You can freely build on How the First Nuclear Reactor Works
This patent expired in 1972. Every claim — 1 independent, 0 dependent — is now unenforceable. Anyone can use, reproduce, manufacture, sell, or offer for sale this technology without a license.
Original assignee
Individual
Patent granted
1955
Expired
1972
Forward citations
232
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.
What is now free to use
All 1 claims of US 2708656 are in the public domain. Specifically:
Claim 1: A NEUTRONIC REACTOR WHICH COMPRISES A MODERATOR OF GRAPHITE AND NATURAL URANIUM RODS DISPOSED IN A GEOMETRIC PATTERN THE
The 0 dependent claims add narrowing limitations and are also free.
What is NOT covered
Patent expiry frees this specific invention. Separately-patented improvements made after expiry may still be protected.
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.
Who is building on this today
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.
Products built on expired version of this technology
Chicago Pile-1
Graphite-moderated nuclear reactors
Early plutonium production reactors
How to cite this patent in your documentation
Individual. US Patent 2708656. Neutronic reactor. Granted 1955, expired 1972. Now in the public domain.
Note: This is a convenience citation. Consult a patent attorney for formal freedom-to-operate analysis.
PatentBrief is an educational resource and does not provide legal advice. Patent expiration information is derived from USPTO records and may not reflect continuation patents, divisional filings, or separately-patented improvements. For commercial use or production decisions, obtain a formal freedom-to-operate (FTO) opinion from a registered patent attorney.