How does nuclear fission produce energy?

Nuclear fission produces energy by splitting heavy atomic nuclei into smaller fragments, converting a small amount of mass into kinetic energy and radiation. When a fissile nucleus such as uranium-235 absorbs a neutron and becomes unstable, it deforms and divides into two lighter nuclei plus additional neutrons. The daughter nuclei have higher binding energy per nucleon than the original heavy nucleus; the difference in binding energy appears as released energy according to Albert Einstein’s mass-energy equivalence E equals m c squared. That energy initially appears as kinetic energy of the fragments, prompt neutrons, and gamma radiation, and is later transferred to surrounding material as heat.

How fission releases usable heat
The kinetic energy of fission fragments is deposited in fuel and cladding as heat within millionths of a second. The emitted neutrons can induce further fissions, producing a chain reaction when conditions support more than one neutron causing another fission on average. Reactor design controls the chain reaction using neutron moderators and control rods so that a steady power-producing state, called criticality, is maintained. John R. Lamarsh at the University of Michigan explains these reactor physics principles, including the role of moderators in slowing neutrons to energies that increase the fission probability for common reactor fuels.

From heat to electricity and practical relevance
In power reactors the heat produced by fission boils water or drives gas or liquid metal heat-transfer systems to produce steam, which turns turbines coupled to electrical generators. The International Atomic Energy Agency collects operational data and guidance showing how reactor systems convert nuclear heat into grid electricity and how safety systems manage heat removal. This conversion process is why nuclear fission has been harnessed for baseload power in many countries: it yields a high energy density fuel source and continuous output independent of weather.

Causes, risks, and consequences
The causes of hazardous outcomes are rooted in the same physics that make fission useful. Uncontrolled chain reactions, loss of cooling, or structural failures can lead to fuel overheating and release of radioactive materials. The International Atomic Energy Agency sets safety standards and documents lessons learned from accidents to reduce these risks. Long-term consequences include management of radioactive waste, which remains hazardous for varying timespans depending on isotope and requires engineered storage and institutional oversight. At the same time, the Intergovernmental Panel on Climate Change notes that nuclear power's lifecycle greenhouse gas emissions are low compared with fossil fuels, a factor influencing energy policy choices amid climate concerns.

Human, cultural, and territorial nuances
Decisions about where to mine uranium, site reactors, or store waste intersect with local communities and territories. Historic uranium mining has affected indigenous lands in some regions, raising environmental justice and health concerns that require remediation and community engagement. Public acceptance of nuclear technology varies widely across cultures and nations, shaping national energy strategies and international collaboration on safeguards, nonproliferation, and safety.