While countries around the world are experiencing a resurgence of nuclear energy projects, questions from the place and how to eliminate nuclear waste is as political as ever. The United States, for example, has indefinitely blocked its only long-term underground nuclear repository. Scientists use both modeling and experimental methods to study the effects of the elimination of underground nuclear waste and, ultimately, they hope, strengthen public confidence in the decision -making process.
New research by MIT scientists, Lawrence Berkeley National Lab and the University of Orleans are making progress in this direction. The study shows that the simulations of underground nuclear waste interaction, generated by new high performance software, align with the experimental results of a research installation in Switzerland.
The study, which was co-written by student Phd du MIT, Dauren Sarsenbayev, and assistant professor Haruko Wainwright, as well as Christophe Tournassat and Carl Steefel, appears in the newspaper PNA.
“These new powerful calculation tools, associated with experiences of the real world such as those of the Mont Terra research site in Switzerland, help us to understand how radionuclides will migrate to coupled underground systems,” explains Sarsenbayev, who is the first author of the new study.
The authors hope that research will improve the confidence of political decision -makers and the public in long -term security of the elimination of underground nuclear waste.
“This research – coupling both for calculation and experiences – is important to improve our confidence in waste safety assessments,” explains Wainwright. “With nuclear energy re -emerging as a key source to combat climate change and ensure energy security, it is essential to validate the elimination routes.”
Comparison of simulations with experiences
The elimination of nuclear waste in deep underground geological formations is currently considered the safest long -term solution to manage high -level radioactive waste. As such, many efforts have been devoted to the study of the migration behavior of radionuclides from nuclear waste within various natural and modified geological materials.
Since its foundation in 1996, the Mount Terrier research site in the north of Switzerland has served as an important test bed for an international consortium of researchers interested in studying materials such as Opalinus clay – thick and abundant water clay in the mountain tunneled areas.
“It is largely considered to be one of the most precious real world experimentation sites because it provides us with decades of datasets around cement and clay interactions, and these are the main materials offered to be used by countries around the world for designed barrier systems and geological standards for nuclear waste,” explains Sarsenbayev.
For their study, Sarsenbayev and Wainwright collaborated with the Tournassat and Steefel co-authors, who have developed high performance computer software to improve the modeling of interactions between nuclear waste and engineering and natural materials.
To date, several challenges have a limited understanding of scientists of the way nuclear waste reacts with cement barriers. On the one hand, the barriers are made up of materials irregularly mixed deep underground. In addition, the existing class of models commonly used to simulate the interactions of radionuclides with cement-argoue does not take into account the electrostatic effects associated with clay minerals charged negatively in barriers.
The new Tournassat and Steefel software explains the electrostatic effects, which makes it the only one who can simulate these interactions in a three -dimensional space. The software, called Crunchoditi, has been developed from established software known as Crunchflow and has recently been updated this year. It is designed to be executed on many high performance computers both in parallel.
For the study, the researchers examined a 13 -year experience, with a first emphasis on the interactions of the cement rock. In recent years, a mixture of ions loaded negatively and positively has been added to the drilling located near the center of the cement set up in the formation. The researchers concentrated on an area of thickness to 1 centimeter between the radionuclides and the cement-acre called the “skin”. They compared their experimental results to the software simulation, finding the two sets of aligned data.
“The results are quite important because before, these models would not adapt very well to the data in the field,” explains Sarsenbayev. “It is interesting to see to what extent the final scale phenomena with” skin “between cement and clay, whose physical and chemical properties change over time, could be used to reconcile experimental and simulation data.”
The experimental results have shown that the model successfully represented the electrostatic effects associated with the formation rich in clay and the interaction between the materials of Mount Terra over time.
“All this is motivated by decades of work to understand what is happening in these interfaces,” explains Sarsenbayev. “It has been hypothesized that there is mineral precipitation and clogging of the porosity at this interface, and our results strongly suggest this.”
“This application requires millions of degrees of freedom because these multibarrier systems require high resolution and a lot of computing power,” explains Sarsenbayev. “This software is really ideal for the experience of Mont Terra.”
Evaluation of waste elimination plans
The new model could now replace the older models that have been used to carry out safety and performance assessments of underground geological standards.
“If the United States finally decides to have nuclear waste in a geological benchmark, these models could dictate the most suitable materials to use,” says Sarsenbayev. “For example, at the moment, clay is considered an appropriate storage material, but salt formations are another potential support that could be used. These models allow us to see the fate of radionuclides during the millennia. We can use them to understand the interactions in terms of time that vary from months to years to several million years. ”
Sarsenbayev claims that the model is reasonably accessible to other researchers and that future efforts can focus on the use of automatic learning to develop less expensive substitution models.
Other experiences will be available later this month. The team plans to compare this data to additional simulations.
“Our employees will essentially obtain this block of cement and clay, and they will be able to carry out experiments to determine the exact thickness of the skin as well as all the minerals and processes present at this interface”, “ Said Sarsenbayev. “It's a huge project and it takes time, but we wanted to share the initial data and this software as soon as possible.”
For the moment, researchers hope that their study will lead to a long -term solution to store nuclear waste that political decision -makers and the public can support.
“This is an interdisciplinary study which includes real world experiences showing that we are able to predict the fate of radionuclides in the basement,” explains Sarsenbayev. “The motto of the MIT science and engineering department is” Science. Systems. Company “. I think that merges the three areas. »»
