Earlier I said that the explosion at #1 plant was probably just a hydrogen explosion. It blew equally in all directions -the characteristic of rapidly expanding gas explosions. If so, there would be little to worry about, insofar as spreading nuclear fallout.
After seeing #3 blow, I can't help but get the sinking feeling in my gut that this second explosion wasn't JUST a hydrogen explosion. The way it shot straight up for a thousand feet or more and then EXPANDED up in the sky would indicate that something was still generating heat while way up there. Hydrogen doesn't do that; it blows and goes out immediately.
I suspect that the nuclear vessel itself ... suffered a steam explosion, (where injected water comes in contact with red-hot nuclear fuel from melted fuel rods inside of the reactor vessel), created an instant ball of steam which then ripped the vessel apart ... shot it up like a cannon ball, broke through the concrete roof of the containment structure, set the hydrogen bubble up there on fire (the big yellow burst of flame we saw) ... and continued to drive it 1000+ feet into the atmosphere ...... with the CORE still generating heat way high up to give the expanding "mushroom" cloud.
My gut instinct is that reactor #3 was totally disintegrated by an internal steam explosion. The stuff we saw falling out of that cloud was huge pieces of (probably containment roof)
Now, the question is -if the blowup was complete- where would the radioactive particles "land"?
Most of them would drop back to the ground within miles of the epicenter but ... a hefty amount would go way up into the atmosphere and then be carried by wind. This is precisely what happened with Chernobyl. Flames drove the particles way up high and then the wind carried that all across Europe. HOWEVER ... the particles didn't fall uniformly all across Europe; they fell wherever it rained ... creating "hot spots" in places as far away as Italy. These hot spots remain hot, even today -25 years later- and will CONTINUE to be hot for a few hundred years!!
Wind is strange. When we experienced a local explosion at an oil refinery in 1999, I watched the sky fires for many hours from near enough (maybe a mile) to feel the heat in my face like standing in front of an opened oven door. I noted the smoke plume go up -to a certain level- then flatten out and go clear across the city. Later, it turned out that tar fallout was heavy in NE Calgary ... 20 miles away! Now, I live only about 3 miles from this former refinery and we didn't have a drop of fallout anywhere in our yard or on our house.
This visual example, where I could SEE the smoke in the wind gives an example of how wind can carry and CONCENTRATE fallout at locations FAR AWAY from the source.
The prevailing winds actually DO GO from Japan to the Pacific northwest of the U.S. That means there -*could*- be some fairly concentrated fallout dropping on the U.S. if rain doesn't take it down over the Pacific ocean.
Now, it's fairly easy to get potassium iodide or iodate pills or kelp ... to protect against radioactive iodine but there is no known protection again plutonium. Reactor #3 used plutonium enrichment.
I guess, apart from loading up on iodine supplement, it's a wait and see situation.
If there HAS BEEN a total blowout of the reactor vessel in #3, we SHOULD be hearing reports of large numbers of people dying from radiation poisoning in a few days. From my understanding, plutonium poisoning kills people very rapidly. Of course, the stupid media might cover it up regardless until it's too late to do anything preventative.