I used to work as an emergency planner for my state office of emergency management. Part of my responsibility involved developing response plans for and test exercises for both a nuclear power plant and a defense installation that processed radioactive material.
My first comment would be lets not get carried away, with speculation. Second
DO NOT TRUST THE MEDIA to give you accurate and useful information on this event. They have a 50 year history of being technologically incompetent with things like radiological emergencies, and the vast majority of what you see in the news will be half truths, misinterpreted facts, and just plain stupid. Almost everything the media said about 3 mile island was wrong or exaggerated (of course the fact that the local government officials were idiots did not help).
The Chernobyl accident did turn out to be a major problem to the emergency responders, but that was due to an un-contained design (no pressure vessel), an inherently unstable design that was prone to run away at low power levels (a design that would never have been approved in any other industrial country), and intentional efforts by the operational staff to by-pass and turn off safety devices. There is still conflicting information regarding Chernobyl and if there are any statistically significant long term impacts to the exposed populations.
The Japanese designs should be a far cry from both those earlier reactor designs.
Second, just because the media says "radiation is leaking" does not mean it is bad. Radiation can be detected at extraordinarily low levels. For example following the Three Mile Island incident they collected tongues from white tail deer from an area within 50 mi of the plant. They did test to have higher levels of CS137 than deer in nearby counties but those levels were still less than seen in deer in other parts of the country when we were actively testing nuclear weapons.
"The average radiation dose to people living within ten miles of the TMI plant was eight millirem, and no more than 100 millirem to any single individual. Eight millirem is about equal to a chest X-ray, and 100 millirem is about a third of the average background level of radiation received by US residents in a year. These are radiation exposures we all receive on a routine basis. My average daily radiation exposure just due to living in Colorado is about 2 mr/day, so the total average exposure received within 50 miles of the TMI plant was roughly equivalent to visiting Denver Colorado for 4 days.
http://www.ornl.gov/sci/env_rpt/aser95/tb-a-2.pdfhttp://users.rcn.com/jkimball.ma.ultranet/BiologyPages/R/Radiation.htmlAssessing radiation exposure after a release is very complex and the media are no where near qualified to condense that information into a sound bite for the 5:00 news.
Iodine 131 is the isotope that will probably be of the most concern, and it has a half life (time it takes for 1/2 of it to decay and cease to be radioactive) of just a tad over 8 days. It emits a soft gamma ray and a beta particle. Beta particles are stopped by a thin layer of any material. It will not penetrate a thin sheet of aluminum and only penetrates the skin about 1-2 mm. It is not a significant external radiation hazard, but is an inhalation risk. Its absorption can be blocked by natural iodine or potassium iodide pills to flood the body with non-radioactive iodine so it is not absorbed. Any radiological release in Japan from this will not make it across the Pacific ocean in any significant dose even if an absolutely catastrophic release were to happen.
Bottom line the media's representation of the risk is probably 100 - 1,000,000 times higher than reality. Radiological consequences of medical significance are only likely in the very nearby area.
We simply do not have enough information to determine what the facts are yet. They are trying to shut the reactor down, now and even the on scene experts will have no clue what the damages are for days or weeks.
Given Japan's experience with large scale radiation effects you can be certain that they are being extremely cautious in their evacuation actions.
I personally would not worry at all about the radiological consequences from these incidence for any one outside of the immediate area of the plant. You would likely get more radiation exposure on the airplane flight over to Japan than the local residents will receive outside the local plant area.
By the way just to show how we routinely accept radiation exposure on a daily basis -- did you guys know that bananas are radioactive? Bananas are high in potassium which has a naturally occurring radioactive isotope. You are surrounded by and eat radioactive material all the time. It is a natural part of our world and there is some evidence that low levels of radiation actually stimulate the immune system for damaged tissue repair in the body.
http://chemistry.about.com/b/2010/03/08/bananas-are-radioactive-2.htmLarry
