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Novel nuclear rocket fuel test could accelerate NASA's Mars mission

A team from the Department of Energy's Oak Ridge National Laboratory, joined by university students, recently traveled to The Ohio State University Research Reactor to conduct a novel experiment on nuclear thermal rocket fuel coatings—one that could help propel NASA's astronauts to Mars faster and more efficiently.

"Our experiment aimed to test a fuel coating technique and evaluate if it can withstand the intense environment of a nuclear thermal rocket," said Brandon Wilson, an R&D staff member in ORNL's Nuclear and Extreme Environment Measurement group. "Testing materials at exceptionally high temperatures is a first and a crucial step toward helping NASA mature and qualify nuclear fuels for manned space exploration using nuclear thermal propulsion technology."

Nuclear thermal propulsion, or NTP, is a potentially game-changing technology for NASA's crewed missions to Mars in the 2040 timeframe. NTP engines use a nuclear reactor to heat hydrogen to ultra-high temperatures and then expel the heated hydrogen through a nozzle, which generates thrust and moves the rocket through space more efficiently than a traditional chemical rocket. In effect, NTP engines could drastically reduce transit times to Mars while reducing overall mission costs and the effects of radiation and zero gravity on astronauts.

However, developing and testing materials to withstand conditions unlike anything else on Earth has remained a challenge.

ORNL has pioneered a technique to coat fuel and reactor core materials in zirconium carbide, which can protect these critical components from hydrogen infiltration and corrosion without impacting the reactor's neutronics. To test this coating under the combined effects of high temperature and high radiation, researchers in the lab's Nuclear and Extreme Environment Measurement group designed the In-Pile Steady-State Extreme Temperature Testbed (INSET), a specialized high-temperature furnace designed to operate within a nuclear reactor.

A second iteration of INSET is now the only available technology that can rapidly heat materials from room temperature to 2,200 degrees Celsius in about five minutes while allowing for quick handling after neutron irradiation.

Developed at ORNL with significant design contributions from University of Tennessee graduate student Emily Hutchins, INSET 2.0 is a cost-effective option for conducting multiple experiments both inside and outside a reactor. Because of its versatile design, INSET can be used to evaluate any research reactor with a port diameter greater than eight inches, offering unmatched versatility for high-temperature materials testing.

INSET was used to perform irradiation testing of coated surrogate particles at The Ohio State University Research Reactor. There, four different nuclear thermal rocket fuel sample surrogates coated in zirconium carbide were placed in INSET and irradiated for two days under repeated temperature cycling.

The experiment team included Wilson, Hutchins, and Bryan Conry, an ORNL post-doc research associate, as well as Pavel Shilenko, a cadet at West Point. Hutchins and Shilenko were the primary operators of the experiment, setting up the INSET furnace and recording data throughout the two-day test.

"I am exceptionally proud of Emily and Pavel," said Wilson. "Their contributions to this project produced an important milestone for this research, in addition to a learning experience that I hope will shape their future as leaders in nuclear science and engineering."

Later this spring, the team will conduct post-irradiation analysis at ORNL to assess the coatings' performance and their ability to protect the fuel under operational conditions.

"The findings from this experiment will represent a crucial step in advancing nuclear thermal propulsion technology for future human space exploration," said Wilson.

ORNL's Katherine Montoya, Eddie Lopez Honorato, Craig Gray, Bob Sitterson, Nick Prins and N. Dianne Bull Ezell also contributed to this experiment. The team acknowledges the support of the Ohio State University Nuclear Reactor Laboratory and the assistance of the reactor staff members.