32 died and dozens more suffered radiation burns on the first day following the explosion. Eventually, possibly 5,000 Soviet citizens, and countless others, died of cancers caused by the high levels of radiation.

The accident was initially reported to the world by Sweden and the, later, by the Soviet authorities after their attempt at a cover-up failed.

The accident happened after a poorly designed experiment on the plant's fourth reactor (of four) went wrong.

To undertake the experiment the engineers apparently recklessly disconnected the reactor's emergency safety systems and power-regulating systems.

Despite initial evidence that the reactor was becoming unstable, it is said that they then removed too many of the reactor's control rods.

The eventual explosion was caused when, in an attempt to regain control of the unstable reactor, all 200-some control rods were apparently reinserted. Unfortunately the rods had graphite tips and the result of all those rods being inserted at once caused a chemical (not a nuclear) explosion which blew off a heavy steel and concrete lid at the top of the reactor, releasing 50 tons of radioactive material into the atmosphere.