Deep Fission, Inc. (Nasdaq: FISN) announced it successfully installed and retrieved a full-size prototype reactor canister from a borehole using standard commercial drilling equipment on Sept. 3, 2026.

A commercial drilling crew lowered the 20-foot, non-nuclear canister to 100 feet depth inside a 34-inch-wide borehole, then brought it back to the surface. The canister is a full-size replica of the housing designed for the company's Gravity™ reactor core and contained no nuclear fuel.

According to the company, no custom-built or specially adapted equipment was required for the demonstration. The drilling rig and rigging used are available from commercial contractors.

"We did not have to develop new technology," said Liz Muller, CEO and Co-Founder of Deep Fission. "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 Gravity™ reactor is a pressurized water reactor designed to operate approximately one mile underground in a water-filled borehole. The company states the surrounding water column and rock provide containment, operating pressure, heat transfer, and emergency cooling, reducing the need for surface infrastructure typical of conventional nuclear facilities.

The demonstration is one step in a broader validation program that also includes drilling, system integration, and regulatory approvals. The company recently received approval from the U.S. Department of Energy for its Nuclear Safety Design Agreement for the Gravity™ reactor, as part of the DOE Reactor Pilot Program. Deep Fission is advancing its first reactor project in Parsons, Kansas.