What actually went wrong at Three Mile Island, Chernobyl and Fukushima?

Each failed in a different way. Three Mile Island (1979) was a failure of the human-machine interface: after a valve stuck open, operators misread the data and manually shut off the emergency cooling pumps — yet four feet of reinforced concrete containment held and no one died. Chernobyl (1986) was a design failure: the RBMK had a positive void coefficient and no containment dome. Fukushima (2011) was a failure of imagination: a 14-metre tsunami over a 5.7-metre seawall.

Act one, Three Mile Island, Pennsylvania, 1979. A stuck pressure-relief valve caused a loss of coolant, but the real disaster happened in the control room. Overwhelmed by a Christmas-tree wall of flashing alarms, operators misread their instruments and manually shut down the emergency cooling pumps, wrongly convinced the reactor had too much water. By the time the error was recognised, the core had begun to melt. The massive concrete containment held and prevented any major radiation release: the accident killed no one. The psychological damage was absolute — TMI ended the US nuclear industry for thirty years, and no plant newly ordered after 1979 was completed in those decades.

Seven years later Chernobyl exposed the dark side of cost-cut design. The RBMK reactor had no containment dome and a positive void coefficient, so the reaction sped up as water boiled off. During a badly managed safety test, power surged out of control; a steam explosion blew off the 1,000-tonne building lid, and a graphite fire that burned for ten days ejected 400 times the radioactive material of the Hiroshima bomb. The Soviet Union mobilised more than 600,000 'liquidators' to work in the highly radioactive ruins and raise a concrete-and-steel sarcophagus. The New Safe Confinement completed in 2016 — the largest movable land-based structure ever built, costing over USD 2 billion with a 100-year design life — merely buys time for robots to begin the real dismantling. Nuclear accidents create a transgenerational debt.

Act three, Fukushima Daiichi, 2011. This was neither a design flaw nor operator error but a failure of imagination. The tsunami triggered by a magnitude 9.0 earthquake overtopped the plant's 5.7-metre seawall; a 14-metre wave flooded the basements housing the emergency diesel generators and cut all power. With no electricity for the cooling pumps, three reactors suffered full core meltdowns within days. A zirconium-water reaction generated hydrogen, and the resulting explosions blew the roofs off the reactor buildings, releasing radioactivity into the atmosphere and the Pacific. Fukushima's other legacy is the stress test it forced on every nuclear nation on earth.

Before the trilogy there was the 1957 Windscale fire in Britain, where burning radioactive graphite spread isotopes over the UK and northern Europe for three days; the authorities then renamed the site Sellafield to sever the association and downplayed health effects for years. Set against the statistics, nuclear causes about 0.03 deaths per TWh including Chernobyl and Fukushima, against 24.6 for coal and 18.4 for oil. That is nuclear's risk paradox: statistically among the safest ways to generate electricity, yet its failures are rare, locally devastating tail events. For a city-state such as Singapore the lesson is unambiguous — when there is no land to evacuate to, the 0.1% failure case is unacceptable.

A cover-up can damage public trust as much as the accident itself — the lesson the Soviet Union failed to learn at Chernobyl and TEPCO failed to learn at Fukushima.

This question is covered in depth in The Full Spectrum Every Energy Source Explained — A Singapore Perspective，第六章 6.14