Abstract

ABSTRACT: Secure storage of nuclear spent fuel is of great concern for protecting public health and safety. The standard long-term solution for nuclear waste disposal is containment in geological repositories. Nuclear spent fuel, stored in canisters, is placed deep underground with one or more Engineered Barrier Materials (EBM) forming a buffer between the waste containers and the natural rock. Bentonite clay is commonly used as an EBM for its low cost, long-term stability, low hydraulic permeability in a saturated state, high thermal resistance, high radionuclide retardation capacity, high swelling pressure, and "self-healing" capability. However, bentonite clay subjected to heating from nuclear waste decay may undergo desiccation cracking. In this study, inorganic microfiber reinforcement was evaluated as a method of reducing desiccation cracking in EBM. A restrained ring test method for soils coupled with digital image correlation (DIC) was employed to capture free shrinkage and desiccation cracking. Reinforcement of bentonite clay with 1.0 % wt. basalt fibers was shown to be effective in reducing crack propagation and separation. 1. INTRODUCTION 1.1 Research Significance Each nuclear power reactor generates 20-30 tons of highly radioactive waste, annually. Secure long-term storage of nuclear waste is a great concern for public health and safety. A preferred long-term solution for highly radioactive waste disposal is containment in geological repositories. Canisters filled with radioactive waste are placed in tunnels, with one or more Engineered Barrier Systems (EBS) encapsulating them. A material like bentonite clay, which is physio-chemically compatible with both natural rock and nuclear waste, can be used in EBS. In fact, bentonite is preferred as an Engineered Barrier Material (EBM) for its advantageous properties including low cost, long-term stability, low hydraulic permeability and conductivity in a saturated state, high thermal resistance, high radionuclide retardation capacity, high swelling pressure, and good "self-healing" capability. However, heat-induced desiccation cracking of bentonite can cause transmission of radiation in EBS (Allen & Wood, 1988; Bharat et al., 2017; Hirose & Matsubara, 2018; Mohammad, 2020; Soujanya & Thyagaraj, 2017).

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