Grants and Contributions:

Grant or Award spanning more than one fiscal year (2017-2018 to 2020-2021).

Many countries are studying long-term solutions for safe storage of used nuclear fuel. One such solution,x000D
selected by the Canadian Nuclear Waste Management Organization (NWMO), is the use of deep geologicalx000D
repositories (DGRs) that would be located several hundred metres below ground level. DGRs would store usedx000D
fuel canisters (UFCs) surrounded by an engineered barrier system (EBS), composed of copper coatings to act asx000D
a corrosion barrier and highly compacted bentonite (HCB) that surrounds the UFC. HCB swells upon contactx000D
with water and can therefore seal gaps within the repository and provide a moderately thermally conductivex000D
medium. It can also slow groundwater infiltration and retard the movement of radionuclides in the event of ax000D
UFC breach. In addition, the HCB can suppress microbial activity near the container by restricting space andx000D
water availability to microbes that may be present. However, diffusion of sulphide can result in microbiallyx000D
influenced corrosion (MIC), potentially causing early failure of the barrier. The proposed research willx000D
investigate the factors that can affect sulfide diffusion to the UFC surface. The project will include diffusionx000D
experiments performed under a range of potential repository conditions, based on current Canadian designx000D
specifications and predictions for DGR conditions. The results of the experimental studies will be used tox000D
further expand and validate a three-dimensional computer model. The resulting model will be capable ofx000D
parametric studies to refine and optimize the design of the Canadian DGR. The results of this study willx000D
identify key parameters that may result in higher corrosion rates, leading to a refinement of NWMO's EBSx000D
design and providing Canadians with a safe and sustainable method of used nuclear fuel disposal. This studyx000D
will address significant scientific questions regarding diffusion of corrosive species through the engineeredx000D
barrier system in sub-surface environments, and will also enhance predictive modelling capabilities tox000D
strengthen the sponsoring agency's long-term DGR design/performance criteria.