MIT model advances nuclear waste disposal, could be used to validate long-term safety
- Prabhat R Mishra
- Jul 22
- 4 min read
Updated: Jul 22
As nations around the globe ramp up their nuclear energy initiatives, the pressing issue of nuclear waste disposal continues to spark intense political debate. In the United States, the only long-term underground repository for nuclear waste remains indefinitely on hold, raising concerns about the future of waste management.
In response, scientists are employing both modeling and experimental techniques to explore the implications of underground nuclear waste disposal, aiming to foster public trust in the decision-making process.
A recent study conducted by researchers from MIT, Lawrence Berkeley National Lab, and the University of Orléans marks a significant step forward in this endeavor.
Simulations of underground nuclear waste interactions
The research, published in the journal Proceedings of the National Academy of Sciences (PNAS), demonstrates that simulations of underground nuclear waste interactions, created using advanced high-performance computing software, closely match experimental findings from a research facility in Switzerland.
Dauren Sarsenbayev, a PhD student at MIT and the study's lead author, emphasized the importance of these new computational tools. "By combining powerful simulations with real-world experiments, such as those conducted at the Mont Terri research site in Switzerland, we can better understand how radionuclides migrate in complex underground systems," he stated.
The authors of the study hope that their findings will bolster confidence among policymakers and the public regarding the long-term safety of underground nuclear waste disposal.
Assistant Professor Haruko Wainwright, a co-author, noted, "This research is crucial for enhancing our understanding of waste disposal safety assessments. As nuclear energy re-emerges as a vital solution for addressing climate change and ensuring energy security, validating disposal pathways becomes essential."
Understanding Radionuclide Migration
Deep geological formations are currently viewed as the safest long-term solution for managing high-level radioactive waste. Consequently, extensive research has focused on the migration behaviors of radionuclides within various natural and engineered geological materials. The Mont Terri research site in northern Switzerland, established in 1996, has become a key testing ground for an international consortium of researchers studying materials like Opalinus clay, a dense, water-tight claystone found in the region.
Sarsenbayev explained, "Mont Terri is highly regarded for its extensive datasets on the interactions between cement and clay, which are critical materials proposed for engineered barrier systems and geological repositories for nuclear waste."
High-performance computing
In their study, Sarsenbayev and Wainwright collaborated with co-authors Christophe Tournassat and Carl Steefel, who developed high-performance computing software to enhance the modeling of interactions between nuclear waste and both engineered and natural materials. Previous challenges in understanding how nuclear waste interacts with cement-clay barriers stemmed from the irregular composition of these materials deep underground and the limitations of existing models, which often overlooked electrostatic effects associated with negatively charged clay minerals.
The new software, named CrunchODiTi, accounts for these electrostatic effects and is unique in its ability to simulate interactions in three-dimensional space. It was developed from the established software CrunchFlow and has recently been updated to run on multiple high-performance computers simultaneously.
The researchers revisited a 13-year-old experiment focused on cement-clay rock interactions, incorporating a mix of charged ions into the borehole at the center of the cement formation. They concentrated on a 1-centimeter-thick zone, referred to as the "skin," between the radionuclides and the cement-clay. The results showed a strong alignment between experimental data and software simulations.
"The significance of these results lies in the fact that previous models struggled to accurately fit field data," Sarsenbayev remarked. "Our findings suggest that fine-scale phenomena at the interface between cement and clay, which evolve over time, can reconcile experimental and simulation data."
MIT model could replace older models
The MIT model has the potential to replace older models used for safety and performance assessments of underground geological repositories. Sarsenbayev noted, "If the U.S. decides to pursue geological disposal for nuclear waste, these models could guide the selection of appropriate materials. While clay is currently favored, salt formations are another viable option. Our models allow us to track the fate of radionuclides over millennia."
The researchers aim to make the model accessible to other scientists, with future efforts potentially incorporating machine learning to create less computationally intensive surrogate models. Additional data from the experiment is expected to be released later this month, allowing for further comparisons with simulations.
"Our collaborators will receive a block of cement and clay to conduct experiments that will help determine the exact thickness of the skin and the minerals present at this interface," Sarsenbayev explained. "It's a significant project that requires time, but we wanted to share our initial findings and software as soon as possible."
Ultimately, the researchers hope their work will contribute to a sustainable solution for nuclear waste storage that garners support from both policymakers and the public. "This interdisciplinary study combines real-world experiments with predictive modeling of radionuclide behavior in subsurface environments," Sarsenbayev concluded.
"At MIT's Department of Nuclear Science and Engineering, our motto is 'Science. Systems. Society.' This research embodies the intersection of all three domains."
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