Radioactive contamination. Radiation symbol and sign warning that the area has been contaminated with radioactive fallout from the Tomsk-7 nuclear plant in Siberia, Russia. The plant reprocesses spent uranium fuel to obtain plutonium for military uses. On 6 April 1993 a tank filled with a solution of uranium and plutonium exploded, contaminating about 200 square kilometres of forest with radioactivity. Radioactive chemicals can remain dangerous for tens of thousands of years. Radiation from them can cause tissue death, cancers and genetic alterations which are passed on to offspring.