bluuebunny/crossref_metadata_2025_split huggingface dataset:
Correlation of Laboratory and Stripa Field Leaching Studies
Authors: Zoitos B. K. , Clark D. E. , Lodding A. R. , Wicks G. G. 
Published: March 2011

ABSTRACTA variety of surface sensitive techniques has been used to assess surface layers formed on SRL 165 waste glass specimens from the Stripa burial study and from a laboratory study designed to simulate conditions of the Stripa environment. The laboratory study included static and slow flow tests carried out for periods up to 6 and 24 months, respectively. Comparisons of leached layers formed in the two studies are based upon secondary ion mass spectrometry (SIMS), Fourier transform infrared reflection spectroscopy (FTIRRS), and scanning electron microscopy-electron microprobe (SEM-EMP) analysis.Results demonstrate that surface layers having similar trends in elemental profiles were developed in both lab and field tests. It was also found that both sets of samples showed similar changes in FTIRR spectra. One significant difference between the lab and field samples was that surface alteration, as indicated by changes in FTIRR spectra and leached layer thickness (from SIMS), occurred more rapidly in the lab tests.
Long Term Crystallization Behavior of Glasses at Temperatures T < Tg
Authors: Stalios A. D. , De Batist R. , Van Iseghem P. 
Published: March 2011

ABSTRACTBoulos et al. [1], derived a mathematical expression predicting the minimum time needed for a glassy system to experience fractional crystallization, not exceeding a few volume percent at temperatures lower than the glass transition temperature, T. The range of applicability of this expression is extended to include crystallization processes governed by either homogeneous or heterogeneous nucleation and by diffusion controlled one-, two-, and three-dimensional crystal growth. This study demonstrates that the Boulos et al. expression is fairly independent of the nucleation, growth habit and dimensionality of the crystallization process. Moreover, the inherent theoretical as well as experimental limitations of the technique are reviewed and discussed.The calculation for evaluating this minimum time limit has been applied for an alkali ferrisilicate alpha-waste reference glass. It is found that, for this system, a barely observable crystallized volume fraction (less than 5 % vol) will be reached at 25°C only after storage for more than 10 years. This time period is certainly beyond the times to be considered for evaluations of geological disposal. In addition some preliminary calculations of the minimum time limit for two types of borosilicate high level waste glass forms (HLW) are presented. These indicate safe time limits of the order of 10–100 years at 450°C, suggesting that crystallization effects cannot be ignored if the assumptions made in the calculations are valid.
Leaching Studies of Synroc Crystalline Ceramic Waste Forms
Authors: Solomaha A. G. , Matzkeb Hj. 
Published: March 2011

ABSTRACTThe leaching performance of pressureless sintered SYNROC crystalline ceramic waste forms containing simulated high-level radioactive waste has been evaluated under different leach conditions, i.e. in deionized water and in a simulated brine (Q-brine) at different leach temperatures. The leach solutions were analyzed using inductively coupled plasma and atomic absorption spectrometry (ICPS and AAS) to determine the concentrations of the simulated waste elements and the matrix components released into the leachants. The leach rates of Ba and Ca were in the range of 0.1 to 0.02 g/(m2.d) after one week of leaching in deionized water at 150 °C. No significant difference in the leach behaviour of SYNROC was observed in distilled water and in simulated brine. The leached surfaces of SYNROC were characterized using Rutherford backscattering spectrometry (RBS), secondary ion mass spectrometry (SIMS), scanning electron microscopy (SEM) and elastic recoil detection analysis (ERDA). RBS and SIMS analyses revealed the existence of near-surface layers enriched in Ti and depleted in Ba and Ca. Elastic recoil detection analysis showed the existance of hydrated surface layers on the leached SYNROC which were much thinner than those observed in parallel work with borosilicate waste glasses. Radiation damage produced by ion implantation increased the otherwise very-small leach rates of SYNROC. At high damage levels, SYNROC was shown to become amorphous (metamict).
Alpha-Decay Damage and Annealing Effects in Natural Pyrochlores: Analogues for Long-Term Radiation Damage Effects in Actinide, Pyrochlore, Structure Types
Authors: Lumpkin G. R. , Ewing R. C. 
Published: March 2011

ABSTRACTCubic pyrochlore structure types, A2-mB2O6(O, OH, F) i-n*pH2O, and their derivatives (e.g., monoclinic zirconolite) are important actinide-bearing phases in polyphase, ceramic waste forms (e.g., SYNROC). These waste form phases may typically accumulate alpha-decay doses of 1025 alpha-events/m3 in 1, 000 years or 1026alpha-events/m3 in one million years (i.e., for SYNROC with 20 wt. % HLW). Natural pyrochlores have calculated doses ranging from 1024 to 1027 alpha-events/m3 (= 0.02 to 50 dpa) which have accumulated over ten to a thousand million years. Actinide doping experiments typically reach doses of 1025 alpha-events/m3over periods of several years. Detailed x-ray diffraction analysis of natural samples reveals that the alpha-decay dose at which there is an initial loss of crystallinity (i.e., transition from crystalline to the aperiodic, metamict state as a result of alpha-decay damage) increases as a function of the geologic age of the sample. The increase in the calculated alpha-decay dose which is associated with a specific degree of damage (e.g., loss of x-ray diffraction intensity) is attributed to annealing of isolated alpha-recoil tracks back to the original, crystalline structure. Based on a model of gradual track fading, the alpha-recoil tracks in natural pyrochlores have mean lives on the order of 108 years. In contrast, minerals which remain crystalline (e.g., uraninite, UO2) despite doses of over 1027 alpha-events/m3 have mean alpha-recoil track lives of approximately 104 years. This demonstrates that the microstructure of alpha-decay damaged materials depends not only on the total alpha-event dose, but also on the annealing kinetics of alpha-recoil track fading. Therefore, the prediction of the long-term performance and final state of crystalline phases in ceramic nuclear waste forms requires the determination of alpha-recoil damage annealing as a function of time and temperature.
Leaching of Whole, Defected Used Candu™ Fuel Elements in Saline Solutions Under Argon Pressure
Authors: Stroes-Gascoyne S. , Johnson L. H. , Tait J. C. , Sellinger D. M. 
Published: March 2011

ABSTRACTIn the context of the Canadian Nuclear Fuel Waste Management Program, experiments were performed in which whole, intentionally defected used CANDU™ fuel elements were exposed to deoxygenated saline solutions at 100°C for 484 days. Results suggest that both 90Sr and 99Tc are preferentially released from grain boundaries and that 85Kr release is a good measure of the extent of grain-boundary dissolution. Severe grain-boundary attack in particular areas of the fuel is also evident from scanning electron microscope observations. It is hypothesized that such localized attack is related to fuel porosity. Because of its poor corrosion performance in saline solutions, the Zircaloy sheath cannot be considered as a radionuclide release barrier.
Leaching of Used Candu™ Fuel in the Presence of Clay, Titanium and Granite Rock
Authors: Tait John C. , Stroes-Gascoyne Simcha , Porth Robert J. , Wood Don , Heimann Robert B. 
Published: March 2011

ABSTRACTDissolution experiments have been performed at 95 or 100°C on used fuel in the presence of various components of a disposal system: granite rock, clay (Na-montmorillonite, illite), container (titanium), and two groundwaters with different ionic strengths (0.0015, 0.28). The results showed that Cs and Sr release to solution is highest in the high-ionic-strength groundwater and that clay type is less important in determining short-term release from the fuel. It also appears that after an initial release period lasting about 10 to 20 days, radionuclide release from the fuel to solution slows considerably. Cs was found to sorb more effectively than Sr on illite and montmoril-lonite, while Sr sorbed more effectively than Cs on the granite.
Localized Corrosion and Stress Corrosion Cracking of Candidate Materials for High-Level Radioactive Waste Disposal Containers in U.S.: A Critical Literature Review
Authors: Farmer Joseph C. , Daniel McCright R. 
Published: March 2011

ABSTRACTThree iron-based to nickel-based austenitic alloys and three copper-based alloys are being considered in the United States of America as candidate materials for the fabrication of high-level radioactive waste containers. The austenitic alloys are Types 304L and 316L stainless steels as well as the high-nickel material Alloy 825. The copper-based alloys are CDA 102 (oxygen-free copper), CDA 613 (Cu-7A1), and CDA 715 (Cu-3ONi). Waste in the forms of spent fuel assemblies from reactors and borosilicate glass will be sent to a proposed repository at Yucca Mountain, Nevada. The decay of radionuclides will result in the generation of substantial heat and in gamma radiation.
The Long-Term Prediction of Corrosion of Stainless Steel Nuclear Waste Canisters
Authors: Sharland S. M. , Newton C. J. 
Published: March 2011

ABSTRACTIn this paper, we describe the preliminary stages of the development of a mathematical model of the evolution of the solution chemistry within a corroding crevice on passive stainless steel. It is based on a formulation by Oldfield and Sutton [1], but models the physical and chemical processes which determine the crevice solution in a more rigorous manner. The model will eventually be used to assess whether a ‘critical solution composition’, which results in the depassivation of the crevice and the onset of localised corrosion, is attainable for a range of repository conditions, steel types and canister designs etc. We also describe experiments that provide input data in the form of passive currents for this model. Preliminary sensitivity tests with the model have indicated a need for accurate thermodynamic data for the chemical equilibria constants (particularly those for the chromium reactions). These tests also suggest that there are certain critical relationships between various parameters in the system (such as crevice dimensions, the composition of solution outside the crevice and the passive current) that mark different behaviour in the evolution of the solution composition. Further experiments will be performed, as part of this work, both to validate the predictions of the model and to determine whether the predicted compositions of the crevice solutions are sufficiently aggressive to initiate crevice corrosion.
Corrosion Induced Hydrogen Evolution on High Level Waste Overpack Materials in Synthetic Groundwaters and Chloride Solutions
Authors: Simpson J. P. , Schenk R. 
Published: March 2011

ABSTRACTHydrogen evolution from anoxic corrosion of cast steel overpacks in high-level waste repositories is an important issue for design if, as has been estimated, the hydrogen is prevented from escaping by diffusion by a low permeability compacted bentonite backfill.Evaluation of the corrosion results showed three basic types of corrosion behaviour: general corrosion with oxide layer formation, unstable corrosion behaviour with pitting or macro-element formation and stable passive behaviour.Cast steel containers under Swiss repository conditions are expected to suffer general corrosion with oxide layer formation. This behaviour gives the highest long term corrosion rates (2–5 μm/a) without local attack, above the 0.03–0.8 μm/a tolerated for hydrogen escape by diffusion but below the 20 μm/a assumed for overpack design.
Calculation of the Radiolytic Gas Production in Cemented Waste
Authors: Offermann P. 
Published: March 2011

ABSTRACTHydrogen production by radiolysis of water in cement waste forms has to be limited due to safety requirements. Specific generation rates (g-values) are derived from data obtained in laboratory scale experiments and measurements on 200 1 drums containing real waste. To interpret the data model calculations are carried out including those for PH, dose rate, nitrate concentration and diffusion. An OH depleting reaction is added to the radiolytical reaction mechanism of water to model the hydrogen production rate observed for γ-irradiated cement.
Degradation and Material Transport for Thin Plates of Cement Pastes
Authors: Nilsson Karen , Brodersen K. 
Published: March 2011

ABSTRACTA ‘thin-plate’ technique, which is well suited for laboratory studies on cements, has been used in equilibrium experiments aimed at studying material transport between concretes of different composition. The extent of material transport is small, but there appear to be a movement of calcium towards thin plates containing excess silica fume, where supposedly the pozzolanic reaction takes place, an aspect which can be of interest for crack-healing of cements. A model concerned with crack healing of cement is discussed. Preliminary data have been obtained in a study where thin plates have been employed to investigate the effect of leaching on the microstructure of cements using the technique of Small Angle Neutron Scattering (SANS).
Physical Properties and Leachability of MLW Stream Containing Cr, Ni and Cd Immobilized in a Cement Matrix
Authors: Zamorani E. , Sheikh I. A. , Della Rossa M. , Serrini G. 
Published: March 2011

ABSTRACTCement samples containing variable amounts of Cr(III) or Ni(II) or Cd(II) as chloride admixtures present in a MLW stream from reprocessing of spent fuel were prepared under established procedure. Due to the high pH generated in the cement clinker hydration, respective metal hydroxides are formed and improve the physical characteristics of the cement matrix. An increase in the value of the compressive strength was observed when about 7% of the above elements were blended in cement. The increase depends on the nature of the element in the sequence Cr >Ni >Cd.The leach tests confirm the formation of insoluble hydroxide presenting a low concentration in the leachate corresponding to 0.05, 0.004 and 0.052 mg.L−1 for Cr, Ni and Cd, respectively. On the other hand, the hydro-lyzed chloride ions seem to react with calcium with consequent increased degradation of the cement matrix.
Freshwater Alteration of Basaltic Glass, Hanauma Bay, Oahu, Hawaii: A Natural Analogue for the Alteration of Borosilicate Glass in Fresh Water
Authors: Cowan Rachel , Ewing Rodney C. 
Published: March 2011

ABSTRACTAlteration (fresh water) products (palagonite and zeolites) of a 12, 000–28, 000 year old basaltic glass from Hanauma Bay, Hawaii, were examined by electron microprobe analysis, scanning electron microscopy, and X-ray diffraction analysis. The palagonite, 0 to 300 microns thick, is depleted in Si, Al, Ca, Na, and K and enriched in Ti and Fe. Ca-rich zeolites are associated with palagonite that is slightly more depleted in Ca; all samples contain zeolites and low Al-palagonite. The rate of palagonitization (0.002–0.005 volume percent/year) is less than the experimentally predicted rate for basalt glasses due to the episodic presence of the percolating groundwater. The Si/AI ratio of the zeolites decreases with increasing pH of the groundwater as it passes through the vertical section. Zeolite paragenesis is (first to last): analcime (NaAlSi2O 6·H2O), phillipsite [(1/2 Ca, Na, K)(Al3Si5O16).6H2O], chabazite (CaAl2SiO16.6H2O).
Performance Assessment of a High-Level-Waste Repository in Clay
Authors: Marivoet Jan L. , Volckaert Geert , Bonne Arnold A. 
Published: March 2011

ABSTRACTPerformance assessment studies have been undertaken on the geological disposal of high-level waste in a clay layer in the framework of the CEC project PAGIS. The methodology applied consists of two consecutive steps : a scenario and a consequence analysis. The scenario analysis has indicated that scenarios of normal evolution, of human intrusion, of climatic change, of secondary glaciation effects and of faulting should be evaluated. For the consequence analysis as well deterministic “best estimate” as stochastic calculations, including uncertainty, risk and sensitivity analyses, have been elaborated.The calculations performed show that most radionuclides decay to negligible levels within the first fewjneters of the clay barrier. Just a few radionuclides, 99Tc, 135Cs and 237Np with its daughter nuclides 233U and 229Th can eventually reach the biosphere. The maximum dose rates arising from the geological disposal of HLW, as evaluated by the “best-estimate” approach are about 10−11 Sv/y for river pathways. If the sinking of a water well into the 150 m deep aquifer layer in the vicinity of the repository is considered together with a climatic change, the maximum calculated dose rate rises to a value of 3×10−7 Sv/y. The maximum dose rates evaluated by stochastic calculations are about one order of magnitude higher due to the considerable uncertainties in the model parameters. In the case of the Boom clay the estimated consequences of a fault scenario are of the same order of magnitude as the results obtained for the normal evolution scenario. The maximum risk is estimated from the results obtained through stochastic calculations to be about 5×10−8 per year. The sensitivity analysis has shown that the effective thickness of the clay layer, the retention factors of Tc, Cs and Np, and the Darcy velocity in the aquifer are parameters which strongly influence the calculated dose rates.
Alteration of Basaltic Glass in Iceland as a Natural Analogue for Nuclear Waste Glasses: Geochemical Modelling with DISSOL
Authors: Crovisier J. L. , Advocat T. , Petit J. C. , Fritz B. 
Published: March 2011

ABSTRACTThe long term geochemical consequences of basaltic glass dissolution in fresh water at 0°C have been calculated with the computer code DISSOL. The clay minerals were represented by an ideal solid solution model (CISSFIT) able to describe variations in chemical composition of a clay phase in response to variations of the solution chemistry. The predicted mineral phases were iron hydroxides followed by kaolinite, TOT clays, chabazite and cli-noptilolite. These results are in reasonably good agreement with experimental results and observations of altered subglacial hyaloclastites from Iceland. The formation of secondary products are mainly controlled by thermodynamic constraints. Kinetic effects, such as diffusion in the near glass surface are not important.
The Brine Migration Test - A Nuclear Waste Repository Simulation Experiment at the Asse Salt Mine - Federal Republic of Germany
Authors: Rothfuchs T. , Wieczorek K. , Mcnulty E. G. , Gupta S. K. , Clark D. 
Published: March 2011

ABSTRACTA joint US/FRG nuclear waste repository simulation experiment was performed at the Asse Salt Mine in the Federal Republic of Germany (FRG). The High Level Waste (HLW) disposal in boreholes was simulated by the simultaneous emplacement of electrical heaters and cobalt-60 sources at four individual test sites located in a special underground test room at the 800 m-level.In order to resolve the issues of rock mass/waste package interaction the temperature field, brine migration into the heater boreholes, borehole gas pressure and composition, and rock mass stresses and displacements were monitored during the test. In order to validate computer code predictions the acquired data were compared to calculational results. Corrosion specimens remained in the heater boreholes during the course of the experiment and were afterwards examined.
A Channeling Experiment to Study Flow and Transport in Natural Fractures
Authors: Abelin Harald , Birgersson Lars , Ågren Thomas , Neretnieks Ivars 
Published: March 2011

ABSTRACTModel calculations show that channeling may have a detrimental effect on radionuclide transport because fast channels may carry some of the mass of the radionuclides considerably faster than the average flow would and may give this portion considerably less time to decay. Channeling further aggravates the retardation of the sorbing nuclides because less surface area is available for sorption in a channel within a fracture than if the whole fracture is exposed to the flowing water. An ongoing experiment in the Stripa mine aims at studying some aspects of channeling. A special packer of a new design is used. Preliminary results show that there is uneven flow in the fractures which indicates channeling.
Possible Complex Formation of Actinides with Organic Matter and Phosphate in Deep Groundwaters. Speciation Calculations and Data Evaluation
Authors: Aidersson Karin 
Published: March 2011

ABSTRACTCalculations of solubility and speciation of U, Th, Ip, Pu, and An in a deep groundwater, containing humlc acid and phosphate have been performed, using the PHRBEQB equilibrium code. Where equilibrium data are missing, estimates have been made.Some of the studied complexes and solid phases may be of importance to the actinide behaviour in deep groundwaters, eg AmPO4(s) and several aqueous phosphate species and also humic acid for trivalent actinides.
Characterisation of Natural Colloids in a Shallow Glacial Aquifer and Their Radionuclide Loading
Authors: Longworth G. , Wilkins M. A. , Ivanovich M. 
Published: March 2011

ABSTRACTThis paper presents the results of a physical, chemical and actinide characterisation of the groundwater in a shallow glacial sand aquifer, in which tracer tests aie currently being conducted by t lu- British Geological Survey (BGS).Uranium Series disequilibrium measurements have been used to determine the partition of natural actinide activities betueen the particulate, colloid and solution phases of the groundwnters from sevpral geologically dissimilar sites. The activity fractions associated with the colloid phase were found to be (0.1–0.52) for uranium and (1–52) for thorium.Scanning electron microscopy analysis yielded values of 103−101 particles/litre for the colloid concentration. Mean mobilities for the colloids determined by electrophoresis were in the range -(1–2) × 10−6 m2S−1v−1.
The Influence of Microbial Activity on the Movement of Uranium at Osamu Utsumi Mine, Poços De Caldas, Brazil
Authors: West Julia M , Mckinley Ian G , Vialta Airton 
Published: March 2011

ABSTRACTThe Osamu Utsumi uranium mine, Poços de Caldas, Brazil is a roll front uranium deposit currently under investigation in an international natural analogue project involving Brazil, Sweden, Switzerland, the United Kingdom and the United States. This is a multi-disciplinary study (see the paper at this meeting by Smellie et al (1)), one component of which is an examination of the movement of natural series radionuclides across redox fronts. The processes at such fronts are analogous to those which could occur at radiolytic redox fronts found in the near- or far-field of deep repositories for HLW or spent fuel. Microbiological investigations have been carried out to determine the presence and activity of microbes known to be important in the uranium biogeochemical cycle; to define their importance in the movement of uranium across the redox front and to assess the significance of these observations to relevant safety assessment issues. This paper will summarise the results of these findings.