Summary report on Phase 1 feasibility study of in-drift diffusion

Abstract

This report summarizes the work performed and findings obtained during the Phase 1 (feasibility study) of the Engineered Barrier System (EBS) in-drift diffusion evaluation. The objective of this work is to characterize and reduce uncertainties associated with measurements of diffusion coefficients and modeling of diffusion processes. Phase 1 of the study evaluates measurement and modeling uncertainties as well as scoping alternative measurement and modeling approaches.Phase 2 of the study consists of rigorous diffusion testing of invert materials (employing approaches developed from Phase 1) and the development of a calibrated invert diffusion model (with separate surface and internal water components if needed to interpret measured diffusion data) for use in total system performance assessment (TSPA).The invert between the waste package/drip shield and the tuff host rock is integral to both the EBS and the Unsaturated Zone (UZ) performance, and is important to the TSPA dose calculation.

Diffusion in sparsely connected pore spaces: Temporal and spatial scaling

“…However, diffusivity measurements are not the best tool for determining whether a specific medium is at criticality. One better option would be to vacuum‐saturate the sample with a tracer, then examine the tracer profile using a high‐resolution method such as laser ablation inductively coupled plasma mass spectrometry (LA‐ICP‐MS; Hu et al [2001]). This will give an edge‐accessible porosity profile which can then be compared with theoretical predictions for different connectivities [ Ewing and Horton , 2002].…”

Characterizing Unsaturated Diffusion in Porous Tuff Gravel

“…The interior surface was then mapped by adjusting the laser focus at each sampling location for the exposed rough surface. Stable responses were obtained during testing of these tuff elements despite the rough surface (Hu et al, 2001). A series of CT images are shown in Figure 5a for partially saturated 6.3−9.5 mm gravel.…”

“…CRWMS M&O (2000b) reported that this diffusion data set was well correlated in terms of a power-dependence (Archie's law type) on the volumetric water content, and used a resultant "universal" power function to represent diffusive transport of radionuclides through the invert. However, in waste emplacement drifts, characterized by a humid environment with or without the presence of liquid water, crushed porous rock may provide unique characteristics that vary greatly from this generic power function (Wang et al, 2001;Hu and Wang, 2003). For example, Conca (1990) placed four different size fractions of tuff gravel samples (2-4 mm, 4-6.3 mm, 6.3-9.5 mm, and 15-25.4 mm) for equilibrium inside a chamber with a nearly 100% humidity atmosphere.…”

EBS Radionuclide Transport Abstraction

“…Measurements along the outside surface of the sink cube indicated that a nonsorbing tracer (ReO 4 − ) diffused along the surface at a rate similar to its aqueous diffusion rate in bulk water (Hu et al 2001 . This is a factor of 10 5 larger than the measurement.…”