bluuebunny/crossref_metadata_2025_split huggingface dataset:
Effect of as-deposited residual stress on transition temperature of VO2 films
Authors: Tsai Kuang Yue , Chin Tsung-Shune , Shieh Han-Ping D. , Ma Cheng Hsin 
Published: April 2011

ABSTRACTVO2 is a material with reversible thermo-chromic properties. The reversible phase transition of a strain-free single-crystalline VO2, at a transition temperature (Tt) 68°C, is accompanied with changes in crystal structure, optical and electrical properties. With different processing conditions during thin film deposition, different transmittance loops will be resulted upon thermal cycling. The residual stress of the thin films with poor crystallinity, as determined from X-ray diffractometry, is found to be an important factor responsible for the Tt that increases with increasing residual stress. Residual stress affects the hysteresis span of the transmittance loop. The relationship between residual stress of as-deposited VO2 films and the relative positions between vanadium and oxygen under the residual stress are also delineated.
Effect of Gamma and Alpha Irradiation on the Corrosion of the French Borosilicate Glass SON 68
Authors: Abdelouas Abdesselam , Ferrand Karine , Grambow Bernd , Mennecart Thierry , Fattahi Massoud , Blondiaux Gilbert , Houée-Lévin Chantal 
Published: April 2011

ABSTRACTCorrosion experiments with the French borosilicate glass SON 68 were conducted under gamma (60Co source) and alpha (cyclotron) irradiation conditions. Static tests with glass powder were conducted at 90°C under saturation conditions with synthetic solutions rich in Si, B and Na. The initial pH was 9.8 and the SA/V was 3970 m−1. For gamma irradiation tests with the highest dose (∼ 58000 Gy) the pH decreased by almost a unit, which lasted for two weeks. The ion-exchange between glass and solution was enhanced as evidenced by the increase of the Li-normalized mass loss within 93 days. The measured H2O2 concentration in the experiment with the glass was as high as 1.51 10−5. The alpha irradiation tests with a total dose of 1800 Gy did not affect the solution pH and therefore the leaching rate of the glass remained similar to that in the blank experiment after 59 days. However, the measured H2O2 concentration was as high as 2.32 10−5. This work indicates that high irradiation doses may enhance the ion-exchange process due to the pH decrease.
Titanate Ceramic Matrices for Alumina-Rich Wastes
Authors: Begg Bruce D. , Vance Eric R. , Li Huijun , McLeod Terry , Scales Nicholas , Bhati Mugdha 
Published: April 2011

ABSTRACTIn the early 1980s a synroc variant, SYNROC-D, was developed for immobilisation of high-level defence waste stored at the Savannah River Plant, USA. A key phase in the immobilisation matrix was spinel, used to immobilise the large proportion of iron and alumina in the waste. Here we examine the feasibility of this approach for other alumina-rich wastes, not necessarily containing iron, derived from the dissolution of aluminium fuel cladding. The advantages of using a magnesia spinel, as opposed to hercynite (FeAl2O4), as the primary alumina-bearing phase are discussed in terms of an increase in waste loading and process flexibility. Two options for sodium incorporation, glass and the titanate phase freudenbergite, are considered.
Application of an On-line Corrosion Probe and a Reference Electrode for Copper Corrosion Studies in Repository Conditions
Authors: Betova Iva , Heinonen Jussi , Kinnunen Petri , Lilja Christina , Ruokola Esko , Saario Timo 
Published: April 2011

ABSTRACTTwo sensors, an on-line corrosion sensor based on the wire-resistance probe design and a reference electrode which are applicable in repository conditions are introduced. Both sensors have been tested in simulated repository conditions in bentonite saturated with highly saline groundwater at 80 °C temperature and 14 MPa pressure up to 150 h exposure. In addition, it has been demonstrated that after an initial transient period of ca. 5–8 h, Cu corrosion in highly saline groundwater filled with bentonite becomes undetectably low probably because of the anoxic conditions reached in the free groundwater. At the same time, the measured corrosion potential of Cu is still in the active corrosion region. Furthermore, redox potentials in the wetted bentonite remain significantly higher than in the free groundwater. This may mean that the decomposition of oxygen contained in the pores of the bentonite is a process occurring in a time scale larger than that of the present experiments.
Investigations of Resistance Variations in Electrically Heated Canisters for Deep Repository
Authors: Zhu Baohua , Hermansson Hans-Peter , Sjöblom Rolf , Ramqvist Gunnar 
Published: April 2011

ABSTRACTAt the end of 2001, measurements indicated that the resistance between the conductors had fallen in SKB's (Svensk Kärnbränslehantering AB) electrically heated test canisters. Electrochemical impedance spectroscopy (EIS) was employed together with chemical analysis of gas compositions and corrosion products to investigate the causes of the resistance decrease inside the canister. The measured system is complicated and the evaluation not straightforward. However, it seems that the plug connecting the external electrical power supply to the heaters in the canister is a critical component and that a moisture film around the electrical contacts of the plug may explain the resistance decrease. It is suggested to continue to monitor the EIS spectra with time to gain more information about the cause of the resistance drop.
Analysis of Uranium Diffusion Coefficients in Compacted FEBEX Bentonite
Authors: García-Gutiérrez M. , Cormenzana J. L. , Missana T. , Mingarro M. , Alonso U. 
Published: April 2011

ABSTRACTIn the Spanish concept of a high level radioactive waste (HLRW) repository, the canister with the spent fuel would be surrounded by a layer of FEBEX bentonite (Ca-Mg smectite clay) compacted to a dry density of 1.65 g/cm3. Since the permeability of the compacted bentonite is very low, the main mechanism for radionuclide transport in the clay barrier is expected to be diffusion, retarded by the sorption on the solid. Since the mayor component of the radioactive waste is uranium it is very important to study its diffusion behaviour in the compacted clay.Generally, effective (De) and apparent (Da) diffusion coefficients are obtained from "through-diffusion" and "in-diffusion" experiments, respectively. The obtention of both parameters in the same sample is a very interesting issue because the former includes the information on the porous medium structure (connectivity, constrictivity, tortuosity) and the latter takes into account the sorption on the solid phase. In this work, through-diffusion experiments were carried out for studying uranium diffusion and both effective and apparent diffusion coefficients were estimated, from the same experiment, by using different theoretical approaches.
Colloid Transport of Radionuclides: Yucca Mountain Performance Assessment
Authors: Traexler Kathy A. , Utsunomiy Satoshi , Kersting Annie B. , Ewing Rodney C. 
Published: April 2011

ABSTRACTColloids have the potential to enhance transport of contaminants in the subsurface. Kersting et. al.,[1] have shown that plutonium, as well as europium, cobalt and cesium, were associated with groundwater colloids at the Nevada Test Site.240Pu/239Pu isotopic evidence confirmed that the plutonium was from the Benham nuclear test located 1.3 km away. This observation has lead to an increased concern that colloids may be potential vectors for radionuclide transport from an underground geologic repository [1].The Anaylsis/Model Reports (AMRs) describe the characteristics of colloids for sparingly soluble radionuclides. The types of colloids formed, stability of the colloids as a function of pH and ionic strength, and the attachment of radionuclides to the colloids are modeled by the AMRs. The AMRs attempt to present bounding and conservative estimates for key parameters; however, waste form corrosion data, natural system studies, and experimental data do not always support the assumptions made in the AMRs. Most specifically, all colloids at Yucca Mountain, whether generated by the dissolution of waste glass or spent nuclear fuel or occurring naturally in groundwater, are assumed to be either smectite or iron-oxy-hydroxides. Data from waste form corrosion experiments do not support this assumption: numerous other phases have been identified including weeksite, clay particles with brockite inclusions, schoepite, soddyite, uranophane, boltwoodite, calcite, dolomite, Na-silicates, Al-oxides, absolone, birnessite, analcime, hydrated silicates, and apatite. Furthermore, the response of many of these phases to changes in pH or ionic strength is not known. If fundamental data for these phases, such as the point of zero charge (PZC), is different than that of either smectite or iron oxy-hydroxides, the TSPA may not accurately predict colloid transport of radionuclides.We have analyzed colloid samples from groundwater at the Nevada Test Site using high-angle annular dark field scanning transmission electron microscopy (HAADF-STEM) and energy dispersive spectroscopic (EDS) elemental mapping, and found that light rare-earth elements (LREE) and Th are associated with monazite. Cesium and uranium are associated with an unidentified phase that is rich in Si and Fe. In addition, Co-60, a fissiogenic element, is associated with a complex metal colloid that includes Fe, Ni, Mo, and Cr. None of these phases are accounted for in the AMRs and their response to changing geochemical conditions is unknown. In addition, the PZC of several Mn-oxide phases was determined and was found to extend beyond the range of PZCs accounted for in the AMRs by smectite and iron oxy-hydroxides. Pu has been shown to preferentially adsorb onto Mn-oxides in the presence of Fe-oxides [2, 3], and the AMRs may not accurately predict Mn-oxide colloid stability and subsequent transport of radionuclides of interest.
The Compilation of Geochemical Data Bases for Performance Assessment of a Planned Repository in the Opalinus Clay in Northern Switzerland
Authors: Schwyn Bernhard , Wersin Paul 
Published: April 2011

ABSTRACTChemical retention of radionuclides in the near field and in the host rock is an important safety pillar within the Swiss concept for a radioactive waste repository. Geochemical databases for solubility limits in cement and bentonite porewater and sorption / diffusion in cement, compacted bentonite and Opalinus Clay were compiled for use in safety assessment calculations. The databases are presented for selected safety-relevant radioelements. In contrast to earlier safety assessment studies Kdvalues were not truncated at 5 m3kg−1and values well above 10 m3kg−1(e.g. for actinides) are reported.
Dissolution of UO2 by One- and Two-Electron Oxidants
Authors: Jonsson Mats , Ekeroth Ella , Roth Olivia 
Published: April 2011

ABSTRACTIn this work, the efficiency of one- and two-electron oxidants in oxidative dissolution of UO2 has been investigated. This was accomplished by measuring the U(VI)-concentration in solution after exposing UO2-powder to controlled amounts of oxidants in aqueous solution. The oxidants used in this study are H2O2, IrCl62−, CO3• and OH•. H2O2 acts as a two-electron oxidant while the remaining three oxidants are one-electron oxidants. CO3 and OH• were generated using γ-radiolysis. The results clearly show that the dissolution yields for one-electron oxidants (per electron pair) are lower than the yields for two-electron oxidants. Furthermore, the yields for one-electron oxidants increase with increasing amount of oxidant (especially at low amounts of oxidant). The rationale for this is that U(VI) is the main soluble species which is formed directly upon two-electron oxidation. For one-electron oxidants the primary oxidation product is U(V) which can form U(VI) upon reaction with a second oxidant. The probability for a second oxidation is however low at low concentrations of oxidant.
Solute Transport in Fractured Rock. Testing a New and Simple Aapproach
Authors: Moreno Luis , Crawford James , Neretnieks Ivars 
Published: April 2011

ABSTRACTA new and simple approach for modelling solute transport in fractured rock is presented, based on our previously used Channel Network Model (CNM). In our underlying concept, solute transport in fractured rocks takes place through undulating flat channels in the rock fractures. The channels form a 3-dimensional network. For non-interacting solutes the volume of the channels determines the residence time of a stream of water. For sorbing radionuclides the residence time is mainly determined by the ratio between the Flow Wetted Surface (FWS) and the flow rate in the channel (Q), in addition to the parameters that determine the interaction between the rock and the radionuclides. The main question explored in this paper is whether it is necessary to solve the flow problem for each studied case. From previous investigations, we have found that the flow rates in the channels where the solutes travel are closely related to the transmissivities of the channels. Simulations are presented in which streams of water are allowed to randomly select channels and trace out the paths where the path volume and its FWS can be assessed. The results obtained in this manner for the RTD (Residence Time Distribution) show rather good agreement with those obtained by solving the full flow problem and tracing particles in the network.
Microbial Sulphide Production in Compacted Bentonite at the Commencement of Long-Term Disposal of High-Level Radioactive Waste
Authors: Masurat Peter , Pedersen Karsten 
Published: April 2011

ABSTRACTThe use of nuclear reactors produces electrical power but also high-level radioactive waste (HLW). In Sweden it has been decided that the HLW shall be disposed of in a deep geological repository 500 meters underground. The HLW will be encapsulated in copper canisters, surrounded by bentonite and then the access tunnel will be backfilled with a bentonite and crushed rock mixture.We have investigated activity of sulphate reducing bacteria (SRB) in compacted bentonite with densities of 1.5, 1.8 and 2.0 g·cm−3 using stainless steel oedometers with 35SO42- as the main sulphur source for the SRB. The investigations were performed under in situ conditions at a depth of 450 m at the Äspö Hard Rock Laboratory. Canister type copper plates were placed in the oedometers, with the top either in contact with the added groundwater or with 3–4 mm bentonite between the plate and the added groundwater. Radioactive hydrogen sulphide formed by the SRB reacted with the copper and formed radioactive copper sulphide, which was measured by electronic radiography using an Instant Image Micro autoradiography instrument (Packard). A similar set-up with filter-sterilized groundwater (0.2 μm) was used as control. A second experiment was set up as the first experiment but using only filtered groundwater and adding heat treatment of the bentonite in the control. Here, we show that SRB were active and produced hydrogen sulphide during the initial phase of bentonite swelling. The activity of the SRB was inversely correlated with the final density of the bentonite as the highest density had the lowest overall SRB activity. We also found that SRB were present in a dormant state in the commercial MX-80 bentonite. By addition of water, these dormant SRB became active and started to produce hydrogen sulphide.
Mobilisation of Radionuclides by Ligands Produced by Bacteria from the Deep Subsurface
Authors: Arlinger Johanna , Oskarsson Anna , Albinsson Yngve , Andlid Thomas , Pedersen Karsten 
Published: April 2011

ABSTRACTMicrobial processes can influence retention of radionuclides directly or indirectly in several different ways. Many microorganisms produce various kinds of ligands or chelating compounds to increase the bioavailability of essential elements needed for metabolism. These ligands are not always highly specific, and several of them will also mobilise other elements such as heavy metals and radionuclides. Three bacterial species (Shewanella putrefaciens, Pseudomonas fluorescensandPseudomonas stutzerii), isolated from the deep subsurface, and four radionuclides,59Fe(III),147Pm(III),234Th(IV) and241Am(III), were selected for this study. The microbes were cultured in the laboratory, separated from their exudates by centrifugation, and the supernatants were collected. The supernatants were mixed with radionuclide and solid phase (TiO2or SiO2). The pH ranged from 7.5–9.0. All three bacterial species produced ligands that were able to complex up to 90% of the radionuclides in competition with the solid phases. High performance liquid chromatography analysis detected four Fe-complexing substances in the supernatant from P. fluorescens and two peaks and one peak, respectively, fromP. stutzeriiandS. putrefaciens. All substances eluted from the column varied in retention times, indicating that the microbes studied produced several metabolites that have different chelating abilities.
Modelling Biochemical Processes in Rocks: Analysis and exploratory simulations of competition of different processes important for ferrous mineral oxidation and oxygen depletion
Authors: Sidborn Magnus , Neretnieks Ivars 
Published: April 2011

ABSTRACTThere are several oxygen consuming processes occurring in deep subsurface fractured rocks. The importance of each process depends on the prevailing conditions and what function it has in the overall oxygen scavenging process. In the present work, some of these processes are studied. The aim is to build a frame of maximum rates for each parallel process. Therefore, several rate-limiting factors are not included. Rate expressions were obtained from the literature and compared for different cases to address under which conditions each process is important. Some of the processes may be considered parallel and independent while others occur in series. The main reactions accounted for are abiotic and biotic pyrite and ferrous iron oxidation and the non-oxidative dissolution of matrix ferrous minerals. In addition, transport processes of oxygen and other substrates within the rock matrix are considered. The main conclusions are that initially, when the diffusion resistance in the matrix is nonexistent or small, reaction kinetics are important. However, in a longer time perspective, diffusion processes limit the oxygen scavenging process.
Palaeohydrogeological Evidences from Fracture Filling Minerals - Results from the Äspö/Laxemar Area
Authors: Tullborg Eva-Lena 
Published: April 2011

ABSTRACTTwo different EU projects: the EQUIP project (Evidences from Quaternary Infills from Palaeohydrogeology) running from 1997 to 2000 and the ongoing PADAMOT-project (Palaeohydrogeological Data Analysis and Model Testing) have addressed the possibility of using fracture minerals as recorders of past hydrochemical and hydrogeological environments. The Swedish contribution in these two projects has concentrated on studies of fracture filling calcites from the Äspö/Laxemar area, southeast Sweden.The analyses applied in the two projects comprise stable isotope ratios of carbon and oxygen and strontium together with trace element contents and textural studies. The results obtained so far (mainly from the EQUIP project) show that several generations of calcite can be identified, chemical zoning is common, and the influence on calcite precipitation of fresh and marine water decreases with depth. It can be concluded that fine scale zoning, possible dissolution/redistribution of calcite, and the disturbances caused by drilling (where loose material which may contain young calcite precipitates were lost), introduce uncertainties in the recognition of different calcite generations. However, despite these problems it is indicated that calcite fracture fillings in Precambrian bedrock environments can add information e.g. concerning changes in groundwater chemistry and redox conditions in the past. The possibilities and problems with palaeohydrogeological interpretations are discussed based on the available data.
Project Opalinus Clay – Geoscientific Basis for the Demonstration of Feasibility of Disposal (Entsorgungsnachweis) for SF, Vitrified HLW and Long-Lived ILW in Switzerland
Authors: Gautschi A. , Lambert A. , Zuidema P. 
Published: April 2011

ABSTRACTNagra - the Swiss National Cooperative for the Disposal of Radioactive Waste - has completed a study to determine the suitability of Opalinus Clay as a host rock for a SF/HLW/ILW repository in a potential siting area (reference repository site) in the Zürcher Weinland in northeastern Switzerland. Geoscientific information has been used to a wide extent for the demonstration of siting and engineering feasibility, and for the demonstration of long-term safety. It is shown that the selected area in the Zürcher Weinland fulfils the fundamental requirements placed on a siting area for a deep geological repository and that, in terms of the Opalinus Clay host rock option, the geological environment is advantageous.
Project Opalinus Clay (Entsorgungsnachweis) - Illustrating the Safety and Robustness of the Proposed Disposal System for SF, HLW and Long-lived ILW
Authors: Johnson L. H. , Schneider J. W. , Zuidema Piet , Gribi P. , Mayer G. , Smith P. A. 
Published: April 2011

ABSTRACTNagra (the Swiss National Cooperative for the Disposal of Radioactive Waste) has completed a study to determine the suitability of Opalinus Clay as a host rock for a repository for spent fuel (SF), high-level waste from reprocessing (HLW) and long-livedintermediate-level waste (ILW). The proposed siting area is in the Zürcher Weinland region of Northern Switzerland. A repository at this site is shown to provide sufficient safety for a spectrum of assessment cases that is broad enough to cover all reasonable possibilities for the evolution of the system. Furthermore, the system is robust; i.e. remaining uncertainties do not put safety in question.
Scientific Arguments for New – Deterministic Approach to HLLLW Management
Authors: Ninkovic Marko M. , Raicevic Jagos J. 
Published: April 2011

ABSTRACTOne of the greatest challenges in the use of nuclear energy is the high radioactive long-lived waste which is generated during production. It must be dealt with safely and effectively. While technical solutions exist, including deep geological repositories, progress in the disposal of radioactive waste has been influenced, and in many cases delayed, by public perceptions about the safety of the technology. One of the primary reasons for this is the long life of many of radionuclides, actinides and fission products, with half-lives on the order of a hundred thousand to a millions years. Problems of perceptions could be reduced significantly, according to our and many others author's opinion, if there were a way to burn or destroy the most toxic long-lived radioactive wastes. As there are no industrial methods for waste destroying today, in this paper it was suggested a new hybrid, deterministic approach: instead of final waste disposal, long-termed but yet temporal storage only, striving towards final destruction once the appropriate conditions are maintained. This new or modified old approach could affect current HLLLW management and related activities in: changes of processing technology; prolonging the time period of waste storage at temporal depositories; increasing the investment into research regarding the methods and technologies for destructions of these materials, and slowing down the investments into the very expensive final disposal repositories. It is authors' opinion that such deterministic, conceptual approach would contribute the reviving interest in nuclear energy, all over the world and especially in small and developing countries.