Deep Fission Publishes DOE-Approved Nuclear Safety Design Agreement for Gravity™ Pilot Reactor, Demonstrating Commitment to Transparency

Deep Fission releases a DOE‑approved safety design framework for its Gravity pilot reactor and outlines a path toward possible commercial operation.

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-- First company in the DOE Reactor Pilot Program to release its complete NSDA; subject to further DOE authorization and NRC licensing, the Company intends to convert the pilot reactor to full commercial operation --

WASHINGTON--(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 public release of its Nuclear Safety Design Agreement (NSDA) for the Gravity™ Nuclear Reactor. The U.S. Department of Energy (DOE) approved the NSDA as part of the Company’s Reactor Pilot Program taking place in Parsons, Kansas.

The NSDA establishes the safety framework that will guide continued development of the reactor. It reflects the agreement reached between DOE and Deep Fission on applicable design requirements, the planned safety analysis approach, and the regulatory engagement process that will govern the project. Public release of the document isn't required; Deep Fission is choosing to publish it to give the public direct visibility into the safety framework behind its approach as development evolves. DOE's approval of the NSDA is the initial step in the safety review process for the Reactor Pilot Program. Addition documentation and reviews are required before potential DOE authorization for operations.

"We're publishing our full NSDA because we think the public deserves to see the actual safety case behind this reactor, not just our word that DOE reviewed one," said Liz Muller, CEO and Co-Founder of Deep Fission. "A project with this kind of ambition should be built in the open, and we hope more of the industry joins us in doing that."

The Gravity Reactor uses standard, low-enriched uranium fuel and pressurized water reactor technology with a 70-year operating history. Rather than relying on a large above-ground containment structure, the design places the reactor approximately one mile underground, where a hydrostatic column of water and the surrounding geology are designed to provide passive pressure control, cooling, and shielding.

The NSDA was developed and approved under the DOE Reactor Pilot Program, established by Executive Order 14301, which authorizes DOE to approve the design, construction, and initial testing of pilot advanced reactors outside DOE national laboratories, with the NRC observing the process. Unlike a standalone criticality test, the Parsons pilot is designed with the intent that the same reactor unit Deep Fission installs and brings to criticality under DOE authorization could, subject to NRC licensing, transition to commercial power operation rather than being decommissioned once initial testing concludes.

The published document includes a small number of redactions related to security-sensitive design details, consistent with standard practice for advanced reactor safety filings. As with any live engineering and regulatory process, some elements of the design have evolved since the NSDA was first developed, and Deep Fission will share updates as its safety case advances through the next stages of DOE review.

Deep Fission has also published a companion FAQ, alongside the NSDA, to address common questions about this pathway, the reactor's safety basis, and the project's status.

The full NSDA and FAQ are available at https://www.deepfission.com/nuclear-safety-design-agreement-gravity-nuclear-reactor

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, where it intends to convert its DOE-authorized pilot reactor directly into a commercially licensed power plant following successful demonstration, 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.

View source version on businesswire.com: https://www.businesswire.com/news/home/20260915793564/en/

Media Contact
Chloe Frader
media@deepfission.com

Investor Relations Contact
Bob Prag
IR@deepfission.com
(858) 794-9500

Elevate IR
(720) 330-2829

Source: Deep Fission, Inc.

Key Terms

low-enriched uranium technical

Low-enriched uranium is uranium that has been processed so the amount of the fissionable isotope U-235 is raised but kept below 20 percent, making it suitable for use as fuel in most commercial nuclear reactors while reducing its usefulness for weapons. Investors care because it is the primary commodity that powers nuclear plants, so its availability, production costs, regulatory controls and geopolitical supply risks directly affect energy companies, utility revenues and firms involved in mining and enrichment — similar to how gasoline supply and price influence transportation businesses.

pressurized water reactor technical

A pressurized water reactor is a type of nuclear power plant that uses water kept under high pressure to carry heat away from the nuclear core without letting it boil; that hot water then passes through a heat exchanger to make steam that drives turbines to produce electricity. Think of it like a sealed pressure cooker transferring heat into a separate steam system. Investors care because this design influences construction and operating costs, safety and regulatory risk, fuel and maintenance needs, and long-term liabilities such as decommissioning—factors that affect a plant’s profitability and investment risk.

hydrostatic column technical

A hydrostatic column is a vertical section of liquid whose weight creates pressure that increases with depth; the pressure at any point equals the liquid’s density times gravity times the column’s height. Investors encounter the term when it’s used to describe tests or design limits for tanks, pipes, medical devices or packaging, because hydrostatic pressure reveals whether a container or system can withstand real-world loads and meet safety or regulatory standards. Think of it like the increasing squeeze you feel the deeper you dive into a swimming pool.

criticality technical

Criticality measures how important or severe a problem, item, or situation is to the functioning, safety, or regulatory standing of an organization — think of it as how urgent a smoke alarm would be in different rooms of a building. Investors use criticality to judge where risks, costs, or delays are most likely to hit a business, because higher criticality items can drive bigger financial impacts, faster regulatory action, or sudden changes in growth prospects.