Engineered Barrier System: Physical and Chemical Environment

The purpose of this model report is to describe the evolution of the physical and chemical environmental conditions within the waste emplacement drifts of the repository, including the drip shield and waste package surfaces. This report documents the development of a new process-level model, the near-field chemistry (NFC) model, and develops two abstraction models. The resulting seepage dilution/evaporation and integrated invert chemistry abstraction models are used in the total system performance assessment (TSPA) for the license application (LA) to assess the performance of the Engineered Barrier System (EBS) and the waste form.
This report develops one process model (the NFC model) and two abstraction-level models (the seepage dilution/evaporation and the integrated invert chemistry abstraction models) that describe the EBS physical and chemical environment (P&CE). The integrated invert chemistry abstraction utilizes the same lookup tables in the same manner as those developed by the seepage dilution/evaporation abstraction. Therefore, much of the discussion of the development of the TSPA feeds is limited to the seepage dilution/evaporation abstraction model. The implementation in the invert is unique, however, and is discussed in detail in Section 6.15.2. Where possible, these models use information directly from other reports as input, which promotes integration among process models used for TSPA-LA. Specific tasks and activities of modeling the physical and chemical environment are included in Technical Work Plan for Revision of Model Reports for: Near-Field Environment and In-Drift Water Chemistry (SNL 2007 [DIRS 179287], Section 1.2.2). As described in the technical work plan (TWP), the development of this report is coordinated with the development of other engineered barrier system reports.