The safety and efficiency of a large, complex nuclear reactor can be improved by hardware as simple as a tiny sensor that monitors a cooling system. Researchers at the Department of Energy's Oak Ridge National Laboratory (ORNL) are working to make those basic sensors more accurate by combining them with electronics that can withstand the intense radiation inside a reactor.
The ORNL research team recently met with high success using a gallium nitride semiconductor for sensor electronics. A transistor made with this material continued with operations near the core of a nuclear reactor operated by research partner The Ohio State University.
Gallium nitride is a wide-bandgap semiconductor. It had previously been tested against the ionizing radiation encountered when rockets travel through space. Devices that employ wide-bandgap semiconductors can operate at much higher frequencies, temperatures and irradiation rates. However, gallium nitride had not faced the even more intense radiation of neutron bombardment.
Kyle Reed is a member of the Sensors and Electronics group at ORNL. He is the lead researcher for the transistor research. He said, “We are showing it is great for this neutron environment.”
This discovery could offer a big boost for equipment monitoring in nuclear facilities. The information collected by sensors provides early warnings about wear and tear on equipment. This allows timely maintenance to avoid broader equipment failures that cause reactor downtime. Currently, this sensing data is processed from a distance. It must travel through yards of cable connected to electronics with silicon-based transistors.
Reed said, “Our work makes measuring the conditions inside an operating nuclear reactor more robust and accurate. When you have lengthy cables, you end up with a lot of noise, which can interfere with the accuracy of the sensor information. By placing electronics closer to a sensor, you increase its accuracy and precision.” In order to meet that goal, scientists need to develop electronics that can better tolerate radiation.
Researchers irradiated gallium nitride transistors for three days at temperatures up to one hundred and twenty-five degrees Celsius close to the core of The Ohio State University Research Reactor.
Reed added, “We fully expected to kill the transistors on the third day, and they survived. The team pushed the transistors all the way to the reactor's safety threshold which was seven hours at ninety percent power.”
The gallium nitride transistors were able to withstand at least one hundred times higher accumulated dose of radiation than a standard silicon device, said researcher Dianne Ezell, leader of ORNL's Nuclear and Extreme Environment Measurements group and a member of the transistor research team.
She said that the transistor material must be able to survive at least five years, the normal maintenance window, in the pool of a nuclear reactor. The research team exposed the gallium nitride device to days of much higher radiation levels within the core itself. They concluded that the transistors would exceed that requirement.
This is a critical technical advance as researchers turn from the large-scale existing fleet of nuclear energy plants to microreactors that could generate from tens to hundreds of megawatts of power. These novel reactor designs are still in the development and licensing stage. Their potential portability could allow them to be deployed on the back of a truck to a military or disaster zone.