bluuebunny/crossref_metadata_2025 huggingface dataset:
Up-and Down-Conversion,and Multi-Exciton Generation for Improving Solar Cells:A Reality Check
Authors: Shpaisman Hagay , Niitsoo Olivia , Lubomirsky Igor , Cahen David
Published: April 2011

Because conventional photovoltaic (PV) cells are threshold systems in terms of optical absorption, “photon management“is an obvious way to improve their performance.

Calculations to optimize photon utilization in a single-junction PV cell show ˜1.4 eV to be the optimal bandgap for terrestrial solar to electrical power conversion. For Si, with a slightly sub-optimal gap, continuous efforts have yielded single-junction laboratory cells, quite close to the theoretical limit.

One of the repeatedly proposed directions to improve photon management is that of up- and down-conversion of photon energy. In up-conversion two photons with energy hv < EG (the band gap) create one photon with hv > EG, while in down-conversion one photon with energy hv > 2EG, yields two photons with energy hv > EG.

Multi-exciton generation (MEG), although not a "photon management" process, can achieve effects like down-conversion, which, though, is more limited than MEG. In MEG one photon with energy hv > nEG yields n electron-hole pairs with energy EG. Because MEG has clear advantages over down-conversion, in the following we will, instead of considering both, consider MEG.

We find that a straightforward analysis of this approach to “photon management” for a single junction cell under the detailed balance limit shows clearly that, even if we assume (highly unrealistic) 100% efficient up-conversion and MEG, a new theoretical PV conversion limit of 49 %, instead of 31% is arrived at, a maximum possible gain of ≈60%. The main attractive feature of the combination of up-conversion and MEG is a significant broadening of the optimal band-gap range. Rough estimates for the very highest possibly feasible efficiencies for up-conversion and MEG (25% and 70% respectively), yield at most slightly less than 40% PV conversion efficiency, i.e., only a ˜25% gain over conventional single band gap semiconductor.

These results show that up-conversion or MEG are fascinating scientific areas of research, whose implementation can indeed improve PV cell performance. However, truly formidable challenges need to be met to have UC + MEG lead to the type of radical decrease in the (cost)/ (efficiency × lifetime × yield) ratio that we need to allow large-scale economic introduction of PV cells. Parallel pursuit of alternative approaches to improved photon management, such as, for example, lowering the costs of arrangements with multiple solar absorbers and/or multi-junction systems, appears, therefore, critical for the future of PV.
Enhanced Light-trapping in Solar Cells by Directional Selective Optical Filters
Authors: Ulbrich Carolin , Kirchartz Thomas , Rau Uwe
Published: April 2011

Directional selective optical filters increase the photon confinement of solar cells with a Lambertian light-trapping scheme. These filters restrict the transmission of incoming sunlight to a cone of limited acceptance angle. This paper models the efficiency gain or loss caused by an ideal directional and energy selective filter on top of a solar cell, and compares it to a cell with Lambertian surface and a planar absorber. The enhancement of light trapping by the directional filter is illustrated by the enhancement of the quantum efficiency of normally incident light. Simulations of the annual yield demonstrate that the improved light trapping results in an overall energy gain of more than 10 % for a tracked system.To achieve this gain at the equator,a filter with small acceptance angle of 5 ° that is active below the threshold energy ˜1.5 eV has to used.
Size-Controlled Silicon Quantum Dots Superlattice for Thin-Film Solar Cell Applications
Authors: Kurokawa Yasuyoshi , Miyajima Shinsuke , Yamada Akira , Konagai Makoto
Published: April 2011

We prepared size-controlled silicon quantum dots superlattices (Si-QDSLs) by thermal annealing of stoichiometric hydrogenated amorphous silicon carbide (a-SiC:H)/silicon rich hydrogenated amorphous silicon carbide (a-Si1+xC:H) multilayers for thin-film solar cell applications. Transmission electron microscope (TEM) observation revealed that the size of silicon quantum dots can be controlled by the thickness of the a-Si1+xC:H layers. It was found that hydrogen plasma treatment (HPT) significantly enhanced the photoluminescence (PL) of the Si-QDSLs. From the results of the PL measurement, the bandgap of the Si-QDSLs can be controlled from 1.1 eV to 1.6 eV by varying the diameter of silicon quantum dots. ESR measurement indicated that HPT reduced the defect density in a Si-QDSL from 1.83 ×1019 to 1.67 sup1018 cm-3.
Optical Enhancement by Textured Back Reflector in Amorphous and Nanocrystalline Silicon Based Solar Cells
Authors: Yan Baojie , Yue Guozhen , Jiang Chun-Sheng , Yan Yanfa , Owens Jessica M. , Yang Jeffrey , Guha Subhendu
Published: April 2011

We present the results of systematic studies of optical enhancements by textured Ag/ZnO back reflectors in a-SiGe:H and nc-Si:H solar cells. First, the back reflector materials were characterized by AFM, XRD, and TEM. The results showed that the ZnO layers deposited by sputtering exhibit an increased surface texture with the deposition temperature and film thickness. The material structure showed a strong (002) preferential orientation. The large columnar crystal structure determines the surface texture. Second, the solar cell performance was correlated to the back reflector structure. We found that with a thin ZnO layer, a textured Ag layer results in more light scattering than a flat Ag layer. However, when a thick ZnO layer is used, a flat Ag layer can produce similar or more light scattering than a textured Ag layer. Third, we developed a method to estimate the optical enhancement for a-SiGe:H and nc-Si:H solar cells on various structures of Ag/ZnO back reflectors. Comparing the quantum efficiency data from solar cells made using the same recipe but one on a flat stainless steel substrate and another on a textured Ag/ZnO BR substrate revealed that the optical enhancement for the long wavelength light can be as high as 20 to 30. Compared to the theoretical value of 4n2, there is still scope for further improvement
Quantum Dot Solar Cells Based on CdSe-Assembled Titania Semiconductors
Authors: Wang Chien-Tsung , Yeh Chung-Hsiao
Published: April 2011

In the study, semiconductor quantum dots (QDs) of CdSe nanocrystals have been demonstrated effective as the light energy harvesting assemblies in solar cells. Colloidal CdSe QDs were synthesized by the one-pot approach and linked through a surface modifier onto titania (TiO2) nanoparticles. The TiO2-CdSe composite, while employed as the photoanode in a photoelectrochemical apparatus, exhibited a higher photon-to-electron conversion efficiency (3-fold) than the TiO2 alone, and also a higher stability for photocurrent generation, according to photocurrent transient responses. The optical absorbance and photoluminescence of the CdSe colloid showed a blue shift in the absorption edge with decreasing the particle size (band energy gap shifts from 2.0 to 2.19 eV), suggesting a quantum size effect. The CdSe particle size was determined up to 5 nm by a transmission electron microscopy. A scheme describing the charge carrier rectification for the coupled semiconductor system is proposed.
Organic:PbS-nanocrystal:Fullerene Hybrid Photovoltaics
Authors: Dissanayake Nanditha , Hatton Ross A , Giusca Cristina , Lutz Thierry , Curry Richard , Silva Ravi
Published: April 2011

Single and multi junction hybrid devices comprising oligoacenes, PbS quantum dots (PbS-QD) and C60 are demonstrated. A greatly improved performance of the PbS-QD /C60 system was obtained in this work. Furthermore, a study of using acenes (pentacene, tetracene) as light absorbers and photoinduced electron donors to PbS-QD was carried out. Fabricated devices were characterized under 1 Sun simulated solar irradiation and external quantum efficiency (EQE) measurements. The initial hybrid devices demonstrated up to 0.14 % power conversion efficiency under AM1.5G illumination and up to 16 % EQE at 400 nm. The single junction (PbS-QD/C60) devices demonstrated greater than 1.2 % EQE at 1100 nm while multi junctional tetracene/PbS-QD/C60 devices exhibited up to 0.2 % EQE in the infrared region (1100 nm). Ultraviolet photoelectron spectroscopy was used to measure the molecular energy levels in the system under discussion to justify the photoinduced charge transfer. This work demonstrates new device systems which can be potentially be utilized to fabricate high efficient broad band absorbing hybrid photovoltaics.
High Pressure Phase Transformations in Heavy Rare Earth Metals and Connections to Actinide Crystal Structures
Authors: Vohra Yogesh K. , Sangala Bagvanth Reddy , Stemshorn Andrew K. , Hope Kevin M.
Published: April 2011

High-pressure studies have been performed on heavy rare earth metals Terbium (Tb) to 155 GPa and Holmium (Ho) to 134 GPa in a diamond anvil cell at room temperature. The following crystal structure sequence was observed in both metals hcp ⟶ Sm-type ⟶ dhcp ⟶ distorted fcc (hR-24) ⟶ monoclinic (C2/m) with increasing pressure. The last transformation to a low symmetry monoclinic phase is accompanied by a volume collapse of 5 % for Tb at 51 GPa and a volume collapse of 3 % for Ho at 103 GPa. This volume collapse under high pressure is reminiscent of f-shell delocalization in light rare earth metal Cerium (Ce), Praseodymium (Pr), and heavy actinide metals Americium (Am) and Curium (Cm). The orthorhombic Pnma phase that has been reported in Am and Cm after f-shell delocalization is not observed in heavy rare earth metals under high pressures.
Theory of Photoemission in Actinides
Authors: Svane Axel
Published: April 2011

A theory is presented which describes the photoemission spectra of actinide compounds starting from the atomic limit of isolated actinide ions. The multiplets of the ion are calculated and an additional term is introduced to describe the interaction with the sea of conduction electrons. This leads to complex mixed-valent ground states, which describes well the rich spectrum observed for PuSe. In particular, the three-peak feature, which is often seen in Pu and Pu compounds in the vicinity of the Fermi level originates from f6 → f5 emission. The theory is further applied to PuSb, PuCoGa5 and Am.
Accelerated Dissolution Process of the Spent Fuel (UO2) under Repository Conditions
Authors: Iglesias Eduardo , Quiñones Javier , Rodriguez Nieves
Published: April 2011

Nowadays, nuclear energy is one of the options for developed countries in order to maintain the demand of electric energy. One of the problems of this kind of energy generation is the residual waste form after a fuel cycle (spent fuel). These kind of material is so difficult to characterize -due to their composition and the thermal treatment in the reactor- that exhaustive studies are necessaries for a complete knowledge, helping to build, with complete reliability, a very safety underground facility. In this way, the option known as Deep Geological Repository (DGR) is been developed by each country taking part in the nuclear energy industry. The unique via for the migration to the biosphere of the radionuclides -actinides and lanthanides content in the spent fuel pellet (UO2) after the closing of the deep geological repository is by the water transport phenomena. It is a fundamental question to know how much time they will spend in their trip; and the first step is the rate of liberation of these radionuclides from the spent fuel pellet. In this way, the matrix dissolution rate of the spent fuel pellet no dependent on the specific surface area after a normalization by the initial value- is a key parameter to begin the performance assessment for any deep geological repository and the specific surface value is, following the Matrix Alteration Model (MAM) sensitivity analysis, one of the most important parameters controlling the radionuclides liberation. In this way, several measurements were carried out to obtain values in different conditions for different sieves of UO2 powder, treated as fresh fuel. First of all, the specific surface area was measured with a multi-point isothermal procedure with N2 and Kr, the both. The values obtained were presented in order to obtain a general law for the evolution with the particle size. These data are part of a bigger project about the complete description of the spent fuel analogous; very useful to obtain new dissolution rates for the spent fuel under repository simulated conditions.
Toward Modeling Charge-Defect Reactions at the Atomistic Level
Authors: Valone Steve
Published: April 2011

Defect reactions involving charged species are commonplace in nuclear fuels fabrication and burn-up. Even the simplest of these fuels, uranium dioxide (UO2), typically involves the nominal charge states of +3, +4, and +5 or +6 in U and -1 and -2 states in O. Simulations that attempt to model evolutionary processes in the fuels require tracking changes among these charge states. At the atomistic level, modeling defect reactions poses a particularly vexing problem. Typical potential energy surfaces do not have this type of physical phenomena built into them. Those models that do attempt to model charge-defect reactions do not have especially strong physical bases for the models. For instance, most do not obey established limits of charge behavior at dissociation or lack internal consistency. This work presents substantial generalizations to earlier work of Perdew et al. No matter the size of the system, total system hamiltonians can be decomposed into subsystem or site hamiltonians and coulombic interactions. Site hamiltonians can be evaluated in a spectral representation, once an integer number of electrons are assigned. For both pair and individual site hamiltonians a dilemma emerges in that many sites are better understood as possessing a fractional charge. The dilemma is how to weight the site integer-charge states in a physically consistent manner. One approach to solving the dilemma results in two distinct charge-dependent energy contributions emerge, arising from intra- and inter-subsystem charge transfer. Further analysis results in a model of the intra-subsystem charge-transfer that can accommodate the mixed valence states of either U or O in nuclear fuels. Mixed valence properties add complications to the model that originate in the phenomenological fact that it typically requires different amounts of energy to increase or decrease charge. As a result of the inherent complexity one has the option of using multiple charges, a concept with strong ties to shell models, or modeling parameters not directly related to charge as functions of charge. This latter approach is illustrated by invoking a minimization principle that does preserve the important dissociation limits of Perdew et al., in order to complete the model.
Intrinsically Localized Modes in Uranium and the Prospect for Finding them in Plutonium
Authors: Manley Michael
Published: April 2011

Dynamic nonlinear localization, an emerging new area of materials physics, has the potential to fundamentally change our understanding of materials properties. These intrinsically localized modes (ILM) have been found forming in uranium above about 450 K. Comparisons with data from the literature shows that these ILMs influence many properties, including heat capacity, thermal transport, thermal expansion, and mechanical deformation. The existence of ILMs helps to explain many anomalies in uranium, some of which have been known for more than fifty years. Here, the possibility that ILMs may also play a role in the properties of plutonium is considered. The mechanism helps to explain the success of an “Invar-like” two-level model for the thermal expansion of Pu without the need to invoke local magnetic states, which have been ruled out experimentally. It also helps to explain an excitation observed in δ-plutonium that has energy consistent with the two-level model, but momentum dependence consistent with lattice vibrations. This excitation, energy and momentum dependence, is consistent with the non-equilibrium generation of ILMs and the thermal excitation properties of these ILMs are consistent with a two-level model. High-temperature inelastic x-rays scattering measurements of the phonon dispersion curves of δ-plutonium are needed to test this hypothesis.
Find the Nano in Your Life: Using Interactive Museum Demonstrations to Engage a Public Audience in Nanotechnology Research and Policy
Authors: Das Jayatri , Francies Allison B. , Redwing Ronald D.
Published: April 2011

To many Americans, nanotechnology remains a science of the future; most are unaware that nanoscale science is already being incorporated into products they use in their everyday lives. Informal learning environments are an ideal venue in which to not only educate the public about current applications of nanotechnology but also engage them in a discussion of its impacts. Developed through a partnership between two NSF-funded Materials Research Science and Engineering Centers at Penn State and Cornell Universities and The Franklin Institute in Philadelphia, the “Small Wonders: Find the Nano in Your Life” program has been distributed to 20 science and children's museums around the United States. This cart-based program includes interactive demonstrations of commercially available products that use nanoscale technology, including sunblock, nanosilver food containers, and nanoiron for environmental remediation. Macroscale models enable visitors to understand the underlying science, while real products allow visitors to explore the hope, hype, and reality of each. Here, we discuss the educational goals of the program, our approach to presenting questions of both science and policy, and methods and results of visitor evaluation. This third collaborative project continues to build on a model of program development and distribution that has been highly successful at reaching a broad audience.
The Humacao Strange Matter Exhibition: Prem Brings Materials Science and Nanotechnology to Puerto Rican Communities
Authors: Ramos Idalia , Rivera Ramón A. , Pinto Nicholas J. , Sotero José , Vega Esther , Zimbovskaya Natalya , Negrón Pablo , Rivera Mirza , Colón Gladys
Published: April 2011

The “UPRH-PENN Partnership for Research and Education in Materials” (PREM) is sponsored by the Division of Materials Research of the National Science Foundation and since 2004 it has contributed to increasing the participation of Puerto Rican men and women in materials research and education. The program integrates K-12, undergraduates, graduate students, and faculty collaborating through research and education in a partnership between the University of Puerto Rico at Humacao (UPRH) along with UPRC and UPRRP and the University of Pennsylvania Materials Research Science & Engineering Center. The UPRH-PREM has strong links with schools in the eastern region of Puerto Rico and has successfully integrated K-12 students and teachers into the program through workshops, web resources, open houses, a Summer Program and research experiences during the academic year. In an effort to integrate the wider community into the outreach efforts, from October to December 2007 PREM hosted the presentation of the Interactive Materials Science Exhibition “Strange Matter”. “Strange Matter” was designed and produced by the Materials Research Society (MRS) in conjunction with the Ontario Science Centre in Toronto. Funding for the project is being provided by the National Science Foundation and industrial partners 3M, Dow, Ford, Intel, and Alcan. The exhibition brings interactive activities that highlight the fact that materials science is all around us. This exhibition is the first and only one in the island of Puerto Rico and was presented at UPRH's Casa Roig Museum, a historic plantation house located in downtown Humacao. Local scientists complemented the exhibition with live demonstrations and talks to provide deeper explanations and motivate young visitors to study materials. To make the exhibition possible, PREM integrated UPR-Humacao administration, faculty, students, non-teaching workers, Casa Roig staff, schools, Humacao municipality, local businesses and individual citizens. Dozens of students, faculty and other members of the community were mobilized as volunteers to support all aspects of the exhibition.
R & D and Business Opportunities for Nanotech Companies in Singapore
Authors: Liu Lerwen
Published: April 2011

Singapore, located at the centre of Asia, is an ideal dynamic hub to converge advanced R & D and industry leaders, robust alliances, new technologies and world class infrastructure. In the field of nanotechnology, Singapore is equipped with state of the art facilities (one of the best in the world) for nanotechnology R & D and it has unique open research environment for encouraging and attracting international collaboration and industry cooperation. Combining its efficient government administration and international business and financial environment, Singapore is becoming an attractive place for setting up leading R & D centres, research and development partnerships for research institutions and industries, and for locating company regional headquarters. Singapore government is aggressively promoting innovation and launched attractive funding schemes in help fostering SMEs and spin offs from research institutions. Singapore government has committed SGD 13.55 Billion (USD10B) on R & D for the period of 2006-2010 (over 200% increase from the previous 5 year period), making Singapore GERD to 3% of GDP by 2010. Singapore is not only a melting point of diverse cultures but most importantly a place for exciting converging technologies, global partnerships and creates growth nanotech industries. In this article we give an overview on the Singapore public and private financing schemes for nanotech R & D and commercialisation. Incentives for supporting start-ups as well as R & D partnerships with research institutes are summarized. We outlined the world-class infrastructure for nanotech R & D. Summary of nanotech R & D efforts are highlighted.
Nanomonitors: Electrical Immunoassays for Protein Biomarker Profiling
Authors: Bothara Manish , Reddy Ravi K , Barrett Thomas , Carruthers John , Prasad Shalini
Published: April 2011

The objective of this research is to develop a “point-of-care” device for early disease diagnosis through protein biomarker characterization. Here we present label-free, high sensitivity detection of proteins with the use of electrical immunoassays that we call Nanomonitors. The basis of the detection principle lies in the formation of an electrical double layer and its perturbations caused by proteins trapped in a nanoporous alumina membrane over a microelectrode array platform. High sensitivity and rapid detection of two inflammatory biomarkers, C-reactive protein (CRP) and Myeloperoxidase (MPO) in pure and clinical samples through label-free electrical detection were achieved. The performance metrics achieved by this device makes it suitable as a “lab-on-a-chip” device for protein biomarker profiling and hence early disease diagnosis.
Exploiting Nanotech Opportunities: A Strategic Entrepreneurship Perspective
Authors: Baglieri Daniela , Giordani Sara
Published: April 2011

This paper analyzes the main challenges nanotech start-ups face in turning nanotech inventions into valuable and marketable nanotech innovations, also considering that nanotechnology discoveries could represent “inventions of methods of inventing” (Rothaermel et al., 2007). In the last decades, nanotechnologies have been a burgeoning area of science and engineering which show an increasing potential to transform a broad range of industries, and to boost the US and European firms' competitiveness (OECD, 1998). Although these emerging technologies share some problems with new ventures in other emerging industries ( e.g. biotech), nanotechnology firms have to balance the management of high technical and high market risk, still evolving regulatory frameworks (Bowman et al. 2006) and strategies for entering the business network and for attracting investments, e.g. in the form of potential venture capitalists. Potential investors, in turn, will face the well-known hurdle of the due diligence, considering for example health or safety concerns, manufacturing, availability of distribution channels, etc. (Burden, 2007).We propose that configuring their network and choosing the right market segment are the key strategies nanotech ventures should adopt in pushing their early growth in the global market. We analyze a sample of 15 European nanotech firms which confirm our predictions. Due to the novelty of the topic covered in this study, this research is exploratory in nature.
The Immobilisation of Clinoptilolite Within Cementitious Systems
Authors: Gordon L. E. , Milestone N. B. , Angus M. J.
Published: April 2011

The zeolitic ion exchanger clinoptilolite was encapsulated within various cementitious systems in order to assess their suitability for the retention of the radioelements, Cs and Sr. The pozzolanic reaction of clinoptilolite is reduced in composites containing BFS and PFA and appears not to continue after 7 days of hydration. Ca(OH)2 persists up to 360 days of hydration in a 9:1BFS:OPC system with 10% clinoptilolite added, despite the presence of unreacted pozzolan. This may be due to low pH of the pore solution, if Na and K act as counter cations in the aluminous C-S-H, a product of pozzolanic hydration or are exchanged onto the clinoptilolite. Saturation of the pore solution with Ca may prevent further dissolution of Ca(OH)2. Cs leaching occurs in all samples during accelerated tests due to breakdown of the clinoptilolite structure.

The alternative cement system calcium sulfoaluminate cement (CSA) has a different hydration chemistry and properties to OPC and OPC composites with a lower pore solution pH. Clinoptilolite appears to react in a hydrating CSA system with significant reaction continuing between 28 and 90 days of hydration. Leaching of Cs from CSA is higher than from an OPC system, in which almost all of the clinoptilolite crystallinity is lost. The major product of CSA hydration is ettringite. Cs may be adsorbed within cation sites of the C-S-H in an OPC system but not by ettringite which does not retain Cs so Cs has high mobility and leachability through the CSA matrix.
Processes Related to the Water Uptake by EUROBITUM Bituminised Radioactive Waste: Theoretical Considerations and First Experimental Results
Authors: Mariën An , Smets Steven , Li Xiangling , Valcke Elie
Published: April 2011

According to the present Belgian radioactive waste management program, Eurobitum bituminised radioactive waste will be disposed of in a geologically stable underground clay formation. The Boom Clay is studied as a potential host formation because of its low diffusion and high retention properties towards radionuclides. The presence of the radioactive waste should not disturb these properties. Due to the presence of hygroscopic salts (25 to 30 weight% NaNO3), Eurobitum will take up pore water which will result in a swelling and possibly in a very high swelling pressure. First scoping calculations suggest that the swelling pressure exerted to Boom Clay should remain below 7 to 8 MPa to avoid the formation of fractures. If the bitumen in EUROBITUM behaved like a perfect semi-permeable membrane and if no swelling were allowed after the dissolution of NaNO3 into a saturated solution of 10.8 M, osmotic pressures of ∼50 MPa could be attained. To better understand the interaction between the swelling Eurobitum and the host formation, coupled hydro-chemical-mechanical constitutive laws for Eurobitum have to be developed. To this purpose, water uptake tests under constant volume (‘confined’) and constant stress (‘semi-confined’) conditions are being performed. After ∼2 years of hydration of small inactive Eurobitum samples in constant volume conditions, the swelling pressure has raised to ∼12 MPa. The volume of samples that can swell against counter pressures of 2.2, 3.3, or 4.4 MPa (constant stress tests) increased with ∼5 to 11 volume%, independently of the applied counter pressure. Approximately 10 weight% of the initial NaNO3 content has been leached.
Determination of the Forward Rate of Dissolution for SON68 and PAMELA Glasses in Contact With Alkaline Solutions
Authors: Ferrand K. , Lemmens K.
Published: April 2011

In the new Belgian disposal design, the nuclear waste glass will be surrounded by a 3 cm thick carbon steel overpack and a 70 cm thick concrete buffer. An initially high pH is expected after water intrusion in the concrete buffer and this may have an effect on the radionuclide release from the waste glass. This study was performed in order to determine the forward rate of dissolution for SON68 and PAMELA glasses (SM513 LW11 and SM539 HE 540-12), conducting dynamic tests at 30°C in contact with alkaline solutions. In these experiments, the silicon concentration in solution was determined by UV/Visible spectrophotometry according to the blue â-silicomolybdenum method. The forward rates of dissolution were quite similar for the three glasses except at the highest pH for which a slightly higher value was found for SM539 glass. For SON68 glass, a good agreement with the previously established interpolation law was observed until pH 11.5, but at higher pH, the interpolation law slightly overestimates the dissolution rate [1].
Single Idealized Cracks: A Tool for Understanding Fractured Glass Block Leaching
Authors: Chomat Laure , Bouyer Frédéric , Gin Stéphane , Roux Stéphane
Published: April 2011

Within the scope of the long term behaviour of the R7T7 glass, which is the French nuclear glass, leaching and its coupling with transport mechanisms is studied. Experiments carried out on a SON 68 glass (inactive R7T7 type glass) model cracks in static basic conditions show a strong coupling between solution transport and glass leaching, depending on crack aperture. Moreover, gravity driven convective transport was evidenced for vertical model cracks, whereas only molecular diffusion was detected for horizontal model cracks under the same alteration conditions. In addition, an original device was developed to study the influence of temperature gradients on alteration kinetics as a convective driving force. These experiments show conclusively that thermally- or gravity-induced convective flow must be taken into account, even if such convective effects have not been established experimentally in neutral condition, which is more realistic condition for geological storage. A modeling, based on a porous geochemical software (HYTEC) accounting for both chemistry and transport, has been successfully applied to describe alteration within simple silicate glass cracks. It will be extended to study SON 68 glass model cracks, and more complex fracture networks.
Plutonium Feed Impurity Testing in Lanthanide Borosilicate (LaBS) Glass
Authors: Fox Kevin M. , Marra James C. , Edwards Thomas B. , Hoffman Elizabeth N. , Crawford Charles L.
Published: April 2011

A vitrification technology utilizing a lanthanide borosilicate (LaBS) glass is a viable option for dispositioning excess weapons-useable plutonium that is not suitable for processing into mixed oxide (MOX) fuel. A significant effort to develop a glass formulation and vitrification process to immobilize plutonium was completed in the mid-1990s. The LaBS glass formulation was found to be capable of immobilizing in excess of 10 wt % Pu and to be tolerant of a range of impurities. A more detailed study is now needed to quantify the ability of the glass to accommodate the anticipated impurities associated with the Pu feeds now slated for disposition.

The database of Pu feeds was reviewed to identify impurity species and concentration ranges for these impurities. Based on this review, a statistically designed test matrix of glass compositions was developed to evaluate the ability of the LaBS glass to accommodate the impurities. Sixty surrogate LaBS glass compositions were prepared in accordance with the statistically designed test matrix. The heterogeneity (e.g. degree of crystallinity) and durability (as measured by the Product Consistency Test – Method A (PCT–A)) of the glasses were used to assess the effects of impurities on glass quality.
Radionuclides Release From the Spent Fuel Under Disposal Conditions: Re-evaluation of the Instant Release Fraction
Authors: Ferry Cécile , Piron Jean-Paul , Poulesquen Arnaud , Poinssot Christophe
Published: April 2011

The so-called Instantaneous Release Fraction (or IRF) corresponds to the rapid release of radioactivity by the spent fuel rod at the canister breaching time in repository and depends on the spent fuel evolution in a closed system. The effect of He accumulation on the spent fuel pellet microstructure and diffusion processes are here re-assessed in the light of the recent results issued from the projects Near-Field PROcesses and PRECCI. It allows diminishing the conservatism of the former IRF values of key safety relevant radionuclides for PWR UO2 fuels.
Effect of Weak Acid Additions on the General and Localized Corrosion Susceptibility of Alloy 22 in Chloride Solutions
Authors: Carranza Ricardo M. , Giordano C. Mabel , Rodríguez Martín A. , Rebak Raul B.
Published: April 2011

Electrochemical studies such as cyclic potentiodynamic polarization (CPP) and electrochemical impedance spectroscopy (EIS) were performed to determine the corrosion behavior of Alloy 22 (N06022) in 1M NaCl solutions at various pH values from acidic to neutral at 90°C. All the tested material was wrought Mill Annealed (MA). Tests were also performed in NaCl solutions containing weak organic acids such as oxalic, acetic, citric and picric acids.

Results show that the CR of Alloy 22 was significantly higher in solutions containing oxalic acid than in solutions of pure NaCl at the same pH. Citric and Picric acids showed a slightly higher CR, and Acetic acid maintained the CR of pure chloride solutions at the same pH. Organic acids revealed to be weak inhibitors for crevice corrosion. Higher concentration ratios, compared to nitrate ions, were needed to completely inhibit crevice corrosion in chloride solutions.

Results are discussed considering acid dissociation constants, buffer capacity and complex formation constants of the different weak acids.
Repassivation Potential of Alloy 22 in Sodium and Calcium Chloride Brines
Authors: Rebak Raul B. , Ilevbare Gabriel O. , Carranza Ricardo M.
Published: April 2011

A comprehensive matrix of 60 tests was designed to explore the effect of calcium chloride vs. sodium chloride and the ratio R of nitrate concentration over chloride concentration on the repassivation potential of Alloy 22. Tests were conducted using the cyclic potentiodynamic polarization (CPP) technique at 75°C and at 90°C. Results show that at a ratio R of 0.18 and higher nitrate was able to inhibit the crevice corrosion in Alloy 22 induced by chloride. Current results fail to show in a consistent way a different effect on the repassivation potential of Alloy 22 for calcium chloride solutions than for sodium chloride solutions
Modeling of Radionuclide Migration Through Fractured Rock in a HLW Repository With Multiple Canisters
Authors: Lim Doo-Hyun , Uchida Masahiro , Hatanaka Koichiro , Sawada Atsushi
Published: April 2011

An integrated numerical model for groundwater flow and radionuclide migration analyses in a water-saturated HLW repository with a multiple-canister configuration is developed by incorporating the heterogeneity of fractured host rock based on the previous multiple-canister model (MCFT2D [1, 2]). The current model incorporates i) heterogeneity of the fractured host rock represented stochastically by discrete fractures, ii) disposal-pit vertical emplacement concept, iii) representation of the waste package consisting of a waste canister and a bentonite-filled buffer, and iv) a user-determined repository configuration of multiple canisters using the repository parameters such as disposal tunnel spacing, waste package pitch, tunnel diameter, the number of tunnels in a repository, and the number of canisters in a tunnel. The current model can facilitate investigations into the effects of heterogeneous fractured host rock on water flow and nuclide migration for the different configurations of multiple canisters, as well as optimization of the repository design parameters in terms of release of nuclides from the repository.
Development and Validation of a Model of Uranium Release to Groundwater From Legacy Disposals at the UK Low Level Waste Repository
Authors: Small J.S. , Lennon C. , Kwong S. , Scott R.J.
Published: April 2011

A previous radiological assessment of the UK Low Level Waste Repository (LLWR) has considered how the prevailing reducing chemical conditions in disposal trenches, may limit uranium release through the extreme low solubility of U(IV) solids. This study considers the additional effects that the physical and chemical nature of the uranium wastes may have on the release of uranium. Fluoride process residues produced by refining of uranium metal comprise the majority of the legacy inventory. Based on historic records and descriptions of the uranium wastes a conceptual model has been developed which bounds the release rate of uranium present as inclusions and dissolved in the solid residues by the dissolution rate of a magnesium fluoride matrix. The model is represented in a 3-dimensional groundwater flow and geochemical model. Initial findings indicate that the model correctly represents the range of fluoride and uranium concentrations that are measured in leachate from the LLWR trenches. Incorporation of this model in future safety assessments, together with a reduction in the derived inventory of uranium, is likely to result in a significant lowering of the peak groundwater dose to acceptable levels, even in the case that the site re-oxidizes. The study builds confidence in the inherent safety features that are provided by the sparingly soluble uranium waste residues and the reducing chemical conditions of the LLWR trenches.
Illustration of HLW Repository Performance: Using Alternative Yardsticks to Assess Modeled Radionuclide Fluxes
Authors: Miyahara Kaname , Kato Tomoko
Published: April 2011

Complementary indicators have been used in developing a safety case in order to avoid uncertainties in the biosphere modeling used to estimate conventional dose or risk. For example, radionuclide fluxes can be used to evaluate the effectiveness of barrier performance. However, it is difficult to define relevant yardsticks for comparison, because the fluxes of naturally occurring radionuclides due to geological processes vary considerably depending on time and location. This paper discusses the relevance of alternative yardsticks for assessing modeled radionuclide fluxes by selecting yardsticks calculated from fluxes of natural radionuclides at the groundwater discharge point from the geosphere to an aquifer; these are then compared with fluxes of repository-derived radionuclides at the same point. Such yardsticks avoid surface geological processes that may also contribute to natural fluxes, allowing comparison at a suitable, common evaluation point that avoids dependence on site-specific conditions. The effectiveness and robustness of barrier performance is demonstrated using the developed yardsticks and the sensitivity of the analysis to groundwater flux is illustrated.
Fabrication and Photoelectrical Properties of AZO/SiO2/p-Si Based Device
Authors: Ma Z.Q. , He B. , Xu J. , Zhao L. , Li F. , Zhang N.S. , Meng X. J. , Shen L. , Shen C.
Published: April 2011

In order to fabricate AZO/SiO2/p-Si heterojunction device and let it be an absorber of ultraviolet response cell. Zinc oxide (ZnO) thin films doped with aluminum (AZO) were deposited on p-Si(100) substrates covered with silicon dioxide (SiO2) by radio frequency magnetron sputtering. The optical and electrical properties of the Al doped - ZnO films were characterized by UV-VIS spectrophotometer, current-voltage measurement, and four point probe technique, respectively. The results show that the device is a typical tunneling diode for minority carrier and a strong obstructing effect from majority carriers. The potential rectifying behavior and photovoltaic characteristic is present at dark current and weak light illumination, respectively.
Method of Fast Hydrogen Passivation to Solar Cell Made of Crystalline Silicon
Authors: Sun Wen-Ching , Lin Jian-Hong , Chang Wei-Lun , Huang Tien-Heng , Wang Chih-Wei , Lin Jia-De , Kou Chwung-Shan , Lin Jian-You , Chen Sheng-Wei , Hwang Jenn-Chang , Gan Jon-Yiew
Published: April 2011

Plasma immersion ion implantation (PIII) is a technique of material processing and surface modification, using controllable negative high voltage pulsed bias to attract the ion generated from the plasma. The method using PIII treatment quickly improves the performance of solar cell made of crystalline silicon, including monocrystalline, multicrystalline and polycrystalline silicon. Hydrogen ions are attracted and quickly implanted into solar cell under a predetermined negative pulse voltage, thus, the passivation of the crystal defects of the solar cell can be realized in a short period. Meanwhile, the properties of the antireflection layer can not be damaged as the proper operating conditions are used. Consequently, the series resistance can be significantly reduced and the filling factor increases as a result. Both the short-circuit and the open-circuit voltage can be increased. The efficiency can be enhanced.
CuIn(Se,S)2 Absorbers Processed using a Hydrazine-Based Solution Approach
Authors: Liu Wei , Mitzi David B. , Chey S. Jay , Kellock Andrew
Published: April 2011

With tunable bandgap and demonstrated high efficiency, the chalcopyrite CuInSe2 and its alloys have shown great potential as absorbers for single and multi-junction solar cells. However, the current deposition techniques mostly rely on expensive vacuum-based processing or involve complicated precursor solution preparation. These higher-cost absorber preparation processes make it difficult to commercialize this technology. In this work, CuInSe2−xSx (CIS) absorbers are deposited using a simple hydrazine-based solution process. Precursor solutions were prepared by dissolving the component metal chalcogenides and chalcogen in hydrazine, forming homogeneous solutions containing adjustable concentrations of desired elements mixed on a molecular level. These precursor solutions are then spin coated on substrates followed by a heat treatment in an inert environment to produce high quality CIS thin films. Significantly, no post deposition selenization process is required using this technique. Laboratory scale devices with conventional glass/Mo/CIS/CdS/i-ZnO/ITO structure have been fabricated using CIS absorbers deposited via this process. For the baseline low-bandgap CIS system with no Ga added (to compare with our previously reported results with Ga incorporated), AM1.5G conversion efficiency of as high as ∼9% has been achieved for devices with 0.45 cm2 effective area.
Ultrafast Laser Textured Silicon Solar Cells
Authors: Nayak Barada K. , Iyengar Vikram , Gupta Mool C.
Published: April 2011

A novel ultrafast laser texturing method has been developed to produce arrays of nano/micro surface textures in silicon. Laser processing conditions have been optimized for achieving appropriate optical and electronic properties for photovoltaic applications. The textured silicon surfaces absorb greater than 99% of incident light over the entire solar spectrum and the material appears complete black to bare eye. Textured silicon surfaces are characterized for surface morphology and optical properties. Chemical etching and thermal annealing steps have been performed to remove laser slag and induced defects. Finally, we report the total and external quantum efficiency results on photovoltaic devices fabricated on the textured silicon wafers, which can be further improved.
Vitrification of High-Level Waste at the Savannah River Site
Authors: Fox Kevin M. , Peeler David K.
Published: April 2011

The objective of this study was to experimentally measure the properties and performance of a series of glasses with compositions that could represent high level waste Sludge Batch 5 (SB5) as vitrified at the Savannah River Site Defense Waste Processing Facility. These data were used to guide frit optimization efforts as the SB5 composition was finalized. Glass compositions for this study were developed by combining a series of SB5 composition projections with a group of candidate frits. The study glasses were fabricated using depleted uranium and their chemical compositions, crystalline contents and chemical durabilities were characterized. Trevorite was the only crystalline phase that was identified in a few of the study glasses after slow cooling, and is not of concern as spinels have been shown to have little impact on the durability of high level waste glasses. Chemical durability was quantified using the Product Consistency Test (PCT). All of the glasses had very acceptable durability performance. The results of this study indicate that a frit composition can be identified that will provide a processable and durable glass when combined with SB5.
Treatment of Graphite Waste to Minimize Disposal Volume
Authors: Meyer Willie C.M.H. , Walt I.J. van der , Kabila Vusi , Badenhorst Jacoba J. , Moolman Danie , Klopper Wouter
Published: April 2011

South Africa initiated a program to significantly expand its total nuclear energy capacity by acquiring additional Pressurized Water Reactors (PWRs) and is currently researching Pebble Bed Modular Reactors (PBMRs) as next generation nuclear energy sources. The result of such an expansion in the current nuclear program will be a need for the disposal of additional nuclear waste. However, as an alternative strategy for spent PBMR fuel, the separation of the spent fuel into TRISO particles for disposal and graphite for re-use in the nuclear industry could also be considered.
On radiation-induced fluidization (quasi-melting) of silicate glasses
Authors: Ojovan Michael , Mobus Gunter
Published: April 2011

The effect of intensive electron radiation on viscous flow in silicate glasses is analysed and shown that it can result in a many orders of magnitude decrease of viscosity and stepwise decrease of activation energy of flow. Fluidisation or quasi-melting of glasses on intensive electron irradiation is caused by bond breaking via the radiation-chemical reaction ≡Si-O-Si≡ + e− Si-O + Si + (e−)′ which weakens the silicate glass network and leads tofive-fold coordination of oxygens around the silicon. An explicit equation of viscosity wasobtained for irradiated glasses as well as an equation for glass transition temperature. Theassessments of temperature increase by electron radiation show that radiation-inducedfluidisation of glasses can occur at minimal thermal effects. Radiation-induced fluidisation ofglasses can result in nanoscale patterning effects caused by surface tension forces. Changes inthe viscous flow behaviour are also important in conditions of long-term irradiation for glassesused in nuclear installations as well as for nuclear waste glasses.