ℹ ABOUT
WHAT IS THIS?
A nuclear fission chain reaction simulator. Fire neutrons into a field of uranium atoms and watch the cascade unfold.
WHAT'S IT FOR?
Visualise how nuclear reactors and weapons work at the atomic level — the difference is control rods and enrichment levels.
HOW TO USE
Click an atom to fire a neutron at it
Insert control rods to absorb neutrons
• Adjust enrichment for more/fewer U-235 atoms
• Watch the chain reaction spread!
THE SCIENCE
U-235 (cyan) is fissile — it splits when hit, releasing 2–3 more neutrons and ~200 MeV of energy.

U-238 (grey) just absorbs the neutron. Higher enrichment = more chain reactions = closer to critical mass.
⚡ Nuclear calculators →
REACTOR CONTROL
SETTINGS
U-235 density 35%
Neutron speed 1.0×
REACTOR STATUS
0ATOMS
0FISSIONS
0NEUTRONS
0MeV
COLDCRITICAL
⚠ CRITICAL MASS
CLICK ATOM Fire neutron U-235 Fissile (cyan) U-238 Fertile (grey) CONTROL RODS Absorb neutrons