bluuebunny/crossref_metadata_2025_split huggingface dataset:
A Theoretical Study of the Effect of the Leach Interval on a Semidynamic Leach Test (Ansi/Ans-16.1-1986)
Authors: Spence Roger D. , Cox Richard L. 
Published: March 2011

ABSTRACTNumerical solution of Fick's second law of diffusion demonstrated that the error introduced in the ANSI/ANS-16.1-1986 procedure, by assuming a zero surface concentration, varied from about 30% for a leachability index of 5 to about 0.1% for an index of 10. Waste forms typically have indexes of 7 or greater, implying errors of less than 5% with this assumption. The estimated leachability index differs from the actual value by less than 0.2 when the numerical solution is analyzed as input experimental data, except for a leachability index as low as 5 (essentially the value for water).
Porosity and Ion Diffusivity of Latex-Modified Cement
Authors: Nishi Takashi , Kuriyama Osamu , Matsuda Masami , Chino Koichi , Kikuchi Makoto 
Published: March 2011

ABSTRACTLatex-modified Portland cement, which would be expected to have low permeability and ion diffusivity, was studied for possible application as a solidification agent for radioactive wastes generated from nuclear power plants. In order to predict the leaching ratio of radionuclides from the cementitious waste forms, the effect of water and latex content in the fresh cement paste on total porosity and ion diffusivity of hardened paste was quantitatively estimated.Total porosity of hardened cement paste decreased with the reduction of water content in the fresh paste and it was also reduced by latex addition. This latter effect could be attributed to the latex emulsion forming a water-proof film and filling the capillary pores. Also Cs ions diffusivity, which is the ratio of the diffusion coefficient in pore water to that in bulk water, showed an exponential correlation with total porosity for both cement materials. An empirical equation, expressing ion diffusivity as a function of total porosity, was derived from the consideration that the water constrictivity in this porous medium could cause an increase of the apparent viscosity of pore water. These results suggested a possibility that the transport behavior of radionuclides through the cementitious matrix could be estimated from the mixing parameters of the original cement pastes.
Durable Concrete for a Waste Repository - Measurement of Ionic Ingress
Authors: Feldman R.F. , Beaudoin J.J. , Philipose K.E. 
Published: March 2011

ABSTRACTA waste repository for the below ground disposal of low level radioactive waste is planned at Chalk River Nuclear Laboratories. It relies greatly on the durability of concrete for the required 500 year service life. A research program to design durable concrete and predict its service life is in progress.The degradation of the concrete depends to a large extent on the rate of ingress of corrosive agents. Penetration of chloride and sulphate ions are particularly relevant. Twenty mix formulations were developed to create various types and qualities of concrete, and to study their behaviour in different site environmental conditions. A total of 1000 concrete specimens are being exposed at 20°C and 45°C to 25 different combinations of the corrosive agents including CO2. Procedures to measure the ionic profiles and to determine the factors controlling diffusion of the ions in the various concretes have been developed. Results of selected concrete systems exposed to chloride and sulphate solutions for 1 year are presented and discussed in terms of pore structure and permeability parameters of the concrete.
Mechanistic Model for the Durability of Concrete Barriers Exposed to Sulphate-Bearing Groundwaters
Authors: Atkinson Alan , Hearne John A. 
Published: March 2011

ABSTRACTThe durability of concretes in radioactive waste repositories is likely to be limited by their reaction with sulphate-bearing groundwaters. In such a situation the concrete slowly degrades by sulphate penetrating into the concrete where it reacts with the cement to cause stress and eventual disruption. Experiments have been carried out to quantify these reactions and the resulting expansions. The data have been incorporated into an overall mechanistic model for sulphate degradation in which the criterion for disruption is the accumulation of a critical amount of stored elastic energy in the reaction zone. The results of this model are in good agreement with those of an earlier empirical model and enable extrapolations to be made to different concretes and groundwaters.
A Kinetic Model for Borosilicate Glass Dissolution Based on the Dissolution Affinity of a Surface Alteration Layer
Authors: Bourcier William L. , Peiffer Dennis W. , Knauss Kevin G. , McKeegan Kevin D. , Smith David K. 
Published: March 2011

ABSTRACTA kinetic model for the dissolution of borosilicate glass, incorporated into the EQ3/6 geochemical modeling code, is used to predict the dissolution rate of a nuclear waste glass. In the model, the glass dissolution rate is controlled by the rate of dissolution of an alkalidepleted amorphous surface (gel) layer. Assuming that the gel layer dissolution affinity controls glass dissolution rates is similar to the silica saturation concept of Grambow [1] except that our model predicts that all components concentrated in the surface layer, not just silica, affect glass dissolution rates. The good agreement between predicted and observed elemental dissolution rates suggests that the dissolution rate of the gel layer limits the overall rate of glass dissolution. The model predicts that the long-term rate of glass dissolution will depend mainly on ion concentrations in solution, and therefore on the secondary phases which precipitate and control ion concentrations.
Dissolution Mechanisms of the Perovskite and Hollandite Phases in the Synroc Assemblage
Authors: Nyhra S. , Pham D.K. , Smart R.St.C. , Turner P.S. 
Published: March 2011

ABSTRACTPerovskite (CaTiO3 )and hollandite ([BaxCsy,][(Ti,Al) 3+ Ti4 + ]016) 2x+y 8-2x-y are two of the three major phases of the Synroc titanate mineral assemblage. The chemical durabilities of these two phases have been investigated by solution analysis, surface analysis and electron microscopy. While a detailed model of the durability of perovskite has evolved from previous work, much less is known about the mechanisms which affect the durability of hollandite. The present investigations show that, for single-phase hollandite, selective extraction by ion exchange of Cs+ and Ba 2+ does not play a significant role. On the other hand, total dissolution of the network does seem to occur as a result of base-catalysed hydrolysis. Also, complexation and precipitation of Al and TI species in solution has the effect of driving the system to low pH. These results can be correlated with the more complete model for dissolution of perovskite in order to infer the overall effects of aqueous attack on the Synroc HLW solid.
A Comparison of the Behaviour of Vitrified HLW in Repositories in Salt, Clay and Granite: Part II: Results
Authors: Marples J.A.C. , Lutze W. , Kawanishi M. , van Iseghem P. 
Published: March 2011

ABSTRACTA ‘Round Robin’ test of the European Commission 's “Repository Systems Simulation Test” has been undertaken. This involved testing an inactive simulant of the French high-level waste glass SON68 (RTT7) in containers which also held backfill, geological materials and water. Ten laboratories undertook the granite option, six salt and three clay. The test procedure was closely specified and is given in detail in a companion paper [1]. Experiments with glass powder and (optionally) solid specimens in contact with aqueous solutions were run for periods of up to one year at 90 °C and the solutions were analysed for Si, B, Li and Mo (compulsory) and other constituents of the corroded glass (optional). The analytical results are used to compare the performance of the glass under conditions representing those that might occur in future repositories in the three media.
The Long-Term Corrosion and Modelling of Two Simulated Belgian Reference High-Level Waste Glasses - Part II
Authors: Patyn J. , Iseghem P. Van , Timmermans W. 
Published: March 2011

ABSTRACTThe long term corrosion of two reference Belgian high-level waste glasses (SAN60 and SM58) were investigated in pure water. The corrosion was studied using powdered glass at a high surface area to volume ratio and temperatures of 90 and 120°C. The experimental data at 90°C reveal a “final” leach rate which decreases with time. At 120°C this “final” state is transient and followed by an enhanced dissolution, which was correlated with extensive surface crystallization. Modelling using the PHREEQE and GLASSOL computer codes described the initial corrosion, but was unable to account for the enhanced dissolution at 120°C.
Product Consistency Leach Tests of Savannah River Site Radioactive Waste Glasses
Authors: Bibler Ned E. , Bates John K. 
Published: March 2011

ABSTRACTThe Product Consistency Test (PCT) is a glass leach test developed at the Savannah River Site (SRS) to confirm the durability of radioactive nuclear waste glasses that will be produced in the Defense Waste Processing Facility. The PCT is a seven day, crushed glass leach test in deionized water at 90°C. Final leachates are filtered and acidified prior to analysis. To demonstrate the reproducibility of the PCT when performed remotely, SRS and Argonne National Laboratory have performed the PCT on samples of two radioactive glasses. The tests were also performed to compare the releases of the radionuclides with the major nonradioactive glass components and to determine if radiation from the glass was affecting the results of the PCT.The test was performed in triplicate at each laboratory. For the major soluble elements, B, Li, Na, and Si, in the glass, each investigator obtained relative precisions in the range 2–5% in the triplicate tests. This range indicates good precision for the PCT when performed remotely with master slave manipulators in a shielded cell environment. When the results of the two laboratories were compared to each other, the agreement was within 20%. Normalized concentrations for the nonradioactive and radioactive elements in the PCT leachates measured at both facilities indicated that the radionuclides were released from the glass slower than the major soluble elements in the glass. For both laboratories, the normalized releases for both glasses were in the general order Li∼B∼Na>Si>Cs-137>Sb-125>Sr-90. The normalized releases for the major soluble elements and the final pH values in the tests with radioactive glass are consistent with those for nonradioactive glasses with similar compositions. This indicates that there was no significant effect of radiation on the results of the PCT.
The Reaction of Synthetic Nuclear Waste Glass in Steam and Hydrothernal Solution
Authors: Ebert W. L. , Bates J. K. 
Published: March 2011

ABSTRACTGlass monoliths of the WVC4M4, WVCM50, SRL 165, and SRL 202 compositions were reacted in steam and in hydrothermal liquid at 200°C. The glass reaction resulted in the formation of leached surface layers in both environments. The reaction in steam proceeds at a very low rate until precipitates form, after which the glass reaction proceeds at a greater rate. Precipitates were formed on all glass types reacted in steam. The assemblage of phases formed was unique to each glass type, but several precipitates were common to all glasses, including analcime, gyrolite, and weeksite. Reaction in steam occurs in a thin layer of condensed water which becomes saturated with respect to the observed phases after only a few days of reaction. The reaction in steam is accelerated relative to reaction in hydrothermal liquid In the sense that secondary phases form after a shorter reaction time, that is, after less glass has reacted, because of the smaller effective leachant volume present in the steam environment. A knowledge of the secondary phases which form and their influence on the glass reaction rate is crucial to the modeling effort of the repository program.
Characterization of Highly Active Waste Glasses Produced in a Hot Vitrification Pilot Plant
Authors: Cantale C. , Glatz J-P. , Toscano E.H. , Donato A. , Coquerelle M. , Fuger J. 
Published: March 2011

ABSTRACTFully radioactive waste glasses produced in a hot vitrification pilot plant were characterized in the hot cells at the JRC-Karlsruhe. The work includes microstructural analysis before and after leaching by SOXHLET extractors (MCC-5S), as well as leachate and gel-layer chemical analysis. Partial devitrification, with phases enriched in metals and rare earths, was observed in one of the products. In the gel layers formed during the dissolution tests, enrichment in some elements (Fe,Ti,Gd,Nd,Ce) and depletion in glass constituents (Si,B,K,Ba,Ca,Na) as well as in Mo and Cs, were determined. This was in good qualitative agreement with the leachate chemical analysis.
Calculation of the Viscosity of Nuclear Waste Glass Systems
Authors: Shah R. , Behrman E.C. , Oksoy D. 
Published: March 2011

ABSTRACTViscosity is one of the most important processing parameters and one of the most difficult to calculate theoretically, particularly for multicomponent systems like nuclear waste glasses. Here, we propose a semi-empirical approach based on the Fulcher equation, involving identification of key variables, for which coefficients are then determined by regression analysis. Results are presented for two glass systems, and compared to results of previous workers and to experiment. We also sketch a first-order statistical mechanical perturbation theory calculation for the effects on viscosity of a change in composition of the melt.
Identification of Secondary Phases Formed During Unsaturated Reaction of UO2 with EJ-13 Water
Authors: Bates J. K. , Tani B. S. , Veleckis E. , Wronklewicz O. J. 
Published: March 2011

ABSTRACTA set of experiments, wherein UO2 has been contacted by dripping water, has been conducted over a period of 182.5 weeks. The experiments are being conducted to develop procedures to study spent fuel reaction under unsaturated conditions that are expected to exist over the lifetime of the proposed Yucca Mountain repository site. One half of the experiments have been terminated, while one half are ongoing. Analyses of solutions that have dripped from the reacted UO2 have been performed for all experiments, while reacted UO2 surfaces have been examined for the terminated experiments. A pulse of uranium release from the UO2 solid, combined with the formation of schoepite on the surface of the UO2, was observed between 39 and 96 weeks of reaction. Thereafter, the uranium release decreased and a second set of secondary phases was observed. The latter phases incorporated cations from the EJ-13 water and include boltwoodite, uranophane, sklodowskite, compreignacite, and schoepite. The experiments are continuing to monitor whether additional changes in solution chemistry or secondary phase formation occurs.
Theoretical Modeling of Crevice and Pitting Corrosion Processes in Relation to Corrosion of Radioactive Waste Containers
Authors: Walton John C. 
Published: March 2011

ABSTRACTA mathematical and numerical model for evaluation of crevice and pitting corrosion in radioactive waste containers is presented. The model considers mass transport, mass transfer at the metal/solution interface, and chemical speciation in the corrosion cavity. The model is compared against experimental data obtained in artificial crevices. Excellent agreement is found between modeled and experimental values for the potential. The importance of full consideration of complex ion formation in the aqueous solution is emphasized and illustrated.
The Use of Additives for Reducing Hydrogen Yield in Mortar Containing Slag and Chloride Salts
Authors: Lewis Michele A. , Warren David W. 
Published: March 2011

ABSTRACTCementitious waste forms are being considered for immobilizing nuclear waste before disposal. In earlier work, it was found that irradiation of a mortar formulation consisting of slag, portland cement, fly ash, water, and up to 10 wt % KCI-LiCl salt resulted in the generation of hydrogen. Yields were relatively high and the rates of generation were constant for the irradiation period investigated. The addition of small amounts of oxygenrich electron scavengers (NaN03, NaI04, KMn04, or Ag20) to the mortar was investigated as a means for reducing hydrogen yields. The addition of NaN03 reduced the hydrogen yield; changed the radiolytic products from hydrogen to a mixture of hydrogen, nitrogen, and N20; and reduced the pressurization rate after exposure to 400 Mrads. The addition of NaI04 and KMn04 reduced hydrogen yields slightly while the addition of Ag20 increased the yield. Moreover, the addition of FeS to a non-slag mortar changed the radiolysis mechanism but the addition of FeO did not. The results of these experiments provided an insight into the nature of the radiolytic reactions occurring in the mortar formulations and indicated that the radiolytic generation of gases might be controlled with the proper choice of additive.
Potentiodynamic Polarization Studies of Candidate Container Materials in Simulated Tuff Repository Environments
Authors: Beavers John A. , Thompson Neil G. , Harper William V. 
Published: March 2011

ABSTRACTCortest Columbus is investigating the long-term performance of container materials used for high-level waste packages as part of the information needed by the Nuclear Regulatory Commission to assess the Department of Energy's application to construct a geologic repository for high-level radioactive waste. In one task of the program, a cyclic potentiodynamic polarization (CPP) technique was used to evaluate the corrosion behavior of the candidate container materials. In order to evaluate the expected range of environmental variables, a statistical experimental design approach was used. A Resolution IV experimental design for 15 variables was selected. The variables included temperature, pH, species present in the groundwater, and those generated by radiolysis. Complete matrices of CPP tests, which consist of tests in 33 environments, were performed on two candidate container materials; Type 304L Stainless Steel and Incoloy Alloy 825. In these tests, both alloys exhibited a wide range of behavior; including passive behavior, pitting and active corrosion. For each alloy, the environmental variables that affected corrosion behavior were identified.
Verfication of matrix diffusion by means of natural decay series disequilibria in a profile across a water-conducting fracture in granitic rock
Authors: Alexander W.R. , McKinley I.G. , MacKenzie A.B. , Scott R.D. 
Published: March 2011

ABSTRACTData from a rock drillcore, taken perpendicular to a water-bearing fracture in crystalline rock, clearly indicate water-rock interactions in and around the fracture. Although there is evidence of microfracturing at some distance from the main fracture, and therefore potential advective flow across the entire shear zone, simple calculations indicate that transport of Ra-226 in the vicinity of the main fracture can be described simply by matrix diffusion. This is a useful simplification for safety assessment studies and the consequences to the estimated radionuclide retardation in the vicinity of the fracture are discussed with respect to the probably over-conservative assumptions made in Nagra's safety assessment model base case.
The Solubility and Sorption of Uranium (VI) in a Cementitious Repository
Authors: Brownsword M , Buchan A B , Ewart F T , McCrohon R , Ormerod G J , Smith-Briggs J L , Thomason H P 
Published: March 2011

ABSTRACTThe solubility behaviour of uranium(VI) has been studied in a number of waters representative of the pore waters to be expected in candidate repository backfill concretes and also in solutions of calcium and sodium hydroxides. The sorption of uranium has been studied on one of these candidates, a Portland cement with a slag filler. The same cement has been hydrothermally treated to simulate the temperature conditions in the repository and the product used for comparative studies.The paper describes the experimental measurements and the results. The aqueous concentration of uranium over the uranates formed in the presence of sodium and calcium hydroxides was constant above pH 7 at 3 × 10−6 M. In the concrete pore waters the solubility of uranium was equal to or lower than this value. The distribution coefficient, Rd, for the sorption of uranium onto the slag cement was 2.5 × 104 ml g−1, and was increased by a factor two after hydrothermal treatment.
Modelling and Experimental Studies of Sorption in the Near Field of a Cementitious Repository
Authors: Brown P.L. , Haworth A. , McCrohon R. , Sharland S.M. , Tweed C.J. 
Published: March 2011

ABSTRACTA joint experimental and modelling programme is reported, which aims to improve our understanding of sorption processes of radionuclides onto repository materials. Diffusion/sorption experiments of sorption onto cement are described, although results are limited at this stage. The modelling studies use the coupled chemical equilibria and transport code CHEQMATE to simulate some of these experiments. The chemical part of the model is based on a simple mass-action model of sorption. More detailed comparisons will continue when the experiments are terminated, and the samples are sectioned.
Study on Relation Between Migration Behaviors and Chemical Forms of Cobalt
Authors: Ueta Shinzo , Katoh Naotake 
Published: March 2011

ABSTRACTMigration experiments focused on the relationship between sorption mechanism and chemical form of cobalt were carried out by means of column method. Adsorbents packed in the column were natural sand and artificial materials, for instance, charcoal. The experimental results were compared with three different migration models based on ion exchange, filtration, and adsorption, respectively.Cobalt existed as cation in the low pH region, where the migration behavior of cobalt was described by the ion exchange model. Cationic and colloidal species of cobalt coexisted in the pH 8.5 solution. The migration behavior of cobalt in this solution was satisfactorily described by the coupled model of the ion exchange and the filtration. Chelated anionic cobalt was not retained on the sand but retained on the charcoal and the other artificial materials to considerable extent. Breakthrough curves of cobalt in the charcoal column were successfully described by the adsorption model. Chelated cobalt was retained on the charcoal better than cationic cobalt. Distribution coefficients of chelated cobalt and cationic one were 670 ml/g and 130 ml/g, respectively.
Thermal Behaviour of Backfill Material for a Nuclear Fuel Waste Disposal Vault
Authors: Yong R.N. , Mohamed A.M.O. , Cheung S.C.H. 
Published: March 2011

ABSTRACTThe concept of disposing of used nuclear fuel in engineered rock formations is being studied in the Canadian Nuclear Fuel Waste Management Program. After the used fuel is emplaced in the vault, the vault would be backfilled. The backfill has to satisfy a number of engineering requirements. A reference backfill with satisfactory hydraulic, thermal and mechanical properties has already been selected.As the used fuel in the waste containers decays, heat will be generated and this heat will raise the temperature of the backfill material. The performance of the reference backfill material was evaluated over the temperature range 20–100°C. This paper addresses the results of experiments on thermal response and pressure development in the backfill for the period shortly after vault closure.
Multifractal Phenomena in Porous Rocks
Authors: Muller J. , Hansen J.P. , Skjeltorp A.T. , Mccauley J. 
Published: March 2011

ABSTRACTThe multifractal spectra of porespace of different types of porous sedimentary rocks are obtained using optical microscopy and a boxcounting technique. The computed f(α) functions were based on the canonical formalism, and can be used as a tool for rock characterization.