Current Search:  uranium (x)

View All Items

  • CSV Spreadsheet
(1 - 7 of 7)
Interdiffusion reaction between uranium-zirconium and iron
Title
Interdiffusion reaction between uranium-zirconium and iron.
Creator
Park, Young Joo, Sohn, Yongho, Coffey, Kevin, Fang, Jiyu, University of Central Florida
Abstract / Description
U-Zr metallic fuels cladded in Fe-alloys are being considered for application in an advanced Sodium-Cooled Fast Reactor (SFR) that can recycle the U-Zr fuels and minimize the long-lived actinide waste. To understand the complex fuel-cladding chemical interaction of the U-Zr metallic fuel with Fe-alloys, a systematic multicomponent diffusion study was carried out using solid-to-solid diffusion couples. The U-10 wt.% Zr vs. pure Fe diffusion couples were assembled and annealed at temperatures,...
Show moreU-Zr metallic fuels cladded in Fe-alloys are being considered for application in an advanced Sodium-Cooled Fast Reactor (SFR) that can recycle the U-Zr fuels and minimize the long-lived actinide waste. To understand the complex fuel-cladding chemical interaction of the U-Zr metallic fuel with Fe-alloys, a systematic multicomponent diffusion study was carried out using solid-to-solid diffusion couples. The U-10 wt.% Zr vs. pure Fe diffusion couples were assembled and annealed at temperatures, 630, 650 and 680(&)deg;C for 96 hours. Development of microstructure, phase constituents, and compositions developed during the thermal anneals were examined by scanning electron microscopy, transmission electron microscopy and X-ray energy dispersive spectroscopy. A complex microstructure consisting of several layers that include phases such as U6Fe, UFe2, ZrFe2, ?-U, ?-U, Zr-precipitates, ?, ?, and ? was observed. Multi-phase layers were grouped based on phase constituents and microstructure, and the layer thicknesses were measured to calculate the growth constant and activation energy. The local average compositions through the interaction layer were systematically determined, and employed to construct semi-quantitative diffusion paths on isothermal U-Zr-Fe ternary phase diagrams at respective temperatures. The diffusion paths were examined to qualitatively estimate the diffusional behavior of individual components and their interactions. Furthermore, selected area diffraction analyses were carried out to determine, for the first time, the exact crystal structure and composition of the ?, ? and ?-phases. The ?, ? and ?-phases were identified as Pnma(62) Fe(Zr,U), I4/mcm(140) Fe(Zr,U)2, and I4/mcm(140) U3(Zr,Fe), respectively.
Show less
Date Issued
2013
Identifier
CFE0004908, ucf:49616
Format
Document (PDF)
PURL
http://purl.flvc.org/ucf/fd/CFE0004908
Phase transformation and growth kinetics in reaction zone between uranium alloy and zirconium diffusion barrier
Title
Phase transformation and growth kinetics in reaction zone between uranium alloy and zirconium diffusion barrier.
Creator
Park, Young Joo, Sohn, Yongho, Coffey, Kevin, Fang, Jiyu, University of Central Florida
Abstract / Description
U-10wt.%Mo (U10Mo) alloy as a part of monolithic fuel system is being developed under Material Management and Minimization Reactor Conversion (MMMRC) program, tasked with replacing high-enriched uranium (HEU) fuel with low-enriched uranium (LEU) fuel in civilian research and test reactors. Use of U10Mo fuel alloy entails a Zr diffusion barrier to avoid the undesirable interdiffusion and reactions between the U10Mo and Al-alloy cladding. To better understand the interaction between these fuel...
Show moreU-10wt.%Mo (U10Mo) alloy as a part of monolithic fuel system is being developed under Material Management and Minimization Reactor Conversion (MMMRC) program, tasked with replacing high-enriched uranium (HEU) fuel with low-enriched uranium (LEU) fuel in civilian research and test reactors. Use of U10Mo fuel alloy entails a Zr diffusion barrier to avoid the undesirable interdiffusion and reactions between the U10Mo and Al-alloy cladding. To better understand the interaction between these fuel system constituents, microstructural development and diffusion kinetics in U-Mo-Zr, U-Zr and fuel plate assembly processed by co-rolling and hot isostatic pressing (HIP) were investigated using a variety of analytical techniques accompanying scanning electron microscopy and transmission electron microscopy.Phase constituents, microstructure and diffusion kinetics between U10Mo and Zr were examined using solid-to-solid diffusion couples annealed at 650 (&)deg;C for 240, 480 and 720 hours. Concentration profiles were mapped as diffusion paths on the isothermal ternary phase diagram. Within the diffusion zone, single-phase layers of (?U,?Zr) were observed along with a discontinuous layer of Mo2Zr between the ?Zr and ?U layers. In the vicinity of Mo2Zr phase, islands of ?Zr phase were also found. In addition, acicular ?Zr and U6Zr3Mo phases were observed within the ?U(Mo). Growth rate of the interdiffusion-reaction zone was determined to be 1.81 (&)#215; 10-15 m2/sec at 650 (&)deg;C, however with an assumption of a certain incubation period.Investigation for interdiffusion and reaction between U and Zr were carried out using solid-to-solid diffusion couples annealed at 580, 650, 680 and 710 (&)deg;C. The interdiffusion and reaction layer consisted of ?U containing Zr acicular precipitate, ?' (oC4-variant) and (?U,?Zr) solid solution at 650, 680 and 710 (&)deg;C. The ?-UZr2 phase, instead of (?U,?Zr) solid solution phase, was observed in the couple annealed at 580 (&)deg;C. The interdiffusion fluxes and coefficients were determined for the ?U, (?U,?Zr) and ?-UZr2 (580 ?C only) phases using both Sauer-Freise and Boltzmann-Matano analyses. For the ?'-phase with negligible concentration gradient, integrated interdiffusion coefficients were determined via Wagner method. Marker plane was found in (?U,?Zr) (cI2) solid solution from the couples annealed at 650, 680 and 710 (&)deg;C and ?-UZr2 from the couple at 580 (&)deg;C. Intrinsic diffusion coefficients at the compositions corresponding to the marker plane were determined based on Heumann analysis: U intrinsically diffused an order magnitude faster than Zr. Arrhenius temperature-dependence, Darken relation, and comparison to existing literature data demonstrated consistency in results.Monolithic fuel plate assembly was fabricated by sequential process of (1) co-rolling to laminate the Zr barrier onto the U10Mo fuel alloy and (2) HIP to encase the fuel laminated with Zr, within the Al-alloy 6061 (AA6061). In this study, HIP process was carried out as functions of temperature (520, 540, 560 and 580 (&)deg;C for 90 minutes), time (45, 60, 90, 180 and 345 minutes at 560 (&)deg;C) with ramp-cool rate (35, 70 and 280 (&)deg;C/hour). At the interface between the U10Mo and Zr, following the co-rolling, the UZr2 phase was observed to develop adjacent to Zr, and the ?U phase was found between the UZr2 and U10Mo. Mo2Zr was found as precipitates mostly within the ?U phase. Observable growth due to HIP was only observed for the (Al,Si)3Zr phase found at the Zr/AA6061 interface, however, with a large activation energy of 457 kJ/mol. Decomposition of ?U into ?U and ?' was observed in the U10Mo alloy. The volume fraction of ? and ?' increased as the HIP temperature and ramp-cool rate decreased. The UC-UO2 inclusions within the U10Mo fuel alloy were observed, but the volume percent of the UC-UO2 inclusions within the U10Mo alloy, ranging from approximately 0.5 to 1.8, did not change as functions of HIP temperature and holding time. However, the inclusions located near the surface of the U10Mo alloy, were frequently observed to interfere the uniformity of interdiffusion and reaction between the U10Mo alloy and Zr diffusion barrier. The regions of limited interaction between the U10Mo and Zr barrier associated with UC-UO2 inclusions decreased with an increase in HIP temperature, however no significant trend was observed with an increase in HIP duration at 560 (&)deg;C.
Show less
Date Issued
2016
Identifier
CFE0006371, ucf:51499
Format
Document (PDF)
PURL
http://purl.flvc.org/ucf/fd/CFE0006371
Assessment of Microstructure and Mechanical Behavior of Materials and Phases Observed in Low-Enriched Uranium Monolithic Fuel Plates After Fabrication
Title
Assessment of Microstructure and Mechanical Behavior of Materials and Phases Observed in Low-Enriched Uranium Monolithic Fuel Plates After Fabrication.
Creator
Newell, Ryan, Sohn, Yongho, Florczyk, Stephen, Fang, Jiyu, Keiser, Dennis, Kwok, Kawai, University of Central Florida
Abstract / Description
Low enriched uranium (LEU) fuels are being developed to reduce the use of highly enriched uranium in power generation to reduce proliferation risks. Challenges arise in providing sufficient fissile U in LEU without reactor redesign. As such, a novel monolithic fuel plate design employs LEU alloyed with 10 wt. % Mo. Throughout fabrication of these fuel plates, metallurgical transformations and reactions take place as a result of elevated temperatures during processing. The transformations...
Show moreLow enriched uranium (LEU) fuels are being developed to reduce the use of highly enriched uranium in power generation to reduce proliferation risks. Challenges arise in providing sufficient fissile U in LEU without reactor redesign. As such, a novel monolithic fuel plate design employs LEU alloyed with 10 wt. % Mo. Throughout fabrication of these fuel plates, metallurgical transformations and reactions take place as a result of elevated temperatures during processing. The transformations include decomposition of the metastable body-centered cubic ? phase in the fuel and metallurgical interactions at interfaces between fuel plate components. This work aims to provide further understanding into physical and mechanical behavior of these constituents as they relate to fuel plate processing and performance. Fuel plate processing includes alloying the U, applying a Zr diffusion barrier, and cladding in AA6061 via hot isostatic press. Experimental Zr barriers were applied via electroplating, plasma-spraying, or roll-bonding and characterized using optical and electron microscopy, demonstrating that roll-bonded Zr exhibits the most favorable properties. During fabrication, regions of the ?-U decompose into ? and ?' which revert to ? during annealing or irradiation and heat treatments were designed to induce similar transformations and characterize them using x-ray diffraction and electron microscopy, resulting in a model describing the reversion as a function of time and temperature. The mechanical properties of the fuel and other constituent phases were investigated via instrumented indentation of fuel plates. Phases that occurred in small, discontinuous regions were fabricated in diffusion couples for more reliable indentation. The kinetic and mechanical data produced from this study can be used to estimate the phase constitution of the fuel plates and subsequently, its behavior in response to fabrication and irradiation.
Show less
Date Issued
2018
Identifier
CFE0007349, ucf:52109
Format
Document (PDF)
PURL
http://purl.flvc.org/ucf/fd/CFE0007349
Diffusion and reaction in selected uranium alloy system
Title
Diffusion and reaction in selected uranium alloy system.
Creator
Huang, Ke, Sohn, Yongho, An, Linan, Xu, Chengying, Coffey, Kevin, Heinrich, Helge, University of Central Florida
Abstract / Description
U-Mo metallic fuels with Al alloys as the matrix/cladding are being developed as low enriched uranium fuels under the Reduced Enrichment for Research and Test Reactor (RERTR) program. Significant interactions have been observed to occur between the U-Mo fuel and the Al alloy during fuel processing and irradiation. U-Zr metallic fuels with stainless steel claddings have been developed for the generation IV sodium fast reactor (SFR). The fuel cladding chemical interaction (FCCI) induced by the...
Show moreU-Mo metallic fuels with Al alloys as the matrix/cladding are being developed as low enriched uranium fuels under the Reduced Enrichment for Research and Test Reactor (RERTR) program. Significant interactions have been observed to occur between the U-Mo fuel and the Al alloy during fuel processing and irradiation. U-Zr metallic fuels with stainless steel claddings have been developed for the generation IV sodium fast reactor (SFR). The fuel cladding chemical interaction (FCCI) induced by the interdiffusion of components was also observed. These interactions induce deleterious effects on the fuel system, such as thinning of the cladding layer, formation of phases with undesirable properties, and thermal cracking due to thermal expansion mismatches and changes in molar volume. The interaction between the fuel and the cladding involves multi-component interdiffusion. To determine the ternary interdiffusion coefficients using a single diffusion couple, a new method based on regression via the matrix transformation approach is proposed in this study. This new method is clear in physical meaning and simple in mathematical calculation. The reliability and accuracy of this method have been evaluated through application to three case studies: a basic asymptotic concentration profile, a concentration profile with extrema and a smoothed concentration profile with noise. Generally, this new method works well in all three cases.In order to investigate the interdiffusion behavior in U-Mo alloys, U vs. Mo diffusion couples were assembled and annealed in the temperature range of 650 to 1000(&)deg;C. The interdiffusion microstructures and concentration profiles were examined via scanning electron microscopy (SEM) and electron probe microanalysis (EPMA), respectively. Interdiffusion coefficients and activation energies were calculated as functions of temperature and Mo composition. The intrinsic diffusion coefficients of U and Mo at the marker composition were also determined. The activity of U and the thermodynamic factor of the U-Mo alloy have been calculated using the ideal solution, the regular solution, and the subregular solution models based on the molar excess Gibbs free energy of the U-Mo alloy. The calculated intrinsic diffusivities of U and Mo along with the thermodynamic factor of the U-Mo alloy were employed to estimate the atomic mobilities and the vacancy wind effects of U and Mo according to Manning's description.To explore potential diffusion barrier materials for reducing the fuel cladding chemical interaction between the U-Mo fuel and the Al alloy matrix/cladding, the interdiffusion behavior between U-Mo alloys and Mo, Zr, Nb and Mg were systematically studied. U-10wt.%Mo vs. Mo, Zr and Nb diffusion couples were annealed in the temperature range from 600 to 1000(&)deg;C. A diffusion couple between U-7wt.%Mo and Mg was annealed at 550(&)deg;C for 96 hours. SEM and transmission electron microscopy (TEM) were applied to characterize the microstructure of the interdiffusion zone. X-ray energy dispersive spectroscopy (XEDS) and EPMA were utilized to examine the concentration redistribution and the phase constituents. For the U-Mo vs. Mo diffusion couples, the interdiffusion coefficients at high Mo concentrations ranging from 22 to 32 at.%Mo were determined for the first time. In the U-Mo vs. Zr diffusion couples, the Mo2Zr phase was found at the interface. The diffusion paths were estimated and investigated according to the Mo-U-Zr ternary phase diagram. Thermal cracks and pure U precipitates were found within the diffusion zone in the U-Mo vs. Nb system. The growth rate of the interdiffusion zone was found to be lower by about 103 times for Zr, 105 times for Mo and 106 times for Nb compared to those observed in the U-10wt.%Mo vs. Al or Al-Si systems. For the diffusion couple of U-Mo vs. Mg, the U-Mo was bonded very well to the Mg and there was negligible diffusion observed even after 96 hours annealing at 550(&)deg;C.For a more fundamental understanding of the complex diffusion behavior between U-Zr fuels and their stainless steel claddings, U vs. Fe, Fe-15wt.%Cr and Fe-15wt.%Cr-15wt.%Ni diffusion couples were examined to investigate the interdiffusion behaviors between U and Fe and the effects of the alloying elements Cr and Ni. The diffusion couples were annealed in the temperature range from 580 to 700(&)deg;C for various times. Two intermetallic phases, U6Fe and UFe2, developed in all of the diffusion couples with the U6Fe layer growing faster than the UFe2 layer. For the diffusion couples of U vs. Fe, extrinsic growth constants, intrinsic growth constants, integrated interdiffusion coefficients and activation energies in each phase were calculated. The results suggest that U6Fe impeded the growth of UFe2, and the boundary condition change caused by the allotropic transformation of U played a role in the growth of the U6Fe and UFe2 layers. The reasons why U6Fe grew much faster than UFe2 are also discussed. The additions of Cr and Ni into Fe affected the growth rates of U6Fe and UFe2. The solubility of Cr and Ni in U6Fe and UFe2 were determined, and it was found that Cr diffused into U more slowly than Fe or Ni.
Show less
Date Issued
2012
Identifier
CFE0004548, ucf:49238
Format
Document (PDF)
PURL
http://purl.flvc.org/ucf/fd/CFE0004548
Phase Transformations and Microstructural Evolution in the U-10 wt.% Mo Alloy with Various Zr Additions at 900C and 650C
Title
Phase Transformations and Microstructural Evolution in the U-10 wt.% Mo Alloy with Various Zr Additions at 900C and 650C.
Creator
Eriksson, Nicholas, Sohn, Yongho, Challapalli, Suryanarayana, Coffey, Kevin, University of Central Florida
Abstract / Description
The Reduced Enrichment for Research and Test Reactor (RERTR) now known as the Material Minimization and Management Reactor Control program (MMMRC) seeks to replace the use of highly enriched uranium (HEU) fuels used in research and test nuclear reactors around the world. The low enriched uranium (LEU) fuels must have fissionable uranium densities comparable to the HEU fuels. After extensive investigation by various researchers around the world, the U-Mo alloys were selected as a promising...
Show moreThe Reduced Enrichment for Research and Test Reactor (RERTR) now known as the Material Minimization and Management Reactor Control program (MMMRC) seeks to replace the use of highly enriched uranium (HEU) fuels used in research and test nuclear reactors around the world. The low enriched uranium (LEU) fuels must have fissionable uranium densities comparable to the HEU fuels. After extensive investigation by various researchers around the world, the U-Mo alloys were selected as a promising candidate. The Mo alloyed with U allows for the stabilization of the face-centered cubic ?-U phase, which demonstrated favorable irradiation behavior. However, deleterious diffusional interaction between the fuel and the cladding, typically Al-base alloy, remain a challenge to overcome for application of U-Mo alloys as the LEU fuel. Zr has been identified as a potential diffusion barrier between monolithic U-10 wt.% Mo (U10Mo) metallic fuel and AA6061 cladding alloys for the development of a LEU fuel system. However, interdiffusion and reaction between the Zr barrier and U10Mo fuel can produce phases such as Mo2Zr, and promote the destabilization of ?-U phase into ?'-U (U2Mo) and ?-U. In order to better understand this phenomenon, this study examined the phases that are present in the U10Mo alloys with varying Zr concentration, 0, 0.5, 1.0, 2.0, 5.0, 10.0, 20.0 wt.% at room temperature after heat treatment at 900(&)deg;C for 168 hours and 650(&)deg;C for 3 hours. These two temperatures are relevant to fuel plate fabrication process of homogenization and hot-rolling, respectively. Scanning electron microscopy and X-ray diffraction were employed to identify and quantitatively document the constituent phases and microstructure to elucidate the nature of phase transformations. For U10Mo alloys containing less than 1.0 wt.% Zr, there was no significant formation of Mo2Zr after 900?C homogenization and subsequent heat treatment at 650?C for 3 hours. The ?-U phase also remained stable correspondingly for these alloys containing less than 1.0 wt.% Zr. For U10Mo alloys containing 2 wt.% or more Zr, a significant amount of Mo2Zr formation was observed after 900?C homogenization and subsequent heat treatment at 650?C for 3 hours. For these alloys, destabilization of ?-U into ?'-U (U2Mo), UZr2 and ?-U was observed. The alloy containing 20 wt.% Zr, however, did not demonstrate ?-U decomposition even though Mo2Zr was observed after heat treatments. The formation of Mo2Zr effectively reduced the stability of the metastable ?-U phase by depleting the ?-stabilizing Mo. The destabilization of ?-U phase into the ?-U phase is not favorable due to anisotropic and poor irradiation behavior of ?-U phase. Therefore the formation of Mo2Zr at the interface between U10Mo fuel and Zr diffusion barrier must be carefully controlled during the fabrication of monolithic LEU fuel system for successful implementation.
Show less
Date Issued
2015
Identifier
CFE0005943, ucf:50812
Format
Document (PDF)
PURL
http://purl.flvc.org/ucf/fd/CFE0005943
INTERDIFFUSION BEHAVIOR OF U-MO ALLOYS IN CONTACT WITH AL AND AL-SI ALLOYS
Title
INTERDIFFUSION BEHAVIOR OF U-MO ALLOYS IN CONTACT WITH AL AND AL-SI ALLOYS.
Creator
Perez, Emmanuel, Sohn, Yong-Ho, University of Central Florida
Abstract / Description
U-Mo dispersion and monolithic fuels embedded in Al-alloy matrix are under development to fulfill the requirements of research reactors to use low-enriched molybdenum stabilized uranium alloys as fuels. The system under consideration in this study consisted of body centered cubic (gamma) U-Mo alloys embedded in an Al structural matrix. Significant interaction has been observed to take place between the U-Mo fuel and the Al matrix during manufacturing of the fuel-plate system assembly and...
Show moreU-Mo dispersion and monolithic fuels embedded in Al-alloy matrix are under development to fulfill the requirements of research reactors to use low-enriched molybdenum stabilized uranium alloys as fuels. The system under consideration in this study consisted of body centered cubic (gamma) U-Mo alloys embedded in an Al structural matrix. Significant interaction has been observed to take place between the U-Mo fuel and the Al matrix during manufacturing of the fuel-plate system assembly and during irradiation in reactors. These interactions produce Al-rich phases with physical and thermal properties that adversely affect the performance of the fuel system and can lead to premature failure. In this study, interdiffusion and microstructural development in the U-Mo vs. Al system was examined using solid-to-solid diffusion couples consisting of U-7wt.%Mo, U-10wt.%Mo and U-12wt.%Mo vs. pure Al, annealed at 600°C for 24 hours. The influence of Si alloying addition (up to 5 wt.%) in Al on the interdiffusion microstructural development was also examined using solid-to-solid diffusion couples consisting of U-7wt.%Mo, U-10wt.%Mo and U-12wt.%Mo vs. pure Al, Al-2wt.%Si, and Al-5wt.%Si annealed at 550°C for 1, 5 and 20 hours. To further clarify the diffusional behavior in the U-Mo-Al and U-Mo-Al-Si systems, Al-rich 85.7Al-11.44U-2.86Mo, 87.5Al-10U-2.5Mo, 56.1Al-18.9Si-21.9U-3.1Mo and 69.3Al-11.9Si-18.8U (at.%) alloys were cast and homogenized at 500°C to determine the equilibrium phases of the system. Scanning electron microscopy (SEM), transmission electron microscopy (TEM) and electron probe microanalysis (EPMA) and X-ray diffraction (XRD) were employed to examine the phase development in the diffusion couples and the cast alloys. In ternary U-Mo-Al diffusion couples annealed at 600°C for 24 hours, the interdiffusion microstructure consisted of finely dispersed UAl3, UAl4, U6Mo4Al43, and UMo2Al20 phases while the average composition throughout the interdiffusion zone remained constant at approximately 80 at.% Al. The interdiffusion microstructures observed by EPMA, SEM and TEM analyses were correlated to explain the observed morphological development in the interdiffusion zones. The concept of thermodynamic degrees of freedom was used to justify that, although deviations are apparent, the interdiffusion zones did not significantly deviate from an equilibrium condition in order for the observed microstructures to develop. Selected diffusion couples developed periodic bands within the interdiffusion zone as sub-layers in the three-phase regions. Observation of periodic banding was utilized to augment the hypothesis that internal stresses play a significant role in the phase development and evolution of U-Mo vs. pure Al diffusion couples. The addition of Si (up to 5 wt.%) to the Al significantly reduced the growth rate of the interdiffusion zone. The constituent phases and composition within the interdiffusion zone were also modified. When Si was present in the Al terminal alloys, the interdiffusion zones developed layered morphologies with fine distributions of the (U,Mo)(Al,Si)3 and UMo2Al20 phases. The U6Mo4Al43 phase was observed scarcely in Si depleted regions within the interdiffusion zone. The phase development and evolution of the interdiffusion zone was described in terms of thermodynamic degrees of freedom with minimal deviations from equilibrium.
Show less
Date Issued
2011
Identifier
CFE0003747, ucf:48778
Format
Document (PDF)
PURL
http://purl.flvc.org/ucf/fd/CFE0003747
A NEW PARADIGM OF MODELING WATERSHED WATER QUALITY
Title
A NEW PARADIGM OF MODELING WATERSHED WATER QUALITY.
Creator
Zhang, Fan, Yeh, Gour-Tsyh, University of Central Florida
Abstract / Description
Accurate models to reliably predict sediment and chemical transport in watershed water systems enhance the ability of environmental scientists, engineers and decision makers to analyze the impact of contamination problems and to evaluate the efficacy of alternative remediation techniques and management strategies prior to incurring expense in the field. This dissertation presents the conceptual and mathematical development of a general numerical model simulating (1) sediment and reactive...
Show moreAccurate models to reliably predict sediment and chemical transport in watershed water systems enhance the ability of environmental scientists, engineers and decision makers to analyze the impact of contamination problems and to evaluate the efficacy of alternative remediation techniques and management strategies prior to incurring expense in the field. This dissertation presents the conceptual and mathematical development of a general numerical model simulating (1) sediment and reactive chemical transport in river/stream networks of watershed systems; (2) sediment and reactive chemical transport in overland shallow water of watershed systems; and (3) reactive chemical transport in three-dimensional subsurface systems. Through the decomposition of the system of species transport equations via Gauss-Jordan column reduction of the reaction network, fast reactions and slow reactions are decoupled, which enables robust numerical integrations. Species reactive transport equations are transformed into two sets: nonlinear algebraic equations representing equilibrium reactions and transport equations of kinetic-variables in terms of kinetically controlled reaction rates. As a result, the model uses kinetic-variables instead of biogeochemical species as primary dependent variables, which reduces the number of transport equations and simplifies reaction terms in these equations. For each time step, we first solve the advective-dispersive transport of kinetic-variables. We then solve the reactive chemical system node by node to yield concentrations of all species. In order to obtain accurate, efficient and robust computations, five numerical options are provided to solve the advective-dispersive transport equations; and three coupling strategies are given to deal with the reactive chemistry. Verification examples are compared with analytical solutions to demonstrate the numerical accuracy of the code and to emphasize the need of implementing various numerical options and coupling strategies to deal with different types of problems for different application circumstances. Validation examples are presented to evaluate the ability of the model to replicate behavior observed in real systems. Hypothetical examples with complex reaction networks are employed to demonstrate the design capability of the model to handle field-scale problems involving both kinetic and equilibrium reactions. The deficiency of current practices in the water quality modeling is discussed and potential improvements over current practices using this model are addressed.
Show less
Date Issued
2005
Identifier
CFE0000448, ucf:46405
Format
Document (PDF)
PURL
http://purl.flvc.org/ucf/fd/CFE0000448