The Soviet Government Lied To The World
One thing that is hard to do is hiding the fact that a giant cloud of radiation is blowing from Ukraine to countries all over Europe. Governments outside of the Soviet Union began trying to find out what had happened, but the secrecy that surrounded the Soviet government prevented them from telling what had happened and possibly getting outside help for dealing with the disaster.
In fact, the day after Chernobyl was evacuated, on May 6, the Soviet government announced that the problem had been entirely contained and that there was no longer any threat. However, the danger is still there, over three decades later. The land is still uninhabitable because of the high levels of radiation that are still present.