Novel transistor material shows nuclear potential

Sensors are used to gather information from a reactor and can identify potential equipment failures before they happen, helping prevent costly unscheduled shutdowns. But the complex circuitry the sensors are connected to must be placed away from the reactor core to protect the electronics from heat and radiation. The long cables used to transmit data from the sensors via can pick up additional noise and degrade the signal.

Gallium nitride is a so-called wide-bandgap semiconductor that is more resistant to heat and radiation than silicon, and is commercially available, although not currently widely used. Researchers from the US Department of Energy lab tested its properties by placing gallium nitride transistors close to a research reactor core at The Ohio State University where they successfully withstood high heat and radiation for three consecutive days. The transistors were able to handle a 100 times higher accumulated dose of radiation than standard silicon devices at a sustained temperature of 125°C, performing beyond expectations.

Kyle Reed and Dianne Ezell gather data as the sensor transistor is tested in the reactor pool, which can be seen behind them (Image: Michael Huson/The Ohio State University)

"We fully expected to kill the transistors on the third day, and they survived," said lead researcher Kyle Reed, a member of the Sensors and Electronics group at ORNL, adding that the work makes measuring the conditions inside an operating nuclear reactor "more robust and accurate".

By exposing the transistors to days of high radiation levels in the reactor core itself, the researchers were able to conclude that gallium nitride transistors are capable of surviving at least five years in a reactor, the normal maintenance window for such components.

The research may also be important for advanced microreactors, which due to their compact size will need sensors capable of withstanding more adverse radiation conditions than currently operating reactors. However, the testing at Ohio State University showed that heat was more harmful to gallium nitride than radiation. The researchers are now working to further understand the heat effects.

Better nuclear monitoring means increased safety and reduced operating costs, and reducing the frequency of maintenance outages reduces human safety risks, Dianne Ezell, leader of ORNL’s Nuclear and Extreme Environment Measurements group, said. "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," she said. "You're able to avoid putting people in harsh radiation environments or handling radioactive material as often," she added.