Structural Engineering

Aerospace Biological Civil Geotechnical Mechanical

“Understanding the Use of Bentonite as a Buffer Material for the Geological Disposal of High-Level Radioactive Waste: Experiments and Numerical Modeling

Seminar Speaker
LianGe Zheng
Seminar Date
Wednesday, Mar 9, 2022 - 12:00 pm
Seminar Location - Room
Speaker Bio

LianGe Zheng is a staff scientist and head of the Nuclear Energy and Waste Program at the Energy Geoscience Division in Lawrence Berkeley National Lab. His research interests are centered on numerical modeling of non-isothermal multiphase flow and reactive transport in porous media. His research work is mainly related to coupled thermal, hydrological, mechanical and chemical (THMC) processes modeling for radioactive waste repositories and the impact of CO2 geological sequestration on groundwater.  He holds a PhD in Civil Engineering from University of La Coruna, Spain

Disposal of high-level radioactive waste in geologic repositories involves a multi-barrier system that comprises of an engineered barrier system (EBS) and the host rock (or natural barrier system). One of the common components of the EBS is a bentonite buffer material which has several beneficial features such as a low permeability as well as a high swelling and retardation capacity. Bentonite is a very complex geo-material: it is composed of swelling clay minerals (i.e. smectite) and non-swell minerals, it has a very complex pore structure which can be characterized by different ways; pores associated with clay minerals has charged surface and other pores do not. Bentonite backfill undergoes heating from the waste package and hydration from the host rock, which triggers a series mechanical and chemical alterations that evolve spatially and temporally. All this makes it very scientifically interesting to understand how bentonite behaves as a buffer material. This presentation summarizes the studies at LBNL that use experiments and models ranging from nanometers to kilometers scale to deepen the understanding and enhance the capability of predicting the evolution of bentonite.  We will start with a brief review of the relevant short-term and long-term behavior of bentonite exposed to strong hydrological, thermal, mechanical, and chemical perturbations. We will then present experiments using micro-oedometer and imaging using cryo-TEM, laboratory column tests and related modeling analysis, and observations from several large heater experiments with heating temperature around 100  degrees C conducted at underground laboratories. Finally, we will present results from exploratory modeling work to evaluate the impact of higher temperature ( up to 200  degrees C) on bentonite and an ongoing large-scale field test with temperature up to 200 degrees C. 


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