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

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 REIII-doped UO2, the onset of matrix dissolution was accompanied by the enhanced oxidation of the matrix to UIV1−2xUV2xO2+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 OI (interstitial oxygen)to deeper locations and destabilization of the fluorite lattice. A further investigation of the doping effect was performed on a series of (U1−yGdy)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 (Ov)s (oxygen vacancy) and a contraction in the lattice constant.

Name thesis:degree_name

Ph D

Discipline thesis:degree_discipline

Chemistry

Grantor dc:publisher

The University of Western Ontario

Year dc:date.issued

2017

Author dc:creator

• Liu, Nazhen

Advisors dc:contributor.advisor

• David Shoesmith
• James Noël

• Uranium dioxide
• Corrosion
• Nuclear waste disposal
• Modelling
• Electrochemistry
• Rare earth doping

Language dc:language.iso

en_ca

Handle dc:identifier.uri

https://hdl.handle.net/20.500.14721/34508

OAI identifier oai:identifier

oai:uwo.scholaris.ca:20.500.14721/34508