PPolySim OS
Launch Studio

Fission Chain Reaction

One number decides whether a pile of uranium sits quiet, powers a city, or runs away: k, the neutron multiplication factor. Watch it play out.

Fission Chain ReactionLive

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Each fission releases neutrons that can trigger more fissions. The multiplication factor k is how many of those neutrons cause a new fission on average. Below 1 the chain dies out; exactly 1 sustains steady power — a running reactor; above 1 it grows exponentially. Control rods nudge k around 1 to hold a reactor critical.

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Data Inspector

k factor1.000
Generation0
Statecritical (steady)

Governing equation

Reading this result: k is essentially 1: on average one neutron per fission triggers the next, a self-sustaining steady chain — a running reactor.

Runs locally in your browser — free forever. Scale to the cloud when reality gets heavy.

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How it works

Each fission emits neutrons that may trigger more fissions. The multiplication factor k is the average number that succeed. Below one, the chain dies; exactly one holds steady power — a critical reactor; above one, the population grows exponentially. Control rods absorb neutrons to keep k balanced at one. Educational model, not an operational simulation.

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Frequently asked questions

Is this fission chain reaction criticality tool really free?▾
Yes. Fission Chain Reaction runs entirely in your browser using your device's own compute, so local use is free forever. You only pay Compute Tokens if you scale a job to the cloud.
Do I need to install anything?▾
No. Everything runs client-side in a modern browser — no downloads, no license, no account required to start.
Can I save or share my simulation?▾
Create a free account to save projects, and use a shareable embed or minted DOI to publish a live, interactive version anywhere.
How accurate are the results?▾
The solver uses established numerical methods, but results are for research and educational purposes and should be validated against experiment or professional review before you rely on them.