bluuebunny/crossref_metadata_2025_split huggingface dataset:
Perspectives on the Review of AECL's Proposal for Disposing of Canada's Nuclear Fuel Waste
Authors: Dormuth K.W. , Gillespie P.A. , Whitaker S.H. 
Published: April 2011

ABSTRACTA federal Environmental Assessment Panel has completed public hearings on the proposed concept for geological disposal of Canada's nuclear fuel waste. The Panel will make recommendations to assist the governments of Canada and Ontario in reaching decisions on the acceptability of the proposed concept and on the steps that must be taken to ensure the safe long-term management of nuclear fuel waste in Canada. It is instructive to review the background to the public hearings, to consider the issues that have been important in the public review, and to reflect on the opposing points of view presented at the hearings.
Modeling the Radionuclide Migration Experiments at Grimsel. What Have We Learned?
Authors: Heer W. , Smith P.A. 
Published: April 2011

ABSTRACTFor several years, tracer migration experiments at Nagra's Grimsel Test Site have been performed with an exceptionally high degree of precision. A summary of the main findings obtained by modelling these experiments is presented, addressing, in particular the influence of sorption. A consistent description of tracer behaviour is achieved, giving confidence when applying broadly similar methodologies and models in geosphere performance assessment.
Removal and Containment of High-Level Radioactive Polonium From Liquid Lead-Bismuth Coolant
Authors: Yefimov E.I. , Pankratov D.V. , Ignatiev S.V. 
Published: April 2011

ABSTRACTThe channels of polonium nuclide formation in lead-bismuth target irradiated by high energy protons and secondary neutrons are considered. Under off blanket condition the activity of 200po -210Po, as well as the fission and spallation product activity are calculated for 15 MW target after 1 year operation. Polonium separation methods, including removal using alkaline extraction, vacuum sublimation, and so-called carrier method are analyzed. The engineering design for experimental apparatus to test polonium removal and containment using alkaline extraction using tellurium as a chemical analog of polonium is developed. The necessary degree of polonium removal to keep concentration below levels appropriate to meet the US and Russia safety standards is estimated. Comparative analysis of alkaline extraction and vacuum sublimation techniques from the viewpoint to achieve the necessary removal depth is carried out.
Oxidation Phenomena and Processes in Opalinus Clay: Evidence From the Excavation-Disturbed Zones in Hauenstein and Mt. Terri Tunnels and Siblingen Open Clay Pit
Authors: Mäder Urs K. , Mazurek Martin 
Published: April 2011

ABSTRACTConstraints on oxidation phenomena and processes in Opalinus Clay are derived from studies at three localities: the 140-year old Hauenstein tunnel, the six-year old Mt. Terri tunnel, and an open clay pit at Siblingen that documents processes active over thousands of years. The excavationdisturbed zone (EDZ) in both tunnels is characterized by an extensive fracture network that extends to at least 1.6 m. The network consists of saturated fractures as well as some air-filled fractures with apertures up to several mm that contain effervescent gypsum. At Hauenstein, the fracture network displays regularly developed brownish oxidation zones extending 3-15 mm into matrix rock. Such oxidation zones are absent at Mt. Terri. Siblingen displays a remarkable decrease of both fracturing and oxidation phenomena with depth below surface.Microscopic observations, mass balance constraints, and estimated diffusion coefficients of oxygen indicate a minor extent of pyrite oxidation at Hauenstein possibly controlled by diffusionlimited oxygen transport into water saturated rock. Oxidation of siderite is quantitatively dominating over pyrite oxidation at Siblingen. There is evidence at Hauenstein and Siblingen that rock alteration penetrated deeper than the visible alteration zone.During the operational phase (20-100 years) of a deep repository at least the major EDZ fractures are expected to become unsaturated, and gypsum to be precipitated. Fracture apertures reach locally several millimeters within a few years, which enhances hydraulic and gas conductivities. Oxidation rims bordering fractures in the EDZ develop over timescales of 10-100 years, but mass transfers are quantitatively minor.
Charge Compensation and the Incorporation of Cerium in Zirconolite and Perovskite
Authors: Begg B.D. , Vance E.R. , Lumpkin G.R. 
Published: April 2011

ABSTRACTThe incorporation of cerium, as a simulant for plutonium, has been investigated in both zirconolite and perovskite under oxidising and reducing conditions. The Ce valence in zirconolite was very sensitive to the processing atmosphere, whilst in perovskite the valence of the Ce was determined essentially by the chemical design of the perovskite. Charge compensation in zirconolite and perovskite samples displaying an apparent excess of positive charge was inferred to occur by the formation of cation vacancies, in samples prepared under oxidising conditions, and by trivalent Ti being produced in samples subject to a reducing atmosphere. Oxygen vacancies are inferred to be present in samples exhibiting an apparent excess of negative charge.
On EBS Modeling for Performance Assessment: Using Shadow Models to Identify Robust System Responses
Authors: Takase H. , Grindrod P. , Einchcomb S.J. , Lee A.J. , Makino H. , Umeki H. 
Published: April 2011

ABSTRACTA new approach to identifying and characterising system responses of the EBS based on analysis of ensemble runs of a generic and flexible source term model is developed and applied. A discussion of issues relating to the use of this methodology as a complementary approach to existing scenario development/safety case definition is also included.
Excavation Disturbed Zone: Assessment of Its Hydraulic Properties Based on Surface Investigations
Authors: Vomvoris S. , Blomling P. , Lanyon G. W. , Watson C. R. 
Published: April 2011

ABSTRACTThe approach followed by Nagra for the assessment of the hydraulic properties of the excavation disturbed zone (EDZ) around a potential future underground repository site for low-level and medium-level short-lived radioactive wastes is presented. In the approach particular emphasis was placed on assessing, under realistic-conservative assumptions1, an appropriate way to represent the EDZ within the context of performance assessment (PA). Calculated stress changes due to the openings were mapped onto changes of the mechanical aperture of the rock fractures. The resulting changes of hydraulic properties of the EDZ were then computed, with analytical (simple, continuum-type approximation) and numerical (fracture network representation) methods. The results of both computations were used as the basis to: i) provide hydraulic properties for the EDZ used in PA models; ii) assess whether these properties are conservative, i.e., higher values than expected, or not.
Preliminary Evaluation of Thermodynamic Mixing Properties and Miscibility Limits for Cubic Dioxide (Zr, M)O2 and Zircon (Zr, M)SiO4 Solid Solutions (M = An4+, Ln4+)
Authors: Kurepin V.A. 
Published: April 2011

Cubic zirconia ZrO2 and zircon ZrSiO4 are considered as perspective crystalline form for immobilization of U, Pu and other radionuclides [1, 2]. The present study was undertaken to determine temperature dependence of solid solution limits in these compounds using thermodynamic theory of solid solutions and available equilibrium data. Thermodynamic mixing properties has been evaluated by means of the relationship between Margules parameter W and interatomic distances R in end-members AX and BX of a solid solution (A1−xBx)XW = α(ΔR/R)2where ΔR = R(BX) - R(AX), R = (1−x) R(AX) + x R(BX), α is a constant for isotypic isostructural compounds. According to the Urusov's energetic theory of enthalpy of mixing [3] such relationships exist between parameters W, AR and R of solid solutions with similar bonds between isomorphous atoms and their neighbors
Radionuclide Release From Spent MOX Fuel
Authors: Loida A. , Grambow B. , Karsten G. , Dressler P. 
Published: April 2011

ABSTRACTIn Germany certain quantities of spent MOX fuel will be disposed in a rock salt repository. In order to assess the safety of the repository the corrosion behavior of spent MOX fuel in salt solution must be understood. Since material properties of spent MOX fuel are different compared to these of spent LWR UO2 fuel, it is not possible to deduce from corrosion behavior of the latter to that one of spent MOX fuel. It is expected that the most significant differences will occur in the dissolution kinetics, whereas similar solid alteration products are expected from the similar overall composition of the fuels. Various experiments were performed focused on the effect of fuel type on the dissolution kinetics. The results of this work are summarized and evaluated
Modeling of Radionuclides Sorption on Bentonite by Using Single Oxides Surface Complexation Models
Authors: Marmier N , Delisée A. , Fromage F , Giffaut E. 
Published: April 2011

ABSTRACTBentonite could be one of the materials used in Engineered Barrier Systems. The aim of this work is to assess its sorbing properties using surface complexation modelling of Cs+, Ni2+ and Yb3+ sorption on single oxides
CORALUS: An Integrated In Situ Corrosion Test on α-Active Glass
Authors: Iseghem Pierre Van , Valcke Elie , Godon Nicole , Jockwer Norbert 
Published: April 2011

ABSTRACTAs part of the evaluation of the safety of the geologic disposal of HLW glass, a new in situ test on α-active glass will be started up in the underground research facility HADES (SCK•CEN, Mol, Belgium), situated in the Boom Clay formation, at a depth of 223 m. Besides a demonstration of the safe disposal of HLW glass containers in Boom Clay formation, the overall objective of this CORALUS test (CORrosion of Active gLass in Underground Storage conditions) is to study the performance of active HLW glass specimens in direct contact with different types of backfill materials, under conditions as representative as possible for those expected to prevail in a geologic repository in the Boom Clay formation. In order to meet this objective, the CORALUS test will integrate not only the experience of previous in situ tests performed at SCK•CEN and other research institutes, but also the expertise of the cooperating institutes. The paper presents the motivation for this new in situ test, its objectives, and the current status of its design
Use of Selective Sorbents for Liquid Wastes Treatment
Authors: El-Naggar I.M. , Belacy N. , Abou-Mesalam M.M. , Aly H.F. 
Published: April 2011

ABSTRACTAcidic salts of polyvalent metal antimonates(M-antimonates(M-Sb); M=Cerium, Tin, Titanium and Silicon) have been synthesized under different conditions( 1,2). The products were characterized by powdered X-ray diffraction patterns, Differential Thermal Analysis(DTA) and infrared spectrometry. Chemical stability of the product materials were studied by mixing 50 mg of the prepared materials with 50 ml of the desired medium(H20, HNO3 and HCI) with determination for the concentration of the metalions dissolved(Sb, Ce, Sn, Ti and Si) which showed high chemical stabilities in water and acid media up to I OM HNO 3 and 6M HCI.The data of the distribution coefficients showed that the selectivity decrease in the order; Eu3+> Co2+> Sr2+> Cs+ for cerium(IV) antimonate(CeSb), tin(IV) antimonate(SnSb) and silicon(IV) antimonate(SiSb), while the selectivity decrease in the order UO22+>Th4+ for titanium(IV) antimonate(TiSb). Besides, the effect of EDTA, citric acid, ferric nitrate and sodium nitrate as interfering ions in solution on the distribution coefficient of the studied cations for CeSb and SnSb were studied under certain conditions. The results showed that, the Kj values of CS+, Co2+ and Eu3+ are decreases with increasing the concentrations of ferric and sodium nitrates in the feed solutions for both materials and also Kd values are effected to some extent in case of EDTA and citric acid. Based on the obtained results, practical separation experiments on column were performed(3).The following figures represents the break-through curves for CeSb and SnSb columns for some radionuclides 60Co (10-3M ) as example. From the above studies we conclude that, CeSb and SnSb have been successfully used for the quantitative separation of cesium which suggests its use in the treatment of radioactive liquid waste.
Microcrystalline Single-Junction and Micromorph Tandem Thin Film Silicon Solar Cells
Authors: Meier J. , Keppner H. , Dubail S. , Kroll U. , Torres P. , Pernet P. , Ziegler Y. , Selvan J.A. Anna , Cuperus J. , Fischer D. , Shah A. 
Published: April 2011

ABSTRACTHigher open circuit voltages of the microcrystalline silicon bottom cell have a direct impact on the efficiency of the micromorph (μc-Si:H/a-Si:H) tandem cell. In this paper it is shown that open circuit voltages over 500 mV can be achieved leading to gc-Si:H cell efficiencies of 8.5 %. The behaviour of such cells is characterised both by the illuminated and the dark I-V characteristics in function of cell temperature. Microcrystalline cells with Voc-values higher than 500 mV and micromorph tandems possess in general a lower value of the temperature coefficient of the fill factor and thus of the efficiency, when compared to c-Si. Temperature-dependent dark I-V measurements suggest that the dominant recombination mechanism in lgc-Si:H cells is different from that prevailing in a-Si:H solar cells.
Excess Charge Carrier Kinetics in Amorphous Silicon/Crystalline Silicon Heterojunctions
Authors: Aichberger S. v. , Hahneiser O. , Löffler J. , Feist H. , Kunst M. 
Published: April 2011

ABSTRACTBy contactless transient photoconductivity measurements it is shown that i a-Si:H films, both of standard quality films and annealed low temperature films, passivate the c-Si surface for electron-hole pairs generated in the c-Si substrate. Films deposited at low temperature without annealing do not lead to passivation of the c-Si surface. The injection of excess electrons from a standard a-Si:H film into c-Si with a time constant of a few microseconds and a rather high efficiency was observed. For an annealed 120°C a-Si:H film a slower and less efficient injection was measured, whereas an annealed 50°C a-Si:H shows no appreciable injection.
Electric Field Profile in Jic-Si:H P-I-N Devices
Authors: Wyrsch N. , Beck N. , Meier J. , Torres P. , Shah A. 
Published: April 2011

ABSTRACTSolar cells based on microcrystalline silicon (ptc-Si:H) have demonstrated remarkable efficiencies and have been successfully incorporated in tandem structures; however, little work has so far been devoted to the understanding of these devices. The objective of this paper is to obtain more insight into their physical functioning by extensive characterisation of μc-Si:H devices. Charge-collection experiments shows that high electric field E(x) is present throughout the entire i-layer of thick p-i-n device. Furthermore, from capacitance studies, one concludes that the electric field profile is partly concentrated at grain boundaries. In contrast with these two observations, spectral response under forward bias voltage show that thick [tc-Si:H p-i-n devices are (unlike a-Si:H p-i-n devices) not fully field-controlled.
Internal Electric Field Profile of A-Si:H And A-Sige:H Solar Cells
Authors: Geng Xinhua , Wu Lei , Price Kent , Deng Xunming , Wang Qi , Han Daxing 
Published: April 2011

ABSTRACTBy using the transient-null-current method, we have measured the internal electric field profiles Ei(x) near the p/i interface for two groups of solar cells: (a) a-Si:H p-i-n solar cells with varied i-layer thicknesses, and (b) a-SiGe:H cells with varied Ge content. When using an exponential function of Ei(x) to fit the experimental results, we obtained the field strength at the p/i interface E0, the screening length Lo, and the density of defect states Nd in the i-layer. The thinner the i-layer, the stronger the field strength obtained. For i-layer thickness increasing from 0.1 to 0.5 μm, the field strength E0 decreases from 1.15×105 to 2.0×104 V/cm; Lo decreases from 0.89 to 0.14 μm; and Nd is 3-4×1016 (cm3eV)−1. For the a-SiGe:H cells, as the Ge content increases from 40 to 55 %, E0 increases from 9.3×104 to 1.2×105 V/cm. The correlation of the internal electric field parameters with the cell‘s performance is discussed.
Amorphous Silicon/Crystalline Silicon Heterojunctions in Nuclear Radiation Detector Fabrication
Authors: Walton J.T. , Amman M. , Conti G. , Hong W.S. , Luke P.N. , Ziemba F.P 
Published: April 2011

ABSTRACTApplication of amorphous silicon/crystalline silicon heterojunctions formed by RF sputter deposition and plasma enhanced chemical vapor deposition to the fabrication of nuclear radiation detectors is described. The performance of these heterojunctions as blocking contacts on highresisitivity p-type and n-type single crystal silicon and on lithium-ion compensated silicon (Si(Li)), which are commonly used in silicon detector fabrication, is presented. It is shown that an aluminum/amorphous-silicon contact on Si(Li) x-ray detectors results in about a factor of two reduction in the background counts when compared to a normal gold barrier contact.
Compact Spice Modeling and Design Optimization of Low Leakage a-Si:H TFTs for Large-Area Imaging Systems
Authors: Murthy R.V.R. , Pereira D. , Park B. , Nathan A. , Chamberlain S.G. 
Published: April 2011

ABSTRACTWe present a SPICE model that takes into account the different mechanisms contributing to leakage current in hydrogenated amorphous silicon (a-Si:H) thin film transistors (TFTs). The main sources of leakage current in these devices have been identified to be the parasitic reverse-biased p-i-n diode at the vicinity of the drain as well as diffusion of phosphorous atoms from micro-crystalline (n+ μc-Si:H) contact layer into the intrinsic a-Si:H region. The latter gives rise to ohmic conduction which dominates at very low drain voltages (< I V) and very low gate voltages (< 5 V). At higher gate voltages (5V ≤ VG ≤ 20 V), the reverse current of the parasitic p-i-n diode can be attributed to thermal generation of electrons from the valence to conduction bands through the mid-gap states in the a-Si:H. At even higher gate voltages (> 20 V), the reverse current is due to trap-assisted tunneling, whereby the electrons tunnel to the conduction band via the mid-gap states. A systematic characterization of TFTs with different a-Si:H layer thicknesses shows that the optimal thickness for low leakage current is around 50 nm. The bias dependent leakage current behavior has been modeled and implemented in SPICE using simple circuit elements based on voltage controlled current sources (VCCS). Simulated and measured reverse leakage current characteristics are in reasonable agreement.
Kinetics of Light-Induced Deffect Formation and Annealing in Hydrogenated Amorphous Silicon Alloyed with Sulfur
Authors: Yan Baojie , Chen Shenlin , Taylor P. C. 
Published: April 2011

ABSTRACTThe creation and annealing kinetics of light-induced defects in a-SiSx:H are studied by ESR and LESR measurements. The dispersion of defect creation after prolonged illumination with white light is greater for a-SiSx:H than that for undoped a-Si:H. In addition, the saturated value of the dark spin density is slightly lower for a-SiSx:H than that for a-Si:H. The annealing behavior can be fitted with a Gaussian distribution of annealing activation energies as is the case for undoped a-Si:H. The incorporation of sulfur decreases the peak energy and increases the width of the distribution of activation energies. Light-soaking does not change the low temperature LESR spectrum and LESR spin density.
Hydrogenated Amorphous Silicon Alloyed with Selenium
Authors: Chen Shenlin , Taylor P. C. , Viner J. M. 
Published: April 2011

ABSTRACTHydrogenated amorphous silicon alloyed with selenium has been made by plasma enhanced chemical vapor deposition (PECVD). The activation energy for electrical conduction is essentially unchanged for selenium concentrations < 1 at.%. The photo conductivity changes for selenium concentrations > 0.5 at. %. Photothermal deflection spectroscopy (PDS) and electron spin resonance (ESR), respectively, show that the width of the valence band tail states and the density of neutral silicon dangling bonds also change for selenium concentrations > 0.5 at. %.
Deposition of Nanostructured Silicon Thin Films by Means of the Selective Contribution of Particles in Pecvd
Authors: Costa J. , Roura P. , Cabarrocas Procai , Viera G. , Bertran E. 
Published: April 2011

ABSTRACTPECVD processes are the most common way of growing amorphous and microcrystalline silicon thin films. These low pressure plasmas are known to generate large amounts of particles in the gas phase which may be a source of contamination in the production of silicon based devices. In this report, however, we show that these particles can be incorporated profitably into a growing film, provided that their size is controlled. The Modulation of the RF power is a direct method of controlling particle size. Plasma characteristics determine the dynamics of particle formation, whereas the duration of the plasma-on period controls the particle's size and atomic structure. The size and atomic structure of particles from two different periods of the same discharge were investigated. Their main characteristics, monodisperse size distribution and ordered atomic structure, are discussed in the context of the latest findings on particle nucleation and coagulation.A semi-phenomenological model was used to show that, during the first milliseconds of the discharge, particles of 1–2 nm that are electrically neutral may leave the plasma and contribute to the growth of the film. Although these particles could not be observed on the TEM grid, their contribution to film growth might be relevant.
Performance of μ-Si:H Solar Cells with Amorphous P-Layer
Authors: Siebke Frank , Yata Shigeo , Hishikawa Yoshihiro , Tanaka Makoto 
Published: April 2011

ABSTRACTWe investigated p-i-n solar cells with microcrystalline absorber but amorphous contact layers. Fill factor and open circuit voltage depend sensitively on the p/i interface. Using an optimized design of the p/i interface, cells with fill factors up to 65% and open circuit voltages of 0.45 V were deposited on amorphous p-layers. They are comparable to cells on micro- crystalline p-layers. A further increase of the open circuit voltage was achieved by variation of the p/i interface treatment but up to now it was accompanied by a decrease of the fill factor. We attribute this effect to a thin undoped amorphous layer at the p/i interface. Under non-optimized deposition conditions an amorphous instead of a microcrystalline silicon layer is grown at the p/i interface which can be detected by Raman measurements on cell structures. While the proper design of the p/i interface is crucial for the cell performance we did not observe significant differences between cells with amorphous and microcrystalline n-layers. The results reveal that the open circuit voltage is limited by the bulk properties of the undoped microcrystalline silicon.
Grazing Incidence Measurements of Polarized Electroabsorption and Light Soaking Effect on Amorphous Silicon Based Solar Cells
Authors: Jiang Lin , Schiff Eric A. , Wang Qi , Guha S. , Yang J. 
Published: April 2011

ABSTRACTGrazing-incidence measurements of polarized electroabsorption (EA) in p-i-n solar cells based on hydrogenated amorphous silicon (a-Si:H) are presented. We confirm polarized electroabsorption effect of a-Si:H with the present “sandwich” electrodes, in fact, we find a significantly stronger polarization dependence compared with earlier work based on electroabsorption detected using coplanar electrodes on a-Si:H thin films. We did not reproduce the significant dependence of the polarized electroabsorption upon light soaking, which was found in previous work with coplanar electrodes. We speculate the difference between two electrode geometries is due to the space charge and two dimensional fields.