Theory and numerical application of subsurface flow and transport for transient freezing conditions
Protective barriers are being investigated for the containment of radioactive waste within subsurface environments. Predicting the effectiveness of cryogenic barriers and near-surface barriers in temperate or arctic climates requires capabilities for numerically modeling subsurface flow and transpor...
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| Format: | Report |
| Language: | English |
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Pacific Northwest Laboratory
1995
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| Online Access: | https://doi.org/10.2172/106505 https://digital.library.unt.edu/ark:/67531/metadc620350/ |
| Summary: | Protective barriers are being investigated for the containment of radioactive waste within subsurface environments. Predicting the effectiveness of cryogenic barriers and near-surface barriers in temperate or arctic climates requires capabilities for numerically modeling subsurface flow and transport for freezing soil conditions. A predictive numerical model is developed herein to simulate the flow and transport of radioactive solutes for three-phase (water-ice-air) systems under freezing conditions. This physically based model simulates the simultaneous flow of water, air, heat, and radioactive solutes through variably saturated and variably frozen geologic media. Expressions for ice (frozen water) and liquid water saturations as functions of temperature, interfacial pressure differences, and osmotic potential are developed from nonhysteretic versions of the Brooks and Corey and van Genuchten functions for soil moisture retention. Aqueous relative permeability functions for variably saturated and variably frozen geologic media are developed from the Mualem and Burdine theories for predicting relative permeability of unsaturated soil. Soil deformations, caused by freezing and melting transitions, are neglected. Algorithms developed for predicting ice and liquid water saturations and aqueous-phase permeabilities were incorporated into the finite-difference based numerical simulator STOMP (Subsurface Transport Over Multiple Phases). Application of the theory is demonstrated by the solution of heat and mass transport in a horizontal cylinder of partially saturated porous media with differentially cooled ends, with the colder end held below the liquid water freezing point. This problem represents an essential capability for modeling cryogenic barriers in variably saturated geologic media. |
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