Which process is commonly used to release energy by splitting heavy atoms in reactors?

• A. Fusion
• B. Fission
• C. Photoelectric effect
• D. Neutron capture

Answer: (B)

Energy released in nuclear reactors comes from fission of heavy nuclei. When a heavy nucleus such as uranium-235 absorbs a neutron, it becomes unstable and splits into two lighter nuclei plus several neutrons. The fission fragments and the released neutrons carry away kinetic energy, which manifests as heat in the reactor coolant to drive steam generation. The energy comes from the increase in binding energy per nucleon when heavy nuclei split into mid‑mass nuclei, effectively converting a small amount of mass into energy (via E=mc²). Fusion would release energy by joining light nuclei, not splitting heavy ones, so it’s a different process. The photoelectric effect involves ejecting electrons from atoms with light, not releasing nuclear energy. Neutron capture is the absorption of a neutron to form a heavier isotope and is not the primary energy source in reactors.