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Multispecies random walk simulations in radial symmetry: model concept, benchmark, and application to HTO, 22Na and 36Cl diffusion in clay

By
Shuo Meng
Shuo Meng
Paul Scherrer Institut, 5232 Villigen-PSI, Switzerland
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Wilfried Pfingsten
Wilfried Pfingsten
Paul Scherrer Institut, 5232 Villigen-PSI, Switzerland
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Published:
January 01, 2017

Abstract

Modelling of radionuclide transport in clay can be simplified and accelerated by exploiting radial symmetry of laboratory experiments or nuclear waste repositories design. Consequently, the multispecies reactive transport code MCOTAC has been extended to radial symmetry, exploiting the advantages of its random walk transport description. Random walk in radial r-symmetry is mimicked by two-dimensional (2D) random walk projected to a radial coordinate for geochemical calculations. This guarantees fast 2D(x, y) transport calculations, together with complex geochemical calculations in 1D(r) only. The new model concept has been benchmarked for simple geochemical systems and applied to laboratory diffusion experiments with HTO, 22Na and 36Cl in Opalinus Clay using higher spatial resolution for modelling than reported in the literature. This makes it possible to distinguish between the transport properties of the sample and the filters, and yields more careful determination of radionuclide transport parameters: for example, there was a difference of a factor of 2 between the diffusion coefficient and log Kd sorption coefficient in the case of 22Na compared to the former best-fit analysis.

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Contents

Geological Society, London, Special Publications

Radioactive Waste Confinement: Clays in Natural and Engineered Barriers

S. Norris
S. Norris
Radioactive Waste Management, UK
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J. Bruno
J. Bruno
Amphos 21, Spain
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M. van Geet
M. van Geet
ONDRAF/NIRAS, Belgium
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E. Verhoef
E. Verhoef
COVRA, The Netherlands
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Geological Society of London
Volume
443
ISBN electronic:
9781786203267
Publication date:
January 01, 2017

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