In my "other life" I am in radiation protection - and first off - the info from NEI that Cleo posted is a good overview of what is really going on without the sensationalist journalism that unfortunately the media has been dipping in lately.(again???)
The dose rates that they list being double normal site levels are probably in the reactor building/containment and although a little higher than normal, not something that would have an effect on the outside world.(It just affects how you do your recovery inside the plant as you have to take extra protective measures)
The precautionary distrubution of Potassium Iodide is very conservative in my opinion, as there has been very little released during the hydrogen explosions - and is more than likely just a political move to calm fears. And for you hunters out there if you like your venison - you eat more cesium in your meat than anyone came close to inhaling at Three Mile Island
One statement in an earlier post kinda rubbed me the wrong way, as while there are a few plants in the US of the same design, they all have been changed since they were built because of the accident at TMI ages ago....the hydrogen buildup that occurred in Japan would not have happened in the US...all of the plants installed hydrogen recombiners that basically turn the excess hydrogen back into water vapor...as this was the same issue that TMI had when they had their explosion.
The US plants also revamped their core cooling systems to not require any type of power to inject water and "poison"(boron) that would keep the reactor covered and shut down till it was in cold shutdown (about 36 hours).
Cleo - in your picture you are correct - it is not a "dome" but the common term for the concrete layers just above and around the yellow colored spere in the center is called a dome since on other designs it is dome shaped. The rust red colored cylinder in the center is the reactor vessel which encloses the fuel and is where the water is boiled. The yellow cover above that is called the "drywell" head. That section is immersed in a pool of water which is the likely source of the creation of the hydrogen in these Japanese plants. When water gets irradiated it separates into hydrogen and oxygen. The hydrogen forms pockets after it vents into the atmosphere of the upper building where they show a crane (orange and yellow at the top in your picture) Anything that can cause a spark (theres lots of electrical panels in there) will light off the hydrogen and blow the roof and walls off that building - which is what you are seeing in all of the explosion pics and vids you see on the net.
The reactor vessel in the center (again the red cylinder) is more than likely still intact on these plants containing the fuel even if there were damage to the fuel. Even at TMI the fuel was in the bottom of that vessel - and while the news loves the term "meltdown" - the damaged fuel just piles up at the bottom of that vessel and stays there - hopefully one of these days we can educate the media to let them know that the fuel isnt going to go anywhere else like it does in the movies.
For those of you wondering about radiation dose if you have any questions Ill check in here and will be glad to answer anything - however I may disappoint if you are looking for sensationalism as even at TMI - the dose to the press corps who wanted to stay right at the fence to film what was going on was 1/10th of what they would have gotten getting one side of a dental xray. They got more radiation dose flying to the site in a plane from cosmic rays than they did sitting outside the plant for weeks on end misinforming the public