The specificity of contamination of permafrost-affected soils with radionuclides derived from an accidental underground nuclear explosion at the Kraton-3 polygon located in the northern taiga subzone has been studied in northwestern Yakutia. It is shown that the high density of the radioactive contamination is preserved in the soils 23 years after the nuclear accident. The concentrations of 137Cs and 90Sr vary from 34 to 1025 and from 57 to 781 kBq/m2, respectively, which is 30–1000 times higher than the global fallout of these radionuclides.