bluuebunny/crossref_metadata_2025_split huggingface dataset:
39-years Performance of Cemented Radioactive Waste in a Mound Type Repository
Authors: Sobolev Igor A. , Dmitriev Sergey A. , Barinov Alexander S. , Varlakova Galina A. , Golubeva Zoya I. , Startceva Irene V. , Ojovan Michael I. 
Published: April 2011

ABSTRACTLong-term field tests of cemented aqueous radioactive wastes in an experimental mound type surface repository were carried out at Moscow Scientific and Industrial Association “Radon” from 1965 to 2004. Aqueous radioactive wastes of different compositions containing short-lived radionuclides including 90Sr and 137Cs at concentrations from 0.34 to 1.8 MBq/L were immobilized using cementation technology. Water solution to cement ratio was 0.66, grout mixing time 10-15 minutes, and cement paste hardening time 7 days. 73 cement blocks with a volume of 0.027 m3 were disposed of for long-term tests in a simple mound type surface repository. The atmospheric precipitates, which contacted radioactive cement blocks, were collected and analyzed for the content of radionuclides. In August 2004 the experimental repository was opened, cemented blocks, underlying and covering materials were retrieved for analyses. XRD analyses showed that along with amorphous tobermorite gel the main crystal phases in cements are calcite and portlandite. Both visual inspection and radiometric analyses demonstrate that cemented blocks are in good condition and that the cement paste has retained radionuclides from the wastes. Thus after 39 years of storage in the mound type repository the cemented aqueous wastes are reliable immobilized.
The Boom Clay geochemistry: Natural evidence
Authors: De Craen M. 
Published: April 2011

ABSTRACTIn Belgium, the Boom Clay is studied as the reference formation for geological disposal of high-level radioactive waste and spent fuel. As the Boom Clay is considered as the main barrier for radionuclide migration/retention, a thorough characterisation of the clay and its pore water was done. This facilitates better understanding of the long-term geological processes and the distribution of the trace elements and radionuclides.From a mineralogical/geochemical point of view, the Boom Clay is considered as a rather homogeneous sediment, vertically as well as laterally. It is composed of detrital minerals, organic matter and fossils. Minerals are mainly clay minerals, quartz and feldspars. Minor amounts of pyrite and carbonates are also present. Small variations in mineralogical/geochemical composition are related to granulometrical variations. The radiochemical study indicates that the Boom Clay is in a state of secular radioactive equilibrium, meaning that the Boom Clay has not been disturbed for a very long time.Pore water sampling is done in situ from various piezometers, or by the squeezing or leaching of clay cores in the laboratory. These three pore water sampling techniques have been compared and evaluated. Boom Clay pore water is a NaHCO3 solution of 15 mM, containing 115 mg·1−1 of dissolved natural organic carbon. Some slight variations in pore water composition have been observed and can be explained by principles of chemical equilibrium.
Porous Alumina-Silica (Gubka) as a Matrix for REE-TUE Strip Solution Immobilization
Authors: Aloy A.S. , Kol'tsova T.I. , Sapozhnikova N.V. , Strelnikov A.V. 
Published: April 2011

ABSTRACTThe immobilisation of strip product (TUE + REE), collected at Russian research centers and laboratories during R&D on partitioning technology for liquid high–level radioactive waste (HLW), was studied using simulated solutions.Ultraporous glass crystalline material “Gubka”(G) and multiple processing stages were used to immobilize the simulated strip product. The processing consisted of the following stages: Gubka saturation by solution – drying into Gubka pores – compaction by cold uniaxial pressing followed by sintering (CUPS) or hot uniaxial pressing (HUP).
Leach Resistant Cesium and Strontium-bearing Wasteforms from Hexagonal Tungsten Bronze-Polyacrylonitrile Composite Adsorbers
Authors: Griffith Christopher S. , Luca Vittorio , Sebesta Ferdinand , Yee Patrick , Drabarek Elizabeth 
Published: April 2011

ABSTRACTImmobilization of adsorbed Cs+ and Sr2+ on a molybdenum-doped, hexagonal tungsten bronze (HTB)-polyacrylonitrile (PAN) composite adsorbent can be achieved by heating in air at temperatures in the range 600 - 1200 °C. Thermal treatment of the parent composite material at 800 – 1000 °C undergoes a ca. 60% reduction in volume and retains its spherical morphology. For materials prepared at 800 – 1200 °C the full complement of Cs+ and the majority of Sr2+ partition into HTB phases (A∼0.16-0.3MO3; A = Cs, Sr, Na; M = Mo,W), along with sodium cations. The presence of high concentrations of Na+ relative to either Cs+ or Sr2+ does not appear to interfere with the formation of the HTB phase. The fraction (f) of Cs+ and Sr2+ leached from the tungstate phase assemblages is better or comparable with cesium hollandite (Cs0.8Ba0.4Ti8O18; f = ca. 8 × 10−5; rate = <1.2 × 10−4 g m−2d−1) and strontium titanate (SrTiO3; f = 3.1 × 10−3; rate = 2.63 × 10−4 g m−2day−1), respectively, using a modified PCT test. Furthermore, where aggressive leaching conditions are employed (0.1M HNO3; 150 °C; 4 days), the tungstate phase assemblages display leach resistance orders of magnitude better than the reference phases (Cs+ - f = ca. 5 × 10−3; rate = ca. 1.4 × 10−3 g m−2day−1; Sr2+ - f = ca. 8 × 10−2; rate = ca. 2.5 × 10−2 g m−2day−1).
Effects of alpha self-irradiation on actinide-doped spent fuel surrogate matrix
Authors: Roudil Danièle , Jégou Christophe , Deschanels Xavier , Peuget Sylvain , Raepsaet Caroline , Gallien Jean-Paul , Broudic Véronique 
Published: April 2011

ABSTRACTDuring the initial period after disposal, in which no mass transfer occurs with environmental materials, spent fuel undergoes modifications mainly arising from the effects of α self-irradiation damage. To simulate this aging phenomenon and estimate the consequences on the matrix, an experimental study was carried out in which old UO2 samples doped with short-lived actinides were characterized and analyzed. Changes that occur rapidly at the beginning of the aging process were identified in two lots of actinide-doped samples. Volume and microscopic swelling increased, reaching a maximum relative level of 1.5%. At the same damage level, microscopic swelling remained below 0.9%, suggesting that helium formation and atomic defects have a role in this regard. Similarly, the sample microhardness rapidly increased by up to more than 12%. Characterizing 238PuO2 sources showed at very high integrated and instantaneous doses, irradiation damage and helium accumulation at the grain boundaries resulted in grain decohesion or even powder formation. Helium mobility appeared to be modified by the presence of defects, and local implantation experiments were devised in the CEA's Pierre Süe Laboratory at Saclay to quantify this thermally enhanced diffusion component. The physical condition of the sintered PuO2 pellets after 30 years of storage revealed a purely athermal diffusion mechanism, depending on the sample α activity.
Evolution of the spent nuclear fuel during the confinement phase in repository conditions: Major outcomes of the French research
Authors: Ferry C. , Piron J.P , Poinssot Ch. 
Published: April 2011

ABSTRACTThe effects of the temperature and high radioactivity on the chemical and physical state of the fuel during a confinement phase were evaluated in the framework of the PRECCI program. No significant evolution of the fuel chemistry is expected. The radionuclides mobility due to thermal diffusion can be neglected in the temperature range of disposal and diffusion enhanced by α self-irradiation appears to be limited. Microscopic swelling due to alpha self irradiation cumulated damage corresponds to a low volume increase of about 1%. Macroscopic swelling will depend on the helium behavior in the spent fuel. Literature data and results from the project indicate that helium solubility is low in UO2 and should be reached after a few centuries of cooling for MOX fuels. Although the thermal diffusion of helium is some orders of magnitude faster than the thermal diffusion of xenon, it remains low in the temperature range of disposal. Therefore, the first step of physical damage due to helium production should be the precipitation of He bubbles in grains, causing micro-cracks, which could enhance the He release to the grain boundaries. These processes and their consequences on the stability of grain boundaries still need to be quantified today.
Determination of alpha dose rate profile at the UO2/water interface
Authors: Poulesquen A. , Jégou C. , Peuget S. 
Published: April 2011

ABSTRACTIn this paper, an evaluation of the alpha dose rate profile at the UO2/water interface is presented. The calculation is performed in spherical geometry by considering the position of alpha emitters in the material. Moreover it proceeds to an iterative way. The fuel matrix and water is divided in spherical layers of 0.1 μm of thickness. The alpha emitters have an average energy of 5.3 MeV corresponding to a maximum distance of 13.2 μm in UO2 matrix and 42 μm in water. The direction of emission and the energy deposition, described by the Bragg curve, in the nuclear fuel are also taken into account. It appears that the alpha dose rate strongly decreases towards the calculated maximum penetration depth in water namely 42 μm. The concentrations of oxidising and reducing species are largely higher at the UO2/water interface than in solution. This alpha dose profile is used as input file in a model coupling a radiolysis kinetic model and a diffusion model. This kind of calculation is particular suitable for HTR kernels which have a spherical form of few hundreds microns of diameters (200-500 μm).
Radiation-induced decomposition of U(VI) alteration phases of UO2
Authors: Utsunomiya Satoshi , Ewing Rodney C. 
Published: April 2011

ABSTRACTU6+−phases are common alteration products of spent nuclear fuel under oxidizing conditions, and they may potentially incorporate actinides, such as long-lived 239Pu and 237Np, delaying their transport to the biosphere. In order to evaluate the ballistic effects of α-decay events on the stability of the U6+−phases, we report, for the first time, the results of ion beam irradiations (1.0 MeV Kr2+) for six different structures of U6+-phases: uranophane, kasolite, boltwoodite, saleeite, carnotite, and liebigite. The target uranyl-minerals were characterized by powder X-ray diffraction and identification confirmed by SAED (selected area electron diffraction) in TEM (transmission electron microscopy). The TEM observation revealed no initial contamination of uraninite in these U6+ phases. All of the samples were irradiated with in situ TEM observation using 1.0 MeV Kr2+ in the IVEM (intermediate-voltage electron microscope) at the IVEM-Tandem Facility of Argonne National Laboratory. The ion flux was 6.3 × 1011 ions/cm2/sec. The specimen temperatures during irradiation were 298 and 673 K, respectively. The Kr2+-irradiation decomposed the U6+-phases to nanocrystals of UO2 at doses as low as 0.006 dpa. The cumulative doses for the pure U6+-phases, e.g., uranophane, at 0.1 and 1 million years (m.y.) are calculated to be 0.009 and 0.09 dpa using SRIM2003. However, with the incorporation of 1 wt.% 239Pu, the calculated doses reach 0.27 and ∼1.00 dpa in ten thousand and one hundred thousand years, respectively.Under oxidizing conditions, multiple cycles of radiation-induced decomposition to UO2 followed by alteration to U6+-phases should be further investigated to determine the fate of trace elements that may have been incorporated in the U6+-phases.
Electrochemical, SECM, and XPS Studies of the Influence of H2 on UO2 Nuclear Fuel Corrosion
Authors: Broczkowski Michael E. , Zhu R. , Ding Z. , Noël J.J. , Shoesmith D.W. 
Published: April 2011

ABSTRACTA combination of electrochemical, scanning electrochemical microscopy (SECM), X-ray photoelectron spectroscopic (XPS), and time of flight secondary ion mass spectrometry (TOF - SIMS) techniques are being employed to investigate the effects of dissolved hydrogen on the aqueous corrosion of uranium dioxide (UO2) under nuclear waste disposal conditions. Corrosion potential (ECORR) measurements indicate that the oxidation of dissolved hydrogen on noble metal ε-particles polarizes the UO2 nuclear fuel surface to reducing potentials (−300 – −400 mV vs. SCE; i.e., to ECORR values more negative than those observed under anoxic (argon-purged) conditions (−200 mV vs. SCE). A comparison of the behaviors observed on SIMFUEL specimens with and without incorporated noble metal ε-particles indicate that these particles may act as catalytic electrodes for H2 oxidation. It is the galvanic coupling of these particles to the UO2 matrix which suppresses the fuel corrosion potential thereby preventing oxidation of the fuel surface.
Factors influencing the sulphate incorporation in radioactive waste glasses
Authors: Manara D. , Grandjean A. , Pinet O. , Dussossoy J.L. , Neuville D.R. 
Published: April 2011

ABSTRACTSulphur is present in several kinds of nuclear waste destined to confinement in a glass matrix.. These species are hardly incorporated in borosilicate glasses, due to the poor miscibility of molten sulphates and glass melt at high temperature. This point constitutes one of the main technological difficulties in the current fabrication of nuclear glasses. Several studies carried out in the last two decades indicate that the liquid state miscibility of sulphates and glass melt, determining the waste incorporation in the final glass, is dependent on the composition of the glass and on the temperature and duration of its preparation. In particular, the ratios K = [SiO2] / [B2O3] and R = [Na2O] / [B2O3] (where [.] indicates the mol %), as well as the presence of V2O5 in the glass matrix play an important role in the determination of both kinetics and thermodynamics of sulphates incorporation in the vitreous matrix. In this work a study on the physico-chemical effects of the ratio R, the melt reactivity, the type of sulphate added, and the presence of V2O5 on the solubility of sulphates in borosilico-vanadate glasses is presented.Glass samples were prepared at the laboratory scale (up to 50-100 g) by melting oxide and sulphate powders in Pt/Au or Pt/Rh crucibles at a fixed viscosity level of 100 Po in air. Several glass specimens were powdered and re-melted at 1200°C in the presence of sulphates in order to simulate conditions as close as possible to those of an industrial melter. XRF and ICP AES chemical analysis, SEM EDS and Raman spectroscopy were employed to characterise the fabricated samples. Raman spectra, in particular, reveal the structural modifications that condition the sulphate incorporation in the glass. A critical review of the obtained results is compared with the literature data, to yield a more systematic description of the mentioned factors effects on sulphate behaviour in the borosilico-vanadate / system.
Static dissolution tests of α-doped UO2 under repository relevant conditions: Influence of Boom Clay and α-activity on fuel dissolution rates
Authors: Salah Sonia , Cachoir Christelle , Lemmens Karel , Maes Norbert 
Published: April 2011

ABSTRACTSince reprocessing is no longer the reference policy in Belgium, studies on the direct disposal of spent fuel in a clay formation have gained increased interest in the last years. In order to determine to what extent the clay properties and the α-activity influence the dissolution kinetics of spent fuel for the long term disposal, static dissolution tests have been performed on 5 different types of α-doped UO2, representing a PWR fuel with a burn-up of 45 or 55 GWd · tHM−1 and fuel ages ranging between 150 and 90,000 years, in different Boom Clay (BC) media at room temperature and in an anoxic atmosphere for 90 to 720 days. The uranium activity in the clay fraction over time was found to be much higher than the U-activity in the leachates, which has been mainly ascribed to the high retention capacity of the BC. The average dissolution rate between 0 and 90 days obtained for the 5 types of α-doped UO2 were all found to be high and quite similar at ~263 µg · m−2 · d−1and a “longer-term” rate (181 to 720 days) ranging between zero and 15 µg · m−2· d−1. These results suggest that the activity of the fuels does not seem to have an effect on the UO2 dissolution rates under the considered test conditions. In order to study the partition/redistribution of U during UO2dissolution, sequential extraction experiments were performed. Results of the latter have provided a better mechanistic understanding of BC/spent fuel interaction processes as well as information on the role of the different minerals controlling the U-retention/immobilization.
HLW-Glass Dissolution and Co-Precipitation Studies
Authors: Luckscheiter Berthold , Nesovic Maria 
Published: April 2011

ABSTRACTTo determine the maximum attainable solution concentrations of U, Th and fission products during long-term glass corrosion, co-precipitation studies were performed. The HLW-glass GPWAK 1 was dissolved in highly acid and basic media (100 g glass/L) at 80°C and by preparing acid solutions containing the various elements in soluble form. After dissolution the pH of the solution was slowly lowered/increased and the high concentrated solutions become super-saturated and strong precipitation takes place. The found pH-dependent concentrations of the various elements reflect their different solubility, lowest concentration for Th, Zr and Fe and highest for B, alkalis and alkaline earths. To find out the solid phases controlling the solution concentration, the run of the concentrations of some elements is compared with the solubility data of their pure solid phases (e.g. hydroxides) from literature. It was found that the concentrations of Nd, Th and U in dependence on pH agree quite well with solubility data of AmOHCO3, ThO2/Th(OH)4 and Schoepite UO2·(OH)2) ·H2O. Therefore, it can be assumed that the maximum attainable concentrations of many elements are controlled by such pure solid phases.
Leaching and migration of Np, Pu, and Am from α-doped SON68 HLW glass in contact with dense clay
Authors: Valcke Elie , Gysemans Mireille , Moors Hugo , Van Iseghem Pierre , Godon Nicole , Jollivet Patrick 
Published: April 2011

ABSTRACTIn the frame of an integrated in situ test on the alteration of the SON68 reference glass in realistic disposal conditions, the leaching of Np, Pu, and Am from α-doped SON68 glass samples and their migration in three clay-based backfill materials at high density was measured. The addition of powdered glass frit to a Ca-bentonite decreased the glass alteration by two orders of magnitude, and resulted in a concomitant decrease of the radionuclide leaching in comparison with dried Boom Clay, which is the more agressive backfill. All actinides were selectively retained in the alteration layer, but the retention degree was lower for Np than for Pu and Am. All backfill materials proved to be efficient barriers against radionuclide migration. For nearly all radionuclides and backfill materials, the migration profile showed a contribution of colloidal transport.
Son68 Glass Dissolution Kinetics at High Reaction Progress: Mechanisms Accounting for The Residual Alteration Rate
Authors: Frugier P. , Gin S. , Lartigue J.E. , Deloule E. 
Published: April 2011

ABSTRACTIn a highly confined medium corresponding to geological repository conditions, the alteration rate of the French SON68 inactive nuclear reference glass drops by about four orders of magnitude below the initial rate. However, extended experiments lasting months or years provide evidence of a virtually constant or slowly decreasing residual alteration rate. Although very low, this rate could account for most of the altered glass thickness after 10 000 years. Experiments at high temperatures and especially high glass-surface-area-to-solution-volume ratios were performed to reveal and quantify the predominant mechanisms underlying the residual rate. The authors describe the characterization of the solution chemistry, the crystallized secondary phases, and the amorphous gel observed after alteration of the French SON68 inactive reference glass, and discuss their implications in terms of long-term behavior modeling. A slow diffusion mechanism is identified in the solid, involving alkalis in particular but also boron. This mechanism results in higher concentrations in solution that affect the system chemistry, not only by slightly modifying the pH and element speciation in solution (e.g. silicon), but also by inducing the precipitation of new crystallized secondary phases that can consume glass constituent elements in the same way as simple solution renewal. Diffusion and the precipitation of secondary phases are two mechanisms to be considered to account for the residual rate.
Pulsed Laser Deposition of Chromium Oxides: Substrate Effects
Authors: Jalili Helia , Heinig Nina , Leung K. T. 
Published: April 2011

ABSTRACTPulsed Laser Deposition (PLD) was used to grow chromium oxides (CrOx) on MgO(100), Al2O3(0001), SrTiO3(100), LaAlO3(100), and Si(100) under different growth conditions, including substrate temperature, O2 pressure, and laser fluence. SEM, AFM and XRD measurements show that various phases of CrOx films with different morphologies could be obtained on different substrates under the same growth conditions. Half-metallic CrO2 needle-like nanostructured films were only observed on MgO(100) under a special set of conditions.
Magnetization, Magnetotransport and Ferromagnetic Resonance in A Permalloy Antidot Array with Square Holes
Authors: Yu Minghui , Malkinski Leszek , Spinu Leonard , Zhou Weilie 
Published: April 2011

ABSTRACTA Permalloy antidot array with square hole size 800?800 nm2 has been fabricated by the means of electron-beam lithography and lift-off techniques. An out-of-plane anisotropy was found in both the reference film of Permalloy and the antidot array with the thickness of 100 nm. Inhomogeneous current-density distribution and complex domain structures in the antidot nanostructure result in unique behavior of the magnetoresistance. Quantized standing spin-wave modes originating from the lateral confinement of the antidot nanostructure were clearly observed for the magnetic field applied normal to the array plane. Two uniform precession resonance modes occurred when the field deviated more than 30 degrees from the normal to the plane. These two resonances originate from different regions of the array having distinct dipolar field patterns with different orientation and magnitude of magnetostatic field. The easy axes of the anisotropy in these regions are in-plane and orthogonal to each other.
Analysis of Electrodeposited NiFe Thin Films for the Development of Planar Fluxgate Magnetic Sensors
Authors: dos Santos Thais Cavalheri , Mulato Marcelo 
Published: April 2011

ABSTRACTNife alloys are potential candidates for the development of planar fluxgate magnetic microsensors. In this work, electrodeposition was used to produce NiFe thin films on top of copper substrates. When using this technique the variation of the electric potential, and thus the current density, alters the final stoichiometry of the deposited films, while the final thickness is determined by the total deposition time. We used current densities varying from 4.0 mA/cm2 to 28 mA/cm2, with steps of 4.0 mA/cm2. For each current density, total deposition times of 10, 20, 30 and 40 minutes were used. The morphology was characterized using scanning electron microscopy, structure was characterized using X-ray diffraction experiments, and the composition of the films were determined using energy dispersive spectroscopy. The magnetic properties were investigated evaluating the materials hysteresis cycle. The materials were optimized aiming for lowest coercivity values, and the final result was about 0.215 kA/m.