Uploaded August 2026 | Updated September 2026, 2 weeks ago
A nuclear reactor produces energy through a self-sustaining fission chain reaction, but that reaction cannot simply be allowed to grow without limit. The reactor must maintain a carefully controlled population of neutrons.
Each fission event can release additional neutrons, which may strike nearby fuel nuclei and trigger more fissions. The number of neutrons that continue the process determines whether reactor power rises, falls, or remains steady.
Control rods provide one of the main ways to regulate that balance. They contain materials that readily absorb neutrons. Pushing the rods farther into the reactor core removes more neutrons from the chain reaction and reduces power. Withdrawing them leaves more neutrons available to cause fission, allowing power to increase.
This is why the word “critical” has a special meaning in reactor physics. A critical reactor is not necessarily in danger. It means that each generation of fission events produces enough neutrons to sustain the next generation at a steady rate.
Nuclear power depends on an enormous amount of energy being released through microscopic events, while carefully engineered systems keep those events happening at a controlled pace.
A nuclear reactor produces energy through a self-sustaining fission chain reaction, but that reaction cannot simply be allowed to grow without limit. The reactor must maintain a carefully controlled population of neutrons.
Each fission event can release additional neutrons, which may strike nearby fuel nuclei and trigger more fissions. The number of neutrons that continue the process determines whether reactor power rises, falls, or remains steady.
Control rods provide one of the main ways to regulate that balance. They contain materials that readily absorb neutrons. Pushing the rods farther into the reactor core removes more neutrons from the chain reaction and reduces power. Withdrawing them leaves more neutrons available to cause fission, allowing power to increase.
This is why the word “critical” has a special meaning in reactor physics. A critical reactor is not necessarily in danger. It means that each generation of fission events produces enough neutrons to sustain the next generation at a steady rate.
Nuclear power depends on an enormous amount of energy being released through microscopic events, while carefully engineered systems keep those events happening at a controlled pace.
