bluuebunny/crossref_metadata_2025 huggingface dataset:
Thermodynamic Driving Forces for Martensitic Phase Transformations in Shape-Memory Alloys
Authors: Jannetti C. , Bassani J.L. , Turteltaub S.
Published: April 2011

A macroscopic constitutive model for the martensitic phase transformations in single-crystal shape-memory alloys (SMAs) is developed in the framework of irreversible thermodynamics with internal variables. Central to the model is the notion that the rate of progression of structural rearrangements on the microscale depends on the stress state through the thermodynamic forces conjugate to the rearrangements. These thermodynamic forces, i.e. the driving forces for the phase transitions, are shown to have an important contribution that arises from changes in the effective elastic response of the SMA, which in turn depend upon the state of transformation. This contribution is shown to have a significant effect on the overall macroscopic stress-strain response.
Fluorination of Cup-stacked Carbon Nanotubes, Structures and Properties
Authors: Touhara Hidekazu , Yonemoto Akiko , Yamamoto Kazunao , Komiyama Shingo , Kawasaki Shinji , Okino Fujio , Yanagisawa Takashi , Endo Morinobu
Published: April 2011

Cup-stacked carbon nanotubes (Cup-CNTs) was fluorinated in a temperature range RT-500• •by 0.5–1 atm elemental fluorine. The F/C atomic ratio (CF0.4-CF1.2) and the color are strongly dependent on the fluorination conditions. The color of fluorinated Cup-CNTs (F-Cup-CNTs) varies from black, through gray and yellow to white. The form and morphology of the pristine tubes were well preserved after fluorination, and the fluorination results in the functionalization and modification of pristine Cup-CNTs with respect to electrochemical properties. The F-Cup-CNTs as cathodes for primary Li cells discharge satisfactorily with 100% cathode utility.
Carbon Nanotube-Induced Planarization of Conjugated Polymers in Solution
Authors: Chen Jian , Ramasubramaniam Rajagopal , Liu Haiying
Published: April 2011

The understanding of the conformational interaction between conjugated polymers and carbon nanotubes in solution is essential to develop the applications of carbon nanotubes, particularly conjugated polymer-carbon nanotube hybrid materials. The visible absorption spectroscopic study shows that curved carbon nanotube surfaces can induce the planarization of individual conjugated polymers such as poly(p-phenyleneethynylene)s and poly(3-alkylthiophene)s in solution. The impact of nanotube surface quality on the interaction between carbon nanotubes and conjugated polymers is investigated.
Polymer Functionalized Carbon nanotubes for sensor application
Authors: Vedala Narasimha Harindra , Choi Young C. , Zhou X. Y. , Kim Gene , Choi WonBong
Published: April 2011

Surface modification of carbon nanotubes with polyvinyl alcohol (PVOH) showed detection for humidity variation implying a possible application as a nanoscale humidity sensor. Wettability studies on single-wall, Y junction single wall and multiwall carbon nanotubes revealed that these nanotubes tend to become highly hydrophilic surfaces by this functionalisation. From the raman analysis it was determined that the majority of the nanotubes in our Y-junction single wall nanotubes were semiconducting in nature. The conductivity studies revealed that the Y junction nanotubes with PVOH functionalisation show large change in conductivity for varying relative humidity (RH). We propose a possible charge transport mechanism in these functionalized nanotubes.
An Experimental Estimate of the Free Energy of Formation of Single Walled Carbon Nanotubes
Authors: Wagg L. M. , Hornyak G. L. , Grigorian L. , Dillon A. C. , Jones K. M. , Blackburn J. , Parilla P. A. , Heben M. J.
Published: April 2011

Single walled carbon nanotubes (SWNT) were synthesized by methane CVD on a supported mixed transition metal (Fe/Mo) catalyst. Gas feed composition and reaction temperature were varied to identify the threshold conditions for the growth of SWNT. These reaction conditions closely approximate pseudo-equilibrium conditions with some active reaction intermediate (likely chemisorbed carbon atoms) that proceeds to nucleate and grow SWNT. This value also serves as an estimated upper limit of the free energy of formation ΔG*(T)SWNT since the active intermediate proceeds to form SWNT through a process that is thought to be essentially irreversible. The difference relative to graphite is in good agreement with literature values predicted from simulations for SWNT nuclei containing approximately 80 atoms, while considerably larger than that predicted for bulk 5, 5 SWNT. Our estimate over the range 700 to 1000 °C of 16.1 to 13.9 kJ/mol is considerably greater than the free energy of formation for diamond (between 5.8 and 6.9 kJ/mol from 700 to 925 °C).
A Dual-RF-Plasma Approach for Controlling the Graphitic Order and Diameters of Vertically-Aligned Multiwall Carbon Nanotubes
Authors: Menda Jitendra , Vanga Lakshman Kumar , Ulmen Benjamin , Yap Yoke Khin , Pan Zhengwei , Ivanov Ilia N. , Puretzky Alex A. , Geohegan David B.
Published: April 2011

Plasma enhanced chemical vapor deposition (PECVD) is a unique technique for growing vertically-aligned multiwall carbon nanotubes (VA-MWNTs) at controllable tube densities. This technique is of considerable importance for low temperature growth of VA-MWNTs at desired locations. However, the graphitic order of these MWNTs is inferior to those grown by laser ablation, arc discharge, and thermal CVD techniques. Previously, these VA-MWNTs were grown by a one-plasma approach (DC, microwave etc), either for gas decomposition or substrate biasing. Here, we describe a dual-RF plasma enhanced CVD (dual-RF-PECVD) technique that offers unique capability for controlling the graphitic order and diameters of VA-MWNTs.
Homogeneous Dispersion of the Surface Modified MWNTs in the PU Matrix and Electrical Conductivity of the MWNTs/PU Composites
Authors: Kim Yoon Jin , Jang Yong Gyun , Choi Jun Whan , Yoon Ho Gyu
Published: April 2011

Dispersion characteristics of the surface modified MWNTs (Miltiwalled nanotubes) in the PU (polyurethane) matrix and electrical conductivity of the MWNTs/PU composites are investigated using SEM and DEA (Dielectric analyzer) with respect to the chemical treatment of MWNTs, the kind of surfactants and their content. Several chemical treatments of the MWNTs' surfaces were performed with the acids type, acidic concentration, treatment temperature, and oxidation time. All the surface of modified MWNTs are negatively charged and functionalized with carboxylic group; however, the external walls of some MWNTs were severely damaged so that they were frequently thinned and partially cracked. Compared to those of the composites without the addition of surfactant, the surfactant embedded into composites show much better dispersion of the MWNTs and higher electrical conductivity, these results are in good agreement with the two step adsorption model of cationic surfactants proposed by Y. Gao. Both the optimized MWNTs and cationic surfactant filled PU composites show very low percolation threshold, pc = 0.0089±0.007 vol. %, and relatively higher conductivity after percolation than other carbon nanotubes composite systems reported elsewhere.
Carbon nanotube growth on metal-catalyzed substrates in a laser oven apparatus
Authors: Suda Y. , Tanaka A. , Okita A. , Bratescu M. A. , Sakai Y. , Nakamura J. , Xiong G. Y. , Ren Z. F.
Published: April 2011

Carbon nanotubes (CNTs) were grown on Ni- and Fe-coated SiO2/Si substrates in a laser oven apparatus. The grown CNTs were analyzed by scanning electron microscopy. It is speculated that the CNTs grow out from the metal nanoparticle after laser-ablated carbon clusters have been dissolved in it. In a range of oven temperatures between 800 and 1100°C, growth of CNTs was achieved at a temperature ≥ 1000°C. The thickness of the Ni film controlled the CNTs diameter.
Characterization of Single-walled Carbon Nanotube Fibers and Correlation with Stretch Alignment
Authors: Chen Michelle , Guthy Csaba , Vavro Juraj , Fischer John E. , Badaire Stéphane , Zakri Cécile , Poulin Philippe , Pichot Vincent , Launois Pascale
Published: April 2011

Structural, electrical and thermal methods are applied to characterize single-walled carbon nanotube (SWNT) fibers with post-extrusion stretching as the independent variable. HiPco SWNTs are dispersed in water using sodium dodecyl sulfate (SDS), and then co-extruded with polyvinyl alcohol (PVA)/water through a long syringe into a rotating water/PVA coagulation bath. Partial axial alignment is thereby achieved, and further enhanced by applying tension to the flexible green fibers in the coagulation bath. Our findings include: (1) X-ray diffraction shows that the full width at half maximum (FWHM) of the Bragg peaks decreases from 55 (as-extruded) to less than 30 degrees by 80% elongation. That is, SWNT alignment increases linearly with stretch (up to 80%). (2) In resistivity at room temperature vs. stretch ratio, result shows an initial rapid decrease followed by saturation; essentially all the improvement in electronic transport is obtained once alignment reached 40° FWHM. (3) Annealing in hydrogen at 1000°C is performed to drive out PVA, to improve inter-tube and inter-bundle contacts, and to heal damage on the tube walls. Such annealing is found to increase conductivity by at least 4 orders of magnitude. (4) Below 25 K, resistivity vs. temperature of the annealed fiber is well-represented by Coulomb gap variable range hopping (CG-VRH). It is rationalized that the Coulomb interactions in disordered systems open a gap at the Fermi energy. Above 25 K, the thermal energy is greater than the Coulomb gap, so thermal activation is more probable than correlated electron hops. (5) Finally, a measurable thermal conductivity is observed as stretch alignment increases.
Mechanical Properties of CVD Grown Multi-walled Carbon Nanotubes (MWNTs)
Authors: Gaillard J. , Skove M. , Rao A. M.
Published: April 2011

We have measured the bending modulus of several different CVD (chemical vapor deposition) grown MWNTs using a vibrating reed technique. The MWNTs are produced from a thermal decomposition of three different precursors: (i) xylene/ferrocene, (ii) xylene/ferrocene/melamine (nitrogen-doped), and (iii) trimethylamine (TMA)/ferrocene. The first two precursors are used to compare the mechanical properties of typical CVD-grown to bamboo-type MWNTs. Nanotubes prepared using the third precursor shows relatively fewer walls (∼ 4–20 compared to ∼15–40)) and defects compared to those prepared from the xylene/ferrocene mixture. The resonant frequencies of these nanotubes were measured optically in air using a dark field light microscope. The diameters of these nanotubes range from 50 – 160 nm as determined from TEM and the average length is ∼ 10 microns. For the xylene/ferrocene and trimethylamine/ferrocene tubes, the average bending modulus is estimated to be 0.1 and 0.3 TPa, respectively. However, the bending modulus for the nitrogen-doped tubes is ∼9 GPa which is significantly lower compared to regular MWNTs implying that the bending modulus decreases with an increase in wall defects. These findings are in reasonable agreement with those reported previously by Wang et al.
Carbon nanotube surface chemistry and its effects on interfacial nanomechanics
Authors: Barber Asa H. , Cohen Sidney R. , Daniel H.
Published: April 2011

Individual multi-walled carbon nanotube pullout experiments were used to measure the adhesion strength at a nanotube-epoxy polymer interface. The interfacial strength was found, as expected, to increase when the nanotubes were chemically treated to induce strong bonding with the polymer matrix. At long nanotube embedment lengths within the polymer, the nanotubes were seen to fracture in preference to failure at their interface with the polymer. Interfacial mechanics models are applied to the data to describe interfacial adhesion at the nano-level.
Kohn Anomalies in Graphite and Nanotubes
Authors: Piscanec S. , Lazzeri M. , Ferrari A. C. , Mauri F. , Robertson J.
Published: April 2011

Atomic vibrations are partially screened by electrons. In a metal this screening can change rapidly for vibrations associated to certain points of the Brillouin zone, entirely determined by the shape of the Fermi surface. The consequent anomalous behaviour of the phonon dispersion is called Kohn anomaly. Graphite is a semimetal. Nanotubes can be metals or semiconductors. We demonstrate that two Kohn anomalies are present in the phonon dispersion of graphite and that their slope is proportional to the square of the electron-phonon coupling. Metallic nanotubes have much stronger anomalies than graphite, due to their reduced dimensionality. Semiconducting nanotubes have no Kohn anomalies.
Beyond-Mean-Field Treatments of Island Formation during Submonolayer Deposition: Island Size Distributions for Large Critical Sizes
Authors: Li Maozhi , Bartelt Maria C. , Evans J. W.
Published: April 2011

Kinetic Monte Carlo (KMC) simulation of atomistic models reveals the failure of mean-field treatments of the island size distribution (ISD) for islands formed by homogeneous nucleation during submonolayer deposition on perfect surfaces. KMC also facilitates analysis of scaling properties of the ISD, although here some misperceptions persist which we attempt to clarify. However, KMC becomes inefficient for highly reversible island formation (e.g., for large values of a critical size, i, above which islands are stable) due to the high density of diffusing adatoms on the surface. This reduced efficiency is quantified here with results for CPU time versus i. This feature has motivated development of alternative beyond-mean-field coarse-grained approaches which should be more efficient for large i. We provide results for the ISD for a range of i = 1, 2, 3, and 6 using one such approach, a stochastic geometry-based simulation (GBS) strategy.
Diffusion in Potential Fields: Time-Dependent Capture on Radial and Rectangular Substrates
Authors: Venables J. A. , Yang P.
Published: April 2011

In models of nucleation and growth on surfaces, it is usually assumed that the energy surface of the substrate is flat, that diffusion is isotropic, and that capture numbers can be calculated in the diffusion-controlled limit. We lift these restrictions analytically, and introduce a hybrid discrete FFT method of solving for the 2D time-dependent diffusion field of adparticles on general non-uniform substrates. The method, with periodic boundary conditions, is appropriate, for example, following nucleation on a regular (rectangular) array of defects. The programs, which have been realized in Matlab®6.5, are instructive for visualizing potential and diffusion fields, and for producing illustrative movies of crystal growth under various conditions. Here we demonstrate the time-dependence of capture numbers in the initial stages of annealing at high adparticle concentration in the presence of repulsive adparticle-cluster interactions; however it is clear that the method works in general for deposition, growth and annealing at all times.
Employing Microfluidics in the Demonstration of Cell Encapsulation
Authors: Ravgiala Rebekah R.
Published: April 2011

Many states, including Massachusetts, have invested valuable time and energy to develop science education standards that incorporate concepts from the field of engineering. Most engineering standards are implemented in a more intensive manner at the high school level in order to encourage secondary science students to participate in the research and design process. Similarly, the Research Experience for Teachers program offered through Harvard University engages secondary science teachers in the engineering process by providing participants with real research experiences and opportunities to develop tools that can be used to demonstrate that research in a secondary science classroom.
Evaluating R&D Progress in the Context of the Safety Case
Authors: Johnson L.H. , Zuidema P.
Published: April 2011

The strategic approach and structuring of safety cases for nuclear waste repositories have seen marked improvements over the past ten to fifteen years as a result of the collective experience of national agencies in developing their safety cases and their efforts, under the auspices of the OECD Nuclear Energy Agency (NEA), to develop a systematic and thorough approach, as well as through systematic reviews by regulators and expert teams. A safety case can be developed at any stage in a program and it provides a remarkably effective method for reassessing design and siting requirements and refocusing R&D needs. The process of developing a safety case for a repository is the critical test of the quality of understanding that exists for a given repository concept, because it forces an integration of the siting and design strategies and the assessment approach. This integration demands that one evaluates all relevant R&D results available and addresses the questions i) is the system good? and ii) is the understanding sufficient, taking the stage of the programme into account?

Here we address some questions on the relationship between R&D work and the development of a safety case, including:

1) Is the R&D performed in Europe evolving in concert with safety case development for European repositories?

2) How much generic work is still needed when robust site-specific repository concepts obviously lead to much more focused R&D?

3) How good is good enough and how do we measure this at each successive stage of repository development?

There are no easy answers to such questions, but they must increasingly be addressed as national programs progress.
Determining the Transport Properties of Rock Specimens Using an Improved Laboratory Through-Diffusion Technique
Authors: Zhang M. , Takeda M. , Nakajima H.
Published: April 2011

The safe disposal of radioactive nuclear wastes using multi-barrier systems requires a good understanding of their transport properties in geological materials. When groundwater flow is very slow, the most important mechanisms of transport and retardation are diffusion through and sorption onto geological materials, and an evaluation of relevant parameters, particularly the effective diffusion coefficient and rock capacity factor (or sorption coefficient), is of fundamental importance to any safety assessment. Although laboratory diffusion tests can be used to determine these two parameters, conventional through-diffusion testing has some limitations, such as the need for a relatively long test time, cumbersome test procedures and the possibility of errors due to differences between analytical assumptions and actual test conditions. In this paper, we offer a rigorous solution to the through-diffusion test. Boundary conditions are improved by taking into account concentration changes in both the source and the measurement cells. A companion approach for back-calculating the effective diffusion coefficient and rock capacity factor is also proposed. The effectiveness and advantages of this improved technique are demonstrated using experimental data derived from a sedimentary rock sample taken from a research site in Japan.
Coupling of Chemical Processes in the Near Field
Authors: Grambow B. , Giffaut E.
Published: April 2011

Coupled modelling has been performed using geochemical/transport codes and radiolysis models to describe the chemical evolution of the waste forms “high-level waste glass” and “spent nuclear fuel” together with its waste package and engineered barrier surroundings. Near field processes considered include container corrosion, hydrogen generation, mass transfer for radionuclides and other waste matrix components in corrosion products and buffer materials, geochemistry of near field solution chemistry, sorption of radionuclides on surface sites in the nano-sized pore space of near field materials and the radiolytic decomposition of pore water. The rate limiting steps in waste form dissolution and secondary phase formation mechanism and the associated radionuclide mobilisation chemistry (solubility, solid solution formation, speciation, redox stability) are strongly influenced by the near field constraints.
Determining Sorption Coefficients in Intact Rock Using an Electrical Potential Gradient as a Driving Force for Migration
Authors: André Magnus , Malmström Maria E. , Neretnieks Ivars
Published: April 2011

The transport of radionuclides in indigenous rock is greatly affected by the sorption of cations in the porous rock matrix. For the determination of sorption coefficients, batch experiments have traditionally been used. For these experiments, the rock sample is crushed into fine particles to reduce the experimental time. However, this procedure increases the specific surface area of the sample and the new surfaces created could have different sorption qualities than the naturally occurring surfaces, which may impair the results of sorption coefficient determinations. A new method for determining sorption coefficients in intact rock is being developed, using electromigration as a means to speed up the transport process, thereby allowing for faster equilibration between the rock sample and the tracer solution. Here, we report results from preliminary experiments, using cesium as a sorbing tracer, showing a consistent difference between sorption coefficients obtained using electromigration methods on intact rock samples and traditional batch experiments on crushed samples.
The Role of the Engineered Barrier System in Safety Cases for Geological Radioactive Waste Repositories: An NEA Initiative in Co-operation with the EC
Authors: Bennett David G. , Hooper Alan J. , Voinis Sylvie , Umeki Hiroyuki
Published: April 2011

Radioactive waste derives from all phases of the nuclear fuel cycle and from the use of radioactive materials in industrial, medical, military and research applications; all such wastes must be managed safely. The most hazardous and long-lived wastes, such as spent nuclear fuel and waste from nuclear fuel reprocessing, must be contained and isolated from humans and the environment for many thousands of years. Many Nuclear Energy Agency (NEA) member countries are, therefore, researching plans for the management of long-lived radioactive waste in engineered facilities, or repositories, located deep underground in suitable geological formations.
Further Steps Towards Licensing: Underground Characterisation Started for the Spent Fuel Repository in Finland
Authors: Vira Juhani
Published: April 2011

Pursuant to the Decision-in-Principle of 2001 the Finnish programme for geologic disposal of spent fuel has now moved to the phase of underground characterisation of the repository site. The main objective of this programme phase is to confirm – or refute – the suitability of the Olkiluoto site by investigations conducted underground at the actual depth of the repository. The construction work of the access tunnel to the rock characterisation facility (ONKALO) started in the late summer of 2004. The site research and investigations work aims at the maturity needed for submission of the application for construction license of the actual repository in 2012. This requires, however, that also the technology has reached the maturity needed. The design and technical plans form the necessary platform for the development of the safety case for spent fuel disposal. A plan, “road map”, has been produced for the portfolio of reports that should demonstrate the safety of disposal as required by the criteria set by the government and further detailed by the safety authority, STUK.
Role of ion exchange in the corrosion of nuclear waste glasses
Authors: Ojovan M.I. , Lee W.E. , Hand R.J.
Published: April 2011

The ion exchange phase of corrosion of nuclear waste glasses was modelled using Doremus' theory of interdiffusion and numerically analysed for British Magnox waste and Russian K-26 glasses. It is shown that even in non-silica -saturated conditions the ion exchange phase plays a significant role in the overall radionuclide release inventory particularly for short-lived radionuclides.
Migration Behavior of Cesium in Compacted Bentonite Under Reducing Conditions Using Electromigration
Authors: Idemitsu Kazuya , Yamamoto Masaru , Yamasaki Yosuke , Inagaki Yaohiro , Arima Tatsumi
Published: April 2011

Carbon steel overpack will be corroded by consuming oxygen introduced by repository construction after closure of repository and then will keep the reducing environment in the vicinity of repository. The migration of iron corrosion products through the buffer material will affect migration of redox-sensitive radionuclides. Therefore the authors have carried out electromigration experiments with source ofiron ions supplied by anode corrosion of iron coupons in compacted bentonite. However, their migration behavior was complex and difficult to explain. Thus, authors tried to use cesium, whose migration behavior is well known, inthis experimental configuration to obtain knowledge of the migration behavior of cations. The concentrationsof iron and sodium showed nearly complementary distributions. It is expected that iron ion could migrate as ferrous ion through the interlayer of montmorillonite replacing exchangeable sodium ions in the interlayer. On the other hand, cesium profiles seemed to be controlled by ordinary diffusion. Drift of the cesium profile by electric potential gradient could be observed clearly only after 240 h. Apparent dispersion coefficients of cesium were calculated from the profiles and were in reasonable agreement with literature values of apparent diffusion coefficients. Thus this experiment can provide a diffusion field for cations under a reducing condition with ferrous ions in water-saturated bentonite. The effect of electro-osmotic flow on ion migration was negligibly small in this experiment because electro-osmotic flow was compensated by hydraulic pressure caused by the water content gradient developed in the specimen within 24h.
Modeling Corrosion Processes for Alloy 22 Waste Packages
Authors: Dunn D.S. , Pensado O. , Pan Y.-M. , Yang L.T. , He X.
Published: April 2011

The proposed waste package design for the disposal of high-level radioactive waste at the potential repository at Yucca Mountain, Nevada, consists of an outer container made of Alloy 22, a corrosion resistant Ni-Cr-Mo-W alloy, surrounding an inner container made of Type 316 nuclear grade stainless steel. Models to assess the influence of waste package degradation modes on the overall system performanceconsider uniform and localized corrosion processes. Based on measurements of passive anodic current density, the uniform aqueous corrosion rate of Alloy 22 is estimated to be slow, and long waste package lifetimes are projected in the absence of conditions that promote accelerated degradation processes. The initiation of localized corrosion is possible in chloride-containing waters with low concentrations of inhibiting oxyanions such as nitrate. Although propagation rates for localized corrosion are typically orders of magnitude greater than the passive uniform corrosion rates, the maximum penetration depth of localized attack may be limited to depths significantly less than the container thickness as a result of stifling andarrest of localized corrosion.
A Model for Predicting Stress Corrosion Cracking of Copper Containers in A Deep Geologic Repository
Authors: Maak Peter , King Fraser
Published: April 2011

A model has been developed to predict the stress corrosion cracking behaviour (SCC) of used-fuel copper containers in a deep geologic repository. By comparison of the predicted evolution of the environment with criteria for the SCC of pure copper, it is concluded that copper containers in a deep geologic repository will not be susceptible to SCC. In particular, the requirement for the simultaneous presence of a thermodynamically stable Cu2O/CuO surface film and a significant concentration of SCC agents is not satisfied at any time during the 106 year simulation period.
Radiation stability of natural britholites
Authors: Yudintseva Tatiana S.
Published: April 2011

Britholite, Ca-REE silicate with apatite structure, is an actinide host phase occurred in vitreous borosilicate waste forms. Such glass-ceramics are considered as potential host phases for immobilization of actinide-containing high-level waste. Crystalline phases have to be radiation resistant for this application. Radiation stability of the britholites was mainly studied by either heavy ions irradiation or incorporation of Cm-244 or Pu-238 and 240. A wide range of critical doses (0.15 - 0.6 dpa at 25°C) and temperatures have been obtained depending on the compositions of the samples. Natural analogue study of the waste forms allows to predict the behavior of actinide host phases for long periods after disposal. Britholites with age from 320 to 2600 millions years, ThO2+UO2 content from 1.0 to 12 wt.%, and cumulative doses from 0.6×1019 to 7.7×1019 α-decays/g have been studied. The britholite becomes amorphous at a dose of 1 dpa (0.9×1019 α-decays/g) and higher. Critical doses for natural minerals are higher than those for synthetic samples, most likely due to re-crystallization during annealing.
Creep of the copper canister in the Swedish program
Authors: Bowyer William H
Published: April 2011

The Swedish programme for disposal of high level nuclear waste includes the development of a container which comprises a cast iron load bearing canister contained in a 50 mm thick copper corrosionshield.

The temperature of the outside of the canister is likely be up to 100°C, and repository processes may lead to long term loads of up to 50MPa. Creep of the copper is therefore an issue. SKB (The Swedish Nuclear Fuel and Waste Management Co.) have been conducted tests on three materials, OF copper containing 10ppm sulphur (OF1), OF copper containing 6ppm sulphur (OF2) and OF copper containing 6ppm sulphur and 50ppm phosphorus (OFP). In order to improve confidence in extrapolation of test results to practical temperatures and stresses, it is desirable to support the extrapolation procedures with a physical model.

Life predictions made using the Frost and Ashby model [5] together with a simplification of the Cocksand Ashby model [6] provide good agreement with published experimental data for OF2 and OFPmaterials. Extrapolation of this data using the model leads to life predictions of 12,000 years for the OF2material and 120,000 years for OFP material. The prediction for OFP depends on an assumption that an observed strengthening mechanism conferred by phosphorus at high stresses and temperatures, is equally as effective under repository conditions.

OF1 material fails after a relatively short life and by a different mechanism to OF2 and OFP. The changein mechanism may be explained, using the model [6], for cases where segregating species reduce surface energy of grain boundary voids. It is suggested that in this case the segregating species is sulphur.
Further Studies of the Anaerobic Corrosion of Steel in Bentonite
Authors: Smart Nick R. , Rance Andrew P. , Carlson Liisa , Werme Lars O.
Published: April 2011

In the horizontal emplacement concept (KBS-3H) for the disposal of radioactive waste, which is being developed in Sweden and Finland, copper canisters with cast iron inserts will be surrounded by bentonite buffer and mounted in perforated carbon steel support structures in boreholes within the bedrock. The groundwater will be reducing, leading to anaerobic corrosion of the ferrous material. It is important to understand both the effect of bentonite on the corrosion behaviour of the steel and the effect of the corrosion products on the performance of the bentonite. Previous work on the corrosion of steel in bentonite was extended to investigate a wider range of conditions, including the possible effects of alkaline plumes released from concrete support structures and the effect of chloride concentration and temperature on the corrosion rate of steel in bentonite. Corrosion rates were measured by collecting hydrogen produced by the anaerobic corrosion of iron. In addition, a range of analytical techniques was applied to study the composition and morphology of the corrosion products and the distribution and chemical state of the iron released into the bentonite. Comparison was also made between corrosion in compacted bentonite and artificial bentonite porewater. In the presence of bentonite, the corrosion product layer was relatively thin compared to fully aqueous conditions, probably because the ferrous ions released by corrosion exchanged with the bentonite interlayer or attached to the surface of the bentonite grains, rather than forming a separate iron oxide phase.
A Review of Corrosion Considerations of Container Materials Relevant to Underground Disposal of High-Level Radioactive Waste in Belgium
Authors: Kursten Bruno , Druyts Frank
Published: April 2011

The underground formation that is currently being considered in Belgium for the permanent disposal of high-level radioactive waste and spent fuel is a 30-million-year-old argillaceous sediment (Boom Clay layer). This layer is located in the northeast of Belgium and extending under the Mol-Dessel nuclear site at a depth between 180 and 280 meter.

Within the concept for geological disposal (multibarrier system), the metallic container is the primary engineered barrier. Its main goal is to contain the radioactive waste and to prevent the groundwater from coming into contact with the wasteform by acting as a tight barrier. The corrosion resistance of container materials is an important aspect in ensuring the tightness of the metallic container and therefore plays an important role in the safe disposal of HLW. The metallic container has to provide a high integrity, i.e. no through-the-wall corrosion should occur, at least for the duration of the thermal phase (500 years for vitrified HLW and 2000 years for spent fuel).

An extensive corrosion evaluation programme, sponsored by the national authorities and the European Commission, was started in Belgium in the mid 1980's. The main objective was to evaluate the long-term corrosion performance of a broad range of candidate container materials. In addition, the influence of several parameters, such as temperature, oxygen content, groundwater composition (chloride, sulphate and thiosulphate), γ-radiation, … were investigated. The experimental approach consisted of in situ experiments (performed in the underground research facility, HADES), electrochemical experiments, immersion experiments and large scale demonstration tests (OPHELIE, PRACLAY). Degradation modes considered included general corrosion, localised corrosion (pitting) and stress corrosion cracking.

This paper gives an overview of the more relevant experimental results, gathered over the past 25 years, of the Belgian programme in the field of container corrosion.
Interaction Swelling Bitumen – Host Formation: Scoping Calculations
Authors: Li Xiang Ling , Bernier Frédéric , Valcke Elie
Published: April 2011

The Eurobitum bituminised waste product (BWP) from the former EUROCHEMIC reprocessing plant in Mol-Dessel (Belgium) contains a lot of salts, mainly NaNO3 and CaSO4. In contact with pore water in an underground repository, the dehydrated salts in the BWP will rehydrate, resulting in swelling and, possibly, a swelling pressure build-up. A high swelling pressure might impede the integrity and the safety of the repository by creation of preferential pathways for radionuclide migration. In Belgium, the Boom Clay is studied as a reference host formation.

The interaction between the swelling BWP and the host formation is a very complicated hydromechanical process. It depends not only on the hydromechanical behaviour of the Boom Clay, but also on that of the BWP. The hydromechanical constitutive law of Eurobitum is not yet established. We have therefore realised scoping calculations to assess the stress redistribution and deformation due to the recompression of the clay around a disposal gallery caused by a swelling pressure. Sensitivity studies have evidenced some important influencing factors.

The scoping calculations showed that the swelling pressure exercised to the Boom Clay should be limited to 7 - 8 MPa. Beyond this limit, the Boom Clay host formation will be subject to important deformation, and the risk of preferential paths for radionuclide transport becomes very high. The convergence during the excavation of the disposal galleries is of primary importance for a safe waste disposal system design. Indeed, excess convergence may result in a higher damaged zone before disposal of the bituminised waste.
Bituminized Waste Leaching in Restricted and Free Swelling Conditions: Mechanisms and Analytical Modeling
Authors: Lefebvre X. , Sercombe J. , Ledieu A. , Gwinner B. , Adenot F.
Published: April 2011

The leaching behavior of nuclear wastes embedded in bitumen has been extensively studied for a decade by many teams of researchers. The main conclusion is that both water uptake and salts release obey to a diffusive regime. The most preponderant parameters of the Bituminized Waste Products (BWPs) leaching are, on the one hand, the nature and the content of the salts that are embedded in the bitumen, and on the other hand, the microstructure of bitumen and the external constraint applied to this confining material.

The numerical code COLONBO, designed by the CEA, allows to predict the behavior of the BWPs leaching in the case of salts embedded in soft bitumen and in free swelling conditions (no mechanical constraints during the leaching). This paper intends to achieve two goals: (i) to propose an analytical resolution of the system of equations implemented in COLONBO by using accurate simplification. The validation of this approach relies on the comparison with the predicted solutions of COLONBO and, when available, with the experimental results. (ii) To extend this simplified modeling to the case of restricted swelling conditions. The point is that the validation of this approach would allow us to propose a unified system of equations, allowing to simulate the BWPs leaching in whatever conditions and improving consequently the field of validity of the predictions for the behavior of bituminized waste products.
Mechanisms and Modelling of Waste/Cement Interactions – Survey of Topics Presented at the Meiringen Workshop
Authors: Wieland E. , Johnson C.A. , Lothenbach B. , Winnefeld F.
Published: April 2011

Cementitious matrices are being used worldwide as a containment medium for radioactive and non-radioactive waste in order to retard the mobility of contaminants. The present thrust of research is to further the understanding of contaminant binding in the cementitious matrix in order to predict the long-term behaviour and the potential impact of the waste on the environment.

The workshop “Mechanisms and Modelling of Waste/Cement Interactions”, held in Meiringen, Switzerland, between May 8 and 12, 2005, focused on the chemical understanding and thermodynamic modelling of the processes responsible for the retention of radioactive and non-radioactive species in cementitious systems. The objectives of the workshop were to bring together scientists from different disciplines, i.e. cement chemistry, radioactive and non-radioactive hazardous waste disposal, to stimulate discussions on current developments and to identify future needs in this field of research. The topics treated in the workshop were chosen to maximize the benefit to the different fields of research. Cement chemists reported on developments in the understanding of cement mineralogy and thermodynamic modelling of cement systems. The hazardous and radioactive waste management communities presented their ideas on the mechanisms of contaminant binding to cement minerals as well as field, laboratory and modelling results from practical applications. In this paper important areas of research on waste/cement interactions presented in the workshop will be outlined and briefly discussed. The following overview reflects a subjective perception of the workshop and does not lay claim to deal comprehensively with all the papers that were presented in the workshop.
Molten ceramic solidification during molten state processing of HLW
Authors: Kinoshita Hajime , Uno Masayoshi , Yamanaka Shinsuke , Lee William E.
Published: April 2011

Solidification of molten ceramics during molten state processing of High-Level Waste (HLW) was studied to investigate a possibility of a simpler and flexible process for immobilisation of HLW. Simulated HLW was heated together with different reducing agents (TiN with AlN or TiO2) either at 1673 K or 1873K for 1 to 3 hours under Ar atmosphere. Cooling rates of 5 K/min and 10 K/min did not result in any obvious differences in the products obtained under the standard condition used in the present study. The composition and quantity of the reducing agent had a significant effect on the melting and solidifying behaviour of the simulated HLW. The results suggest the possible further studies to improve the solidification process and the final product.
Mechanical integrity of yttria-stabilised zirconia doped with Np oxide
Authors: Kinoshita Hajime , Kuramoto Ken-ichi , Uno Masayoshi , Yamanaka Shinsuke , Mitamura Hisayoshi , Banba Tsunetaka
Published: April 2011

Mechanical properties of YSZ doped with Np oxide were studied to investigate the sufficiency to be a waste form for immobilisation of highly concentrated TRU. The study was conducted focusing on Vickers (HV) and Knoop (HK) hardness, Young's modulus (E) and fracture toughness (KIC). The results showed that YSZ is harder and more resistant to elastic deformation and crack development than such waste forms as borosilicate glass and synroc. The effects of porosity and Np content on HV, HK, E and KIC are also discussed.
Investigation of Natural and Artificial Zr-silicate Gels
Authors: Burakov Boris E. , Smetannikov Andrey Ph. , Anderson Evgeniy B. , Alexeev Alexander Yu.
Published: April 2011

Sample of natural Zr-silicate gel containing up to 13 wt.% U was characterized using scanning electron microscopy (SEM), X-ray powder diffraction (XRD), high resolution transmission electron microscopy (HRTEM) and electron microprobe analysis (EPMA) method. It was found that gel matrix is amorphous in general; however, it contains non-identified nanocrystallites. No separated oxide phases of U, Zr or Si were observed in a gel matrix. After sintering in air at 1400°C for 1 hour gel transformed largely into crystalline zircon, (Zr,U)SiO4. Uranium was not found in any other phases besides zircon. It was assumed that high chemical durability of natural Zr-P-U-Ti-silicate gel is caused by two competing processes which exist under self-irradiation conditions: 1) crystallization of the gel and 2) metamictization of the crystallized zircon and other phases.

Synthetic samples of Zr-silicate gel doped with Ce, U, Pu and Am were obtained and studied in comparison with natural samples. It was suggested to use artificial solid Zr-silicate gels for durable fixation of actinides for the goal of long-term or intermediate storage.
Leaching behaviour of non-irradiated and irradiated HTR UO2-ThO2fuel particles under reducing conditions
Authors: Alliot Cyrille , Grambow Bernd
Published: April 2011

The dissolution of irradiated HTR UO2-ThO2fuel particle under reducing conditions was studied using a continuous flow-through reactor and compared to the dissolution of unirradiated fuel particle in the same condition. The irradiated fuel particle was leached for more than eight months. A fast137Cs release was observed, corresponding to a labile fraction (“instant release fraction”). Then, a congruent leaching of137Cs and90Sr was measured corresponding to a matrix dissolution rate equal to 1.7 mg/m2/d. A slower release of238Pu probably due to sorption phenomena is observed. Dissolution rates are 100-2000 times higher than for unirradiated material. We can conclude that alpha-radiolysis is responsible for this increase due to local oxic conditions. However we cannot exclude that due to irradiation the accessible surface area has been increased as well.

The coating of this irradiated particle was equally studied to determine the presence of different radionuclides and their leaching properties of leaching
Oxidation kinetics of high burn-up UOX and MOX fuel : the influence of the grain boundaries
Authors: Desgranges Lionel , Rousseau Gurvan , Ferroud-Plattet Marie-Pierre , Ferry Cécile , Giaccalone Hélène , Aubrun Isabelle , Delion Pierre , Untrau Jean-Michel
Published: April 2011

In a dry air storage facility, the oxidation of irradiated nuclear fuel is considered as the main risk induced by a leakage that would put the nuclear ceramics in contact with air. The oxidation of UO2 in U3O8 leads indeed to a relative volume swelling of more than 30% which could cause the ruin of the fuel rod. In order to fill the lack of data on high burn-up fuel, some oxidation experiments are currently conducted in CEA with UO2 and MOX fuel. Fragments as well as slices of fuel rod, with a high burn-up, have been oxidized in air at 200°C for more than 4000 hours. The associated weight gain curves are presented together with the characterization of some samples picked up at different oxidation times. It is shown that the weight gain curve of high burn-up UOX is not parabolic-shaped, as predicted in literature, but sigmoid-shaped. Moreover it is also shown that the grain boundary oxidation is not uniform inside a fragment. This leads to a new description of the oxidation mechanism of irradiated fuel.
Testing of uranium dioxide enriched with 233U under reducing conditions
Authors: Ollila K. , Oversby V.
Published: April 2011

Experiments have been conducted to determine an upper limit to the dissolution rate of UO2 under reducing conditions at great depths in granitic bedrock. The aqueous phase was a dilute, synthetic groundwater that simulates fresh groundwater conditions, so-called modified Allard groundwater. Four dissolution tests of long duration were performed. Test duration ranged from 52 to 140 days. Reducing conditions were produced with metallic iron. Average dissolution rates for the UO2 samples under the test conditions were preliminarily calculated based on the total recovery of U at the end of the tests. The dissolution rates ranged from 0.12 to 0.14 ppm/yr for the sum of the total release from the third and fourth cycles of testing (269 days). There was no indication of an effect of alpha radiolysis on the dissolution rate results for UO2 samples with 0, 5, and 10% 233U.
Study of simulated HLW-glass leaching behavior under low oxygen repository condition
Authors: Hua Zhang , Shanggeng Luo
Published: April 2011

Many countries have recognized vitrification as the suitable solidification method for conditioning high level radioactive waste before they are isolated from biosphere in geologic disposal. This paper studies the leaching behavior of a simulated HLW-glass (90Nd/10) under low oxygen repository condition during 1.5 years. The leaching results showed that the glass was corroded less under low oxygen condition than under ambient atmosphere. XRD analyses showed some little diffraction peak appeared on the leached glass surface at 150°C. At the same time, no diffraction peak appeared on the leached glass surface at 90°C. The secondary products formed on the surface of the leached glass contained mainly Si, Al, Ca and Fe.