reactivity

Nuclear reactors operate on the principle of nuclear fission, where a heavy atomic nucleus splits into smaller fragments, releasing neutrons, subatomic particles, and photons. These neutrons can trigger further fissions, creating a self-sustaining chain reaction. This process releases a significant amount of energy, forming the basis of nuclear power. Unlike atomic bombs, nuclear reactors are designed to maintain this chain reaction at a controlled, constant level to prevent explosions.12

Reactivity is a key parameter in reactor control, indicating whether the reactor is supercritical (positive reactivity), critical (zero reactivity), or subcritical (negative reactivity). Control is achieved by managing neutron absorbers, altering neutron leakage, or adjusting fuel levels. Safety rods, regulating rods, and shim rods are used to manage reactivity for startup, power adjustment, and compensation for fuel depletion, respectively. Delayed neutrons, though less than 1% of all neutrons, are crucial for monitoring and safely controlling reactor operations.13