937 Matching Results

Search Results

Advanced search parameters have been applied.

Radiation Damage Theory

Description: This chapter presents an overview of basic radiation damage theory, including older and more recent models, to provide framework, within which radiation effects, such as void swelling, can be rationalized. A complete review of the literature is not attempted, but sufficient references are given to provide a decent introduction to a quite large number of publications in the field. Many derivations are different from and, in our view, more elegant than in the original publications. The work is directed to both theoreticians and experimentalists, and, especially, to those passionate individuals who are going to take the radiation damage theory (RDT) to the future.
Date: January 1, 2012
Creator: Golubov, Stanislav I; Barashev, Aleksandr & Stoller, Roger E
Partner: UNT Libraries Government Documents Department


Description: Ben Cap, LLC, has a technology that utilizes bebtonite to plug wells. The bentonite is encapsulated in a cardboard capsule, droped down to the bottom of the well where it is allowed to hydrate, causing the bentonite to expand and plug the well. This method of plugging a well is accepted in some, but not all states. This technology can save a significant amount of money when compared to cementing methods currently used to plug and abandon wells. The test objective was to obtain the terminal velocity of the capsule delivery system as it drops through a column of water in a wellbore. Once the terminal velocity is known, the bentonite swelling action can be timed not to begin swelling until it reaches the bottom of the well bore. The results of the test showed that an average speed of 8.93 plus or minus 0.12 ft/sec was achieved by the capsule as it was falling through a column of water. Plotting the data revealed a very linear function with the capsules achieving terminal velocity shortly after being released. The interference of the capsule impacting the casing was not readily apparent in any of the runs, but a siginal sampling anomaly was present in one run. Because the anomaly was so brief and not present in any of the other runs, no solid conclusions could be drawn. Additional testing would be required to determine the effects of capsules impacting a fluid level that is not at surface.
Date: September 7, 2005
Creator: Meidinger, Brian
Partner: UNT Libraries Government Documents Department

Swelling of Uranium Alloys at High Exposures

Description: This reports summarizes the results of postirradiation examinations of a series of unrestrained dilute uranium alloy specimens irradiated to exposures up to 13,000 MWD/T in NaK-containing stainless steel capsules.
Date: March 26, 2001
Creator: McDonell, W.R.
Partner: UNT Libraries Government Documents Department

A fully coupled three-dimensional THM analysis of the FEBEX in situ test with the ROCMAS Code: Prediction of THM behavior in a bentonite barrier

Description: This paper presents a fully coupled thermal-hydrological-mechanical analysis of FEBEX--a large underground heater test conducted in a bentonite and fractured rock system. System responses predicted by the numerical analysis--including temperature, moisture content, and bentonite-swelling stress--were compared to field measurements at sensors located in the bentonite. An overall good agreement between predicted and measured system responses shows that coupled thermal-hydrological-mechanical processes in a bentonite barrier are well represented by the numerical model. The most challenging aspect of this particular analysis was modeling of the bentonite's mechanical behavior, which at FEBEX turned out to be affected by gaps between prefabricated bentonite blocks. At FEBEX, the swelling pressure did not develop until a few months into the experiment when moisture swelling of bentonite blocks had closed the gaps completely. Moreover, the wetting of the bentonite took place uniformly from the rock and was not impacted by the permeability difference between the Lamprophyres dykes and surrounding rock.
Date: September 1, 2003
Creator: Rutqvist, J. & Tsang, C-F.
Partner: UNT Libraries Government Documents Department

Mechanical Properties of Uranium Alloys

Description: Cavitational swelling in uranium-base fuel has been attributed to boundary sliding arising from internal stresses due to anisotrophic growth. This document presents the results of room-temperature tensile tests made on a series of alloys to explore the possibility of such a relation and isolate the specific properties of major importance.
Date: October 30, 2002
Creator: Caskey, G.R. Jr.
Partner: UNT Libraries Government Documents Department

Modified Rate-Theory Predictions in Comparison to Microstructural Data

Description: Standard rate theory methods have recently been combined with experimental microstructures to successfully reproduce measured swelling behavior in ternary steels around 400 C. Fit parameters have reasonable values except possibly for the recombination radius, R{sub c}, which can be larger than expected. Numerical simulations of void nucleation and growth reveal the importance additional recombination processes at unstable clusters. Such extra recombination may reduce the range of possible values for R{sub c}. A modified rate theory is presented here that includes the effect of these undetectably small defect clusters. The fit values for R{sub c} are not appreciably altered, as the modification has little effect on the model behavior in the late steady state. It slightly improves the predictions for early transient times, when the sink strength of stable voids and dislocations is relatively small. Standard rate theory successfully explains steady swelling behavior in high purity stainless steel.
Date: November 3, 2003
Creator: Surh, M P; Okita, T & Wolfer, W G
Partner: UNT Libraries Government Documents Department

Sorption-desorption kinetics for powdered and non-powered coal

Description: Diffusion through macro- and meso-pores with the subsequent filling of open micropores is a relatively fast process and the manometric measurements with fifteen minute pressure stabilization steps provide a good estimate of excess (ad)sorption. This can be followed by a much slower processes of the penetrant diffusion into the macromolecular network, accompanied by its structural relaxation, with or without free volume changes. The “free volume” effect is a change of the sample’s excluded volume because of the penetrant molecules mixing within the formerly excluded volume of the network or because of contraction (either reversible or semi-permanent) due to external pressure. If the resulting swelling of the sample leads to the mixture’s volume equal to the sum of the initial volumes of the components, there is no apparent change to the void volume and no pressure relaxation is observed (b). On the other hand, if the external forces (either macroscopic pressure or microscopic molecular interaction forces) change the excluded volume of the network (its density), without exchange of the sorbent molecules between the sample and the free fluid phase, such change causes a corresponding change in the void volume, which constitutes a pure free volume effect (c). In this case, no post-decompression exodus of the sorbent out of the sample is observed. As a special case, we consider an incorporation of the penetrant molecules into the network without any change in the volume of the mixture (d), though mathematically this can be written as a superposition of the previous two cases
Date: May 1, 2007
Creator: Romanov, V. & Soong, Y.
Partner: UNT Libraries Government Documents Department

Unlimited Damage Accumulation in Metallic Materials Under Cascade-Damage Conditions

Description: Most experiments on neutron or heavy-ion cascade-produced irradiation of pure metals and metallic alloys demonstrate unlimited void growth as well as development of the dislocation structure. In contrast, the theory of radiation damage predicts saturation of void swelling at sufficiently high irradiation doses and, accordingly, termination of accumulation of interstitial-type defects. It is shown in the present paper that, under conditions of steady production of one-dimensionally (1-D) mobile clusters of self-interstitial atoms (SIAs) in displacement cascades, any one of the following three conditions can result in indefinite damage accumulation. First, if the fraction of SIAs generated in the clustered form is smaller than some finite value of the order of the dislocation bias factor. Second, if solute, impurity or transmuted atoms form atmospheres around voids and repel the SIA clusters. Third, if spatial correlations between voids and other defects, such as second-phase precipitates and dislocations, exist that provide shadowing of voids from the SIA clusters. The driving force for the development of such correlations is the same as for void lattice formation and is argued to be always present under cascade-damage conditions. It is emphasised that the mean-free path of 1-D migrating SIA clusters is typically at least an order of magnitude longer than the average distance between microstructural defects; hence spatial correlations on the same scale should be taken into consideration. A way of developing a predictive theory is discussed. An interpretation
Date: September 1, 2008
Creator: Barashev, Aleksandr & Golubov, Stanislav I
Partner: UNT Libraries Government Documents Department

Effects of potential additives to promote seal swelling on the thermal stability of synthetic jet fuels

Description: Synthetic fuels derived from the Fischer-Tropsch (F-T) process using natural gas or coal-derived synthesis gas as feedstocks can be used for powering of ground vehicles, aircraft and ships. Because of their chemical and physical properties, F-T fuels will probably require additives in order to meet specifications with respect to lubricity and seal swell capability for use in ground and air vehicles. These additives can include oxygenates and compounds containing other heteroatoms that may adversely affect thermal stability. In order to understand what additives will be the most beneficial, a comprehensive experimental and computational study of conventional and additized fuels has been undertaken. The experimental approach includes analysis of the trace oxygenate and nitrogen-containing compounds present in conventional petroleum-derived fuels and trying to relate their presence (or absence) to changes in the desired properties of the fuels. This paper describes the results of efforts to test the thermal stability of synthetic fuels and surrogate fuels containing single-component additives that have been identified in earlier research as the best potential additives for promoting seal swelling in synthetic fuels, as well as mixtures of synthetic and petroleum-derived fuels.
Date: October 1, 2007
Creator: Lind, D. D.; Gormley, R. G.; Zandhuis, P. H. & Baltrus, J. P.
Partner: UNT Libraries Government Documents Department

Computer simulation of boundary effects on bubble growth in metals due to He.

Description: Atomistic simulation methods were used to investigate and identify the relevant physical mechanisms necessary to describe the growth of helium gas bubbles within a metal lattice. Specifically, molecular dynamics simulations were performed to examine the material defects that originate from growing spherical He bubbles in a palladium crystal. These simulations consist of a model system containing bubbles within a metal and near a free surface. The simulation code employed was ParaDyn using the Embedded Atom Method to model the constitutive properties of Pd atoms in a FCC lattice. The results of these simulations are compared with previously run calculations of He bubbles in a bulk lattice [l]. These simulations show the influence of the free surface on defect creation and evolution. Features compared include the formation of inter-bubble dislocations, bubble pressure and swelling as functions of He to metal (He/M) concentration.
Date: March 1, 2003
Creator: Zimmerman, Jonathan A.
Partner: UNT Libraries Government Documents Department

Density changes in Ga-stabilized delta-Pu, and what they mean

Description: Ga-stabilized {delta}-Pu undergoes small changes in density with time. These have been associated with four different causes: an initial reversible expansion that saturates after a short time; a continuous change that can be attributed to the in-growth of helium and actinide daughter products from the radioactive decay of plutonium; possible void swelling; and phase instability. We review our present understanding of these processes and evaluate their contributions to density changes. It is shown that the initial transient expansion is intimately connected with the metastability of the {delta}-phase at ambient temperature.
Date: September 8, 2006
Creator: G.Wolfer, W; Kubota, A; S?derlind, P; Landa, A; Oudot, B; Sadigh, B et al.
Partner: UNT Libraries Government Documents Department

A new coal-permeability model: Internal swelling stress and fracture-matrix interaction

Description: We have developed a new coal-permeability model for uniaxial strain and constant confining stress conditions. The model is unique in that it explicitly considers fracture-matrix interaction during coal deformation processes and is based on a newly proposed internal-swelling stress concept. This concept is used to account for the impact of matrix swelling (or shrinkage) on fracture-aperture changes resulting from partial separation of matrix blocks by fractures that do not completely cut through the whole matrix. The proposed permeability model is evaluated with data from three Valencia Canyon coalbed wells in the San Juan Basin, where increased permeability has been observed during CH{sub 4} gas production, as well as with published data from laboratory tests. Model results are generally in good agreement with observed permeability changes. The importance of fracture-matrix interaction in determining coal permeability, demonstrated in this work using relatively simple stress conditions, underscores the need for a dual-continuum (fracture and matrix) mechanical approach to rigorously capture coal-deformation processes under complex stress conditions, as well as the coupled flow and transport processes in coal seams.
Date: October 1, 2009
Creator: Liu, H.H. & Rutqvist, J.
Partner: UNT Libraries Government Documents Department

Model development and calibration for the coupled thermal, hydraulic and mechanical phenomena of the bentonite

Description: In Task A of the international DECOVALEX-THMC project, five research teams study the influence of thermal-hydro-mechanical (THM) coupling on the safety of a hypothetical geological repository for spent fuel. In order to improve the analyses, the teams calibrated their bentonite models with results from laboratory experiments, including swelling pressure tests, water uptake tests, thermally gradient tests, and the CEA mock-up THM experiment. This paper describes the mathematical models used by the teams, and compares the results of their calibrations with the experimental data.
Date: February 1, 2009
Creator: Chijimatsu, M.; Borgesson, L.; Fujita, T.; Jussila, P.; Nguyen, S.; Rutqvist, J. et al.
Partner: UNT Libraries Government Documents Department

Infiltration into Fractured Bedrock

Description: One potential consequence of global climate change and rapid changes in land use is an increased risk of flooding. Proper understanding of floodwater infiltration thus becomes a crucial component of our preparedness to meet the environmental challenges of projected climate change. In this paper, we present the results of a long-term infiltration experiment performed on fractured ash flow tuff. Water was released from a 3 x 4 m{sup 2} infiltration plot (divided into 12 square subplots) with a head of {approx}0.04 m, over a period of {approx}800 days. This experiment revealed peculiar infiltration patterns not amenable to current infiltration models, which were originally developed for infiltration into soils over a short duration. In particular, we observed that in part of the infiltration plot, the infiltration rate abruptly increased a few weeks into the infiltration tests. We suggest that these anomalies result from increases in fracture permeability during infiltration, which may be caused by swelling of clay fillings and/or erosion of infill debris. Interaction of the infiltration water with subsurface natural cavities (lithophysal cavities) could also contribute to such anomalies. This paper provides a conceptual model that partly describes the observed infiltration patterns in fractured rock and highlights some of the pitfalls associated with direct extension of soil infiltration models to fractured rock over a long period.
Date: September 1, 2007
Creator: Salve, Rohit; Ghezzehei, Teamrat A. & Jones, Robert
Partner: UNT Libraries Government Documents Department

Characterization of interphase structure using neutron reflection

Description: Neutron reflection is one of only a few characterization techniques which can be used to study buried interfaces in situ. While restricted to model samples, interfacial density and composition profiles can be obtained with a resolution of {approx}5 {angstrom} using isotopic substitution (typically H/D for organic materials). We are using neutron reflection to address several problems of fundamental importance to the durability of organic/inorganic interphases. One important focus of this study is water adsorption within interphases with and without coupling agents. From the time and temperature dependence of moisture uptake and removal in vacuum, information regarding the nature of the interaction of water with the interphase species can be obtained.
Date: May 1, 1997
Creator: Kent, M.S.; McNamara, W.F. & Domeier, L.
Partner: UNT Libraries Government Documents Department

Microstructural Changes Accompanying Annealing of Cold-Worked Uranium

Description: Recovery of the capacity for plastic deformation by annealing previously cold-worked uranium plays a key role in the mechanism proposed for the cavitational swelling observed in irradiated uranium. Consequently, an investigation of recovery of yield strength was undertaken for unalloyed uranium and several selected alloys. During the course of this study, variations in the volume fraction of twins in the various specimens of unalloyed uranium suggested that twinning might be a mechanism of the recovery process. Results of four experiments in this study are described in this report.
Date: October 30, 2002
Creator: Caskey, G.R. Jr.
Partner: UNT Libraries Government Documents Department