- The nuclear reactor used on the moon will be unlike anything we’ve seen before.
- The requirements are far smaller than all but the most "micro" reactor designs.
- NuScale’s standard-setting small reactor is 100 times too heavy and far too large.
Move over, Zappa—there’s a new Moon Unit in the works.
In a new request for proposals, NASA seeks a nuclear fission reactor that could be carried to and operated on the moon. The reactor will have to go through restrictive conditions on the journey and operate in an unprecedented environment in several key ways, making this a challenge on par with the many others related to space travel.
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If you’re thinking of submitting a design, Keith Ridler at Phys.org reports on the limitations:
“Submitted plans for the fission surface power system should include a uranium-fueled reactor core, a system to convert the nuclear power into usable energy, a thermal management system to keep the reactor cool, and a distribution system providing no less than 40 kilowatts of continuous electric power for 10 years in the lunar environment."
There’s more. The reactor must fit in a cylinder that’s 18 feet long and 12 feet across, which sounds pretty big until you consider that even the current landmark for small modular reactors, NuScale, would require 15 feet in width and three to four times the required length: 65 feet for the reactor itself and 76 feet for the containment vessel. The weight limit for the moon reactor is just 13,200 pounds, or 6.6 tons—NuScale’s reactor weighs 700 tons. Micro-reactor makers Ultra Safe Nuclear have a page dedicated to space power, but it’s light on details.
So it’s safe to say we’re talking about very small or even micro-reactor technology for this project. And while the size is a dramatic limitation, that’s not even the most specific requirement. Ridler continues:
“Some other requirements include that it be capable of turning itself off and on without human help, that it be able to operate from the deck of a lunar lander, and that it can be removed from the lander and run on a mobile system and be transported to a different lunar site for operation.”
The idea of “human help” is interesting because it could mean a reactor that is fully autonomous—as in, shutting itself off when certain conditions are met even without human monitoring—or it could mean remotely supervised and operated but without on-site human workers to push the right buttons on the reactor itself.
Either way, that’s a new kind of nuclear reactor protocol compared to the heavily staffed power plants on Earth. But the next generation of terrestrial nuclear plants also seek to become passively safer and inherently less staff-heavy than the plants we have today. They can do that in several ways, including, as with Ultra Safe Nuclear, materials that shut themselves down if the heat is too high. They do this by using materials that expand with heat, for example, and literally seal off paths in the reactor to shut down the whole process. Some of these reactors never get hot enough to melt down at all.
It’s honestly hard to imagine what the moon reactor will ultimately look like, because everything similar on Earth is still in the prototype or investor phase. Regulation for these new techologies also takes a long time and costs a great deal, partly because of the stigma that still surrounds nuclear energy means decision-makers are hesitant to adjust the rules for new paradigms in the industry.
But maybe the NASA project is an interesting way to help subvert that process. After all, a design approved by them already has a foot in the door of the large government approval machinery, and might be able to get a fresh eye or a fast track on the process.