In:
Water Resources Research, American Geophysical Union (AGU), Vol. 18, No. 5 ( 1982-10), p. 1479-1492
Abstract:
Numerical models for simulating chemical transport in fissured rocks constitute powerful tools for evaluating the acceptability of geological nuclear waste repositories. Due to the very long‐term, high toxicity of some nuclear waste products, the models are required to predict, in certain cases, the spatial and temporal distribution of chemical concentration less than 0.001% of the concentration released from the repository. Whether numerical models can provide such accuracies is a major question addressed in the present work. To this end we have verified a numerical model, TRUMP, which solves the advective diffusion equation in general three dimensions, with or without decay and source terms. The method is based on an integrated finite difference approach. The model was verified against known analytic solution of the one‐dimensional advection‐diffusion problem, as well as the problem of advection‐diffusion in a system of parallel fractures separated by spherical particles. The studies show that as long as the magnitude of advectance is equal to or less than that of conductance for the closed surface bounding any volume element in the region (that is, numerical Peclet number 〈 2), the numerical method can indeed match the analytic solution within errors of ±10 −3 % or less. The realistic input parameters used in the sample calculations suggest that such a range of Peclet numbers is indeed likely to characterize deep groundwater systems in granitic and ancient argillaceous systems. Thus TRUMP in its present form does provide a viable tool for use in nuclear waste evaluation studies. A sensitivity analysis based on the analytic solution suggests that the errors in prediction introduced due to uncertainties in input parameters are likely to be larger than the computational inaccuracies introduced by the numerical model. Currently, a disadvantage in the TRUMP model is that the iterative method of solving the set of simultaneous equations is rather slow when time constants vary widely over the flow region. Although the iterative solution may be very desirable for large three‐dimensional problems in order to minimize computer storage, it seems desirable to use a direct solver technique in conjunction with the mixed explicit‐implicit approach whenever possible. Work in this direction is in progress.
Type of Medium:
Online Resource
ISSN:
0043-1397
,
1944-7973
DOI:
10.1029/WR018i005p01479
Language:
English
Publisher:
American Geophysical Union (AGU)
Publication Date:
1982
detail.hit.zdb_id:
2029553-4
detail.hit.zdb_id:
5564-5
SSG:
13
SSG:
14
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