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NuSTEM researchers
June 11, 2018

UW-Madison research central to next-gen nuclear innovation

Written By: Will Cushman

Researchers in the University of Wisconsin-Madison Department of Nuclear Engineering and Engineering Physics are at the forefront of a nationwide push toward next-generation nuclear power reactors.

Molten salt nuclear reactors are under development by startup companies across the world as a promising next-generation technology—and researchers at UW-Madison support this development by advancing molten salt science and technology.

“To be viable, these future reactors must be more economical and potentially more efficient than current nuclear power technologies that have changed little in decades, while fulfilling the safety requirements of the U.S. Nuclear Regulatory Commission,” says Engineering Physics Assistant Professor Adrien Couet, who researches environmental degradation of nuclear materials. “There needs to be innovation. We need to change how we build nuclear power plants and we need better technologies to compete with other power sources.”

To that end, in April 2018, UW-Madison nuclear engineering and engineering physics Assistant Professor Raluca Scarlat, Couet, and Distinguished Research Professor Kumar Sridharan hosted a team of collaborating researchers from University of Texas A&M, University of California Berkeley and U.S. Department of Energy laboratories across the nation. The meeting served as a multi-institution team-meeting six months into a $3 million, three-year DOE funded research project called Nuclear Science Technology and Education for Molten Salt Reactors, or NuSTEM. It was also an opportunity for Wisconsin researchers to exhibit their highly ranked nuclear engineering research program to visiting colleagues.

“Courses and research opportunities on our campus train students in the necessary skills to enter a future workforce for the emerging molten salt reactor (MSRs) industry,” says Scarlat.

And NuSTEM comes at a time when renewed interest in nuclear energy is spurring federal investment in basic research to fast-track promising new technologies, MSRs being among them.

MSRs use molten salt as a coolant—rather than water as in current nuclear power plants—and as a solvent for uranium fuel. Researchers are enthusiastic about MSRs because they could provide a more economically competitive way to produce electricity. The immense energy produced by small amounts of fuel in a nuclear reactor is what makes nuclear energy such an attractive power source. For example, the state of Wisconsin energy consumption in 2015, short of one million barrels of oil equivalent per day, would be met by less than one barrel of uranium fuel per day. The difference in the volume of the fuel and the volume of the waste products between fossil fuel and nuclear energy is enormous. Taking advantage of the compactness of nuclear power would be of great benefit to society and to the environment. To harness the heat generated by nuclear fission, engineers have to-date largely depended on water, an abundant but imperfect resource for the task, Couet says. That’s because water must be highly pressurized to be contained at the temperatures of nuclear reactors (300 degrees Celsius, which just above the maximum temperature in your cooking oven at home), otherwise it will not have sufficient power to turn the turbines and electrical generators that produce electricity (imagine a pressure cooker). The pressurization necessitates the use of very thick-walled components which are difficult and expensive to manufacture.

“Dealing with pressurized water can be complex and results in many safety systems, which inherently increase nuclear power plant cost,” Couet says.

Meanwhile, molten salt can remain a dense liquid at high temperatures (700 degrees Celsius and above) at ambient pressure (imagine an open pot with liquid salt in it). As a result, MSRs could potentially be smaller, less complex and more economical than their water-cooled counterparts. Molten salts could also facilitate power generation mechanisms that aren’t possible with water-based reactors, such as air turbines, which could concomitantly use natural gas combustion and nuclear heat, according to Scarlat. Such hybrid power plants would be nimbler and capable of increasing power generation to better meet peak demand. The nation’s current crop of nuclear power plants is not designed to temporarily change output to meet increased demand. All of these properties have made molten salt a material of interest for nuclear engineers since the 1950s, though active research on MSRs has been stagnant for decades. But the NuSTEM collaboration is reinvigorating that research.

“This is really exciting for UW-Madison because we have a long history of working in molten salt,” says Scarlat. “And I think it’s also exciting for the molten salt community to have an integrated research project funded by DOE because it is recognition that MSR technology has evolved and there is a case to be made for MSRs.” NuSTEM is an excellent platform for UW-Madison to continue to exercise and advance its leadership in the area of molten salts, says Kumar Sridharan who was the PI for the first molten salt research program at UW in 2005, and has directed many programs in this area since then.

Together with colleagues at Texas A&M and UC-Berkeley, faculty and graduate students here in Madison are already making progress in their research of next-generation nuclear technologies. Couet, Sridharan and Scarlat are investigating how structural materials corrode in nuclear reactors and Scarlat is developing sensors and probes for measuring the chemical composition of molten salts. The NuSTEM project is also striving to establish active educational collaborations with SAMOFAR, a consortium of molten salt educational and research institutions in Europe, to provide a platform for exchange of young students and scientists.

The NuSTEM team’s progress impressed an advisory board of national lab and private industry representatives at the recent meeting in Madison.

“They’re doing great work,” says NuSTEM advisory board chairperson Warren Miller, who is retired from the Los Alamos National Laboratory and was Assistant Secretary of Energy for Nuclear Energy under President Obama and remains active in the nuclear energy sector through private industry and academia. “What these universities are doing—pushing the frontier to develop real-life tools to help in the design of molten salt reactors—is very important, and they’re making real progress even after six months in a three-year effort. This is a very exciting project.”