Publications

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A helium leakage detection system was modified to measure gas permeability on extracted cores of nearly impermeable rock. Here we use a Helium - Mass - Spectrometry - Permeameter (HMSP) to conduct a constant pressure, steady state flow test through a sample using helium gas. Under triaxial stress conditions, the HMSP can measure flow and estimate permeability of rocks and geomaterials down to the nanodarcy scale (10-21 m2). In this study, measurements of flow through eight shale samples under hydrostatic conditions were in the range of 10-7 to 10-9 Darcy. We extend this flow measurement technology by dynamically monitoring the release of helium from a helium saturated shale sample during a triaxial deformation experiment. The helium flow, initially extremely low, consistent with the low permeability of shale, is observed to increase in advance of volume strain increase during deformation of the shale. This is perhaps the result of microfracture development and flow path linkage through the microfractures within the shale. Once microfracturing coalescence initiates, there is a large increase in helium release and flow. This flow rate increase is likely the result of development of a macrofracture in the sample, a flow conduit, later confirmed by post-test observations of the deformed sample. The release rate (flow) peaks and then diminishes slightly during subsequent deformation; however the post deformation flow rate is considerably greater than that of undeformed shale.

The calculation of radionuclide concentrations in a receptor well of a generic reference aquifer is highly dependent on the mixing that occurs in the aquifer and well. This study tests two simple analytical approaches for estimating well concentrations: a Generic Aquifer Transport and Capture (GATC) approach and an adapted IAEA ERB1B model. These approaches are tested against a 3-D generic repository model simulated numerically using PFLOTRAN. Because the PFLOTRAN model in this study simulates a diffusive release to the aquifer and the ERB1B model is designed for advective releases, the ERB1B model had to be adapted to accept a diffusive release. The results show that for this PFLOTRAN simulation the GATC equations accurately predict the initial breakthrough and peak concentration at the well but somewhat overestimate concentrations between these points. The adapted ERB1B model only predicts the peak accurately. Similar studies with broader aquifer domains and different types of advective and diffusive releases to the aquifer are needed to fully test the ranges of these analytical approaches.

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directly, rather than through simplified abstractions. It also a llows for complex representations of the source term, e.g., the explicit representation of many individual waste packages (i.e., meter - scale detail of an entire waste emplacement drift). This report fulfills the Generic Disposal System Analysis Work Packa ge Level 3 Milestone - Performance Assessment Modeling and Sensitivity Analyses of Generic Disposal System Concepts (M 3 FT - 1 4 SN08080 3 2 ).

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In this study, we use PFLOTRAN, a highly scalable, parallel, flow and reactive transport code to simulate the concentrations of 3H, 3He, CFC-11, CFC-12, CFC-113, SF6, 39Ar, 81Kr, 4He and themean groundwater age in heterogeneous fields on grids with an excess of 10 million nodes. We utilize this computational platform to simulate the concentration of multiple tracers in high-resolution, heterogeneous 2-D and 3-D domains, and calculate tracer-derived ages. Tracer-derived ages show systematic biases toward younger ages when the groundwater age distribution contains water older than the maximum tracer age. The deviation of the tracer-derived age distribution from the true groundwater age distribution increases with increasing heterogeneity of the system. However, the effect of heterogeneity is diminished as the mean travel time gets closer the tracer age limit. Age distributions in 3-D domains differ significantly from 2-D domains. 3D simulations show decreased mean age, and less variance in age distribution for identical heterogeneity statistics. High-performance computing allows for investigation of tracer and groundwater age systematics in high-resolution domains, providing a platform for understanding and utilizing environmental tracer and groundwater age information in heterogeneous 3-D systems. Groundwater environmental tracers can provide important constraints for the calibration of groundwater flow models. Direct simulation of environmental tracer concentrations in models has the additional advantage of avoiding assumptions associated with using calculated groundwater age values. This study quantifies model uncertainty reduction resulting from the addition of environmental tracer concentration data. The analysis uses a synthetic heterogeneous aquifer and the calibration of a flow and transport model using the pilot point method. Results indicate a significant reduction in the uncertainty in permeability with the addition of environmental tracer data, relative to the use of hydraulic measurements alone. Anthropogenic tracers and their decay products, such as CFC11, 3H, and 3He, provide significant constraint oninput permeability values in the model. Tracer data for 39Ar provide even more complete information on the heterogeneity of permeability and variability in the flow system than the anthropogenic tracers, leading to greater parameter uncertainty reduction.

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