What if there was a way to solve one of the most significant obstacles to the use of nuclear energy – the disposal of high-level nuclear waste (HLW)? Dauren Sarsenbayev, a third-year doctoral student in MIT’s Department of Nuclear Science and Engineering (NSE), is addressing the challenge as part of his research.
Sarsenbayev focuses on one of the primary problems related to HLW: the decay heat released by radioactive waste. The basic premise of their solution is to extract heat from spent fuel, which simultaneously takes care of two objectives: extracting more energy from the existing carbon-free resource while reducing the challenges associated with storage and handling of HLW. “The value of carbon-free energy is increasing every year, and we want to extract as much of it as possible,” Sarasenbayev explains.
While significant progress has been seen in the safe management and disposal of HLW, there may be more creative ways to manage or take advantage of the waste. Such a step would be particularly important for public acceptance of nuclear energy. “We are redefining the problem of nuclear waste, turning it from a liability to an energy source,” Sarasenbayev says.
intricacies of atom
Sarsenbayev had to make some adjustments in his approach to nuclear energy. Growing up in Almaty, Kazakhstan’s largest city, the collective trauma of Soviet nuclear testing was seared into the public consciousness. Not only is this country, once part of the Soviet Union, scarred by nuclear weapons testing, but Kazakhstan is also the world’s largest producer of uranium. It is difficult to escape the collective psyche of such a legacy.
At the same time, Sarsenbayev watched his native Almaty suffocate under heavy smog every winter due to the burning of fossil fuels for heat. Determined to do his part to accelerate the decarbonization process, Sarsenbayev turned to graduate studies in environmental engineering at the Kazakh-German University. It was during this time that Sarsenbayev realized that practically every energy source, even promising renewables, came with challenges, and decided that nuclear was the way to go for his reliable, low-carbon energy. Sarasenbayev says, “I was exposed to air pollution since childhood; the horizon would be absolutely black. The biggest incentive for me with nuclear power was that as long as we did it right, people could breathe clean air.”
Study of transport of radionuclides
Part of “doing nuclear right” involves studying – and reliably predicting – the long-term behavior of radionuclides in geological repository.
Sarsenbayev discovered an interest in studying nuclear waste management during an internship at Lawrence Berkeley National Laboratory as a junior graduate student.
While at Berkeley, Sarsenbayev focused on modeling the transport of radionuclides from the barrier system of a nuclear waste repository to the surrounding host rock. He discovered how to use the tools of the trade to predict long-term behavior. Sarasenbayev says, “As an undergraduate, I was really fascinated by how far into the future something could be predicted. It’s kind of like predicting what future generations will face.”
The timing of the Berkeley internship was serendipitous. In the same laboratory, she worked with Haruko Murakami Wainwright, who was herself starting out at MIT NSE. (Wainwright is the Mitsui Career Development Professor in Contemporary Technology and NSE and Adjunct Professor of Civil and Environmental Engineering).
Desiring to pursue graduate study in the field of nuclear waste management, Sarsenbayev followed Wainwright to MIT, where he conducted further research on modeling of radionuclide transport. He is the first author of a paper that details mechanisms to increase the robustness of models describing the transport of radionuclides. This work demonstrates the complexity of the interactions between engineered barrier components, including cement-based materials and soil barriers, a typical medium proposed for the storage and disposal of spent nuclear fuel.
Sarsenbayev is pleased with the results of the model’s predictions, which closely mirror experiments conducted at the Mont Terri research site in Switzerland, famous for studying the interaction between cement and soil. “I had the privilege of working with Dr. Carl Stiefel and Professor Christophe Tournasat, who are leading experts in computational geochemistry,” he says.
Real-life transport mechanisms involve many physical and chemical processes, the complexities of which dramatically increase the size of computational models. Reactive transport modeling – which combines the simulation of fluid flow, chemical reactions, and transport of substances through subsurface media – has evolved significantly over the past few decades. However, running accurate simulations comes with trade-offs: the software may require days to weeks of computing time on a high-performance cluster running in parallel.
To reach results faster by saving computing time, Sarsenbayev is developing a framework that integrates AI-based “surrogate models”, trained on simulated data and approximating physical systems. AI algorithms predict radionuclide behavior faster and less computationally intensive than their traditional counterpart.
Doctoral Research Focus
Sarsenbayev is also applying his modeling expertise to his primary doctoral work – evaluating the potential of spent nuclear fuel as an anthropogenic geothermal energy source. “In fact, geothermal heat is largely caused by the natural decay of radioisotopes in the Earth’s crust, so using decay heat from spent fuel is conceptually similar,” he says. Under conservative assumptions, a canister of nuclear waste could generate energy equivalent to 1,000 square meters (slightly less than a quarter of an acre) of solar panels.
Because the heat potential from a canister is significant – a typical canister (depending on how long it was cooled in the spent fuel pool) has a temperature of about 150 °C – but not very large, a process called a binary cycle system is used to extract heat from this source. In such a system, heat is extracted indirectly: the canister heats a closed water loop, which in turn transfers that heat to a secondary low-boiling-point liquid that powers the turbine.
Sarsenbayev’s work develops a conceptual model of a binary-cycle geothermal system powered by heat from high-level radioactive waste. Initial modeling results have been published and look promising. While the possibility of such energy extraction is at the proof-of-concept stage in modeling, Sarsenbayev expects it to be a success when translated into practice. “Converting a liability into an energy source is exactly what we want, and this provides the solution,” he says.
Despite the work taking up so much time – “I’m almost obsessed with my work and love it” – Sarsenbayev finds time to write reflective poetry in both Kazakh, his native language, and Russian, which he learned growing up. He is also interested in astrophotography, taking photographs of celestial objects. Finding the right sky for the night can be a challenge, but the valleys near his home in Almaty are particularly suitable. Whenever he comes home for holidays, he goes on photography sessions and his love for Almaty is reflected. “Almaty means ‘the place where the apple originated.’ This part of Central Asia is very beautiful; Although we have environmental pollution, this is a place with a rich history,” Sarasenbayev says.
Sarsenbayev is particularly passionate about finding ways to transmit both art and science to future generations. “Obviously, you have to be technically rigorous and do the modeling right, but you also have to understand and tell the broader picture of why you’re doing the work, what the end goal is,” he says. Through that lens, the impact of Sarsenbayev’s doctoral work is significant. The ultimate goal? To overcome barriers to nuclear energy adoption by producing carbon-free electricity and ensuring safe disposal of radioactive waste.
