Project title: Pelletized Clay Mixtures with Enhanced Thermal Conductivity for Engineered Barriers in a Geologic Repository for High-Level Nuclear Waste and Spent Nuclear Fuel.

Funding Agency: Nuclear Energy (NEUP). U.S, Department of Energy (DOE), United States. Award DE-NE0009133.

The team:

The research project is led by Dr. Marcelo Sanchez (Texas A&M University, TAMU). The work relies on a close collaboration with scientists from Sandia National Laboratory (SNL). SNL efforts are coordinated by Dr. Thomas Dewers, Dr. Edward Matteo, and Dr. Yongliang Xiong. The project involves two graduate students and contemplates international collaborators.

Overview:

The design of Engineered Barrier System (EBS) for high-level nuclear waste (HLW) and spent nuclear fuel (SNF) has been mainly based on placing blocks of compacted bentonite in the space between the canister (containing the HLW/SNF) and the gallery rock. However, the construction of such a barrier is challenging, and leads to the presence of physical gaps, which jeopardize EBS safety functions. Clay mixtures based on high-density bentonite-pellets are becoming the preferred candidate to construct engineered barriers for HLW/SNF because they present several advantages with respect to other sealing materials, particularly reduction of gaps in the EBS and ease of emplacement because the pellets are directly projected into the openings. The interest for this kind of material has significantly increased in the last few years, with several EBS hydration and heating experiments based on clay-pellets. Even though these previous studies have contributed to improving the understanding of these multiscale materials, there are still several aspects that require further research. For example, studies examining clay-pellets behavior at high temperature are scarce. A potential problem associated with the effect of high temperatures in pellet mixtures is that the combination of strong drying and large inter-pellets pores may negatively impact the buffer’s thermal conductivity, preventing a proper dissipation of the heat emitted by the HLW/SNF. To prevent this type of issue, we will investigate the enhancement of the material’s thermal conductivity by adding highly heat conductive materials (e.g., graphite) to the mixture.

Figure. Schematic representation of a deep geological repository for HLW (Eurad, 2020)