As countries the world over experience a resurgence in nuclear energy projects, the questions of where and how one can get rid of nuclear waste remain as politically fraught as ever. The US, as an example, has indefinitely stalled its only long-term underground nuclear waste repository. Scientists are using each modeling and experimental methods to review the consequences of underground nuclear waste disposal and ultimately, they hope, construct public trust within the decision-making process.
Latest research from scientists at MIT, Lawrence Berkeley National Lab, and the University of Orléans makes progress in that direction. The study shows that simulations of underground nuclear waste interactions, generated by recent, high-performance-computing software, aligned well with experimental results from a research facility in Switzerland.
The study, which was co-authored by MIT PhD student Dauren Sarsenbayev and Assistant Professor Haruko Wainwright, together with Christophe Tournassat and Carl Steefel, appears within the journal .
“These powerful recent computational tools, coupled with real-world experiments like those on the Mont Terri research site in Switzerland, help us understand how radionuclides will migrate in coupled underground systems,” says Sarsenbayev, who’s first creator of the brand new study.
The authors hope the research will improve confidence amongst policymakers and the general public within the long-term safety of underground nuclear waste disposal.
“This research — coupling each computation and experiments — is very important to enhance our confidence in waste disposal safety assessments,” says Wainwright. “With nuclear energy re-emerging as a key source for tackling climate change and ensuring energy security, it’s critical to validate disposal pathways.”
Comparing simulations with experiments
Disposing of nuclear waste in deep underground geological formations is currently considered the safest long-term solution for managing high-level radioactive waste. As such, much effort has been put into studying the migration behaviors of radionuclides from nuclear waste inside various natural and engineered geological materials.
Since its founding in 1996, the Mont Terri research site in northern Switzerland has served as a very important test bed for a world consortium of researchers serious about studying materials like Opalinus clay — a thick, water-tight claystone abundant within the tunneled areas of the mountain.
“It’s widely considered some of the helpful real-world experiment sites since it provides us with a long time of datasets across the interactions of cement and clay, and people are the important thing materials proposed to be utilized by countries the world over for engineered barrier systems and geological repositories for nuclear waste,” explains Sarsenbayev.
For his or her study, Sarsenbayev and Wainwright collaborated with co-authors Tournassat and Steefel, who’ve developed high-performance computing software to enhance modeling of interactions between the nuclear waste and each engineered and natural materials.
Up to now, several challenges have limited scientists’ understanding of how nuclear waste reacts with cement-clay barriers. For one thing, the barriers are made up of irregularly mixed materials deep underground. Moreover, the present class of models commonly used to simulate radionuclide interactions with cement-clay don’t consider electrostatic effects related to the negatively charged clay minerals within the barriers.
Tournassat and Steefel’s recent software accounts for electrostatic effects, making it the one one which can simulate those interactions in three-dimensional space. The software, called CrunchODiTi, was developed from established software generally known as CrunchFlow and was most recently updated this 12 months. It’s designed to be run on many high-performance computers directly in parallel.
For the study, the researchers checked out a 13-year-old experiment, with an initial deal with cement-clay rock interactions. Inside the last several years, a combination of each negatively and positively charged ions were added to the borehole situated near the middle of the cement emplaced within the formation. The researchers focused on a 1-centimeter-thick zone between the radionuclides and cement-clay known as the “skin.” They compared their experimental results to the software simulation, finding the 2 datasets aligned.
“The outcomes are quite significant because previously, these models wouldn’t fit field data thoroughly,” Sarsenbayev says. “It’s interesting how fine-scale phenomena on the ‘skin’ between cement and clay, the physical and chemical properties of which changes over time, could possibly be used to reconcile the experimental and simulation data.”
The experimental results showed the model successfully accounted for electrostatic effects related to the clay-rich formation and the interaction between materials in Mont Terri over time.
“That is all driven by a long time of labor to grasp what happens at these interfaces,” Sarsenbayev says. “It’s been hypothesized that there’s mineral precipitation and porosity clogging at this interface, and our results strongly suggest that.”
“This application requires tens of millions of degrees of freedom because these multibarrier systems require high resolution and a number of computational power,” Sarsenbayev says. “This software is de facto ideal for the Mont Terri experiment.”
Assessing waste disposal plans
The brand new model could now replace older models which have been used to conduct safety and performance assessments of underground geological repositories.
“If the U.S. eventually decides to dispose nuclear waste in a geological repository, then these models could dictate probably the most appropriate materials to make use of,” Sarsenbayev says. “As an illustration, right away clay is taken into account an appropriate storage material, but salt formations are one other potential medium that could possibly be used. These models allow us to see the fate of radionuclides over millennia. We are able to use them to grasp interactions at timespans that adjust from months to years to many tens of millions of years.”
Sarsenbayev says the model within reason accessible to other researchers and that future efforts may deal with the usage of machine learning to develop less computationally expensive surrogate models.
Further data from the experiment can be available later this month. The team plans to check those data to additional simulations.
“Our collaborators will mainly get this block of cement and clay, they usually’ll have the ability to run experiments to find out the precise thickness of the skin together with the entire minerals and processes present at this interface,” Sarsenbayev says. “It’s an enormous project and it takes time, but we desired to share initial data and this software as soon as we could.”
For now, the researchers hope their study results in a long-term solution for storing nuclear waste that policymakers and the general public can support.
“That is an interdisciplinary study that features real world experiments showing we’re in a position to predict radionuclides’ fate within the subsurface,” Sarsenbayev says. “The motto of MIT’s Department of Nuclear Science and Engineering is ‘Science. Systems. Society.’ I feel this merges all three domains.”
