The core wouldnt explode if its turned of, the steam side of the reactor would explode, but the turbines are most likely some distance from the reactor. Let say that the core is split open when still running, then it would explode, sort of! Contaminated fuel rods would be in critical condition and still working after the explosion. The airborne contamination would normally be severe. There are some different types of reactors in use in the world and some are better built than others. With a quick enough warning, the engineers would cut the reactor of. Almost all (if not all) reactors have a safety measure that can shut down the reactor in seconds.
Regarding nuclear pollutants, as I see it there are three things to consider:
Inert Gas Isotopes. Gases that
would most likely disperse
immediately; and mixed
particles like:
| Contaminated Dust spread by
the wind, mixed particles:
| Place of the Meltdown (split
core), half life in the thousands
of years. It would probably
spread and contaminate the
locale soil hundreds of miles
wide:
|
Offered by Geson.