UC Chemist Uses Simulation Method to Unlock Secretes of Molten Salts

Research associate Yu Shi studies computational chemistry in University of Cincinnati’s College of Arts and Sciences. Photo courtesy of Andrew Higley/UC Marketing + Brand.

A chemist at the University of Cincinnati (UC) (Cincinnati, Ohio, USA) has come up with a novel way to study the thermodynamic properties of molten salts, which is salt heated to high temperatures until it becomes liquid. Molten salts have properties that make it a valuable medium for cooling systems in nuclear power plants, and that can be used to transfer heat or store energy in solar towers. 

UC College of Arts and Sciences research association and computational chemist Yu Shi and his collaborators developed a new simulation method to calculate free energy using deep learning artificial intelligence. The group’s study, published in the Royal Society of Chemistry journal Chemical Science, could help researchers examine the corrosion that molten salt can cause in metal containers like those found in the next generation of nuclear reactors. 

According to Shi, while salt is an insulator, molten salt conducts electricity. “Molten salts are stable at high temperatures and can hold a lot of energy in a liquid state,” he says. “They have good thermodynamic properties. That makes them a good energy storage material for concentrated solar power plants. And they can be used as a coolant in nuclear reactors.” 

The UC study provides a reliable approach to study the conversion of dissolved gas to vapor in molten salts, helping engineers understand the effect of different impurities and solutes (the substance dissolved in a solution) on corrosion. Shi says it will help researchers study the release of potentially toxic gas into the atmosphere, which will be extremely useful for fourth-generation molten salt nuclear reactors. 

“We used our quasi-chemical theory and our deep neural network, which we trained using data generated by quantum simulations, to model the solvation thermodynamics of molten salt with chemical accuracy,” Shi says. 

According to Thomas Beck, study co-author and former head of UC’s Department of Chemistry, molten salts do not expand when heated—unlike water, which can create extreme pressure at high temperatures. “The pressure inside a nuclear reactor goes up a lot,” says Beck, who now works at section head of science engagement for the Oak Ridge National Library. “That’s the difficulty of reactor design—it leads to more risks and higher costs.” 

Researchers turned to UC’s Advanced Research Computing Center and the Ohio Supercomputer Center to run the simulations. “At Oak Ridge, we have the world’s fastest supercomputer, so our experiment would take less time here,” Beck says. “But on typical supercomputers, it can take weeks or months to run these quantum simulations.” 

The research team studied sodium chloride, commonly known as table salt. “It’s important to have accurate models of these salts,” Beck says. “We were the first group to calculate free energy of sodium chloride at high temperature in liquid and compare it to previous experiments. So we proved it’s a useful technique.” 

In 2020, Shi and Beck established a free-energy scale for single-ion hydration using quasi-chemical theory and quantum mechanical simulations of the sodium ion in water in a study published in the journal PNAS. It was the first solvation free-energy calculation for the charge solute using quantum mechanics, says Shi. 

Beck added that molten salts will be important for developing new sources of energy—even perhaps, one day, fusion energy. “They’re proposing using molten salts as a coating coolant for the high-temperature reactor,” he says. “But fusion is farther down the road.” 

Source: UC News, www.uc.edu.