Nuclear thermal propulsion (NTP) is one technology that could propel a spacecraft to Mars and back, using thermal energy from a reactor to heat an onboard hydrogen propellant. While NTP is not a new concept, fuels and reactor concepts that can withstand the extremely high temperatures and corrosive conditions experienced in the engine during spaceflight are being designed now.
BWX Technologies announced on December 13 that it has delivered coated reactor fuels to NASA for testing in support of the Space Technology Mission Directorate’s NTP project. BWXT is developing two fuel forms that could support a reactor ground demonstration by the late 2020s, as well as a third, more advanced and energy-dense fuel for potential future evaluation. BWXT has produced a videoof workers processing fuel kernels in a glovebox.
“This is a landmark accomplishment for BWXT, and we’re extremely proud to support these efforts toward one day seeing a crewed spaceflight travel farther than ever before,” said Rob Smith, president of government operations at BWXT. “This is a credit to everyone engaged in this endeavor in our labs and manufacturing facilities, the teams at the national laboratories, and the academic researchers who are all working together to achieve this goal.”
Work continues: Under the terms of a contract awarded to BWXT by Idaho National Laboratory earlier this year, the company will continue to produce fuel kernels, coated fuel kernels, and fuel assembly design materials and manufacturing processes while testing of the delivered fuel gets underway in 2022.
According to the company, BWXT is the first private company to deliver relevant coated fuels that will be used in NASA testing, a milestone reached by leveraging decades of experience in specialty and coated fuel manufacturing, as well as its existing licensed production facilities. BWXT Nuclear Operations Group restarted its TRISO production line in Lynchburg, Va., in November 2020.
More than fuel: BWXT was one of three companies selected in July 2021 by NASA and the Department of Energy to produce a conceptual reactor design that could support future mission needs. INL awarded a 12-month, $5 million contract to BWXT and its partner, Lockheed Martin, while separate contracts went to General Atomics Electromagnetic Systems, partnered with X-energy and Aerojet Rocketdyne, and to Ultra Safe Nuclear Technologies, partnered with Ultra Safe Nuclear Corporation, Blue Origin, GE Hitachi Nuclear Energy, General Electric Research, Framatome, and Materion.
All three teams are designing reactors fueled by high-assay low-enriched uranium (HALEU) TRISO fuel to meet specified performance requirements that could transport crew and cargo missions to Mars and science missions to the outer solar system. At the end of the contracted 12-month performance period, INL will conduct design reviews of the reactor concepts.
Space propulsion primer: Spacecraft using NTP technology would have advantages over conventional chemical propellant designs, including lower mass and more propellant efficiency. NASA wants NTP reactors that heat hydrogen to an outlet temperature of 2700K, which is consistent with a specific impulse of 900 seconds—about double the specific impulse that can be achieved with a chemical propellant rocket.
Specific impulse is a ratio—the change in momentum per unit mass of propellant—that indicates engine efficiency. The increase in specific impulse from NTP comes from the lower weight of the hydrogen exhaust, which is easier to accelerate than the water vapor from a chemical engine. That efficiency could reduce flight times, thereby reducing astronaut exposure to cosmic radiation and enabling more robust space missions.
A successful NTP program could be followed by nuclear electric propulsion, which would use its nuclear fuel to produce electricity, and then generate thrust by ionizing inert gas propellants (such as xenon and krypton) and accelerating the ions using a combination of electric and magnetic fields or an electrostatic field.