1986

Chernobyl

The Chernobyl explosion is one of the most spectacular, apocalyptic engineering failures of all time, made possible by a combination of poor design choices and incorrect operation. It demonstrates how badly things can go wrong when engineers make mistakes.

There were actually three mistakes that worked together to cause the Chernobyl explosion. The first mistake was the way engineers used water in the reactor. They needed water to form steam, because steam is the medium that extracts the heat energy from the reactor so it can become electricity through a steam turbine. The problem is that liquid water absorbs neutrons much better than steam does. So if operators cool down the reactor, its core contains mostly water. If operators then heat up the reactor improperly and water flashes to steam, a power surge can occur. The quick conversion of water to steam causes a quick increase in neutrons—a positive feedback loop.

The second mistake occurred in the design of the control rods. A control rod is supposed to absorb neutrons. Unfortunately, the tips of the Chernobyl control rods were made of graphite. Therefore, as the control rods went into the reactor, the tips displaced water and led to another type of power surge.

And third, the Chernobyl reactor did not have a containment building, so when the explosion occurred there was nothing to contain the contamination.

The accident unfolded in this way: On April 26, 1986, operators improperly cooled down the core. When they started to heat it back up, water flashed to steam, creating a power surge. The control rods were inserted, with the graphite tips creating a catastrophic power surge. Fuel rods burst, jamming the control rods. A steam explosion blew open the core, letting in oxygen and starting a fire that pumped nuclear material into the air. A second explosion, possibly a small nuclear explosion that occurred as enough melting fuel consolidated, compounded the release of nuclear material.

Millions of acres of land received dangerous levels of fallout, and most of Europe received some amount of fallout from the explosion. The design decisions of a small number of engineers and the operating errors of a small number of operators affected millions of people.

SEE ALSO Power Grid (1878), Light Water Reactor (1946), Pebble Bed Nuclear Reactor (1966), CANDU Reactor (1971), Fukushima Disaster (2011).

The Chernobyl disaster was due to human error and issues relating to construction.