20-foot nuclear reactor lowered 100 feet underground using commercial drilling gear

Deep Fission has successfully lowered a 20-foot reactor canister 100 feet underground and retrieved it using commercial drilling equipment, testing a key part of its plan to bury small nuclear reactors a mile below the surface. The demonstration took place on September 3, when a commercial drilling and rigging crew lowered the full-size canister into a 34-inch-wide borehole. The crew aligned the canister at depth before bringing it back to the surface. The test focused on whether the large reactor canister can be handled underground using equipment already available to drilling contractors. Deep Fission said the demonstration did not require equipment invented, custom-built, or adapted for nuclear service. The canister was a full-size, non-nuclear replica of the vessel designed to house the company’s Gravity reactor core. It contained no nuclear fuel, so the test was aimed at validating the physical deployment and retrieval process rather than reactor operation. Commercial drilling goes nuclear “The most important thing about this demonstration is what we did not have to do,” said Liz Muller, CEO and Co-Founder of Deep Fission. “We did not have to develop new technology. We used a rig and rigging that is commercially available in the field today, and our reactor uses pressurized water technology that has been operating in the nuclear industry for decades.” Deep Fission’s reactor concept combines established pressurized water reactor technology with an underground deployment system. The Gravity reactor would use standard low-enriched uranium fuel, while the company’s main change is to place the reactor deep underground. The proposed reactor would sit in a water-filled borehole approximately one mile below the surface. Deep Fission says the water column and surrounding rock could provide containment, operating pressure, heat transfer, and emergency cooling. That configuration could reduce the surface infrastructure normally associated with nuclear plants. Instead of constructing a large reactor facility above ground, the company’s model would shift much of the system underground. The company believes this could simplify construction, reduce costs, and shorten deployment schedules while providing additional safety margins. Mile-deep reactors face hurdles The latest test does not demonstrate that a commercial reactor can operate underground. Deep Fission still has to validate the broader system, including drilling, reactor integration, regulatory requirements, and eventual commercial operation. The company recently received approval from the US Department of Energy for its Nuclear Safety Design Agreement for the Gravity reactor. It is advancing the project under the DOE Reactor Pilot Program and is developing its first reactor project in Parsons, Kansas. The underground approach is also intended to support deployment closer to customers that need reliable electricity. Deep Fission is targeting utilities, industrial customers, and data centers seeking low-carbon baseload power. “Our innovation is in how we put proven pieces together, not in inventing something that has never been built. That is the difference between a science project and something you can deploy,” Muller said.The company now needs to move from a mechanical demonstration to the much harder task of proving that its underground reactor design can meet engineering, safety, licensing, and commercial requirements.Get the latest in engineering, tech, space & science - delivered daily to your inbox.With over a decade-long career in journalism, Neetika Walter has worked with The Economic Times, ANI, and Hindustan Times, covering politics, business, technology, and the clean energy sector. Passionate about contemporary culture, books, poetry, and storytelling, she brings depth and insight to her writing. When she isn’t chasing stories, she’s likely lost in a book or enjoying the company of her dogs.