Tech: NASA built and tested a 'truly astounding' nuclear reactor that may help astronauts travel longer, farther, and faster in space

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Engineers work on the Kilopower nuclear reactor, a system being designed to power NASA missions.

NASA's new Kilopower technology uses nuclear fission and electrical converters to generate enough energy to power human and robotic space missions. Recent tests of a prototype reactor suggest devices may soon be ready for safety and flight tests.

  • NASA is working on a nuclear reactor to power (and later propel) deep-space exploration, such as human missions to the moon and Mars.
  • Kilopower is a 1- to 10-kilowatt design that could theoretically power a US home for hundreds of years.
  • A recent full-power test in Nevada met or exceeded all of the government's expectations.
  • The risk posed by the new technology could be far less than any other reactors in use today.

While nuclear power plants across America are shutting down, NASA is perfecting a new type of fission reactor.

The device, called Kilopower, could enable unprecedented exploration of the moon, Mars, and elsewhere in the solar system. Researchers announced on Wednesday that a prototype has successfully passed a battery of tests.

"This is the first new reactor not just for space and not just for NASA, but of any kind in the US in 40 years," David Poston, the project's chief designer at Los Alamos National Laboratory, said during a press conference Wednesday. "We demonstrated a concept that NASA can use right now. It's ready for a flight program."

NASA and the National Nuclear Security Administration have worked toward this make-or-break test of Kilopower for about five years and announced it in January. During the experiment, researchers ran the uranium-fueled reactor for 28 hours at full power.

"This really is the first step in using fission power in space," Poston said.

A slide shown during the press conference went further: "Kilopower is the first step towards truly astounding space fission capabilities," it said.

The problem of power in space

NASA has some big goals. The agency is developing a huge rocket called the Space Launch System, wants to set up a space station near the moon, plans to send missions to the lunar surface, and, might even rocket astronauts toward Mars sometime in the 2030s.

But to do all that, NASA has to figure out how to generate enough power to run systems that are vital to a long-term presence in space.

"We are likely going to need large power sources not dependent on the sun, especially if we want to live off the land," James Reuter, the acting associate administrator of NASA's Space Technology Mission Directorate, said during the press conference. "For example, water ice is a critical resource present in lunar soil, and it can be extracted and used, but it takes a lot of energy to do so."

Bases off of Earth would also need to power systems that recycle water, refresh air supplies, generate fuel, illuminate greenhouses, and more.

"Our studies say that we would probably need up to 40 kilowatts of power on the moon, and then later on the surface of Mars," Reuter said.

Currently, space missions usually rely on solar power or fuel cells. But a night on the moon lasts about 14 days, and sunlight is about 40% as strong at Mars as it is at Earth, so solar panels may be impossible to wholly depend on. Plus, Martian dust storms can coat solar panels.

Fuel cells, meanwhile, can be hazardous to use and run out of juice relatively quickly.

NASA does have small nuclear power supplies that enable ambitious robotic missions. But they run on the natural decay of plutonium-238 and don't provide more than a few hundred watts of electrical power. This form of plutonium is also expensive, difficult to make, and in short supply.

These power problems have led NASA to develop Kilopower, which runs on fission — the same process harnessed by nuclear power plants on Earth. The reactor is designed to be safe, long-lasting, reliable, scalable, and energy-dense.

"This technology, we believe, will very likely be the most effective means to power human surface missions," Reuter said.

How Kilopower works

Kilopower is a small, patio-umbrella-shaped reactor that's practically immune to melting down.

The hope is that once Kilopower's capacity gets scaled up and the device becomes operational, astronauts could bury several units in the lunar or Martian soil, hook them up to their base, and let the system manage itself for 10 years or more.

That system relies on fission, which happens when atoms split, shoot out one or more neutrons, and release gobs of energy. But only a few variants of elements have the right properties to split nearby atoms, shoot out even more neutrons in the process, and sustain a chain-reaction.

Uranium-235 is one of the just-right atoms for this reaction, and it's what makes up the 6-inch-wide fuel core in Kilopower. On its own, such a small amount of U-235 can't fission well, so it's surrounded by a shield of beryllium – a metal that reflects neutrons back into the fuel, increasing the rate of fission and heat generation.

To turn on and off, Kilopower uses a rod of boron carbide, which absorbs neutrons. When the rod is pulled out, the reactor turns on, since the neutrons can then move freely and fission other atoms. Sliding the rod back into the fuel core shuts down the chain-reaction.

Heat pipes filled with sodium metal soak up the warmth from the reactions and feed it to Stirling converters on top. Those converters use the heat to drive a piston-like device, which generates electricity as the heat moves through it. Keeping the converters cool — and a stream of heat flowing through them — is key to making electrical power. So a foldable, umbrella-like radiator made of titanium metal sits on top and radiates the waste heat out into the air or space.

In March, NASA tested that process in an experiment called Kilopower Reactor Using Stirling Technology, or KRUSTY. The test run generated about 100 watts of electrical power, or enough to run a bright incandescent lightbulb.

But Poston said Kilopower could easily scale up to 10 kilowatts — 100 times more, or enough to power a typical US home — and even megawatts.

He called the experiment "incredibly successful" and said it cost NASA relatively little.

"People thought it would cost billions of dollars to do these reactors," Poston said. "We showed we can design, build, and test a reactor for less than $20 million."

Why the technology is expected be safe

The researchers behind Kilopower say it's incredibly safe to launch and use, even if there's a rocket explosion or other accident.

Unlike most reactors on Earth, Kilopower doesn't use liquid coolants like water. Water can be a problem because it can explosively turn into steam if it gets too hot, and it can more easily spread contaminants. Sodium in Kilopower's heat pipes, on the other hand, remains solid until it's melted by reactor heat.

Plus, uranium-235 isn't very radioactive, contrary to popular belief.

"If we were to have a launch accident, like an explosion or fire … the actual dosage at a kilometer from the launch pad would be far, far less than background radiation, about 1 millirem," Patrick McClure, the project lead for Kilopower at Los Alamos National Laboratory, told Business Insider.

One millirem is roughly equivalent to a whole-mouth dental X-ray and, according to McClure, "vastly lower than an airplane flight."

The biggest risk would be if the device inadvertently turned on, though McClure hinted this is virtually impossible due to the way Kilopower is designed.

"Under all worst-case conditions, we don't think there's any chance the reactor would come on during a launch accident," he said.

The researchers behind the experiment hope to establish a program with NASA to build, test, and fly full-scale Kilopower units starting sometime in the next 18 months.

Poston said he eventually wants to develop space propulsion systems with Kilopower that "could get us places much quicker and much farther out than we could ever do with anything else."

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