ABSTRACT:

The Yucca Mountain Project is evaluating engineered barrier system designs to enhance the performance of a proposed deep geologic nuclear waste repository. Geologic media in the vicinity of the waste package, such as granular backfill or invert ballast material, will undergo changing thermal, hydrologic, and chemical environments over the duration of the repository operation. The Engineered Barrier System (EBS) Thermal-Hydraulic-Chemical (THC) Column Tests provide data needed for model validation and process understanding of these in-drift granular media. The objectives of the THC column testing are to characterize coupled processes that could affect EBS component performance, particularly the impact on hydrologic properties, the nature of minerals produced near the waste package, and chemical fractionation (such as concentrative separation of salts and minerals due to boiling point elevation). Three tests have been conducted in this series. Results of the tests demonstrated significant alteration of the pore water chemistry and redistribution of minerals in the heated zone of the experiment.

INTRODUCTION

The Engineered Barrier System (EBS) ThermalHydraulic-Chemical (THC) column tests provide data needed for model validation and process understanding of the in-drift granular media such as invert or backfill material. The EBS performance predictions will be based on supporting models for in-drift THC coupled processes, and the in-drift physical and chemical environment. These models describe the complex chemical interaction of EBS materials, including backfill and invert materials, with the thermal and hydrologic conditions that will be present in the repository emplacement drifts. Test data are needed for model validation, and to support selection from among candidate materials.

The objectives of the THC column testing are to:

§ Characterize THC coupled processes that could affect engineered barrier system component performance, particularly changes in permeability, the nature of minerals produced at or near the waste package, and chemical fractionation (i.e., concentrative separation of salts and minerals due to boiling point elevation).

§ Analyze the composition of fluid that reenters the backfill after heating, and remobilizes the precipitates.

§ Generate data for validating THC predictive models used in repository design analysis.

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