Improved Creep Testing Approach for Bentonite EBS, Phase I

Project Description: In the United States, the nuclear reactor contributes 18.7 percent of the nation’s total electricity generation and produces a significant amount of spent nuclear fuel (SNF) and high-level waste. Because SNF is being stored for longer periods than initially envisioned, the U.S. Department of Energy Office of Nuclear Energy, Office of Spent Fuel and Waste Science and Technology is assessing the technical performance of the SNF storage systems after extended durations. The concept of a sustainable geologic repository for SNF disposal relies heavily on the safety provided by multiple barriers, such as repository host rock, overlying rock formation, and man-made engineered barrier systems (EBS). One of the major components of EBS is bentonite-based buffer materials that isolate the nuclear-waste canisters from the host rock and fill up the void left in the horizontally drilled boreholes. The resaturated bentonite has a swelling characteristic, which is useful for self-sealing the microcracks in the host rock and supporting the heavy weight of the canister. However, factors such as nonuniformity in the saturation and swelling pressure of bentonite, and the high temperature at the canister-bentonite interface may lead to instability in the placement of waste canister inside the borehole. Therefore, evaluating the long-term deformation of bentonite-based material under complex thermo- mechanical loading conditions is necessary. By using RESPEC’s experience in characterizing the time-dependent creep deformation of salt in its in-house, world-class laboratory and with minor modifications to the existing laboratory system, time-dependent deformation in bentonite-based materials can be better characterized. RESPEC proposes to conduct a series of creep experiments on bentonite-based specimens under low shear stress and high temperature conditions that improves understanding of EBS under typical repository conditions. The project also plans to develop and standardize an innovative laboratory testing program that will eventually be applied across scientific and engineering disciplines where an improved fundamental understanding behavior of clay and shale is required. Commercial Applications and Other Benefits: The systematic creep testing of bentonite-based specimens will help in developing a new standardized testing procedure that will be applicable for analyzing the similar characteristics of shale or clay like materials in different geologic conditions outside repository science, including in civil engineering and infrastructure projects, underground and open pit mining, and deep drilling.