Implications of Grain-Scale Mineralogical Heterogeneity for Radionuclide Transport in Fractured Media
[1];
- AMPHOS 21 Consulting S.L., Barcelona (Spain)
- Forschungszentrum Julich (Germany). Inst. for Energy and Climate Research. Nuclear Waste Management and Reactor Safety
- Computer-Aided Fluid Engineering AB, Lyckeby (Sweden)
- Sandia National Lab. (SNL-NM), Albuquerque, NM (United States). Applied Systems Analysis and Research
- Swedish Nuclear Fuel and Waste Management Company, Stockholm (Sweden)
The geological disposal of nuclear waste is based on the multi-barrier concept, comprising various engineered and natural barriers, to confine the radioactive waste and isolate it from the biosphere. Some of the planned repositories for high-level nuclear waste will be hosted in fractured crystalline rock formations. The potential of these formations to act as natural transport barriers is related to two coupled processes: diffusion into the rock matrix and sorption onto the mineral surfaces available in the rock matrix. Different in situ and laboratory experiments have pointed out the ubiquitous heterogeneous nature of the rock matrix: mineral surfaces and pore space are distributed in complex microstructures and their distribution is far from being homogeneous (as typically assumed by Darcy-scale coarse reactive transport models). We use a synthetically generated fracture–matrix system to assess the implications of grain-scale physical and mineralogical heterogeneity on cesium transport and retention. The resulting grain-scale reactive transport model is solved using high-performance computing technologies, and the results are compared with those derived from two alternative models, denoted as upscaled models, where mineral abundance is averaged over the matrix volume. In the grain-scale model, the penetration of cesium into the matrix is faster and the penetration front is uneven and finger-shaped. The analysis of the cesium breakthrough curves computed at two different points in the fracture shows that the upscaled models provide later first-arrival time estimates compared to the grain-scale model. The breakthrough curves computed with the three models converge at late times. These results suggest that spatially averaged upscaled parameters of sorption site distribution can be used to predict the late-time behavior of breakthrough curves but could be inadequate to simulate the early behavior.
- Research Organization:
- Sandia National Lab. (SNL-NM), Albuquerque, NM (United States); AMPHOS 21 Consulting S.L., Barcelona (Spain); Computer-Aided Fluid Engineering AB, Lyckeby (Sweden)
- Sponsoring Organization:
- USDOE; Swedish Nuclear Fuel and Waste Management Company (SKB)
- Grant/Contract Number:
- AC04-94AL85000
- OSTI ID:
- 1497639
- Report Number(s):
- SAND-2016-5312J; 672254
- Journal Information:
- Transport in Porous Media, Vol. 116, Issue 1; ISSN 0169-3913
- Publisher:
- SpringerCopyright Statement
- Country of Publication:
- United States
- Language:
- English
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