20,000 years is way off. Here's a report by the IAEA (International Atomic Energy Agency) [1]. The main radio-isotopes after the Chernobyl disaster were (see p.

20,000 years is way off. Here's a report by the IAEA (International Atomic Energy Agency) [1]. The main radio-isotopes after the Chernobyl disaster were (see p. 2): "The total release of radioactive substances was about 14 EBq1 (as of 26 April 1986), which included 1.8 EBq of 131I, 0.085 EBq of 137Cs and other caesium radioisotopes, 0.01EBq of 90Sr and 0.003 EBq of plutonium radioisotopes. The noble gases contributed about 50% of the total release of radioactivity." Iodine-131 has a half-life of only 8 days, and it cleared up long ago. The only going concern is Caesium-137, which has a half-life of 30 years, and needs 300 years to go to 1/1000 of the initial levels and 600 years to all but disappear. The other radioisotopes were contained to the location of the reactor. The only one that will be there for millenia is a decay product of Pu-241, namely Am-241 with a half-life of 430 years. However, as stated before, that is localized to the nuclear reactor itself. It will reach a maximum about 100 years after the event (so about 70 years from now). [1] http://www-pub.iaea.org/MTCD/publications/PDF/Pub1239_web.pdf http://www-pub.iaea.org/MTCD/publications/PDF/Pub1239_web.pd...