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As countries across the world experience a resurgence in nuclear energy projects, the questions of where and how to dispose of nuclear waste still looms large. The U.S. has indefinitely stalled its only long-term underground nuclear waste repository project. Scientists are using both modeling and experimental methods to study the effects of underground nuclear waste disposal and they hope to build public trust in the decision-making process.
New research from scientists at MIT, Lawrence Berkeley National Lab, and the University of Orléans are making progress in that direction. Their study indicates that simulations of underground nuclear waste interactions, generated by new, high-performance-computing software, aligned well with experimental results from a research facility in Switzerland.
The study was co-authored by MIT Ph.D. student Dauren Sarsenbayev and Assistant Professor Haruko Wainwright, along with Christophe Tournassat and Carl Steefel. It has been published in the Proceedings of the National Academy of Sciences.
Sarsenbayev said, “These powerful new computational tools, coupled with real-world experiments like those at the Mont Terri research site in Switzerland, help us understand how radionuclides will migrate in coupled underground systems.”
The authors hope their research will improve confidence among policymakers and other stakeholders in the long-term safety of underground nuclear waste disposal.
Wainwright said, “This research—coupling both computation and experiments—is important to improve our confidence in waste disposal safety assessments. With nuclear energy re-emerging as a key source for tackling climate change and ensuring energy security, it is critical to validate disposal pathways.”
Disposing of nuclear waste in deep underground geological formations is currently considered the safest long-term solution for managing high-level radioactive waste such as spent nuclear fuel. Much effort has been put into studying the migration behaviors of radionuclides from nuclear waste within various natural and engineered geological materials.
Since its founding in 1996, the Mont Terri research site in northern Switzerland has served as an important test bed for an international consortium of researchers interested in studying materials like Opalinus clay. This clay is a thick, water-tight claystone abundant in the tunneled areas of the mountain.
Sarsenbayev explained, “It is widely regarded as one of the most valuable real-world experiment sites because it provides us with decades of datasets around the interactions of cement and clay, and those are the key materials proposed to be used by countries across the world for engineered barrier systems and geological repositories for nuclear waste.”
For their research paper, Sarsenbayev and Wainwright collaborated with co-authors Tournassat and Steefel, who have developed high-performance computing software to improve modeling of interactions between nuclear waste and both engineered and natural materials.
Several challenges have limited scientists’ understanding of how nuclear waste reacts with cement-clay barriers. The barriers are made up of irregularly mixed materials deep underground. The existing class of models commonly used to simulate radionuclide interactions with cement-clay do not consider electrostatic effects associated with the negatively charged clay minerals in the barriers.
Tournassat and Steefel’s software takes into account electrostatic effects, making it the only software that can simulate those interactions in three-dimensional space. The software is called CrunchODiTi. It was developed from established software known as CrunchFlow and was most recently updated this year. CrunchODiTi is designed to be run on many high-performance computers at once in parallel.
Lawrence Berkeley National Lab
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