Hardy Transistor Material Could Be Game-Changer for Nuclear Reactor Safety Monitoring
The gallium nitride transistors were able to handle at least 100 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 the transistor material needs to be capable of surviving at least five years, the normal maintenance window, in the pool of a nuclear reactor. After 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 an important technical advance as attention turns from the large-scale existing fleet of nuclear energy plants to microreactors that could generate from tens to hundreds of megawatts of power. Although 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.
Advanced reactors are being designed to operate at higher temperatures using different forms of fuel. Because microreactors will be so compact, all the operating components, including the sensors, will have to be able to function in the radiation field, Ezell said. Gallium nitride transistors could be the key.
Ohio State researchers built devices of different designs and sizes to meet specifications set by ORNL, and then the team compared their responses to radiation, finding that larger devices seemed less susceptible to radiation damage. Ohio State is now developing computer models to project how various circuit designs will perform under different temperatures and radiation levels.
Reed said the radiation testing at Ohio State showed that heat seemed to be more harmful to the gallium nitride than radiation. So, the research team wants to measure how gallium nitride reacts to heat alone. “Since the ultimate goal is to design circuits with these materials, once we understand the temperature and radiation effects, we can compensate for them in the circuit design,” Reed said.
Better nuclear monitoring means increased safety and reduced operating costs, Ezell noted. “Hundreds of thousands of dollars are lost every day a reactor is shut down,” she said. “If we’re going to make nuclear economically competitive with other energy industries, we’ve got to keep our costs low.” Plus, reducing the frequency of maintenance reduces human safety risks. “You’re able to avoid putting people in harsh radiation environments or handling radioactive material as often,” Ezell added.
Although gallium nitride has been commercially available for around a decade, it’s not widely used, Reed said. “We’re opening up different side avenues for using gallium nitride, so we can start to create a more reasonable market demand for investment, research and workforce development for subclasses of electronics beyond consumer-grade,” Reed said.
In the long run, researchers would like to demonstrate that gallium nitride circuits could be used to transmit data from sensors wirelessly. The material is already used for devices that support radio frequency applications, like cell phones, and for power electronics.
