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    APPLICATION OF MULTI-GROUP DIFFUSION THEORY TO MECHANISTIC MODELLING OF LEACHING BEHAVIOR OF SOLIDIFIED LOW-LEVEL RADIOACTIVE WASTE FORMS.

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    Author
    NIMNUAL, SOMKID.
    Issue Date
    1987
    Keywords
    Low-level radiation.
    Radioactive wastes.
    Advisor
    Wacks, M. E.
    
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    Publisher
    The University of Arizona.
    Rights
    Copyright © is held by the author. Digital access to this material is made possible by the University Libraries, University of Arizona. Further transmission, reproduction or presentation (such as public display or performance) of protected items is prohibited except with permission of the author.
    Abstract
    The application of multi-concentration group mathematical modelling to the leaching of radionuclide waste-forms which have continuous porous matrix such as cemented waste form is described. The modelling is illustrated analysing a hypothetical of some transport mechanisms such as molecular diffusion, ionic migration and convective flow for release of interest radionuclide from a solidified waste form which contains discrete particles of radioactive Sr-85 nuclides into the aqueous environment. The group parameters are derived from the classical electrochemistry concept of ion transport in dilute electrolytic solution. The numerical analysis is based on the Crank-Nicolson Implicit Methods which assures the stability of the solution at a practical time step. The results show that, for a short-time period of leaching in demineralized water the leaching behavior follows the predominating diffusion mechanism. After this point, the role of other processes apparent and continue until all radionuclides in the cement waste are leached out when compared to the Semi-Infinite Diffusion model which is based on pure diffusion mechanism. The multi-concentration group model can also be applied to long-term prediction of complicated release mechanisms of the radionuclides in the waste form of a particular disposal environment, unless the variables of interest such as the corrosion rate, the chemical reaction, erosion rate and etc. are determined by experiment or theoretical hypothesis. The appropriate differential equation then can be solved by the same general numerical approach. Also, the results of the modelling indicate which parameters should be measured experimentally in order to provide a quantitative test of the hypothetical release mechanism.
    Type
    text
    Dissertation-Reproduction (electronic)
    Degree Name
    Ph.D.
    Degree Level
    doctoral
    Degree Program
    Nuclear and Energy Engineering
    Graduate College
    Degree Grantor
    University of Arizona
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