Nuclear energy is a key component of a clean, green future, producing more than half of America's zero-emissions electricity.
But with the U.S. generating about 2,000 metric tons of spent fuel waste each year and that waste stored at more than 70 sites in 34 states, research is needed to ensure safe transportation, storage and disposal.
Nebraska Engineering researchers Jinying Zhu and Fadi Alsaleem have received a three-year, $800,000 award from the U.S. Department of Energy (DOE) to develop a dual-sensing, health-monitoring system for a spent nuclear fuel canister.
Both researchers are relying on past research projects to inform their approaches to this work. Zhu led a previous DOE project that developed monitoring system to detect cracks in concrete structures, and Alsaleem has vast experience with micro-electromechanical systems (MEMS), which involve fabrication of tiny sensors on the microscale and nanoscale.
Zhu, associate professor of civil and environmental engineering, said this DOE project will collect data in a similar way to processes used in smart homes.
"Those smart home systems have sensors to monitor temperature and humidity, analyze the collected information, and then determine if the house is in normal operating condition," Zhu said. "If problems are detected, such as a fire, it sets off the smoke alarm."
Most dry storage cask systems in the United States are welded (or bolted) metal canisters inside vented concrete (or steel) overpacks. The meter-thick concrete overpack provides radiation shielding to workers and the public. The steel canister is filled with inert gas (helium or nitrogen), and helium is typically used for its high thermal conductivity. Monitoring the condition of the casks, including internal pressure, temperature, and leak detection are the most critical and challenging tasks. Conventional pressure and temperature sensing methods cannot be used due to radiation hazard and leak tightness restrictions.
This new external dual-sensing system will monitor the canister's wall temperature and internal pressure using ultrasonic waves and sensors specifically designed for this purpose. It would then send alerts – or even "alarms" – when it detects significant changes in temperature or pressure or detects a possible leakage of helium gas. The external sensing system allows replacement or maintenance of these sensors for long-term monitoring.
Zhu is leading the ultrasonic research. She will use the sensitivity of ultrasonic waves to temperature and stress changes to continuously monitor the wall temperature and the internal pressure of the canister. Zhu and her graduate students have built the theoretical framework for thermally induced nonlinearity of ultrasonic waves with the support of previous DOE project.
"This new DOE award provides a great opportunity to implement and validate the innovative nonlinear ultrasonic sensing approach," Zhu said.
Alsaleem, assistant professor in the Durham School of Architectural Engineering and Construction, is proposing a miniature sensor using the micro-electromechanical systems (MEMS) technology to detect helium leakage. This work includes a partner at the University of Dallas to fabricate the tiny sensors.
It's a step in a new direction from current protocols for monitoring spent-fuel disposal sites.
"Our sensors will look at the changes in the property of the air outside the cask. At certain levels, that's when it sends out notifications or sounds the alarm."
That alert system is a key component of the DOE's request, but both Zhu and Alsaleem said it is critical to ensure the alarms are sounded only when there is a problem.
"Everybody talks about clean energy, zero-carbon, but we have to educate the public about nuclear energy because it's going to be a big part of the earth's future," Alsaleem said. "Storage of nuclear waste or spent fuel is a key component, and we'll be training the next generation of researchers who will be at the forefront of solving these issues."
Ph.D. students Clayton Malone, Bibo Zhong, and Sulaiman Mohaidat are working on this research project. Malone also worked on Zhu's previous DOE project while pursuing a master's degree from the UNL College of Engineering. Zhong recently accepted a position as a postdoctoral researcher at DOE's Idaho National Laboratory.
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