How the First Nuclear Reactor Works
The foundational 1955 patent by Enrico Fermi and Leo Szilard describing the design of the first nuclear reactor capable of a self-sustaining chain reaction.
Original patent title: “Neutronic reactor”
The foundational 1955 patent by Enrico Fermi and Leo Szilard describing the design of the first nuclear reactor capable of a self-sustaining chain reaction. Granted to Individual in 1955 with 2 claims and 232 forward citations, and it is now in the public domain.
Key facts
Coverage
What does this patent actually cover?
The patent defines the critical physical requirements for a nuclear reactor to achieve a self-sustaining chain reaction. It specifies a lattice structure where natural uranium rods are embedded in a graphite moderator. The claimclaimA numbered sentence at the end of a patent that legally defines what the inventor owns. The most important section.Read more → explicitly links the geometry, the volume ratio of the graphite to the uranium, and the material purity to the 'k=1.00' curve, which represents the threshold where the number of neutrons produced equals the number of neutrons lost. By maintaining these precise parameters, the system ensures that the fission process continues without external intervention.
The gap
What does this patent NOT cover?
- Does not cover reactors using enriched uranium fuel, as the claimclaimA numbered sentence at the end of a patent that legally defines what the inventor owns. The most important section.Read more → specifies natural uranium.
- Does not cover non-graphite moderation systems, such as heavy water or light water reactors.
- Does not cover specific control rod mechanisms or safety shutdown systems.
These exclusions are unique to PatentBrief — derived from the actual claim language, not patent-office boilerplate.
What made this novel
The inventors realized that the geometric arrangement and the purity of the materials were just as critical as the fuel itself to prevent neutrons from being absorbed by impurities before they could cause further fission.
The Patent Drawing
Schematic visualization of the patent's claim structure. Hand-drawn diagrams in progress for each landmark patent.
Where you've seen this
Real-world examples
Chicago Pile-1
Graphite-moderated nuclear reactors
Early plutonium production reactors
Why it matters
The bigger picture
This is the seminal patent for nuclear power. It codified the physics discovered during the Manhattan Project into a technical blueprint, effectively launching the nuclear age. It remains a primary reference in the history of energy production and nuclear engineering.
Filed
December 19, 1944
Granted
May 17, 1955
Market context
Who's building on this
Companies in this space
The technology originated with the U.S. government and the Manhattan Project. Today, companies like Terrestrial Energy and various national laboratories continue to research advanced graphite-moderated reactor designs.
Market impact
This patent established the feasibility of nuclear fission for energy production. It created the baseline for the entire nuclear power industry and served as the primary intellectual property foundation for early reactor development in the mid-20th century.
Claim 1 — Plain English
What this patent covers
The patent defines the critical physical requirements for a nuclear reactor to achieve a self-sustaining chain reaction. It specifies a lattice structure where natural uranium rods are embedded in a graphite moderator. The claim explicitly links the geometry, the volume ratio of the graphite to the uranium, and the material purity to the 'k=1.00' curve, which represents the threshold where the number of neutrons produced equals the number of neutrons lost. By maintaining these precise parameters, the system ensures that the fission process continues without external intervention.
The clever bit
The inventors realized that the geometric arrangement and the purity of the materials were just as critical as the fuel itself to prevent neutrons from being absorbed by impurities before they could cause further fission.
What it does not cover
- Does not cover reactors using enriched uranium fuel, as the claim specifies natural uranium.
- Does not cover non-graphite moderation systems, such as heavy water or light water reactors.
- Does not cover specific control rod mechanisms or safety shutdown systems.
Patent Journey
From filing to expiry
PatentBrief Score
Impact Score
Moderate
Citation count
40/40
Highly cited
Claim breadth
1/20
Narrow claimsclaimsThe numbered statements at the end of a patent that legally define what the inventor owns.Read more →
Recency
0/20
Older than 20 years
Assignee scale
0/20
Independent or smaller assigneeassigneeThe entity that owns the patent — usually the inventor's employer or a company.Read more →
PatentBrief Impact Score — based on citation count, claim breadth, recency, and assignee scale. Not a legal assessment.
Heuristic Value Estimate
What this patent might be worth
$45K – $144K
Midpoint $90K · expired or expiring · industry ×1.5
Heuristic only — blends forward/backward citation counts, claim scope, time remaining, litigation history, and CPC-derived industry baseline. Real valuations need a professional appraisal.
The original legal language
Original claims
2 claims as filed with the patent office.
Concepts involved
Citations
Patent lineage
Cite this patent
Enrico, F., & Leo, S. (1955). How the First Nuclear Reactor Works (U.S. Patent No. 2,708,656). U.S. Patent and Trademark Office. https://patentbrief.org/patent/us/2708656/nuclear-reactor-fermi-szilard
Auto-generated from the patent record. Double-check author order and the issue date against the official USPTO document before submitting.
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Common Questions
Frequently Asked Questions
What does How the First Nuclear Reactor Works cover?
The foundational 1955 patent by Enrico Fermi and Leo Szilard describing the design of the first nuclear reactor capable of a self-sustaining chain reaction.
Who owns patent US 2708656?
Individual owns this patent, granted in 1955.
When does this patent expire?
This patent has expired and is now in the public domain — anyone can use the invention freely.
What is patent US 2708656 cited by?
This patent has been cited by 232 later patents that build on its ideas.
What problem does this patent solve?
This is the seminal patent for nuclear power. It codified the physics discovered during the Manhattan Project into a technical blueprint, effectively launching the nuclear age. It remains a primary reference in the history of energy production and nuclear engineering.
What does this patent NOT cover?
Does not cover reactors using enriched uranium fuel, as the claim specifies natural uranium.
Same assignee
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