ISSN 1556-6757


SJI 


 

 

 

 

 
 
 

Volume 1, Issue 1, 2011

 
 

Spatial and Temporal Moment Analyses of Decaying Solute Transport in a Single Fracture with Matrix Diffusion

Suresh Kumar, M. Sekhar, and Debasmita Misra
 

Abstract

Knowledge of how nuclear waste migrates and spreads in low-permeability fractured rocks is central to the successful disposal of nuclear waste and creation of a safe environment. The mobility and spreading of decaying solute transport are significantly affected by matrix diffusion in low-permeability hard rocks. Thus, it is important to understand their influence on changes in effective matrix diffusion coefficients of rock matrix for solutes with a range of half-life periods. For this purpose, a numerical model is developed. Spatial moment analysis suggests that the reduction in solute velocity is inversely proportional to the solute decay rate, and solute spreading follows a skewed Gaussian profile. For higher effective matrix diffusion coefficients, time-averaged temporal moment analysis for the fracture-matrix coupled system results in a constant solute front velocity and macro-dispersion coefficient along the fracture, and indicates its spatial independency. The profiles of relative solute mass retention in the fracture indicate that it is difficult to distinguish individual effects of matrix diffusion and first-order decay, while the effective decay rate is found to increase with the effective matrix diffusion coefficient and the first-order radioactive decay constant.
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