France, April 26 -- The failed safety test at Chernobyl caused a massive power surge, leading to two explosions which severely damaged the reactor's core, releasing radioactive nuclides into the atmosphere and causing widespread contamination of the surrounding land - and long-term harm to human health, the effects of which are still being felt today.

The disaster was unprecedented, leaving a declining Soviet regime to deal with what remains the worst nuclear disaster in history.

Hundreds of thousands of responders were mobilised - engineers, firefighters, medical personnel, soldiers and police officers, as well as plant workers - from the very first hours following the explosion, and throughout the years that followed.

Among the early...