bluuebunny/crossref_metadata_2025_split huggingface dataset:
Uncertainties in Container Failure Time Predictions
Authors: Williford R. E. 
Published: March 2011

ABSTRACTStochastic variations in the local chemical environment of a geologic waste repository can cause corresponding variations in container corrosion rates and failure times, and thus in radionuclide release rates. This paper addresses how well the future variations in repository chemistries must be known in order to predict container failure times that are bounded by a finite time period within the repository lifetime. Preliminary results indicate that a 5000 year scatter in predicted container failure times requires that repository chemistries be known to within ±10% over the repository lifetime. These are small uncertainties compared to current estimates.
The Long-Term Properties of Cement and Concretes
Authors: Atkins M. , Glasser F. P. , Moroni L. P. 
Published: March 2011

ABSTRACTThe state of knowledge concerning the internal constitution of cement systems is reviewed. It is concluded that many properties relevant to radwaste immobilization are strongly influenced by the presence of thermodynamically metastable phases. In order to ascertain cement properties at long ages, models have been developed which include compositional and time-dependant factors. These require a validated data base. Progress in developing models and creating the data base are reviewed. In the course of accumulating data, specific radwaste species -cement interactions can also be quantified.
The Effect of Leaching on the Pore Structure of Cement-Based Grouts for Use in Nuclear Fuel Waste Disposal
Authors: Onofrei M. , Gray M. N. , Breton D. , Ballivy G. 
Published: March 2011

ABSTRACTResearch on the longevity of cement-based grout materials for sealing a deep geological disposal vault is an important aspect of the Canadian and other nuclear waste management programs. These studies include assessments of the chemical durability of cement grouts, and the effects of leaching and phase transformation on the long-term hydraulic and diffusion characteristics of grouts.This paper presents the results of laboratory studies carried out to assess the effects of leaching of cement phases on the pore structure of hardened grouts. Measurements of mercury intrusion and scanning electron microscopy with energy dispersive x-ray analysis, have been used to investigate the changes in pore structure of both a reference grout (90% Type 50 cement, 10% silica fume, water-to-cementitious materials ratio between 0.4 and 0.7) and ALOFIX-MC (a fine cement product of Japan), as a function of leaching time.The work discussed here reveals that the porosity of hardened grout does change during leaching, but within limits that depend on grout composition and initial porosity. The results confirm that the materials have the potential to self-seal and maintain their performance for longer periods than those currently predicted by longevity models.Our studies of the porosity and permeability of grouts suggest that pore size distribution rather than total porosity is the more important parameter in determining longevity.
Migration of Cesium, Strontium and Cobalt in Water-Saturated Concretes
Authors: Idemitsu K. , Furuya H. , Tsutsumi R. , Yonezawa S. , Inagaki Y. , Sato S. 
Published: March 2011

ABSTRACTDiffusivities of Cs, Sr and Co were measured in several kinds of water-saturated concretes. The measured penetration profile of every tracer was composed of two parts. Those were a steep slope near the surface and a gradual slope in the deeper part. This profile was successfully explained by considering two diffusion paths in concrete. One diffusion path was possibly fissure with a width of a few microns and another was network of submicron pores. The volume of submicron pores was approximately 90% of the total free space volume in every concrete. The orders of magnitude of apparent diffusivities for all tracers were 10−12–10−11 m2/s through the fissure and l0−16–10−15 m2/s through the network of pores. The difference between the diffusivities of the two paths is thought to be caused by small geometrical factor of the network of submicron pores.
The Effect of Silica Fume and Water/Cement Ratio on the Hydraulic Conductivity of Cement-Based Grout
Authors: Al-Manaseer A. A. , Onofrei M. , Gray M. N. , Shenton B. 
Published: March 2011

ABSTRACTIn situ experiments at Atomic Energy of Canada Limited’s Underground Research Laboratory have demonstrated that a specially developed high-performance cement-based grout, called the reference grout, consisting of 90% sulphate-resistant cement (Canadian Type 50), 10% silica fume (SF) and superplasticizer can seal very fine fissures in granitic rock. Studies are now in progress to determine the longevity of these materials. This paper describes progress in studies of the hydraulic conductivity (i.e. coefficient of permeability), K, of the grout at water/cementitious materials ratios, w/c, between 0.4 and 0.8. The K was assessed with the grouts under compressive and tensile stress using specially designed radial flow permeameters. The results confirm that the K of the reference grout is two to three orders of magnitude lower than that typically observed for intact granite rock (10−12 m/s). Moreover, the data show that adding silica fume and reducing the w/c decreases K. The hydraulic conductivity data coupled with field work and other laboratory data strongly suggest that the reference grout can be successfully used to seal finely fractured rock in the vicinity of a nuclear fuel waste disposal vault.
Research Needs in Cement-Based Waste Forms
Authors: McDaniel E. W. , Spence R. D. , Tallent O. K. 
Published: March 2011

ABSTRACTCement-based waste forms are one of the most widely used waste disposal options, yet definitive knowledge of the fate of the waste species inside the waste form is lacking. A fundamental understanding of the chemistry and microstructure of the waste forms would lead to a better understanding of the mass transfer of the waste species, more confidence in predicting and extrapolating waste-form performance, and improved design of waste forms. Better and cheaper leach tests would lead to quicker and more cost-effective screening of waste-form alternatives, cement-based and otherwise. In addition, assessment of durability may be important to predicting waste-form performance in the field over periods of decades and centuries.
Developments for in Situ Tests on Compacted Bentonite-Based Buffer Material
Authors: Kjartanson B. H. , Gray M. N. , Pulles B.C.M. 
Published: March 2011

ABSTRACTAECL Research is carrying out large-scale in situ experiments at its Underground Research Laboratory (URL). The Buffer/Container Experiment is designed principally to investigate the full scale, in situ performance of bentonite-based buffer material in a single emplacement borehole environment. In addition, the response of the rock to excavation and heating will be investigated. The experiment also allows for the development of the technologies needed to demonstrate some of the vault engineering activities proposed in the Canadian nuclear fuel waste disposal concept. These include excavation of large diameter boreholes for waste emplacement and in situ compaction of a bentonite/sand buffer mixture. Although these methodologies developed for the URL have not been optimized for the commercial, full-scale operations needed for a disposal vault, results show that the equipment and methodologies needed for vault operations are a reasonable extrapolation of existing technology.
Mechanistic Effects of Deuteration on the Aqueous Corrosion of Nuclear Waste Glasses
Authors: Feng X. , Fu L. , Choudhury T. K. , Pegg I. L. , Macedo P. B. 
Published: March 2011

ABSTRACTIsotopically labeled water has been utilized by several researchers to help elucidate the glass dissolution mechanism in aqueous media. However, most of the results have been obtained with simple silicate glasses and have utilized low surface-to-volume (S/V) ratios and relatively short time scales. In this paper we report the results of an extensive study of the leach behavior of the preliminary West Valley nuclear waste glass composition, WV205, in deuterium oxide using multiple S/V ratios at both short and long times. The WV205 glass was leached in parallel in both ordinary deionized water and in deuterated water at five S/V ratios (20, 100, 200, 2000 and 6000 m−1) at 90°C under PCT (the SRL-modified MCC3 procedure) conditions with sampling at 1, 3, 7, 28, 56, 120 days, and four times annually thereafter; the tests will continue for several years. Initial rates were determined by measurements at shorter times with polished monoliths. A significant isotope effect, as measured by the ratio of leach rates, RH20/RD20, was found at all S/V ratios and reached values as large as 360%. Our data yield different values for RH20/RD20 in the diffusion, matrix dissolution, and saturation dominated regimes with the largest effect in the middle stage. Large values of RH20/RD20 would be characteristic of a primary kinetic isotope effect suggestive of a bond breakage involving hydrogen in the rate determining step.
Effects of Mineralogy on the Sorption of Strontium and Cesium Onto Calico Hills Tuff
Authors: Meyer R. E. , Arnold W. D. , Case F. I. , O’Kelley G. D. , Land J. F. 
Published: March 2011

ABSTRACTSorption and desorption measurements were made of strontium and cesium onto clinoptilolite and Calico Hills tuff. The object was to see whether there was a correlation between sorption of strontium and cesium onto Calico Hills Tuff and the clinoptilolite based on the content of clinoptilolite in the Calico Hills Tuff. If sorption onto Calico Hills Tuff is solely due to the presence of clinoptilolite, then the ratios of the sorption ratios on tuff to those on clinoptilolite at similar conditions should be the weight fraction of the clinoptilolite in the tuff. Since the tuff contained about 50% clinoptilolite, the ratios would be expected to be about 0.5 if sorption was due solely to clinoptilolite. The experimental evidence showed that the ratios were generally near 0.5 for both cesium and strontium sorption and that ion-exchange processes were operative for both the clinoptilolite and the tuff. However, the ratios differed to a small extent for different conditions, and there were indications that other sorption processes were also involved.
The Influence of Trace Elements in Consolidated Sedimentary Rocks on the Migration Behaviour of Radionuclides
Authors: Bode W. , Bode B. 
Published: March 2011

ABSTRACTThe effects of trace contents of 15 elements in the sedimentary rocks on the Rs- and Rd-values (Maass, 1983) of the dissolved radionuclides of the elements C (as carbonates), Se, Sr, Tc, I, Cs, Pb, Ra, Ac, Pa, U, Np, Pu, Am. and Cm were investigated and discussed. For this purpose Sr, Ba, B, Corg., Pb, P, F, Cu, Zn, Cd, V, Mn, Fe, Co and N1 contents in the rocks were compared to the sorptlon/desorption coefficients of the above mentioned 15 radionuclides and plotted in x-y diagrammes (a total of 225). While the magnitude of most trace element contents has no or only a slight influence on the retention properties of most radionuclides, a distinct correlation between the trace element contents and the magnitude of the distribution coefficients was found for some radionuclides. Particularly copper, organic carbon, and barium are found to take a positive influence on the Rs-/Rd-values of certain radionuclides. The presence of other trace elements (eg. B and F) can have a negative effect on the retention behaviour of the rock matrix as regards certain dissolved radionuclides. Seen as a whole, the magnitude of the desorption coefficients (Rd-val-ues) appears to be more closely correlated to the trace element contents than to the sorption coefficients (Rs-values).
Diffusion Measurements of Radionuclides In site Specific Sediment/Groundwater-Systems
Authors: Meier Hans , Zimmerhackl E. , Zeitler G. , Menge P. 
Published: March 2011

ABSTRACTResults of systematic measurements on the diffusion of radionuclides through sandy, marlaceous and clayley sediment rocks from strata overlying the Gorleben salt dome are presented. The tracer nuclides used were U-233, Ra-226, Pb-210, and Ni-63. It is shown that, among other parameters, diffusion coefficients and distribution coefficients could be derived from breakthrough curves. Moreover, it is demonstrated that the diffusion behaviour of nuclides such as Pb and Ni can be enhanced enormously in sediment rocks by complex forming agents (EDTA).
Record of Past Contact Between Altered Rocks and Radioactive Solutions Through Radiation-Induced Defects in Kaolinite
Authors: Ildefonse Philippe , Muller Jean-Pierre , Clozel Blandine , Calas George 
Published: March 2011

ABSTRACTA U-deposit located in hydrothermally altered tuff in Mexico, and two tropical weathering systems from Brazil and Cameroon were studied as natural analogues of radionuclide release and migration in the geosphere. In these alteration systems, kaolinite is the main secondary phyllosilicate associated with variable amounts of iron oxides. Defect centers are detected in natural kaolinites by means of electron paramagnetic resonance. The origin of the paramagnetic defect centers (PDC) is from radionuclide irradiation. This interpretation is supported by laboratory experiments on kaolinite using four different types of radiation: x-rays, γ-rays, and He+ and Pb2+ ion beam implantations. Several types of PDC (designated A-, A‵- and B-centers) are clearly identified and can be distinguished with respect to their relative stability. The A-center is stable over geological periods (on the order of 109 years) at surface temperatures. Moreover, it is shown that PDC’s in kaolinites reflect the cumulative radiation dose.PDC’s in kaolinite have been used to trace radionuclide migration in the three natural alteration systems studied. The kaolinites investigated show a significant concentration of PDC’s which corresponds to background natural irradiation. The different types of PDC detected may record successive irradiations of kaolinite directly linked to geochemical conditions prevailing during and after kaolinite growth. Because of their different thermal stability, these different PDC–s may be considered to have formed at different time periods. This makes a unique tool for tracing the dynamics of the transfer of radionuclides and allows the use of kaolinite as an in-situ dosimeter. Because some of the geological settings chosen for nuclear wastes are located in kaolinite-bearing strata, PDC dosimetry could be used in a safety assessment of these wastes.
Three-Dimensional Transient Advective Diffusion by Boundary Element Method using Direct Time Integral of the Fundamental Solution
Authors: Kawamura Ryuji , Isono Akira 
Published: March 2011

ABSTRACTThe advective diffusion analyses have been applied to many fields of science and engineering, such as dispersion for chemically reacting(first-order reaction) substance, thermal transport in fluid, analysis of electromagnetic field caused by a moving magnet. electron transport in semiconductors, underground migration of radioactive waste, and so on. The boundary element method (BEM) has been developed extensively for the last decade to solve these transient advective diffusion equation. The time integrations of the fundamental solution in the boundary integral equation, however, make the BEM application to advective diffusion problems difficult. Therefore, the time integration has been approximated in the past relevant publications. This paper describes the BEM in which the time integration is done analytically, and technique is demonstrated with several examples. Good results have been obtained in the example calculations, where comparisons are made with the results from other numerical codes.
Modelling the Chemical Behaviour of Radionuclides in Waste Disposal Site in a Granitic Environment - a Chemical Thermodynamic Approach
Authors: Fabriol Robert , Ouzounian Gerald , Genter Albert 
Published: March 2011

ABSTRACTLimiting concentrations of radionuclides (RN) in a granitic environment are determined by computer modelling of a disposal site with quartz sand and clay engineered barriers. Six RN (Sr, U, Pu, Np, Th and Tc) are studied. Temperature is varied with distance from the host rock to waste from 25 to 200°C, The behaviour of these elements appears to be iindependent, of the barrier material and strongly dependent on temperature effect on mineral solubilities.
A Novel Conceptual Model for the Flow and Transport in Fractured Rock
Authors: Taivassalo V. , Hautojärvi A. 
Published: March 2011

ABSTRACTIn crystalline rock groundwater flows predominantly in fractures and fissures. Strongly varying fracture aperture guides the flow preferentially in some parts of a fracture plane, in so called channels. In our hydraulic model the degree of channeling together with the aperture variation along a channel is included as a factor which is the ratio of the aperture from transmissivity measurements and the aperture from the tracer tests.The developed transport model takes into account the coupling of molecular diffusion and advection in a velocity field varying linearly over a characteristic width. Various flow velocities in different parts of a channel cause a transient phase with non-Fickian behavior of dispersion. This might erroneously be attributed to other processes e.g. matrix diffusion when not taken into account in the migration modeling of tracers. Molecular diffusion across the flow field, however, tends to smooth out the transport time differences. With time the dispersion diminishes and becomes more symmetric in confined channels.The concept and models have been applied to predict and interpret field experiments aimed to investigate transport over long distances in highly conductive fracture zones. The analyzed experiments have been performed at the Finnsjön research area in Sweden and they belong to the test case 5 of the INTRAVAL project.
Release and Transport of Gaseous C-14 from a Nuclear Waste Repository in an Unsaturated Medium
Authors: Light W.B. , Zwahlen E.D. , Pigford T.H. , ChambrÉ P.L. , Lee W.W.-L. 
Published: March 2011

ABSTRACTThe potential nuclear waste repository at Yucca Mountain is to be in partially saturated rock. Released radioactive gases such as 14CO2 could have a direct pathway to the biosphere. We study the release of 14C released as 14CO2 from partly failed nuclear waste containers by analyzing the flow of gas into and out of a container. We analyze the transport of released 14CO2 in an unsaturated, fractured, porous medium with gas-phase advection and dispersion. We calculate the inhalation dose to a maximally exposed individual above ground, based on some conservative assumptions about release from containers. For the assumed parameter values, a simple atmospheric diffusion model gives very small doses when compared to background radiation doses.
Aqueous Diffusion Coefficients in Unsaturated Materials
Authors: Conca James L. , Wright Judith 
Published: March 2011

ABSTRACTSimple diffusion coefficients, D(θ), in most unsaturated media were found to be primarily a function of water content and not material characteristics except where the characteristics affect or determine water content. At high water contents, D(θ) gradually declines as water content decreases, from 10−5 cm2/sec at a volumetric water content of about 50% to 10−7 cm2/sec at a volumetric water content of about 5%, followed by a sharp decline as surface water films become thin and discontinuous and pendular water elements become very small, from 10−7 cm2/sec at a volumetric water content of about 5% to 10−9 cm2/sec at a volumetric water content of about 0.5% to 1%.
The Role of Laboratory Analog Experiments in Assessing the Performance of Waste Package Materials
Authors: Cunnane James C. , Bates John K. 
Published: March 2011

ABSTRACTThere is an immediate need to begin to validate models that can be used for assessing the performance of waste package materials in an unsaturated repository environment. This paper examines available testing information and testing approaches that could support validation of models for engineering barrier system (EBS) radionuclide release. The content is presented in the context of the general methodology that has been proposed for validating performance assessment models [1], Available experimental observations are used to test some of the EBS release rate modeling premises. These observations include evidence of fluid film formation on waste glass surfaces in isothermal humid environments, accelerated waste glass reaction rates under repository service conditions of large glass surface area to water volume ratio, and mobilization of radionuclides as solutes and colloids. It is concluded that some important modeling premises may not be consistent with available experimental Information. However, it is also concluded that future laboratory testing, which simulates the Integrated waste package system (i.e., laboratory analog testing), is needed to evaluate the significance of these Inconsistencies and to test the system level models. A small-scale apparatus which was developed and tested to examine the feasibility of laboratory analog testing for the unsaturated Yucca Mountain repository environment is described.
Creep Deformation of Dispersion Strengthened NiAl and TiAl Intermetallics
Authors: Sadananda K. , Jones H. , Feng C.R. , Vasudevan A.K. 
Published: March 2011

ABSTRACTIn this study, the creep properties of two intermetallics; NiAl and TiAl have been evaluated. The former was selected based on its relatively high melting point, and the latter was based on its specific strength and high melting point. Tensile creep deformation rates in range of 760 to 930°C were determined as a function of stress for both monolithic NiAl, NiAl reinforced with HfC dispersoids and TiAl reinforced with TiB2 dispersoid. Microstructure and dislocation structures were examined both beore and after creep in both alloys to identify the creep mechanisms. In both systems, deformation occurs by power-law creep with diffusion controlling creep rate. Power-law breakdown regimes have been identified for both systems. In addition, TiAl undergoes dynamic recrystallization during creep resulting in smaller grain sizes than the initial value.
Compression Studies on Particulate Composites of Ternary Al-Ti-Fe, and Quaternary Al-Ti-Fe-Nb and Al-Ti-Fe-Mn L12 Compounds
Authors: Kumar K.S. , Dipietro M.S. , Whittenberger J.D. 
Published: March 2011

ABSTRACTCompression studies were conducted on monolithic and TiB2 particulatereinforced composites of AI22 Fe3 Ti8, both with and without minor quaternary alloying additions (2 at.% Nb and 2 at.% Mn) as a function of temperature and as a function of strain rate at high temperature. The volume fraction of reinforcement was varied between 0 and 20 percent. The particulate reinforcements were found to be effective in increasing ambient- and warm-temperature strength; at high temperatures, the monolithic material is stronger than the composites, although the composites are superior at slow strain rates. The microstructures of the monolithic and composite specimens were examined before and after deformation to explain these observations.