Deep Fission Prototype Reactor Canister Arrives at Kansas Site, Advancing Reactor Proof-of-Concept Program

About this update from Deep Fission, Inc.

-- Company Prepares to Ring Nasdaq Closing Bell Today in Honor of Milestone -- PARSONS, Kan., July 07, 2026 --( BUSINESS WIRE )--Deep Fission, Inc. (Nasdaq: FISN) ("Deep Fission" or the "Company"), an advanced nuclear energy company developing small modular pressurized water reactors installed one mile underground, today announced the arrival of its prototype reactor canister at its Parsons, Kansas site, marking a key milestone in the Company's Proof-of-Concept Well program and its Gravity Nuclear Reactor™ development. In celebration of this milestone and its listing on the Nasdaq Stock Market, Deep Fission will ring the Nasdaq closing bell today at 4:00 PM ET . The factory-built prototype canister completed fabrication, hydrostatic testing, and delivery to Kansas, representing tangible progress toward validating installation, infrastructure readiness, and operational sequencing for the Company's first commercial demonstration well. "The arrival of our prototype reactor canister at the Kansas site is a clear step forward in moving from design to deployed infrastructure," said Mark Pérès, Chief Nuclear Officer of Deep Fission. "Successfully manufacturing, testing, and delivering this hardware demonstrates performance of our design and supply chain capabilities. Upcoming testing using this hardware will validate our approach and provide valuable learnings as we assemble, install and test key systems under non-nuclear conditions in our large diameter borehole." The Proof-of-Concept Well is Deep Fission's nearly full-scale validation program, designed to demonstrate a larger-diameter borehole and end-to-end installation workflow using commercial-grade, non-nuclear components prior to fuel loading. The program is intended to validate each stage of underground deployment under real-world conditions while confirming engineering assumptions at scale and supporting the Company's broader commercialization timeline. The reactor canister is a key component of Deep Fission's Gravity Nuclear Reactor™ design, which places a small modular pressurized water reactor in a borehole approximately one mile underground. The Gravity Reactor™ is based on established pressurized water reactor technology adapted for subsurface deployment, using pressure from a mile-long water column atop and surrounding the reactor in the borehole, to support operating pressure and cooling. In this design, thermal energy is transferred through a closed-loop system from the reactor canister to a heat exchanger, then rises to the surface in a secondary closed-loop for conversion into electricity, like a geothermal system.

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