In the early hours of 26 April 1986 an error during a routine test on Chernobyl's reactor number 4 caused a massive explosion.
It expelled 190t of toxic material into the atmosphere and released 100 times more radiation than the atom bombs dropped on Hiroshima and Nagasaki in World War Two (NCE 8 May 1986).
A second blast then ripped through the south wall exposing the reactor core to the atmosphere.
The next nine months saw construction of a makeshift steel and concrete shell over the reactor.
European Bank for Reconstruction & Development (EBRD) technical manager Ian Heriot describes the shell, or sarcophagus as it known as a house of cards.
High radiation levels dictated that it had to be built without manually created welds or bolted joints using remotely positioned cranes to place steel beams tubes and sheets.
The structure is now at the end of its design life and its lack of joints makes it increasingly vulnerable to the effects of earthquakes and extreme weather.