With countries around the world reviving with nuclear energy projects, the question of where and how to dispose of nuclear waste remains as politically challenging as ever. For example, the United States stalled its only long-term underground nuclear waste storage indefinitely. Scientists use both modeling and experimental methods to study the impact of underground nuclear waste treatment, and ultimately hope that they will build public trust in the decision-making process.
New research from scientists at MIT, Lawrence Berkeley National Laboratory, and Orleans University is progressing in that direction. This study presents simulations of underground nuclear waste interactions produced by new high-performance computing software, which are well matched with experimental results from Swiss research facilities.
The study was co-authored by MIT PhD students Dauren Sarsenbayev and Assistant Professor Haruko Wainwright, and published in the journal Christophe Tournassat and Carl Steelfel pnas.
“These powerful new computational tools, coupled with real-world experiments like the Swiss Monteri research site, will help us understand how radio nuclei move in a combined underground system of underground systems,” says Sarsenbeief, the first author of the new study.
The authors hope that this study will improve trust between policymakers and the public in the long-term safety of underground nuclear waste treatment.
“Combining both this study – calculations and experiments is important to improve confidence in the safety assessment of waste disposal,” says Wainwright. “It is important to examine disposal routes as nuclear energy is re-emerging as an important source of addressing climate change and ensuring energy safety.”
Compare simulations and experiments
Disposal of nuclear waste in deep underground layers is currently considered the safest and long-term solution for managing high levels of radioactive waste. Therefore, much effort is being made to study the migration behavior of radionuclides from nuclear waste within a variety of natural and engineered geological materials.
Since its establishment in 1996, the Montery Research Site in northern Switzerland has served as an important testbed for an international consortium of researchers interested in studying materials such as Oparine Scree, which are abundant in mountain tunnel areas.
“It is widely regarded as one of the most valuable real-world experimental sites as it provides a decades-old dataset on cement-clay interactions. These are important materials proposed to be used by countries around the world for barrier systems and geological repositories designed for nuclear waste.
For their research, Sarsenbayev and Wainwright collaborated with co-authors Tournassat and Steefel. Tournassat and Steefel have developed high-performance computing software to improve the modeling of nuclear waste and interactions with both engineering and natural materials.
To date, some challenges have limited scientists’ understanding of how nuclear waste reacts with cement clay barriers. For one thing, the barrier is made up of deep, irregular mixed materials underground. Furthermore, existing classes of models commonly used to simulate radionuclide interactions with cement clays do not consider the electrostatic effects associated with negatively charged clay minerals of barriers.
Tournassat and Steefel’s new software describes electrostatic effects, making it the only one that can simulate these interactions in three-dimensional space. The software called Crunchoditi was developed from established software known as Crunchflow and was recently updated this year. It is designed to run in parallel at once on many high-performance computers.
In this study, researchers saw an experiment at a 13-year-old that first focused on the interaction of cement claylocks. Within the past few years, a mix of both negative and positive charged ions has been added to a borehole near the center of cement defined in the formation. The researchers focused on a 1-centimeter-thick zone between radionuclides called “skin” and cement clay. The experimental results were compared with software simulations and found that the two datasets were aligned.
“Previously, these models didn’t fit well with field data, so the results are very important,” says Sarsenbayev. “It is interesting that the phenomenon of scale in the ‘skin’ between cement and clay can be adjusted to experimental and simulation data using physical and chemical properties that change over time. ”
Experimental results showed that the model successfully explains the electrostatic effects associated with clay-rich formation and the interactions between Monteri materials over time.
“This is all driven by decades of work to understand what happens at these interfaces,” Sarsemblyev says. “It is assumed that this interface is packed with mineral precipitation and porosity, and the results strongly suggest that.”
“These multivarieties systems require high resolution and a lot of computing power, so this application requires millions of freedom,” says Sarsenbayev. “This software is really ideal for Monterry experiments.”
Evaluation of waste disposal plans
This new model can replace the older model used to perform safety and performance assessments of underground geological repository.
“If the US ultimately decides to dispose of nuclear waste in a geological repository, these models could determine which materials are most appropriate to use,” says Sarsenbayev. “Now, clay is considered a suitable storage material, but salt formation is another potential medium that can be used. These models can see the fate of radionuclides over thousands of years.
According to Sarsenbayev, the model is reasonably accessible to other researchers, and future efforts could focus on using machine learning and developing computationally expensive proxy models.
Further data from the experiment will be available later this month. The team will compare these data with additional simulations.
“Our collaborators can basically get this block of cement and clay and run the experiment to determine the exact thickness of the skin along with all the minerals and processes present in this interface.” Sarsenbayev says. “It’s a huge project and it takes time, but I wanted to share this software with this one as soon as possible.”
For now, researchers hope that their research will lead to long-term solutions to store nuclear waste that policymakers and the public can support.
“This is an interdisciplinary study that involves real-world experiments that show that the fate of radionuclides can be predicted underground,” says Sarsembly. “The motto of MIT’s Faculty of Nuclear Science and Engineering is “Science. Systems. Society.” I think this combines all three domains. ”
