Reactor four at Chernobyl, enclosed by its original protective shelter, photographed in 2007.

Chernobyl:

A Nuclear Disaster

April 26, 1986.

Near Pripyat, Ukraine,
then part of the USSR.

Why It Happened

Simplified RBMK reactor cutaway: control rods enter a graphite core containing vertical fuel and cooling channels. Not to scale.

An unsafe test,
reactor design flaws,
and operator mistakes
caused disaster.

USGS Landsat satellite image of Chernobyl on April 29, 1986, three days after the explosion; not a photograph of the initial blast.

First
Moments

Night explosion.

Firefighters arrived, unaware of radiation.