Deep Fission lowers full-size canister replica 100 feet into a borehole

Deep Fission, Inc. said on September 10, 2026 that a commercial drilling and rigging crew lowered a 20-foot prototype reactor canister to a depth of 100 feet inside a 34-inch-wide borehole, aligned it, and brought it back to the surface on September 3, 2026, according to the company's release, distributed through Business Wire. The canister is a full-size, non-nuclear replica of the one designed to house the core of the company's Gravity reactor and contained no fuel, the release says.

The design calls for a mile. Deep Fission's concept places a small modular pressurized water reactor in a water-filled borehole about one mile underground, where, per the release, the water column and surrounding rock provide containment, operating pressure, heat transfer, and emergency cooling; 100 feet is about 2% of that depth, by The Duck Curve's arithmetic on 5,280 feet to the mile. The release's claim is about the tooling rather than the depth: "Nothing about the demonstration required equipment that had to be invented, custom-built, or adapted for nuclear service," it says, and the release's subhead describes the equipment as already in commercial service in the drilling industry. "The most important thing about this demonstration is what we did not have to do," CEO Liz Muller said in the release.

Where the project stands: the Department of Energy approved the company's Nuclear Safety Design Agreement for the Gravity reactor, Deep Fission said on August 6, 2026, a step it described as confirming the design "warrants advancement" under DOE's Reactor Pilot Program. That is the authorization track under which Oklo's Groves Isotope Test Reactor reached criticality on the night of August 5, 2026, per DOE's August 6, 2026 announcement, which dates the event to "last night" and calls Groves "the fifth DOE-authorized advanced reactor to achieve criticality this summer," the sprint The Duck Curve surveyed in August. The August 6 Deep Fission release puts the company's first project at the Great Plains Industrial Park in Parsons, Kansas, says the company broke ground there in December 2025 and has drilled a data acquisition well to 6,000 feet, and gives no date for first criticality; the company says it intends the Parsons unit to become an NRC-licensed, commercially operating reactor after DOE authorization rather than a one-time criticality test.