Generalized approach for determination of thermal conductivity of buffer materials

Determination of thermal conductivity of buffer materials is an important aspect in the design and characterization of engineered barrier systems (EBS) in deep geological repositories (DGRs) for safe containment of high-level nuclear waste. Several factors, viz. compaction state, particle size distribution, and mineralogical characteristics of buffer materials, influence the thermal conductivity of composite buffer materials. Therefore, it is essential to give due regards to the influence of these factors while estimating thermal conductivity of buffer materials. In view of this, the present study pertains to an extensive laboratory scale determination of thermal conductivity of a wide range of sand-bentonite based buffer materials employing a thermal needle probe. Precision and accuracy of the thermal needle probe are established in relation to a contemporary and widely endorsed thermal property analyzer. Further, the efficacy of several predictive models available in the literature is evaluated to appraise the thermal conductivity of composite buffer materials in relation to the experimental data. Realizing the need of a generalized approach considering the influence of clay mineralogy and particle size fraction present in the geomaterial, the manuscript proposes generalized thermal conductivity prediction models meant for the buffer materials. The developed models are found to deliver satisfactory performance and accuracy in appraising thermal conductivity of sand-bentonite buffers used in DGRs.