{"id":1811,"date":"2026-08-29T04:58:02","date_gmt":"2026-08-29T04:58:02","guid":{"rendered":"https:\/\/physicsfundamentalsinfo.com\/blog\/?p=1811"},"modified":"2026-08-29T21:49:16","modified_gmt":"2026-08-29T21:49:16","slug":"how-nuclear-reactor-works","status":"publish","type":"post","link":"https:\/\/physicsfundamentalsinfo.com\/blog\/nuclear-physics\/how-nuclear-reactor-works\/","title":{"rendered":"How a Nuclear Reactor Works"},"content":{"rendered":"\n
Definition<\/div>

\n\nA nuclear reactor is a machine that splits uranium nuclei in a controlled chain reaction, converting a tiny fraction of their mass into heat. That heat boils water into steam, which spins a turbine and generator to make electricity. Each fission releases about 200 MeV, following Einstein’s mass-energy relation, energy equals mass times the speed of light squared.\n\n<\/p><\/div>\n\n

Somewhere under a slab of concrete a metre thick, a few kilograms of uranium are quietly getting smaller. Not by burning. Nothing in a reactor burns. Atoms are coming apart, and a sliver of what they used to weigh is leaving as heat.<\/p>\n\n

The strange part is how ordinary the rest of it is. Past the reactor vessel, a nuclear power station is a steam engine \u2014 the same basic machine James Watt would recognise, boiling water to push a turbine round. All the exotic physics happens in one room, and its only job is to keep a kettle hot.<\/p>\n\n

What Is a Nuclear Reactor?<\/h2>\n\n

A nuclear reactor is a vessel designed to start, sustain and above all control<\/em> a fission chain reaction, so that the energy locked in atomic nuclei comes out as usable heat rather than all at once.<\/p>\n\n

Picture a room full of dominoes standing on end. Knock one over and it topples two more; those topple four. That is a chain reaction, and left alone it finishes in seconds.<\/p>\n\n

A reactor does something cleverer. It removes just enough dominoes that each falling tile topples exactly one<\/strong> other \u2014 forever. The cascade never dies and never accelerates. That single condition is the whole art of reactor engineering.<\/p>\n\n

The fuel is uranium, and only one isotope really matters. Natural uranium is 99.3% uranium-238 and just 0.72% uranium-235, and it is the rare U-235 that splits readily when a slow neutron nudges it. Reactor fuel is therefore enriched, typically to between 3% and 5% U-235.<\/p>\n\n

Why so little? Because 3% is enough to keep a chain reaction going in a big, carefully arranged, water-filled core \u2014 and nowhere near enough to do anything else. We will come back to that.<\/p>\n\n

The Nuclear Reactor Formula: E = mc\u00b2 and 200 MeV Per Split<\/h2>\n\n

The formula behind every nuclear reactor is Einstein’s mass-energy equivalence, which says the energy released equals the mass that disappears multiplied by the speed of light squared.<\/p>\n\n

E = mc\u00b2<\/div>\n\n