Overview: When the Chernobyl nuclear power plant exploded 33 years ago in Soviet Ukraine, it was the largest ever accidental release of radioactivity into the environment. The cause, and who was to blame, is still being debated. But what's become of the people who refused to leave the exclusion zone, and the wildlife left behind? Just how contaminated is the area now? The BBC's Science correspondent, Victoria Gill, has been given rare permission to go inside the zone - and the plant itself.