NASA announced the successful demonstration of a new nuclear reactor power system that could enable robotic missions to deep space and provide power for crewed spacecraft and human outposts on the Moon and Mars.
NASA and the Department of Energy’s National Nuclear Security Administration (NNSA) announced the results of the demonstration, called the Kilopower Reactor Using Sterling Technology (KRUSTY) experiment, at a news conference on May 2 at NASA’s Glenn Research Center in Cleveland, Ohio. The Kilopower reactor system was developed at NASA Glenn and was tested from November 2017 through March 2018 at NNSA’s Nevada National Security Site, located in the southeastern desert of Nevada.
“When we go to the Moon and eventually on to Mars,
we are likely going to need large power sources not dependent on the Sun,” said James Reuter, Acting Associate Administrator for NASA’s Space Technology Mission Directorate. “Especially if we want to live off the land. The Kilopower design we tested is ingenious in the way it is designed, for simplicity of operations, but also for scalability. While we tested it a 1-kilowatt power production, it is scalable to 10 kilowatts without any large impact on its overall size. So that makes a nice building block as we go forward.”
The KRUSTY reactor unit is small, on the scale of an oversized floor lamp, but is capable of providing enough electrical power to run several average households continuously for at least 10 years. Its developers expect that four of the Kilopower units would provide more than enough power for a future lunar or Martian outpost.
The KRUSTY fission system uses a solid cast uranium-235 reactor core, about the size of a paper towel roll, with eight notches around its perimeter, fitted to the passive sodium heat pipes that transfer reactor heat to the high-efficiency Stirling engines, which convert the heat to electricity.
The Kilopower project is part of NASA’s Space Technology Mission Directorate’s Game Changing Development program. The project’s primary goal was to develop an affordable fission nuclear power system for long-duration performance in space and on planetary surfaces. The project set 2018 as a test deadline so that fission power can become a viable option for mission planners as they develop the future architectures for planetary exploration and surface power system needs.
The Kilopower fission design is quite different from the Radioisotope Thermoelectric Generators (RTG) that have been used for previous deep space probes such as New Horizons, Galileo, and Cassini.
“They are very different in the way they produce heat,” Marc Gibson, NASA Glenn’s Kilopower Lead Engineer, told Spaceflight Insider. “One of the things we find very interesting about the fission side is that we can start the reactor at any time during the mission. So if we’ve got a fifteen-year mission to a Kuiper Belt object or something and it takes a long time to arrive, you don’t actually have to start the reactor up until we get there. So we don’t start the life of the power system until we want it. We’re also able to turn down the power and turn up the power. We can go from 1,000 watts all the way down to 50 or 40 watts, depending on the demands of the spacecraft, and that lowers how much fuel we use.”
To turn the system on and off, the Kilopower design uses a rod of boron carbide which absorbs neutrons. When the rod is pulled out, the reactor turns on as neutrons begin to move freely and fission with other atoms in a chain reaction. When the rod is slid back into the reactor core, the chain reaction is stopped.
“The other thing I find very interesting is that it takes a certain amount of critical mass to make this reactor start and operate,” Gibson told Spaceflight Insider. “On the smaller side, that gives us a lot more fuel than we actually need. So in theory, once you start up the reactor, we designed it with enough excess radioactivity that there’s enough fuel there that it can stay at that temperature potentially for hundreds of years. The challenge then becomes designing the rest of the system to last for that long.”
The purpose of the recent experiment in Nevada was to demonstrate that the system can create electricity with fission power, and show that the KRUSTY prototype is stable and safe no matter what environment it operates in.
“We threw everything we could at this reactor, in terms of nominal and off-normal operating scenarios, and KRUSTY passed with flying colors,” said David Poston, Chief Reactor Designer at NNSA’s Los Alamos National Laboratory.
The experiment progressed in phases, increasing power to heat the core incrementally before moving on to the final phase of a simulated mission. That simulation included reactor startup, ramp to full power, steady nominal operation, and shutdown. Throughout the experiment, the engineers simulated a series of problems to further challenge the design’s performance. These included simulated power reduction, failure of one or more of the Stirling engines, and failed heat pipes, showing that the system could continue to operate successfully despite multiple failures.
“We put the system through its paces,” Gibson said. “We understand the reactor very well, and this test proved that the system works the way we designed it to work. No matter what environment we expose it to, the reactor performs very well.”
The development and test of the KRUSTY prototype was a success, and at a relatively low cost to NASA.
“There were a lot of people who thought it would cost NASA billions of dollars to develop these reactors,” Poston said. “We showed we can design, build, and test the reactor for less than $20 million.”
The new Kilopower system is the first new nuclear reactor of any kind produced in the US in the last 40 years. The design team is awaiting approval from NASA and NNSA to commence further testing on scaled-up versions of Kilopower for eventual spaceflight and surface operations. The team anticipates approval and a commencement of development in the next 18 months.