If you mean when will Chernobyl be completly save - the half-life of Plutonium 239 is 24,000 years. Perhaps we should just say, "not in our lifetimes."
Nuclear EnergyValery Legasov in Chernobyl, Episode 3Comment
The accident is well under control.
Mistakes, Nuclear EnergyViktor Bryukhanov in Chernobyl, Episode 1Comment