 2011

AbstractIron-based amorphous alloys are hard and highly corrosion resistant, which make them desirable for salt water and other applications. These alloys can be produced as powder and can be deposited as coatings on any surface that needs to be protected from the environment. It was of interest to examine the behavior of these amorphous alloys in the standard salt-fog testing ASTM B 117. Three different amorphous coating compositions were deposited on 316L SS coupons and exposed for many cycles of the salt fog test. Other common engineering alloys such as 1018 carbon steel, 316L SS and Hastelloy C-22 were also tested together with the amorphous coatings. Results show that amorphous coatings are resistant to rusting in salt fog. Partial devitrification may be responsible for isolated rust spots in one of the coatings.
Radiolysis and Ageing of C2-BTP in Cinnamaldehyde/Hexanol Mixtures
Authors: Fermvik Anna , Ekberg Christian , Retegan Teodora , Skarnemark Gunnar 
Published: October 2011

AbstractThe separation of actinides from lanthanides is an important step in the alternative methods for nuclear waste treatment currently under development. Polycyclic molecules containing nitrogen are synthesised and used for solvent extraction. A potential problem in the separation process is the degradation of the molecule due to irradiation or ageing. An addition of nitrobenzene has proved to have an inhibitory effect on degradation when added to a system containing C2-BTP in hexanol before irradiation. In this study, 2,6 di(5,6 diethyl 1,2,4 triazin 3 yl)pyridine (C2-BTP) was dissolved in different mixtures of cinnamaldehyde and hexanol and the effects on extraction after ageing and irradiation were investigated. Similar to nitrobenzene, cinnamaldehyde contains an aromatic ring which generally has a relatively high resistance towards radiolysis. Both C2-BTP in cinnamaldehyde and C2-BTP in hexanol seem to degrade with time. The system with C2-BTP in pure hexanol is relatively stable up to 17 days but then starts slowly to degrade. The solution with pure cinnamaldehyde as diluent started to degrade after only ∼20 hours. The opposite is true for degradation caused by radiolysis; hexanol systems are more sensitive to radiolysis than cinnamaldehyde systems. Most of the radiolytic degradation took place during the first days of irradiation, up to a dose of 4 kGy.
Application of a Comprehensive Sensitivity Analysis Method on the Safety Assessment of TRU Waste Disposal in JAPAN
Authors: Ohi Takao , Takase Hiroyasu , Inagaki Manabu , Oyamada Kiyoshi , Sone Tomoyuki , Mihara Morihiro , Ebashi Takeshi , Nakajima Kunihiko 
Published: October 2011

AbstractA comprehensive sensitivity analysis method has been developed with the aim of providing quantitative information in an efficient manner. This methodology is composed of the following two components: (1) a statistical method with random sampling of independent parameters, which identifies important parameters and extracts threshold values of parameters and/or combinations yielding a 'successful condition' where maximum dose does not exceed a target value, (2) A nuclide migration model that as far as possible incorporates a comprehensive set of phenomena occurring within the repository. This approach was applied as part of a safety assessment of the geological disposal of TRU waste in Japan (TRU-2). It was shown that the concept of TRU waste disposal is robust from the point of view of safety.
Development of Ceramic Waste Forms for High-Level Nuclear Waste over the Last 30 years
Authors: Vance Eric 
Published: October 2011

AbstractMany types of ceramics have been put forward for immobilisation of high-level waste (HLW) from reprocessing of nuclear power plant fuel or weapons production. After describing some historical aspects of waste form research, the essential features of the chemical design and processing of these different ceramic types will be discussed briefly. Given acceptable laboratory and long-term predicted performance based on appropriately rigorous chemical design, the important processing parameters are mostly waste loading, waste throughput, footprint, offgas control/minimisation, and the need for secondary waste treatment. It is concluded that the “problem of high-level nuclear waste” is largely solved from a technical point of view, within the current regulatory framework, and that the main remaining question is which technical disposition method is optimum for a given waste.
Hydrothermal Methods as a New Way of Actinide Phosphate Preparation
Authors: Clavier Nicolas , Dacheux Nicolas , Wallez Gilles , Quarton Michel 
Published: October 2011

AbstractPrecipitation processes driven in hydrothermal conditions were applied to the preparation of phosphate-based ceramics. Three systems composed by a crystallized precursor linked with a high temperature compound were particularly examined: M(OH)PO4 / M2O(PO4)2 (M = Th, U), MPO40.5 H2O / MPO4 (M = La - Dy) and Th2-x/2Anx/2(PO4)2(HPO4) H2O / β-Th4-xAnx(PO4)4P2O7 (M = U, Np, Pu). A significant improvement of several physico-chemical properties of the powders, especially in the sintering capability and the homogeneity of the final solids was evidenced when starting from the precursors. Furthermore, these phases were also found to control the solubility of lanthanides and actinides during leaching experiments when reaching the saturation conditions in the solution.
Rare Earth-Bearing Murataite Ceramics
Authors: Stefanovsky Sergey , Yudintsev Sergey , Nikonov Boris , Stefanovsky Olga 
Published: October 2011

AbstractPhase composition of the murataite-based ceramics containing 10 wt.% lanthanum, cerium, neodymium, europium, gadolinium, yttrium, zirconium oxides was studied. The ceramics were prepared by melting of oxide mixtures in glass-carbon ampoules in air at ∼1500° C. They are composed of predominant murataite-type phases and minor extra phases: rutile, crichtonite, perovskite, ilmenite/pyrophanite, and zirconolite (in the Zr-bearing sample only). Three murataite-related phases with five- (5C), eight- (8C), and three-fold (3C) elementary fluorite unit cell are normally present in all the ceramics. These phases form core, intermediate zone, and rim of the murataite grains, respectively. They are predominant host phases for the rare earth elements whose concentrations are reduced in a row: M-5C>M-8C>M-3C. Appreciate fraction of La and Ce may enter the perovskite phase.
Synroc-D Type Ceramics Produced by Hot Isostatic Pressing and Cold Crucible Melting for Immobilisation of (Al, U) Rich Nuclear Waste
Authors: Vance Eric R. , La Robina Michael , Li Huijun , Davis Joel 
Published: October 2011

AbstractA synroc-D ceramic consisting mostly of spinel, hollandite, pyrochlore-structured CaUTi2O7, UO2, and Ti-rich regions shows promise for immobilisation of a HLW containing mainly Al and U, together with fission products. Ceramics with virtually zero porosities and waste loadings of 50-60 wt% on an oxide basis were prepared by cold crucible melting (CCM) at ∼1500°C, and also by subsolidus hot isostatic pressing (HIP) at 1100°C to prevent volatile losses. PCT leaching test values for Cs were < 13 g/L, with all other normalised elemental extractions being well below 1 g/L.
Experimental Study and Monte Carlo Modeling of Calcium Borosilicate Glasses Leaching
Authors: Arab Mehdi , Cailleteau Celine , Angeli Frederic , Devreux Francois 
Published: October 2011

AbstractDuring aqueous alteration of glass an alteration layer appears on the glass surface. The properties of this alteration layer are of great importance for understanding and predicting the long-term behavior of high-level radioactive waste glasses. Numerical modeling can be very useful for understanding the impact of the glass composition on its aqueous reactivity and long-term properties but it is quite difficult to model these complex glasses. In order to identify the effect of the calcium content on glass alteration, seven oxide glass compositions (57SiO2 17B2O3 (22−x)Na2O xCaO 4ZrO2; 0 < x < 11) were investigated and a Monte Carlo model was developed to describe their leaching behavior. The specimens were altered at constant temperature (T = 90°C) at a glass-surface-area-to-solution-volume (SA/V) ratio of 15 cm 1 in a buffered solution (pH 9.2). Under these conditions all the variations observed in the leaching behavior are attributable to composition effects. Increasing the calcium content in the glass appears to be responsible for a sharp drop in the final leached boron fraction. In parallel with this experimental work, a Monte Carlo model was used to investigate the effect of calcium content on the leaching behavior. The glass structure was built with a random distribution of silicon and boron on the lattice points of a diamond lattice with sodium atoms located in interstitial position. The model was upgraded to take into account the effect of zirconium and calcium. Zirconium atoms are placed in interstitial position (with cations acting as charge compensators) and interact with six lattice atoms (Si or B) by decreasing their dissolution probability. Acting like sodium but with less effect, calcium atoms increase the dissolution probability of atoms placed in their neighborhood. Monte Carlo simulations performed with this model are in good agreement with the experimental results. The dependence of the dissolution rate on the calcium content can be described by a quadratic function: fitting the simulated points gives a minimum alteration rate at about 7.4 mol% calcium. This value is consistent with the figure of 8.0 mol% obtained from the experimental work. The model was also used to investigate the role of calcium in the glass structure and it pointed out that calcium act preferentially as a network modifier rather than a charge compensator in this kind of glasses.
The Influence of Preoxidation on the Corrosion of Copper Nuclear Waste Canisters in Aqueous Anoxic Sulphide Solutions
Authors: Smith Jared M. , Qin Z. , Wren J. C. , Shoesmith D. W. 
Published: October 2011

AbstractScandinavian/Canadian high-level nuclear waste repository conditions are expected to evolve from initially warm and oxic to eventually cool and anoxic. During the warm oxic period, corrosion products will accumulate on the container surface. These deposits could impede the reaction of Cu with aqueous sulphide, the only reaction that could lead to the significant accumulation of additional corrosion damage under the long-term anoxic conditions. The kinetics of reaction of Cu with aqueous sulphide solutions have been studied using electrochemical and surface analytical techniques. Corrosion potential measurements were used to follow the evolution of the surface as oxides/hydroxides were converted to sulphides in the sulphide concentration range 10-5 to 10-3 mol/L. Changes in composition were followed by in-situ Raman spectroscopy. Of critical importance is whether or not a period of preoxidation of a Cu container surface can prevent subsequent reaction of the surface with remotely produced sulphide
Geopolymers as Candidates for the Immobilisation of Low- and Intermediate-Level Waste
Authors: Vance Eric , Vance Eric , Kiyama Satoshi , Aly Zaynab , Yee Patrick 
Published: October 2011

AbstractGeopolymers should be serious waste form candidates for intermediate level waste (ILW), insofar as they are more durable than Portland cement and can pass the PCT-B test for high-level waste. Thus an alkaline ILW could be considered to be satisfactorily immobilised in a geopolymer formulation. However a simulated Hanford tank waste was found to fail the PCT-B criterion even for a waste loading as low as 5 wt%, very probably due to the formation of a soluble sodium phosphate compound(s). This suggests that it could be worth developing a “mixed” GP waste form in which the amorphous material can immobilise cations and a zeolitic component to immobilise anions. The PCT -B test is demonstrably subject to significant saturation effects, especially for relatively soluble waste forms.
Frequency Characteristics of Acoustic Emission Signals from Cementitious Wasteforms with Encapsulated Al
Authors: Spasova Lyubka , Ojovan Michael I. 
Published: October 2011

AbstractAcoustic emission (AE) signals were continuously recorded and their intrinsic frequency characteristics examined in order to evaluate the mechanical performance of cementitious wasteform with encapsulated Al waste. The primary frequency in the power spectrum and its range of intensity for the detected acoustic waves were potentially related with appearance of different micromechanical events caused by Al corrosion within the encapsulating cement system. In addition the process of cement matrix hardening has been shown as a source of AE signals characterised with essentially higher primary frequency (above 2 MHz) compared with those due to Al corrosion development (below 40 kHz) and cement cracking (above 100 kHz).
Phase Relations and Elemental Distribution Among Co-Existing Phases in the Ceramics of the Pseudobinary System CaZrTi2O7-LnAlO3 (Ln= Nd, Sm)
Authors: Stefanovsky Sergey , Stefanovsky Sergey , Ochkin Alexander 
Published: October 2011

AbstractIn the ceramics in series (1-õ) CaZrTi2O7 – x NdAlO3 and (1-õ) CaZrTi2O7 – x SmAlO3 (õ = 0.25, 0.5 and 0.75) produced by cold pressing and sintering at 1400, 1450 and 1500 0Ñ zirconolite was found to be a major phase, perovskite was an extra phase and traces of residual baddeleyite occurred. At x = 0.75 the perovskite was major phase and zirconolite and cubic oxide of fianite or tazheranite type were extra phases. Major Nd and Sm host phase at x = 0.25 was found to be zirconolite (about 65% of total Nd2O3 and 74% of total Sm2O3). With the x value increasing perovskite becomes major host phase for Nd and Sm accumulating of up to about 92% of total Nd and about 72% of total Sm. As follows from SEM/EDS data Nd and Sm contents in the zirconolite may reach ∼1 formula unit (fu).