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Title: Radionuclide Transport Models Under Ambient Conditions

Abstract

The purpose of this Analysis/Model Report (AMR) is to evaluate (by means of 2-D semianalytical and 3-D numerical models) the transport of radioactive solutes and colloids in the unsaturated zone (UZ) under ambient conditions from the potential repository horizon to the water table at Yucca Mountain (YM), Nevada. This is in accordance with the ''AMR Development Plan U0060, Radionuclide Transport Models Under Ambient Conditions'' (CRWMS M and O 1999a). This AMR supports the UZ Flow and Transport Process Model Report (PMR). This AMR documents the UZ Radionuclide Transport Model (RTM). This model considers: the transport of radionuclides through fractured tuffs; the effects of changes in the intensity and configuration of fracturing from hydrogeologic unit to unit; colloid transport; physical and retardation processes and the effects of perched water. In this AMR they document the capabilities of the UZ RTM, which can describe flow (saturated and/or unsaturated) and transport, and accounts for (a) advection, (b) molecular diffusion, (c) hydrodynamic dispersion (with full 3-D tensorial representation), (d) kinetic or equilibrium physical and/or chemical sorption (linear, Langmuir, Freundlich or combined), (e) first-order linear chemical reaction, (f) radioactive decay and tracking of daughters, (g) colloid filtration (equilibrium, kinetic or combined), and (h) colloid-assisted solutemore » transport. Simulations of transport of radioactive solutes and colloids (incorporating the processes described above) from the repository horizon to the water table are performed to support model development and support studies for Performance Assessment (PA). The input files for these simulations include transport parameters obtained from other AMRs (i.e., CRWMS M and O 1999d, e, f, g, h; 2000a, b, c, d). When not available, the parameter values used are obtained from the literature. The results of the simulations are used to evaluate the transport of radioactive solutes and colloids, and to determine the processes, mechanisms, and geologic features that have a significant effect on it. They evaluate the contributions of daughter products of radioactive decay to transport from the bottom of the potential repository to the water table. The effect of the various conceptual models of perched water bodies on transport is also evaluated. Note that a more thorough study of perched water bodies can be found in another AMR (CRWMS M and O 1999d, Sections 6.2 and 6.6). The primary caveat for using the modeling results documented here is that the input transport parameters were based on limited site data. For some input parameters, best estimates were used because no specific data were available. An additional caveat is that the RTM is based on the conceptual models and numerical approaches used for developing the flow fields and infiltration maps, and thus they share the same limitations.« less

Authors:
;
Publication Date:
Research Org.:
Yucca Mountain Project, Las Vegas, Nevada (US)
Sponsoring Org.:
US Department of Energy (US)
OSTI Identifier:
837084
Report Number(s):
MDL-NBS-HS-000008, REV 00
MOL.19990721.0529, DC 23356; TRN: US0502313
Resource Type:
Technical Report
Resource Relation:
Other Information: PBD: 12 Mar 2000
Country of Publication:
United States
Language:
English
Subject:
12 MANAGEMENT OF RADIOACTIVE WASTES, AND NON-RADIOACTIVE WASTES FROM NUCLEAR FACILITIES; ADVECTION; CHEMICAL REACTIONS; COLLOIDS; DAUGHTER PRODUCTS; DECAY; DIFFUSION; HYDRODYNAMICS; KINETICS; RADIOISOTOPES; SIMULATION; TRANSPORT; WATER TABLES; YUCCA MOUNTAIN

Citation Formats

G. Moridis, and Q. Hu. Radionuclide Transport Models Under Ambient Conditions. United States: N. p., 2000. Web. doi:10.2172/837084.
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G. Moridis, & Q. Hu. Radionuclide Transport Models Under Ambient Conditions. United States. doi:10.2172/837084.
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G. Moridis, and Q. Hu. Sun . "Radionuclide Transport Models Under Ambient Conditions". United States. doi:10.2172/837084. https://www.osti.gov/servlets/purl/837084.
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@article{osti_837084,
title = {Radionuclide Transport Models Under Ambient Conditions},
author = {G. Moridis and Q. Hu},
abstractNote = {The purpose of this Analysis/Model Report (AMR) is to evaluate (by means of 2-D semianalytical and 3-D numerical models) the transport of radioactive solutes and colloids in the unsaturated zone (UZ) under ambient conditions from the potential repository horizon to the water table at Yucca Mountain (YM), Nevada. This is in accordance with the ''AMR Development Plan U0060, Radionuclide Transport Models Under Ambient Conditions'' (CRWMS M and O 1999a). This AMR supports the UZ Flow and Transport Process Model Report (PMR). This AMR documents the UZ Radionuclide Transport Model (RTM). This model considers: the transport of radionuclides through fractured tuffs; the effects of changes in the intensity and configuration of fracturing from hydrogeologic unit to unit; colloid transport; physical and retardation processes and the effects of perched water. In this AMR they document the capabilities of the UZ RTM, which can describe flow (saturated and/or unsaturated) and transport, and accounts for (a) advection, (b) molecular diffusion, (c) hydrodynamic dispersion (with full 3-D tensorial representation), (d) kinetic or equilibrium physical and/or chemical sorption (linear, Langmuir, Freundlich or combined), (e) first-order linear chemical reaction, (f) radioactive decay and tracking of daughters, (g) colloid filtration (equilibrium, kinetic or combined), and (h) colloid-assisted solute transport. Simulations of transport of radioactive solutes and colloids (incorporating the processes described above) from the repository horizon to the water table are performed to support model development and support studies for Performance Assessment (PA). The input files for these simulations include transport parameters obtained from other AMRs (i.e., CRWMS M and O 1999d, e, f, g, h; 2000a, b, c, d). When not available, the parameter values used are obtained from the literature. The results of the simulations are used to evaluate the transport of radioactive solutes and colloids, and to determine the processes, mechanisms, and geologic features that have a significant effect on it. They evaluate the contributions of daughter products of radioactive decay to transport from the bottom of the potential repository to the water table. The effect of the various conceptual models of perched water bodies on transport is also evaluated. Note that a more thorough study of perched water bodies can be found in another AMR (CRWMS M and O 1999d, Sections 6.2 and 6.6). The primary caveat for using the modeling results documented here is that the input transport parameters were based on limited site data. For some input parameters, best estimates were used because no specific data were available. An additional caveat is that the RTM is based on the conceptual models and numerical approaches used for developing the flow fields and infiltration maps, and thus they share the same limitations.},
doi = {10.2172/837084},
journal = {},
number = ,
volume = ,
place = {United States},
year = {Sun Mar 12 00:00:00 EST 2000},
month = {Sun Mar 12 00:00:00 EST 2000}
}
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DOI:  10.2172/837084
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  • ;
    The purpose of Revision 00 of this Analysis/Model Report (AMR) is to evaluate (by means of 2-D semianalytical and 3-D numerical models) the transport of radioactive solutes and colloids in the unsaturated zone (UZ) under ambient conditions from the potential repository horizon to the water table at Yucca Mountain (YM), Nevada.

  • The purpose of this model report is to document the unsaturated zone (UZ) radionuclide transport model, which evaluates, by means of three-dimensional numerical models, the transport of radioactive solutes and colloids in the UZ, under ambient conditions, from the repository horizon to the water table at Yucca Mountain, Nevada.

  • ; ;
    The current conceptual model of radionuclide transport in unsaturated fractured rock includes water movement in fractures, with migration of the entrained radionuclides being retarded by diffusion into and sorption within the rock matrix. Water infiltration and radionuclide transport through low-permeability unsaturated fractured rock are episodic and intermittent in nature, at least at local scales. Under episodic flow conditions, the matrix is constantly imbibing or draining, and this fluctuating wetness both drives two-way advective movement of radionuclides, and forces changes in the matrix diffusivity. This work is intended to examine, both experimentally and numerically, how radionuclide transport under episodic flow conditionsmore » is affected by the interacting processes of imbibition and drainage, diffusion, and matrix sorption. Using Topopah Spring welded volcanic tuff, collected from the potential repository geologic unit at Yucca Mountain for storing high-level nuclear waste, we prepared a saw-cut fracture core (length 10.2 cm, diameter 4.4 cm, and fracture aperture 100 {micro}m). The dry core was packed into a flow reactor, flushed with CO{sub 2}, then saturated via slow pumping (0.01 mL/min) of synthetic groundwater. The fractured core was then flushed with air at >97% relative humidity (to simulate in situ unsaturated fractured rock conditions at Yucca Mountain), then the episodic transport experiment was conducted. Episodic flow involved 4 cycles of tracer solution flow within the fracture, followed by flushing with high humidity air. Each flow episode contained a different suite of non-sorbing and sorbing tracers, which included {sup 3}H, ReO{sub 4}{sup -} (a chemical analog for {sup 99}TcO{sub 4}{sup -}), I{sup -} (for {sup 129}I{sup -}), Sr and Cs (for {sup 90}Sr and {sup 137}Cs), plus the radionuclides {sup 235}U, {sup 237}Np, and {sup 241}Pu. These radionuclides span a variety of sorption strengths and represent a large fraction of the radionuclides of concern at the potential Yucca Mountain repository. Meanwhile, the non-sorbing {sup 3}H and ReO{sub 4}{sup -} serve as diffusivity tracers with different aqueous diffusion coefficients. Liquid effluent from the flow reactor was collected for multi-elemental analyses using ICP-MS, as well as liquid scintillation counting for {sup 3}H, to obtain the breakthrough curves of non- or less-retarded tracers. After the flow-tests were complete, the flow reactor was opened and the distribution of strongly retarded tracers within the fractured core characterized by laser ablation coupled with ICP-MS. A numerical model was developed, based on the NUFT (Non-isothermal, Unsaturated-saturated Flow and Transport) computer code, to describe the experimental system, compare with, and interpret experimental results.« less

  • An exact solution is derived for one-dimensional radionuclide transport under time-varying fluid-flow conditions including radioactive decay but with the approximation that all radionuclides have identical retardation factors. The solution is used to obtain exact expressions for the cumulative radionuclide mass transported past a fixed point in space over a given time period, and to assess the effects of a periodic perturbation and a step change on the fluid-flow velocity and dispersion coefficient. 14 refs., 3 figs., 3 tabs.

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