bluuebunny/crossref_metadata_2025 huggingface dataset:
Effects of MgO on the Short- and Long-Term Stability of R7T7 and M7 Nuclear Waste Glass in Aqueous Media
Authors: Advocat T. , Crovisier J.L. , Dussossoy J.L. , Vernaz E.
Published: March 2011

Experiments were conducted in initially pure water at 90°C and 100°C with glass specimens enriched in MgO and in alkali metals relative to the standard light water R7T7 reference glass. Three experimental protocols were implemented: Soxhlet testing with leachant renewal, static leaching according to a modified MCC-1 method with an SA/V ratio of 50 m−1, and static leaching with glass powder for an SA/V ratio of 8000 m−1 The results clearly show that the short and, especially, the long term dissolution rates depend on the initial glass composition. Higher MgO, Na2O, Li2O and B2O3 concentrations reduce the glass resistance to aqueous corrosion, as already indicated by the calculated hydration energy values. These experiments illustrate the importance of the glass composition in insuring long-term material integrity.
Effects of α-Decay on Mechanical Properties of Simulated Nuclear Waste Glass
Authors: Inagaki Y. , Furuya H. , Ono Y. , Idemitsu K. , Banba T. , Matsumoto S. , Muraoka S.
Published: March 2011

A simulated nuclear waste glass was self-irradiated by doping with short-lived actinides of 238Pu and 244Cm. Changes in the hardness, the Young's modulus and the fracture toughness, as a function of irradiation dose, were measured by use of indentation techniques. The irradiated glass was annealed at temperatures from 573K to 723K for periods of up to 48hours, and the recovery of these changes were measured as a function of annealing temperature and time.

It was observed that the hardness and the Young's modulus decreased, while the fracture toughness increased exponentially with the cumulative dose. The maximum values of the relative changes in the hardness, the Young's modulus and the fracture toughness were about −25%, −30% and +45%, respectively. The results of the annealing show that the hardness and the Young's modulus were almost recovered to the original values at temperatures above 673K within 10 hours, while the recovery of the fracture toughness was minimal in this region of temperature and time. The changes in the hardness and the Young's modulus can be well explained by the model, in which the changes is proportional to the volume fraction of damaged zones, F, and the recovery of F is first order. On the other hand, the changes in the fracture toughness cannot be explained by the model, which suggests that the mechanism of the change in the fracture toughness is different from that in the hardness and the Young's modulus.
Coupled Process Modeling and Waste-Package Performance
Authors: Mcgrail B. P. , Engel D. W.
Published: March 2011

The interaction of borosilicate waste glasses with water has been studied extensively, and reasonably good models are available that describe the reaction kinetics and solution chemical effects. Unfortunately, these models have not been utilized in performance assessment analyses, except in estimating radionuclide solubilities at the waste form surface. A geochemical model has been incorporated in the AREST code to examine the coupled processes of glass dissolution and transport within the engineered barrier system. Our calculations show that the typical performance assessment analyses using fixed solubilities or constant reaction rate at the waste form surface are not always conservative or realistic predictions of radionuclide release. Varying the transport properties of the waste package materials is shown to produce counterintuitive effects on the release rates of some radionuclides. The use of noncoupled performance assessment models could lead a repository designer to an erroneous conclusion about the advantages of one waste package design or host rock setting over another.
Kinematics and Thermodynamics of Non-Stoichiometric Oxidation Phase Transitions in Spent Fuel
Authors: Stout R. B. , Kansa E.J. , Wijesinghe A.M.
Published: March 2011

At low temperatures (<200°C), spent fuel from power reactors oxidizes from its UO2 lattice to a U4O9 lattice but with an oxygen-to-uranium (O/U) ratio of ∼2.4. Also, the weight gain time response has a plateau as the O/U approaches 2.4. Part of this response results from a geometrical dependency as a U4O9 oxidation front propagates into grain volumes of UO2. It may also be indicative of a metastable, non-stoichiometric U4O9 phase whose existence may inhibit the transition kinetics to the next expected phase of U3O8. To gain a mechanistic understanding and to plan future oxidation tests, lattice kinematic and thermodynamic models are developed for lattice deformations and energetics of lattice phase changes (UO2 → U4O9 → U3O7 → U3O8) that include zeroth order influences on oxidation kinetics due to interstitial oxygen atoms and vacancies plus interstitial and substitutional actinides and fission decay products in spent fuel.
The Possibility for Microbially Influenced Degradation of Cement Solidified Low-Level Radioactive Waste Forms
Authors: Rogers Robert D. , Hamilton Melinda A. , Mcconnell John W.
Published: March 2011

The Nuclear Regulatory Commission (NRC) regulations 10 CFR Part 61, “Licensing Requirements for Land Disposal of Radioactive Waste,” regulate the disposal of radioactive waste and provides, among other stipulations, that class B and C low-level radioactive waste (LLW) be stabilized. This is intended to ensure that solidified waste does not structurally degrade and cause subsidence in the disposal unit's cover system. It is reasoned that deterioration of the waste form could adversely effect the stability of the burial site and lead to the release of radionuclides to the environment. Because of its apparent structural integrity, cement has been widely used as a binder to solidify LLW. However, the resulting preparations called pozzolanic cements are susceptible to failure due to the actions of stress and environment.

This paper presents data from the literature that document the significance of biologically mediated chemical attack on concrete, in general. Concrete is susceptible to aggressive reaction with acids (both mineral and organic) of natural and anthropogenic origin. If persistent, such reactions ultimately lead to structural failure. Groups of microorganisms have been identified that are capable of metabolically converting organic and inorganic substrates into organic and mineral acids.

The literature supports the conclusions that acid-producing bacteria of one type or another could be prevalent in all soils, even at depths expected for burial of LLW. Given the appropriate conditions of micro-environment and suitable substrate for growth, these bacteria will create conditions conducive to concrete deterioration. Growth substrates used by acid-producing bacteria (i.e., ammonia compounds, other reduced nitrogen compounds, sulfur and reduced sulfur compounds, reduced iron compounds, as well as organic carbon) could be naturally present in the disposal environment or be provided by the contents of the waste form.

Sufficient evidence is presented which demonstrates the potential for microbially-influenced deterioration of cement-solidified LLW. These data are the basis for the NRC initiating the development of appropriate tests to determine the resistance of cement-solidified LLW to microbiologically induced degradation.
Effects of Microorganisms Growth on the Long-Term Stability of Cement and Bitumen
Authors: Libert Marie F. , Sellier R. , Jouquet G. , Trescinski M. , Spor H.
Published: March 2011

Cement is used as a coating matrix for nuclear waste or as an engineered barrier of waste repositories situated in geological formations.

The effect of mineral acids excreted by bacteria (Thiobacillus) or organic acids produced by fungi, on the biodegradation of cement is discussed. Organic acids are quantitatively and qualitatively determined during growth of fungi over a two-year period. Even with high pH conditions, pH of the cement ≈ 11, growth of microorganisms occurs.

Biodeterioration of cement is expressed in terms of bioleaching velocity of calcium and is observed by electron microscopy.
The Chemical Behavior of Transuranium Elements and Barrier Functions in Natural Aquifer Systems
Authors: Kim Jae-Il
Published: March 2011

The chemical behavior of transuranium elements in natural aquifer systems is governed by a variety of geochemical reactions, such as dissolution reaction (solubility), hydrolysis, complexation with inorganics or organics, redox reaction, colloid formation, geochemical interaction with surfaces of various minerals, coprecipitation, mineralization, etc. This paper reviews the present state of knowledge on some of these particular reactions. The emphasis here is on how the individual reactions can be appraised for long-term prediction of the geochemical behavior of transuranium elements in the natural environment. of the various possible reactions, the primary thermodynamic processes are discussed with notable examples: dissolution of transuranium compounds in aquatic solution; complexation with important anions present in groundwater; and colloid generation. Various laser spectroscopic methods in use for chemical speciation are mentioned briefly for their spectroscopic capability, as well as for their applicability. The present paper attempts to better understand the migration behavior of transuranium elements in natural aquifer systems.
Solidification of Microbiologically Treated Ion-Exchange Resins Using Portland Cement-Based Systems
Authors: Ipatti Ari
Published: March 2011

Pretreated inactive ion exchange resins from the Loviisa nuclear power plant (NPP) were first reduced to one tenth of the original volume through microbiological treatment. During the process, the granular ion exchange resins were decomposed to result in dregs, which were solidified with two types of Portland cements. The objective of the present experiments was to investigate whether commercial cements are suitable solidification agents for this kind of waste.

A total of ten mixtures were pretested for their rheological and setting properties. On the basis of the pretest results, four additional mixtures were chosen and tested for the spread value, density, air content, setting time and bleeding of the fresh waste product and for the dimensional stability and compressive strength of the hardened waste product. The cementing systems incorporated in the tests were ASTM type V Portland cement and ASTM type P Portland Composite cements. The dregs used in the tests were taken from a Pilot-Plant experiment at the Loviisa NPP and contained 2 wt-% solids.

The test results were promising in showing that microbiological dregs can very easily be solidified with Portland cements to form a high-quality waste product. Thus, the microbiological treatment of spent ion exchange resins will drastically decrease the amount of solidified waste to be disposed of at the Loviisa NPP.
Laboratory Studies of Gas Generation for the Waste Isolation Pilot Plant
Authors: Brush L. H. , Molecke M. A. , Westerman R. E. , Francis A. J. , Gillow J. B. , Vreeland R. H. , Reed D. T.
Published: March 2011

The design-basis, defense-related, transuranic waste to be emplaced in the Waste Isolation Pilot Plant may, if sufficient H2O, nutrients, and viable microorganisms are present, generate significant quantities of gas in the repository after filling and sealing. We summarize recent results of laboratory studies of anoxic corrosion and microbial activity, the most potentially significant processes. We also discuss possible implications for the repository gas budget.
Recent Advances in the Study of Microbiologically Influenced Corrosion
Authors: Little Brenda , Wagner Patricia
Published: March 2011

The study of microbiologically influenced corrosion (MIC) has progressed from phenomenological case histories to a mature interdisciplinary science including electrochemical, metallurgical, surface analytical, microbiological, biotechnological and biophysical techniques. With gene probes and microelectrodes it is now possible to measure interfacial dissolved oxygen, dissolved sulfide and pH and to further determine the microbial species responsible for the localized chemistry. Biofilms can be tailored to contain consortia of specific microorganisms and naturally occurring biofilms can be dissected into cellular and extracellular constituents. Scanning vibrating electrodes can be used to map the distribution of anodes and cathodes so that localized corrosion can be correlated with the location of microorganisms. The development of environmental scanning electron, atomic force, and laser confocal microscopy makes it possible to image cells on surfaces and to accurately determine the spatial relationship between microorganisms and corrosion. Transport of nutrients through biofilms is being modeled using techniques including optical density measurements to precisely locate the water/ biofilm interface and nuclear magnetic resonance imaging to visualize flow characteristics near surfaces colonized with microorganisms. The ways in which these new techniques can be used to understand fundamental mechanisms and to discriminate critical issues of MIC will be discussed.
Electrochemical Studies of Corrosion of Sinfuel: Simulated Used UO2 Fuel
Authors: Sunder S. , Shoesmith D.W. , Miller N.H.
Published: March 2011

The corrosion of SIMFUEL, simulated high-burnup CANDU (CANadian Deuterium Uranium) fuel, was investigated in 0.1 mol·dm−3 NaClO4 solution (pH ∼ 9.5) as a function of dissolved oxygen concentration using electrochemical techniques and X-ray photoelectron spectroscopy (XPS). Electrodes were constructed of SIMFUEL pellets with compositions close to those of a natural UO2 fuel that has undergone burnup of 3 at% and 6 at%. The XPS analysis of freshly polished SIMFUEL pellets showed that the extent of uranium oxidation in SIMFUEL was equivalent to that in stoichiometric UO2. The SIMFUEL electrodes showed higher conductivity and electrochemical reactivity than the pure UO2 electrodes. A comparison of the open circuit corrosion potentials of the SIMFUEL electrodes with that of a pure UO2 electrode in oxygenated solutions showed a much faster increase in the potential for the SIMFUEL electrodes at short times. This suggests that the initial stages of UO2 oxidation, i.e., UO2 → UO2+x → UO2.33, are facilitated by fission product impurities in the UO2 matrix. However, the “steady-state” oxidation of uranium in SIMFUEL by the dissolved O2 was similar to that observed in pure UO2 under similar conditions.
Susceptibility of Stainless Steel Weldments to Microbiologically Influenced Corrosion
Authors: Borenstein Susan Watkins
Published: March 2011

Microbiologically influenced corrosion (MIC) is the term used for the phenomenon where corrosion is initiated or accelerated by microorganisms. Biofilms of bacteria form on metal surfaces when exposed to natural waters. The activity of these biofilms and how they attach themselves to metal surfaces directly influence corrosion mechanisms.

This paper describes the mechanisms for MIC and the factors which influence the susceptibility of austenitic stainless steel weidments to MIC. The metallurgical, microbiological and electrochemical factors that influence MIC are discussed. Case histories of MIC-related failures and field test results of austenitic stainless steel weldments in various welded conditions are presented.
Moisture Adsorption and Volume Change of Partially Saturated Bentonite Buffer Materials
Authors: Kanno Takeshi , Wakamatsu Hisao
Published: March 2011

Water vapor adsorption characteristics of buffer materials to be used for the geologic disposal of high-level radioactive waste have been investigated. Highly compacted blocks of Japanese Na bentonite were used as the buffer material. Initial dry density of the blocks was 1.8 g/cm3. Volume changes and water contents of the blocks in equilibrium with surrounding moist air were measured. The humidity of the surrounding air was kept constant, and the suction of the block at equilibrium has been determined by the humidity. The temperature of the surrounding air was varied between 20°C and 60°C.

The volumetric strain was observed to vary approximately between −3% and 13% depending on the humidity of 0.6% to 95%. Some analytical expressions derived from these experiments on moisture adsorption are presented in this paper. Water vapor adsorption isotherm of the bentonite blocks was also obtained. The swelling pressures calculated from the analytical expressions are compared with literature data for this bentonite.
Radiolytically-Induced Gas Production in Plutonium-Spiked Wipp Brine
Authors: Reed D. T. , Okajima S. , Brush L. H. , Molecke M. A.
Published: March 2011

Gas generation due to alpha particle deposition was investigated in four WIPP relevant brines; WIPP brine A, ERDA-6, DH-36 and G8-B. This was done by spiking each brine with plutonium-239 and periodically sampling the gas phase to determine the nature of the gaseous products and the rates of gas generation. The predominant gas generated radiolytically was hydrogen, with yields ranging from 0.6 to 1.5 molec/100 eV for the four brines tested. Plutonium (VI) was stable in two synthetic brines, WIPP brine A and ERDA-6 but was rapidly reduced in the underground collected brines DH-36 and G8-B, although most of the plutonium remained in solution.
Evaluation of the Retention Capability of Backfill Materials in the Presence of Cement Waste Form
Authors: Ghattas N.K. , Adham K.A.El , Eskander S.B. , Mahmoud N.S.
Published: March 2011

The present study focused on the retention capability of the different local backfill materials and on horizontal and vertical radionuclide migration in simulated repository conditions of a saturated static humid environment, using single or combined components of the near-field. The results obtained from semi-field experiment show that no migration of cesium radionuclide was detected outside the backfill zone within the time interval of the experiment. This reflects the possible efficiency, of the backfill materials used, for the confinement of radioactivity to the disposal site. On the other hand laboratory experiments show the effect of simulated repository condition on the sorption and desorption properties of backfill materials. It is clear from the results obtained that the presence of cement waste forms in equilibrium with underground water affect the retention capability of the backfill materials. The motivation of the work was a desire to provide a basis for minimizing radioactive waste processing by improving nonradioactive engineering barriers.
Study of the Performance of Sealing Systems for Access Shafts in a High-Level Waste Repository
Authors: Saotome A. , Hara K. , Okamoto J.
Published: March 2011

Shaft sealing in a high-level waste(HLW) disposal system functions to minimize the water flow passage, and retard the radionuclide transport from the repository to the accessible environment. It is important to estimate the radionuclide migration along the sealed shaft from the viewpoint of the design and the performance assessment of the sealing system.

This study presents the results of sensitivity analyses on the radionuclide migration in the vicinity of the access shaft of a repository in order to evaluate the effects of the length of a plug, as well as the number of plugs, and curtain grouts.

In this study, the upward hydraulic gradient of the groundwater flow along shafts was used, based on transient coupled thermo-hydraulic analyses around a repository. Hydraulic conductivities of the backfill material and the disturbed zones around the shaft tunnels were also assumed to be one order and two orders of magnitude higher than that of the host rock, respectively.

The results show that the velocity of the groundwater within the shaft and the disturbed zone is reduced by a factor of one third by installing a few plugs into the shaft filled with backfill material. The curtain grouts have the effect of retarding the radionuclide migration from the repository to the ground surface at a factor of approximately five. A few plug installations have the same effect. The sealing system properly constituted with backfill, plugs, and grouts can provide the same performance as the original host rock.
Uranium Mineral – Groundwater Equilibration at the Palmottu Natural Analogue Study Site, Finland
Authors: Ahonen Lasse , Ervanne H. , Ruskeeniemi T. , Jaakkola T. , Blomqvist R.
Published: March 2011

The redox-potential, pH, chemical composition of fracture waters, and uraninite alteration associated with the Palmottu uranium mineralization, have been studied. The data have been interpreted by means of thermodynamic calculations. The results indicate equilibrium between uraninite, ferric hydroxide and groundwater in the bedrock of the study site. Partially oxidized uraninite (UO2.33) and ferric hydroxide are in equilibrium with the fresh, slightly acidic and oxidized water type, while primary uraninite is stable with deeper waters that have a higher pH and lower Eh. Measured Eh-pH values of groundwater cluster within a relatively narrow range indicating buffering by heterogenous redox-processes. A good consistency between measured Eh and analyzed uranium oxidation states was observed.
Oxidative Alteration of Uraninite at the Nopal I Deposit, Mexico: Possible Contaminant Transport and Source Term Constraints for the Proposed Repository at Yucca Mountain
Authors: Leslie Bret W. , Pearcy English C. , Prikryl James D.
Published: March 2011

The Nopal I uranium deposit at Pefla Blanca, Mexico is being studied as a natural analog of the proposed high-level nuclear waste repository at Yucca Mountain. Identification of secondary uranium phases at Nopal I, and the sequence of their formation after uraninite oxidation, provides insight into the source term for uranium, and suggests that uranophane may control uranium release and transport in a silicic, tuffaceous, chemically oxidizing, and hydrologically unsaturated environment. Possible constraints on contaminant transport at Nopal I are derived from the spatial distribution of uranium and from measurements of 238U decay-series isotopes. The analyses indicate that flow of U-bearing fluids was influenced strongly by fracture density, but that the flow of these fluids was not restricted to fractures. Gamma spectroscopic measurements of 238U decay-series isotopes indicate secular equilibrium, which suggests undetectable U transport under present conditions.
A Modelling Study on the Fractionation of Uranium Among Minerals During Rock Weathering
Authors: Ohnuki Toshihiko , Murakami Takashi , Yanase Nobuyuki
Published: March 2011

A modelling study has been carried out to understand the effect of rock alteration on the fractionation of uranium among coexisting minerals (chlorite, vermiculite, kaolinite, amorphous and crystalline iron minerals) at the Koongarra ore deposit, Australia. The model considers the chlorite weathering process, its mechanism and rate, and assumes the presence of reversible and irreversible sorption sites in the secondary minerals. The calculated uranium concentrations at the two different sites in the minerals were compared with the results of sequential extraction experiments. Good agreement between the calculated and observed uranium concentrations was obtained only when an appropriate fraction of uranium is fixed to the irreversible sorption sites of the altered clay minerals. However, a conventional Kd model gave inconsistent uranium concentrations. The calculated results show that the crystalline iron minerals sorb uranium during all stages of weathering, and that the uranium fractionation among the minerals varies with time until the end of the weathering.
Photothermal Deflection Spectroscopy Investigations of Uranium Electrochemistry
Authors: Rudnicki James D. , Russo Richard E.
Published: March 2011

Photothermal Deflection Spectroscopy (PDS) has been successfully applied to the study of uranium oxide electrochemistry. A brief description of PDS and preliminary results that demonstrate the technique are presented. Concentration gradients formed at the electrode surface are measured by this technique. The gradients give insight into the reaction mechanisms. There is some evidence of the initiation of non-electrochemical dissolution of the uranium oxide. Optical absorption by the uranium oxide is measured by PDS and the first results indicate that the absorption of the surface does not change during electrochemical experiments. This result is contrary to literature measurements of bulk samples that indicate that the optical absorption should be strongly changing.
Kinetically Controlled Dissolution of UO2(s) Under Oxidizing Conditions. A Combined Dissolution-Okidation Model.
Authors: Casas Ignasi , Gimenez J. , Marti V. , Torrero M.E. , De Pabloc J.
Published: March 2011

The release of uranium from three samples of UO2(S) with different particle sizes (100–300 μm, 900–1100 μm, pellet) has been studied as a function of time. In all cases, the same pH, ionic medium, temperature, and oxygen partial pressure were used.

Two distinctive trends were observed in the three cases, with a relatively fast initial uranium release followed, after 10–15 days, by a slower dissolution rate. The experiments were continued during 200 days; no change in the second dissolution rate was noticed.

The uranium released as a function of time has been successfully fitted with a mathematical expression which combines an oxidation-dissolution mechanism.
Repassivation Potentials for Long-Term Life Prediction of Localized Corrosion
Authors: Sridhar Narasi , Cragnolino Gustavo
Published: March 2011

The effect of pit growth on repassivation potentials (Erp) of type 316L stainless steel (SS) and alloy 825 is investigated using a decreasing potential staircase technique. The Erp decreases initially with increasing pit depth and then attains a value which is relatively independent of pit depth. The Erp also decreases with increasing potential scan rate because of the decreasing time for repassivation with decreasing potential. The Erp, is explained in terms of the effect of applied potential on changes in solution composition inside growing pits and its use is recommended as a bounding parameter for long-term prediction of localized corrosion.
Dissolution of UO2(s) in MgCl2-Brines Under Different Redox Conditions.
Authors: Casas Ignasi , Gimenez J. , De Pablo J. , Torrero M.E.
Published: March 2011

The dissolution of unirradiated UO2(s), with a particle size of 1 mm, has been studied in MgCl2 brines at 298 K under both reducing and oxidizing conditions. Results obtained under reducing conditions (H atmosphere in the presence of a palladium catalyst) show an initial increase of the total uranium concentration in solution and a subsequent decrease until equilibrium (or steady state) values are reached. Results obtained under oxidizing conditions (nominal oxygen partial pressures of 0.05, 0.21 and 1 atm) show two different trends. A relatively fast initial dissolution rate and, after approximately two or three weeks, a slower dissolution rate. X-Ray Photoelectron Spectroscopy (XPS) has shown that the UO2 surface composition changes during the experiment.
Some Important Mechanisms and Processes in the Near Field of the Swedish Repository for Spent Nuclear Fuel
Authors: Neretnieks Ivars
Published: March 2011

In repositories for nuclear waste there are many processes that will be instrumental in damaging the canisters and releasing the nuclides. Based on experiences from studies of the performance of repositories and of an actual design, the major mechanisms influencing the integrity and performance of a repository are described and discussed. The paper addresses only conditions in crystalline rock repositories. The low water flow rate in fractures and channels plays a dominant role in limiting the interaction between water and waste. Molecular diffusion in the backfill and rock matrix, as well as in the mobile water, is an important transport process, but actually limits the exchange rate because diffusive transport is slow. Solubility limits of both waste matrix and of individual nuclides are also important. Complicating processes include alpha-radiolysis, which may change the water chemistry in the near-field. The sizes and locations of water flowpaths and damages in the canisters considerably influence the release rates. Uncertainties in data are large. Nevertheless the system is very robust in the sense that practically no reasonably conceivable assumptions or data will lead to large nuclide releases. Several natural analogues have been found to exhibit similarities with a waste repository and help to validate concepts and to increase our confidence that all major issues have been considered.
Performance Assessment of Engineered Barriers Using the Vault Model.
Authors: Johnson L.H. , Leneveu D.M.
Published: March 2011

The Vault Model for assessing engineered barrier performance has been developed as part of the preparation of an Environmental Impact Statement to be presented to a Federal Environmental Assessment Review Panel reviewing the Canadian nuclear fuel waste disposal concept. The model describes the behaviour of titanium containers, radionuclide release from used fuel, and migration of radionuclides through buffer and backfill materials and into the surrounding geosphere. Vault Model simulations have shown that the release of radionuclides from the engineered barrier system is dominated by the release from the fuel-sheath gap and grain boundaries in used fuel. Sensitivity and uncertainty analyses have illustrated how releases from the vault are affected by both the uncertainty in model parameters and the assumptions made in the development of the models. It is likely that the combined effects of a number of conservatisms in the model result in the releases from the engineered barrier system being overpredicted by several orders of magnitude.
The IAEA Coordinated Research Programme on the Performance of High-Level Waste Forms and Packages Under Repository Conditions
Authors: Tsyplenkov Vladimir S.
Published: March 2011

The IAEA initiated, in 1991, a Coordinated Research Programme (CRP), with the aim of promoting the exchange of information on the results obtained by different countries in the performance of high-level waste forms and waste packages under conditions relevant to final repository. These studies are being undertaken to obtain reliable data as input to safety assessments and environmental impact analyses, for final disposal purposes. The CRP includes studies on waste forms that are presently of interest worldwide: borosilicate glass, Synroc and spent fuel.

Ten laboratories leading in investigation of high-level waste form performance have already joined the programme. The results of their studies and plans for future research were presented at the first Research Coordination Meeting, held in Karlsruhe, Germany, in November 1991. The technical contributions concentrated on effecting an understanding of dissolution mechanisms of waste forms under simulated repository conditions. A quantitative interpretation of the chemical processes in the near field is considered a prerequisite for long-term predictions and for the formulation of a "source term" for performance assessment studies.
Near-Field Performance Assessment for the Saltstone Disposal Facility
Authors: Seitz Roger R. , Walton John C. , Dicke Craig A. , Cook James R.
Published: March 2011

A near-field performance assessment (PA) was conducted for the Saltstone Disposal Facility (SDF) at the Savannah River Site in South Carolina. The analysis was conducted in four parts: general screening calculations, degradation calculations, and flow and transport through the fractured and nonfractured facility. Modeling approaches and example sensitivity analysis results from the simulations of the fractured facility are discussed. Design considerations that may not be apparent without addressing flow and transport through fractures and lessons learned during the process are also presented.
Bulk Solubility and Speciation of Plutonium(VI) in Phosphate-Containing Solutions
Authors: Weger H. T. , Okajima S. , Cunnane J. C. , Reed D.T
Published: March 2011

The solubility and speciation of Pu(VI) with phosphate is being investigated to determine the ability of phosphate to act as an actinide getter. In the initial studies performed, solubility was approached from oversaturation at an initial pH = 4, 10 and 13.4. Absorption spectra were recorded, the solution filtered, and the filtrate analyzed for Pu content. Absorption spectra were obtained at varying phosphate concentrations, and at pH of 2.7 to 11.9. The effect of complexation on the 833 nm Pu(VI) band was characterized. Evidence for three phosphate complexes was obtained for pH < 10, which have absorption bands at 842, 846 and 849 nm. Evidence for colloid formation was observed, but is not conclusive. The possible presence of colloids prevented an accurate determination of true solubility. A concentration of 10−5 to 10−6M Pu(VI) was measured in solutions at pH ≤ 10 that was filtered with a 50 nm filter. Pu(VI)-phosphate complexes predominated at pH ≤ 11.6. At higher pH, however, only hydrolyzed Pu(VI) was detected. At pH = 12, the concentration of Pu(VI) was as high as 10−4M.
Evidence of Radiolytic Oxidation of 241Am in Na+ / Cl− / HCO−3/ CO2−3 Media.
Authors: Giffaut Eric , Vitorge Pierre
Published: March 2011

This paper examines Americium behaviour in CI− media at room temperature in connection with environmental and waste disposal programs. Most published values on U, Np, Pu and Am complexation in chloride media have been determined using extraction methods. Spectrophotometric techniques are not sensitive enough to prove actinide complexation by chloride, which is confirmed in this paper for Am(III).

Am(OH)3(s), AmOHCO3(s), Am2(CO3)3(s) or NaAm(CO3)2(s) solid phases can control the Am solubility, depending on the chemical conditions of the aqueous phase (usually PCO2). 241Am solubility is here found to be higher in NaCl 4M media than in NaCl 0.1 M (up to 3 orders of magnitude). Addition of a reducing agent (metallic iron) lowers the solubility. After a week, solubilities in NaCl 0.1 M and 4 M are similar. These results are consistent with Am(III) radiolytic oxidation to Am(V), due to cc radiations. Little evidence of Cl− or mixed Cl−-CO2−3 complexes is found in these conditions. In Na+-OH−-Cl− media, 241Am(III) oxidation had also been proposed. Slow kinetics of precipitation could induce experimental uncertainities.
Microbial Effects on the Radionuclide Transport in a Deep Nuclear Waste Repository
Authors: Spor Herve , Trescinski M. , Libert M.F.
Published: March 2011

This study deals with the effects of microorganisms on the transport of radionuclides under deep nuclear-waste disposal conditions. Metabolism of a cellulolytic microorganism is studied. Cellulose, as a carbon source, is representative of nuclear waste.

A pilot device allows the study of the general effect of microrganisms. Bioleaching of radionuclides by a fungal culture is performed on columns of clay and cement used as engineered barriers. Cesium and Uranium had been incorporated into matrices prior to the tests. Operating conditions have been choosen according to realistic conditions of a deep repository. The production of organic acids by microorganisms is qualitatively and quantitatively determined.

In addition, direct effects of microorganisms (biosorption, bioaccumulation) and indirect effects (complexing agents issued from the diodegradation of cellulose) on the transport and/or retardation of radionuclides are studied.
Initial Demonstration of the Vitrification of High-Level Nuclear Waste Sludge Containing an Organic Cs-Loaded Ion-Exchange Resin
Authors: Bibler N. E. , Bibler J. P. , Andrews M. K. , Jantzen C. M.
Published: March 2011

When immobilizing into borosilicate glass the radionuclides in the caustic high-level radioactive wastes stored in the USA, the soluble fission product Cs-137 has to be removed from supernates of the wastes. In the current processes zeolites or an organic precipitant will be used to remove the Cs. These are then treated further and mixed with the radioactive sludges and vitrified into a borosilicate glass. This paper describes the vitrification of a mixture resulting from using a new process to remove Cs from the caustic supernate. A resorcinol based organic ion exchange resin is used. This resin was then mixed with sludge and frit and vitrified. Using an organic ion exchange resin rather than zeolite or the organic precipitant has certain advantages. For example, use of the zeolite increases the amount of glass to be made and use of the organic precipitant produces benzene as a secondary waste stream. Results in the paper indicate that a mixture of the resin, sludge and frit can be successfully vitrified in a joule-heated, slurry fed melter. However, when resin is present in the feed, the glass becomes less durable due to the increased amount of Fe(II) caused by reduction of Fe(III) in the melt. Based on the durabilities of other waste glasses, this glass is still suitable as a canistered wasteform.
Radio-Labelled Humic Materials in Migration Studies
Authors: Carlsen Lars , Lassen Pia , Warwick Peter , Randall Amanda
Published: March 2011

Humic- and fulvic acids are able to complex polyvalent metal ions, e.g. radionuclides, leading to soluble complexes of significant strength, thereby decreasing the sorption of these compounds to soils and sediments. The interaction of humic materials with radionuclides may significantly influence the availability and transport of the latter in the environment. Typically, studies along these lines have focussed almost exclusively on the radionuclides, whereas the actual role of the humic material has been elucidated only indirectly. In order directly to study the behaviour of the naturally occurring organic macro-molecules in relation to the environmental fate of radionuclides, radio-labelled humic- and fulvic acids can advantageously be applied. Radio-labels such as 14C and 125I have successfully been covalently incorporated in humic- and fulvic acids. Labelling of humic substances as well as preliminary migration studies are discussed
Development of a Gas Method for Migration Studies in Fractured and Porous Media.
Authors: VÄÄtÄinen Kusti , Timonen Jussi , HautojÄrvi Aimo
Published: March 2011

A gas method for fast measurements of diffusion properties of porous materials has been developed. Diffusion coefficients in the gas phase are typically four orders of magnitude larger than those in the liquid phase. For samples whose structures do not change much upon drying it is possible to estimate the diffpision properties of the liquid phase when the properties of the gas phase are known. Advantages of the gas method are quick and easy measurements and therefore they can be used to optimize the liquid-phase measurements which may last months or years. For materials with good correlation between the gas and liquid-phase diffusion, the number of liquid phase measurements can be greatly reduced.

Nitrogen was used as the carrier gas and helium as the tracer gas. Helium concentrations were measured by using standard techniques. The equipment was tested for two sample geometries, a column made of a polished granite slab and an acrylic slab with a flow channel in between, and a hollow bore core where diffusion occurs through the sample. Both types of measurement were modelled and apparent diffusion coefficients in the gas phase were determined.
Effects of Some Common Geological Features on Two-Dimensional Variably Saturated Flow
Authors: Bagtzoglou Amvrossios C. , Ababou Rachid , Sagar Budhi , Islam M. Rashidul
Published: March 2011

This paper presents results of unsaturated flow simulations undertaken as an auxiliary analysis for the Iterative Performance Assessment (IPA) project, one of the approaches adopted' by the U.S. NRC to develop repository license application review capabilities. The effects on flow of common geological features, such as nonhorizontal stratification and vertical or near-vertical fault zones intersecting the strata, in a two-dimensional (2D) domain are studied. Results indicate that the presence of layers and crosscutting fault zones tend to induce three-dimensional (3D) unstable flows in the unsaturated zone. The instability is manifested in our simulations by an oscillatory behavior of steady state. This numerical instability imposes extremely stringent criteria on the time step used in the simulation. Finally, once stable steady-state solutions are attained, the effect of the crossing point in the matrix-fault unsaturated hydraulic conductivity curve on groundwater flux vectors and moisture content distributions is studied.
Leach Resistance Properties and Release Processes for Salt-Occluded Zeolite A
Authors: Lewis M. A. , Fischer D. F. , Laidler J. J.
Published: March 2011

The pyrometallurgical processing of spent fuel from the Integral Fast Reactor (IFR) results in a waste of LiCI-KCI-NaCI salt containing approximately 10 wt% fission products, primarily CsCI and SrCI2. For disposal, this waste must be immobilized in a form that it is leach resistant. A salt-occluded zeolite has been identified as a potential waste form for the salt. Its leach resistance properties were investigated using powdered samples. The results were that strontium was not released and cesium had a low release, 0.056 g/m2 for the 56 day leach test. The initial release (within 7 days) of alkali metal cations was rapid and subsequent releases were much smaller. The releases of aluminum and silicon were 0.036 and 0.028 g/m2, respectively, and were constant. Neither alkali metal cation hydrolysis nor exchange between cations in the leachate and those in the zeolite was significant. Only sodium release followed t0.5 kinetics. Selected dissolution of the occluded salt was the primary release process. These results confirm that salt-occluded zeolite has promise as the waste form for IFR pyroprocess salt.
Interpreting Drop-Weight Impact Results in Terms of Deformation Dependent Initiation Criteria
Authors: Baker P. J. , Mellor A. M.
Published: March 2011

The impact sensitivity of energetic materials is frequently measured in small-scale drop-weight tests. Plastic deformation of the sample leads to heating, the onset of chemical reaction, and eventual ignition. An analytic model provides deformation dependent estimates of the energy delivered to the sample, its stress state, and its temperature distribution. Results for hydoxy-terminated polybutadiene (HTPB/AP) propellants are interpreted in terms of two initiation criteria: critical decomposition temperature and critical thickness for shear banding. The influence of friction, impact velocity, and sample size on initiation give possible explanations of experimental results. Sample material properties variations are studied for both initiation criteria. The model includes energy localization by varying the thickness of shear layers at the sample/machine interface.
Ab Initio Study of Electronic Structure of RDX Molecular Crystal
Authors: Gao Guang , Pandey Ravindra , Kunz A. Barry
Published: March 2011

An embedded molecular cluster model is used to study the electronic structure of cyclotrimethylene trinitramine(RDX) molecular crystal. In this model, a molecular cluster describing a local region of the crystal is treated in the Hartree-Fock approximation. The embedding lattice is represented by multipoles that are determined quantum-mechanically. Cluster-lattice orthogonality is achieved by transforming canonical orbitals to orbitals which are localized on individual molecular sites by means of a self-consistent localization potential. Results for the free molecule and the perfect crystal demonstrate the domination of three N-NO2 groups on intermolecular properties. For the defective crystal, results show a significant distortion in the electronic structure caused by local deformations in the lattice that may account for the formation of hot spots.
Electronic Excitations Preceding Shock Initiation in Explosives
Authors: Sharma J. , Beard B. C.
Published: March 2011

Electronic excitations which precede and can facilitate chemical reactivity of explosive molecules during shock passage will be discussed. The structurally similar family of explosives, TATB, DATB, Picramide and TNB were the focus of this work. It has been found that the energy of shake-up transitions observed in x-ray photoelectron spectra of these molecules shows a linear relation with the explosive sensitivity. To the contrary, optical absorption maxima, dependant upon dipole selection rules display a trend opposite that intuitively expected in relation to ease of initiation. The shake-up transitions are governed by monopole selection rules, so that the transitions between initial and final states of the same symmetry are allowed. The forbiddeness of the excited state may favor proton transfer, bond breakage and free radical formation relative to de-excitation by returning to the ground state. Electronic excitations of this type are believed to be important to multiphonon up pumping. The Is core hole resulting from photoionization creates a central coulomb force that shrinks the orbitals, simulating conditions similar to those of high pressure or shock passage. These factors may be at the heart of the correlation between the shake-up promotion energy and explosive sensitivity.
Atomic Force Microscopy of Ammonium Perchlorate
Authors: Yoo Minsun , Yoon Seokwon , Lozanne Alex De
Published: March 2011

We have studied the (210) surface of ammonium perchlorate (NH4ClO4) with an atomic force microscope (AFM) in air. Large scale images show monomoreculat steps that are often aligned with major crystalline directions. Surface modification is clearly observed with forces as low as 30 nN, but is usually limited to the bottom and the sides of the field of view, where the tip scans for a long time and where it turns around, respectively. At the molecular scale we have observed structures with substantial order, with minimum lateral sizes of 3 Å. The identification of these features is difficult due to the large unit cell of this compound (40 atoms per unit cell), and the lack of perfect order in the images. We use the SARCH/LATUSE progrmn developed by Van Hove and Hermann to analyze this structure. Ammonium perchlorate is hygroscopic; it is therefore possible that surface modification is enhanced by the moisture present in air. Experiments in a dry atmosphere have confirmed this explanation. We have therefore designed and built a UHV (ultra-high vacuum) AFM for these studies. The first images from this instrument are presented here.
Energetic Crystal-Lattice-Dependent Responses
Authors: Armstrong R. W. , Ammon H. L. , Du Z. Y. , Elban W. L. , Zhang X. J.
Published: March 2011

The occurrence of [100] direction slip on the (021) slip plane of orthorhombic RDX (cyclotrimethylenetrinitramine, (CH2·N·NO2]3) is shown to favor the formation of 1,3-dinitroso-5-nitro-l,3,5-triazacyclohexane, as detected in drop-weight impact tests at sensitivity height levels near to those measured for initiation. Also, the reported observation of deformation twinning in the chemically-related monoclinic HMX (cyclotetra-methylenetetranitramine, (CH2·N·NO2 ]4) crystal lattice is explained on the basis of the greater flexibility of the larger HMX molecule allowing a number of bond rotations that are required to produce a relatively unusual Type II deformation twinning structure. These examples give support to the consideration that on the molecular level involved in deformation-induced decompositions there may be a direct mechanical force aspect that is additional to the established importance of “hot spot” heating, say, as described for dislocation pile-up avalanches in RDX.