Nuclear Fission Chain Reaction Simulation

Interactive simulation

The physics behind this simulation

Each fission event releases on average k neutrons that go on to cause further fission (after accounting for neutrons lost to absorption or escape). Starting from N₀ neutrons, the neutron population after g generations is:

When k < 1 (subcritical), each generation produces fewer neutrons than the last, and the reaction dies out. When k = 1 (critical), the neutron population stays constant generation after generation — this is the condition maintained in a controlled nuclear power reactor. When k > 1 (supercritical), the neutron population — and the energy release rate — grows exponentially with each generation, the regime used (in a carefully engineered, extremely fast, uncontrolled form) in nuclear weapons.