THC Sensitivity Study of Heterogeneous Permeability and Capillarity Effects

The purpose of this report is to <,locument the sensitivity of the drift-scale thermal-hydrologic- chemical (THC) seepage model (SNL 2007 [DIRS 177404]) to heterogeneities in permeability and capillarity, which could affect predicted fluxes and chemistries of water and gases seeping into the emplacement drifts. This report has been developed following Technical Work Plan for: Revision of Model Reports for Near-Field and In-Drift Water Chemistry (SNL 2007 [DIRS 179287]). Furthermore, this report has been prepared in accordance with the latest version ofSCI-PR0-005, Scientific Analyses and Calculations.
This is a revision of the analysis report THC Sensitivity Study of Repository Edge and Heterogeneous Permeability Effects (BSC 2006 [DIRS 174104]), hereafter referred to as the THC Sensitivity Study. In accordance with Technical Work Plan for: Revision of Model Reports for Near-Field and In-Drift Water Chemistry (SNL 2007 [DIRS 179287], Section 1.1 ), the present revision of the THC sensitivity study will be called THC Sensitivity Study of Heterogeneous Permeability and Capillarity Effects, as it no longer addresses the repository edge effects. Per the technical work plan (TWP) (SNL 2007 [DIRS 179287], Section 1.1), the analyses pertaining to repository edge effects have been moved to the model report Drift-Scale
THC Seepage Model (SNL 2007 [DIRS 177404]).
The objective of this report is to address in part Condition Report (CR) 7037, which notes that information provided in Revision 00 of the THC sensitivity study (BSC 2006 [DIRS 174104]) shows that predicted seepage is enhanced by THC effects not considered in Abstraction of Drift Seepage (BSC 2004 [DIRS 169131]). The observations in the THC sensitivity study were based on limited analyses (such as relying only on one realization of the heterogeneous fracture permeability distribution) of the THC seepage model sensitivity to permeability heterogeneities.. The THC sensitivity study also did not account for the corresponding changes in fracture capillarity associated with spatially/temporally variable fracture permeability distributions. The revised analysis in the present report is based on a more comprehensive evaluation of the sensitivity of the THC seepage model to heterogeneities, both in fracture permeability and capillarity. It also documents the sensitivity of the THC seepage model through implementation of multiple realizations of the heterogeneous fracture permeability distribution, multiple initial fracture capillary-strength parameters of the host rock, and enhanced infiltration fluxes. The ultimate goal of these sensitivity analyses is to evaluate the effects from THC processes on the predicted occurrence of seepage. The other goal of the present report is to provide sufficient technical bases regarding whether any change in abstraction of drift seepage is necessary.