[CCoE Notice] Cullen College Dissertation Defense Announcement- Lotanna Vitus Ohazuruike

[Hutchinson, Inez A]

[cid:925a7f8e-c4ba-4c7a-892b-450b1ff79491]The Petroleum Engineering Department Presents



ANALYTICAL MODELING OF ILLITIZATION OF SMECTITE IN THE BENTONITE BUFFER OF NUCLEAR WASTE DISPOSAL SYSTEMS



Lotanna Vitus Ohazuruike

December 8, 2023; 10:30 AM - 1:30 PM (CST)
Location: Petroleum Engineering Department, Technology Bridge Park



Committee Chair:
Kyung Jae Lee, Ph.D.

Committee Members:
Birol Dindoruk, Ph.D. | Christine Ehlig-Economides, Ph.D. | Lori Hathon, Ph.D.

Guan Qin, Ph.D. | Mohamed Soliman, Ph.D.

Abstract

Nuclear waste is disposed by storing them in canisters in underground repositories and covering with a buffer material. Water flows from the surrounding rock, through the buffer towards the canister while heat flows in the opposite direction. As such, the buffer is the centroid of multiple interacting phenomena. Bentonite is preferred for the buffer because its low hydraulic conductivity and high swelling potential ensure the waste remains isolated from the host rock. However, under high potassium ion concentration at temperatures greater than 100 °C, bentonite is transformed to illite, which is a non-swelling mineral. This research presents analytical models for predicting the evolution of temperature, water saturation, and potassium ion concentration in a bentonite buffer, as well as their effect on the smectite illitization process.

The models are developed by solving partial differential equations (PDEs) based on mass and energy balances for the components. The PDEs are solved analytically using Laplace transformation. The Laplace domain solutions are subsequently inverted analytically using complex integrals and residue theorem. The component solutions are coupled via the change in porosity which is impacted by the smectite swelling and illitization.

Subsequently, the solutions are validated by comparing to published analytical solutions for temperature and experimental results for illitization. Preliminary validation showed that incorporating the effect of the declining reactive surface area leads to a better prediction of illitization. This is because the loss of area captures the loss of interlayer smectite regions, which slows down the illitization process. Once validated, the models are used to predict the multiphysics behavior in a nuclear repository and compared to numerical simulations of the repository using TOUGHREACT and FLAC simulators. The results illustrate the accuracy and usefulness of the models in predicting the evolution of temperature, potassium ion concentration, water saturation and smectite content in a bentonite buffer.

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