# 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.

- **Patent:** US 2708656
- **Original title:** Neutronic reactor
- **Owner:** Individual
- **Granted:** 1955
- **Status:** Public domain (expired)
- **Times cited:** 232
- **Field:** energy, mechanical

## What it does

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 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.

## 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.

## Real-world examples

1. Chicago Pile-1
2. Graphite-moderated nuclear reactors
3. Early plutonium production reactors

## Why it matters

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.

## 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.

**Full plain-English explainer:** https://patentbrief.org/patent/us/2708656/nuclear-reactor-fermi-szilard

**Original patent:** https://patents.google.com/patent/US2708656

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_Source: PatentBrief — https://patentbrief.org. Patent facts are from public records; the plain-English explanation is PatentBrief's._


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