Nuclear reactors do not explode. Yes, they can melt down - that is why American nuclear plants have containments.
As for the rest, you don’t know what you’re talking about. You ought to at least try getting some true knowledge.
The American Nuclear Society has a report on Fukushima at their website.
No doubt about it, this has been a horrifying event. But I’m going to emphasize something here: such catastrophic phenomena cannot be controlled, nor can we ever anticipate what the greatest extent such an incident will be when it does occurr.
We could be hit tomorrow with a large meteor in the northeastern reaches of the Pacific Ocean that would instantly light the clathrate hydrate (frozen methane) in the seabed, setting off volcanism, earthquakes and incredible destruction along the Pacific coast of North America. There is not a dam thing you or I can do to prevent that happening.
And, there is no such thing as a radiation plume.
When I read that last week on SHTF.com, {sigh} I knew it was published just to panic folks.
Here is an analogy that most understand: radioactive material is to a pile of dog shit what radiation is to the shit’s stench.
Atomically unstable elements, such as uranium and plutonium, lose energy by emitting ionizing particles - that is radiation.
Three things block radiation: time, distance, and shielding. Radioactive material has a half-life; the further one is from a radioactive sourse, the less radiation one is exposed to; and, material such as water, concrete and lead effectively shield radiation.
Radiation from the spent fuel at Fukushima is not going to fussily settle in Denver, CO, much less reach that far!
I live in southwest Washington State and weekly consume oysters from Willapa Bay, a shallow Pacific Ocean bay north of the Columbia River estuary. If there was any danger in eating those oysters, I wouldn’t indulge.
Stay safe but most of all, stay calm.
The explosions occurred because the reactors were melting out of the RPV containment. Whenever you see a reactor building explode, you have to assume that the core has escaped containment and that caused the explosion. So the reactor cores exploded via their gas emissions.