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

-- Company Prepares to Ring Nasdaq Closing Bell Today in Honor of Milestone --

PARSONS, Kan.--(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.

Following arrival at the Parsons site, the non-nuclear prototype reactor canister will be prepared for testing as Deep Fission continues preparation for its large diameter drilling program. The Company is advancing permitting with the Kansas Department of Health and Environment (KDHE) for the non-nuclear borehole, which is expected to serve as the next major proof-of-concept milestone.

“This milestone reflects disciplined execution across fabrication, testing, and delivery, and strengthens the foundation for scaled deployment of our Gravity Nuclear Reactor™ system,” said Mike Brasel, Chief Operating Officer of Deep Fission.

The Company is also progressing development of its full-scale nuclear demonstration borehole and advancing design of its primary heat exchanger. These parallel efforts support a phased strategy to accelerate iterative validation of the most unique aspects of Deep Fission’s commercial deployment model.

Deep Fission is participating in the U.S. Department of Energy’s Reactor Pilot Program. Authorized under Executive Order 14301, the program enables reactor testing and deployment in order to accelerate the path to commercialization of nuclear energy.

Tune in to Deep Fission ringing the Nasdaq closing bell today at https://www.nasdaq.com/marketsite/bell-ringing-ceremony

About Deep Fission

Deep Fission is developing technology that places a small modular pressurized water reactor in a borehole approximately one mile underground. The Company’s Gravity Nuclear Reactor™ approach combines established pressurized water reactor technology with a novel underground deployment model designed to simplify construction, enhance safety, and support scalable commercial deployment. Deep Fission is focused on delivering reliable, low-carbon baseload power to meet growing electricity demand from utilities, industrial customers, and data centers. The Company is currently advancing the development of its first reactor project in Parsons, Kansas and was selected for the U.S. Department of Energy’s Reactor Pilot Program.

Forward-Looking Statements

This press release contains forward-looking statements within the meaning of the federal securities laws. Forward-looking statements include, but are not limited to, statements regarding Deep Fission’s business strategy, technology development plans, potential commercial deployments, potential demand represented by non-binding LOIs, expected regulatory activities, planned project milestones, potential commercialization, potential revenue recognition, and the timing, feasibility, scalability, safety, and performance of the Company’s technology. These statements are based on current expectations and assumptions and are subject to risks and uncertainties that could cause actual results to differ materially from those expressed or implied.

Important factors that may cause actual results to differ materially include, among others, risks related to the Company’s early stage of development; the non-binding nature of the LOIs; the Company’s ability to negotiate and enter into definitive commercial agreements; technical, engineering, drilling, construction, regulatory, licensing, financing, supply chain, and deployment risks; the Company’s ability to obtain required approvals from the NRC, DOE, and other governmental authorities; market adoption of the Company’s technology; and the other risks described under “Risk Factors” and “Cautionary Note Regarding Forward-Looking Statements” in Deep Fission’s filings with the Securities and Exchange Commission.

Forward-looking statements speak only as of the date of this press release. Deep Fission undertakes no obligation to update any forward-looking statements, except as required by law.