Electrochemical and Modelling Studies on Simulated Spent Nuclear Fuel Corrosion under Permanent Waste Disposal Conditions

Author

Nazhen Liu, The University of Western OntarioFollow

Degree

Doctor of Philosophy

Program

Chemistry

Supervisor

Dr. David Shoesmith

2nd Supervisor

Dr. James Noël

Joint Supervisor

Abstract

The safety assessment models for the deep geological disposal of spent nuclear fuel require a fundamental understanding of the corrosion of spent fuel in a failed waste container. The overall research goal of this project is to investigate the corrosion of simulated spent fuel under permanent disposal conditions, using both model simulations and experimental investigations. A model for fuel corrosion has been expanded to determine the relative importance of radiolytic hydrogen and hydrogen from corrosion of the steel vessel in suppressing fuel corrosion. It was shown that, for CANDU (CANada Deuterium Uranium) fuel with moderate in-reactor burnup, only micromolar concentrations of hydrogen from steel corrosion are required to completely suppress fuel corrosion. In a partially closed system (i.e., within cracks in the fuel) radiolytic hydrogen alone can suppress corrosion to a negligible level. The model was validated by comparing the calculated corrosion rates with published measurements. Agreement between calculated and measured rates indicated that corrosion is controlled by the rate of radiolytic production of oxidants, in particular hydrogen peroxide, irrespective of the reactivity of the fuel.

Experimentally, the influence of rare earth doping on the reactivity of UO₂ was investigated. For RE^III-doped UO₂, the onset of matrix dissolution was accompanied by the enhanced oxidation of the matrix to U^IV_1−2xU^V_2xO_2+x. This can be attributed to the onset of tetragonal lattice distortions as oxidation proceeds which leads to the clustering of defects, enhanced diffusion of O_I (interstitial oxygen)to deeper locations and destabilization of the fluorite lattice. A further investigation of the doping effect was performed on a series of (U_1−yGd_y)O₂ materials (y = 0, 0.01, 0.03, 0.05, 0.07 and 0.10). Overall the increase in doping up to 10% does not exert a major influence on reactivity possibly due to the competition between an increase in the number of (O_v)s (oxygen vacancy) and a contraction in the lattice constant.

Recommended Citation

Liu, Nazhen, "Electrochemical and Modelling Studies on Simulated Spent Nuclear Fuel Corrosion under Permanent Waste Disposal Conditions" (2017). Electronic Thesis and Dissertation Repository. 4412.
https://ir.lib.uwo.ca/etd/4412