It would be the USSR that would have to be sued, but it no longer exists. The Chernobyl power plant sits in the country of Ukraine today, and the Ukrainian government can't be held responsible for the poor actions of a government that no longer exists.
Everyone is well protected. Japan is a more considerate country when it comes to nuclear disasters, except for the last one where huge amounts of contaminated radio active water will be dumped into the Pacific Ocean. I'm following that closely, very, as I live next to that ocean.
But even if I was closer to the Atlantic Ocean I would still be very concerned for humanity.
We live on a great planet, but miserably managed by a poor bunch of inferior managers.
It's terrible as it affects us all.