I really don't like the fist answer, the second answer is better. In my opinion the main problem with Chernobyl is that the nuclear plant had a lot of radioactive material and the graphite rods burned and spread a lot of the fuel. The nuclear material in the Hiroshima bomb was much smaller. It only considers this in an "edit".<p><i>>Edit: As pointed out, one thing I forgot to mention is that the amount of fissionable material in an atomic bomb is usually considerably less than the amount housed in a nuclear reactor. Obviously, having more fissionable material drastically increases the amount of radiation that can be output.</i><p>And I'm not sure that the other facts are correct, for example:<p><i>> A fission explosion at ground level creates more radioactive isotopes due to neutron activation in soil. Furthermore,</i><p>I think that the amount of radioactive isotopes created by the neutrons is very small, and this effect is negligible in the Chernobyl case. Anyone has some data sources about this?