What has changed at Chernobyl?
In the early hours of 26 April 1986, one of four nuclear reactors at the Chernobyl power station in Ukraine exploded.
Fifty thousand people were forced to move from the nearby town Pripyat, as radioactive material spilled from the plant.
On the 30th anniversary of the disaster, BBC Rewind looks at what was done at the site to stop further damage.