Near-Field Mass Transfer in Geologic Disposal Systems: a Review

Pigford, T.H.

doi:10.1557/proc-112-125

Cited by 8 publications

(5 citation statements)

References 18 publications

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“…This work predicts that temperature and temperature gradient dependent evaporation/condensation of water on salt films and small pores leads to highly variable water chemistry. Radionuclide release rate, spent fuel alteration, and corrosion models, to date, have assumed a highly simplified water chemistry [Pigford et al, 1992;Ross, 1989] and would require extensive modification and additional data requirements to account for more complex chemical environments.…”

Section: Discussionmentioning

confidence: 99%

Influence of evaporation on waste package environment and radionuclide release from a tuff repository

Walton¹

1994

Water Resources Research

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Conceptual and mathematical models are presented for predicting waste package environment and radionuclide release in an unsaturated repository. Presence and ionic strength of water are viewed as a balance between water influx, evaporation, and condensation as modified by salinity-caused vapor pressure lowering. The model is used to examine the influence of thermal loading on waste package environment. Increased thermal gradients near the waste packages are shown to be as important as overall temperature in drying the waste package. The waste package environment is predicted to be highly variable, ranging from a concentrated brine to more dilute solutions. Under certain sets of conditions, water vapor condensation is predicted to occur on the waste package in the absence of liquid water influx. Conceptual ModelThe host rock for the proposed repository for high-level nuclear waste in the United States is in partially saturated tuff host rock at Yucca Mountain, Nevada. Placement of

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Section: Discussionmentioning

confidence: 99%

Influence of evaporation on waste package environment and radionuclide release from a tuff repository

Walton¹

1994

Water Resources Research

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“…These analytical solutions to mass transfer equations have been implemented into the AREST code (liebetrau et al 1987) and used for the analyses in this study. Similar models have been developed for OCRWM by other groups, including the University of California at Berkeley (Pigford and Chambre 1988) and the Lawrence livermore National Laboratory (O'Connel and Drach 1986).…”

Section: Overview Of Waste Package Release Modelmentioning

confidence: 98%

“…A number of mass-transfer models have been developed for diffusive and diffusive/convective transport of radionuclides from waste packages (Chambre et al 1985;Pigford and Chambre 1988) and applied to prediction of longterm release performance of engineered barrier systems (Apted and Engel 1988;Garisto and Leneveu 1988;KBS 1983;Mangin et al 1989;Apted, Liebetrau, and Engel 1989). In these models, both solubility and reaction-rate boundary conditions have been employed.…”

Section: Moist-continuous/diffusive Mass Transportmentioning

confidence: 99%

“…The release of highly soluble, low-sorptive radionuclides from waste packages containing DWPF glass will be controlled by the long-term dissolution rate of the glass and subsequent transport into the host rock. The performance assessment model for release must, therefore, combine a reaction-rate boundary condition with mass transport constraints (Pigford and Chambre 1988}. Glass dissolution models based solely on empirical correlations of data, even massive amounts of data, will probably provide an inadequate basis for the long-term prediction of radionuclide release from waste packages containing DWPF glass.…”

Section: Waste Package Analysismentioning

confidence: 99%

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Preliminary assessment of the controlled release of radionuclides from waste packages containing borosilicate waste glass

Strachan¹,

McGrail²,

Apted³

et al. 1990

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PNL-7591 UC-802 previously reached a similar conclusion (NAS 1983), as have other national repository programs (K8S 1983; NAGRA 1985). Data from the WAPS test is largely irrelevant, therefore, to the release-rate performance at either the waste-packages or EBS level of analysis. Radionuclide solubility limits are key to establishing predictive reliability and safety for geologic disposal; obtaining such data should be one priority for future tests that are intended to support the performance assessment of defense high-level waste glass. Transport parameters, such as extremely low diffusion coefficients in partially saturated tuff, may dominate the release of radionuclides from waste packages, even for highly soluble radionuclides. WASTE GLASS ANALYSIS Glass is a metastable solid and will, in the presence of water or water vapor, alter to a more stable set of phases. These phases will impose solubility limits to the concentration of many radionuclides within the waste package. Mechanistically based models for predicting the long-term glass dissolution and release of soluble radionuclides as a function of environmental variables exist; empirical models cannot be defensibly extrapolated to the long periods relevant to repository performance. There is paucity of test data on the most current defense glass (SRL-202) suitable for modeling of long-term dissolution rate. The WAPS test was intended as a quality control test, not as a performance test suitable for repository licensing. An alternative WAPS test methodology could be designed that would satisfy the original intent as a quality control test, yet provide more relevant data for evaluating the long-term dissolution rate of the defense glass. Because environmental variables such as temperature and pore water chemistry will affect the dissolution behavior of glass, no single performance confirmation test is possible.

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“…These variations in parameter values may have offsetting effects on the overall analysis.This analysis of brine migration shows that advection is relatively minor in the vicinity of a waste sphere in salt.Elsewhere, we have published equations for time-dependent mass transfer rates for both diffusive-advective systems and diffusion-dominated systems [Chambr• et al, 1982, 1985], from prolate spheroids including spheres and cylinders, over all times of interest. Mass transfer rates at near-zero velocity calculated from the equations for diffusion from a prolate spheroid, with dimensions that approximate a finite cylinder, exceed the release rate, obtained by incorrect extrapolation of the Pe m dependency from the high Peclet number region to the pore velocities of a few millimeters per year, by several orders of magnitude[Pigford et al, 1992]. Thus we turn to estimating release rates of radionuclides from waste in salt by diffusive transport.…”

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confidence: 99%

Analyses of mass transport in a nuclear waste repository in salt

Hwang¹,

Pigford²,

Lee³

1992

Water Resources Research

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Salt is the proposed host rock for geologic repositories of nuclear waste in several nations because it is “dry” and probably “impermeable”. To evaluate the safety of nuclear waste disposal in salt, it is necessary to calculate the rate of release of nuclides from solidified waste form and to predict the transport of released radionuclides. Our objective is to develop analytic methods for such prediction, based on mass transfer theory. First, we present an analysis of pressure‐driven brine migration. After consolidation, brine migration analyzed by these equations and using the particular set of parameter values is of a small magnitude, with Darcy velocities of the order of micrometers per year. Brine migration in consolidated salt is very localized, within a few meters from the waste package, and highly transient. We have analyzed diffusion of radionuclides near waste packages in a salt repository, using analytic equations for low Peclet systems. According to this analysis it is unlikely that any low‐solubility species will have difficulty meeting the U.S. Nuclear Regulatory Commission release rate requirement at the bare waste/salt interface. We have also analyzed the role that an interbed might play in being a preferential pathway for radionuclide migration. We calculate the diffusive mass fluxes from an infinitely long bare waste cylinder in salt, facing an interbed. The fractional release rates of solubility‐limited species into the interbed are low for the parameter values used in the numerical illustrations.

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Near-Field Mass Transfer in Geologic Disposal Systems: a Review

Cited by 8 publications

References 18 publications

Influence of evaporation on waste package environment and radionuclide release from a tuff repository

Influence of evaporation on waste package environment and radionuclide release from a tuff repository

Preliminary assessment of the controlled release of radionuclides from waste packages containing borosilicate waste glass

Analyses of mass transport in a nuclear waste repository in salt

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