Part 2 of 2 Parts (Please read Part 1 first)
For their study, the researchers looked at a thirteen-year-old experiment, with an initial focus on cement-clay rock interactions. Over the last several years, a mix of both negatively and positively charged ions were added to the borehole located near the center of the cement emplaced in the formation. The researchers focused on a one-centimeter-thick zone between the radionuclides and cement-clay which is referred to as the “skin.” They compared their experimental results to the software simulation and found that the two datasets aligned.
Sarsenbayev said, “The results are quite significant because previously, these models wouldn’t fit field data very well. It’s interesting how fine-scale phenomena at the ‘skin’ between cement and clay, the physical and chemical properties of which changes over time, could be used to reconcile the experimental and simulation data.”
The new experimental results showed that the model successfully accounted for electrostatic effects associated with the clay-rich formation and the interaction between materials in Mont Terri over time.
Sarsenbayev added, “This is all driven by decades of work to understand what happens at these interfaces. It’s been hypothesized that there is mineral precipitation and porosity clogging at this interface, and our results strongly suggest that. This application requires millions of degrees of freedom because these multibarrier systems require high resolution and a lot of computational power. This software is really ideal for the Mont Terri experiment.”
This new model can now replace older models that have been used to conduct safety and performance assessments of underground geological repositories.
Sarsenbayev said, “If the U.S. eventually decides to dispose nuclear waste in a geological repository, then these models could dictate the most appropriate materials to use. Currently, clay is considered an appropriate storage material, but salt formations are another potential medium that could be used. These models allow researchers to visualize the fate of radionuclides over millennia. They can be used to understand interactions at timespans that vary from months to years to many millions of years.”
Sarsenbayev explained that the model is reasonably accessible to other researchers and that future efforts may focus on the use of machine learning to develop surrogate models that are less computationally expensive. Further data from the experiment will be available later this month. The team plans to compare those data to additional simulations.
Sarsenbayev continued, “Our collaborators will basically get this block of cement and clay, and they’ll be able to run experiments to determine the exact thickness of the skin along with all of the minerals and processes present at this interface. It’s a huge project and it takes time, but we wanted to share initial data and this software as soon as we could.”
The researchers hope that their study leads to a long-term solution for storing nuclear waste that policymakers and the public can support.
Sarsenbayev said that “This is an interdisciplinary study that includes real world experiments showing we’re able to predict radionuclides’ fate in the subsurface. The motto of MIT’s Department of Nuclear Science and Engineering is ‘Science. Systems. Society.’ I think this merges all three domains.”