Transport modelling in the natural analogue study of the Cigar Lake uranium deposit (Saskatchewan, Canada)

A near-field release model is developed both conceptually and mathematically to study the transport of solutes in the Cigar Lake uranium deposit in Saskatchewan, Canada. This model tests the known helium release from the deposit, focusing on the release and transport of various aqueous species, including radionuclides. The findings demonstrate that the uranium release rate predicted by the model is extremely low, aligning with observed field data. Furthermore, the model accounts for in situ generation and decay of other radionuclides like 3H, 14C, and 36Cl. The estimated concentration gradients of hydrogen were utilized to determine the net rate of radiolysis. The results indicate a significant presence of oxidising species, particularly sulfates formed by the oxidation of sulfides. Importantly, the formation rates of the reducing component hydrogen and the oxidising component as indicated by the sulfate concentrations show strong correlation, presenting a comprehensive understanding of the geochemical processes at play in the context of nuclear waste isolation. The application of such a model is crucial for ensuring the long-term safety of geological disposal of spent nuclear fuel.