"From a bit of reading I've the impression that a lot of the harmful isotopes released by accidents like Fukushima and Chernobyl shorter lived than we've been told, though I can't find easy facts about the spread of the longer lived actinides. Cesium 137 is the principle radioactive source in Chernobyl's exclusion zone, which has a half life of 30 years (?). Still harmful but less so for future generations. Different story for epicenter of meltdown containing melted rods.
Compare the risks of nuclear power to coal and the latter probably causes far more cancer and death. The standard American diet is far more destructive to human health and the environment than nuclear power."
As far as I know from the studies I heard of , nobody has died from Fukushima although it is a given the same can not be said of Chernobyl where it is know that at least 100 to about 110 of the operators at the plant as well firefighters that came to the reactor died from various causes. From what I know most of the deaths where not from radiation poisoning itself but from things like being in area that release the steam/water hammer after the reactor went super critical, falls, dying while fight the fire, being vaporized, etc.
There are not any real good numbers for this but one of the rules of thumb I have heard of from some of the people in the nuclear industry is that "IF" for some reason you happen to be in the right place at the wrong time (or perhaps the wrong place at the right time, or wrong place at the wrong time), and you get expose to a lethal dose of radiation then there is still a **BETTER than **50%** you will die from other stuff before the radiation can do anything to you. Of course this may merely a means to suggest that there are many,many, many other things that can kill you in day to day life and/or can kill you if you happen to work in any hard core industry where you are working with any potential dangerous machinery/ technology. And of course it may be that some people are a little cavilier of the dangers of radiation when dealing with all their other issues they deal with at the plant as well.
For the dangers to the public, I'm unaware of any study about Fukushima other than it is believed in some places in Japan the average background radiation has nearly increase to twice to what it was before. This sounds kind of scary (and I'm sure it isn't something that some people in Japan are really happy about either) but to get an idea of what this means, it is useful to note that the average America received around TWICE the amount of background radiation (partly from geography, radiation left over military nuclear bomb testing, and people getting x-rays) and this amount is still considered safe or safe-ish at least.
The numbers are kind of fuzzy to me now, but I think the number is around 2 to 3 rads per year the average american is exposed to from background and other sources. Getting 2 to 3 rads at once or over a couple days (which is a just little more than what you might get while they are checking for or treating cancer), isn't great but it isn't really life treating either. I think when some members of the population gets hit with 10 rad in a few hours or days they can have issues, and there might be some statistical studies suggest there is an increase health risk at this point. I don't even know if it is correct or proper to say there is an increase at this point other than to say it is obviously more dangerous than getting just 2 rad from something like chemo and/or it is something that no organization in western would expect to or even allow it's employees/soldiers be exposed to other than perhaps during a war/combat operations or some kind of an emergency. At 20 rad I believe there is evidence or studies to show that around this point a large percentage of population will develop
some.of the first symptoms of radiation sickness which includes nausea, dizziness, confusion, etc. Such symptoms might sound scary if one know it is coming being exposed to radiation but it might help to realize that such symptoms are common with many, many other health issues (such as getting the flu or other illnesses) and can partly be thought of the bodies way of reacting to discovering everything is not right with it. As a person living with acute chronic pain (from a herniated disk in my neck that I got 'fixed' a couple years ago), I've gotten use to the idea of having to wake up and deal with pain, nausea, etc. and still sort of go about what is left of my day to day life; although saying this I'm not trying to make light of those who have such symptoms for other reasons. I'm merely trying to make a remark on how little it can mean to doctors and/or others when someone has such symptoms and there is no association with them to radiation.
Anyways around 50 rads things become a bit more life threatening. It might helpful to note that at Chernobyl the military conscripts and civilian "liquidators" (ie civilians forced to help in the clean up efforts although this term was often used in reference to the conscripts as well) were sent home if it was know they where in an area where they got a dose above around 35 rad, although it is a given that some of them got higher dosages than that from being in areas that had higher radiation than it was thought to have. At 35 rad (and even to a degree with 50 rads as well) it is plausible that someone could have a good possibility of more or less still leading a happy and health life with only some health issues, but also think it is also a given there is a possibility of them not having such a long and happy life due to exposure.
I'm unaware of any statistical studies that says what that dangers are or what happens at 35 rads or 50 rads, other than a very high probability of them showing signs of radiation sickness, but I think it is a given there would be an increase risk of cancer, organ failure, and other potential problems. It might be also worth while to note of the liquidators/conscripts who did clean up the reactor and where often exposed to high levels of radiation, there is no statistical information to suggest that they have or had any more health issues than the rest of the population. I don't know know if the number of liquidators exposed to 20-50 rads was so few, too many of them died from the immediate effects of radiation sickness (ie. which would exclude them from any study done to determining long term effects), or if the powers that be in the Soviet Union deliberately whitewashed the numbers to protect their backside, but the fact remains there is little to no statistical information done while studying the effects of Chernobyl to suggest for people exposed to less than 100 rad (ie. which would likely kill them) that they had any statistically increased probably of developing one health issue or another. This doesn't mean there wasn't any increased risk, it only means the studies done can not say one way or another what the risks and other issues really are. At around 80 to 100 rad, people develop a severe case of acute radiation sickness including immediate or eventual various kinds of necrosis and at this level most people will not survive the experience. I believe this was about the level that several of the Chernobyl operators and firefighters where exposed to (since the firefights where known to either 'blackout' or become disoriented as they were trying to fight the fire) before anyone could come and get them out of the area before they became overexposed. I believe from what I have read at really, really high levels, (500 rads or more) people don't just eventually develop ARS, headaches, etc. but it can simply knock a person outright.
I believe the theory as to why this happens is radiation exposure can temporarily slightly screws up brain and nervous system functions and at really high levels instead of just disorientation, the entire system gets overwhelmed and has to shut off much like it does when it receives other shocks.
I was trying to give you some idea of the risks of what happens to people when they get exposed to various levels of radiation (so you might be less scared of it) but I guess I got a little carried away.
:D
Also I should note this information *ONLY* pertains to happens when a person is exposed to a quick one time dose and there is little to no information as to what happens if exposure is staggered over a time period much longer than a few days. Dosages are calculated as accumulated and in the nuclear industry they are summed together over the year one works. Like any toxin or drug, radiation is less dangerous if it comes in several smaller dosages than all at once. Think of it like what would happen to your average teenager was exposed to the caffeine (which is actually a neurotoxin in higher dosages) in the sodas they drink in a year, which I'm pretty sure wouldn't be good. The highest known recorded radiation dose ever adsorb and some still survived (ie they didn't die from radiation sickness) was a lifetime dose of 5,000 rad which is obviously 50 times the dose which usually kills someone. Part of the reason they survived was the dosage was a little bit every hour of their life (after they got injected with radioactive plutonium) instead of any particularly high dose at any one time. While the idea of having plutonium injected into you may not be a good thing, it is sort of less helpful to think that if something like that did happen one might be able to survive it if the amount isn't too much. Then again I don't think such a substance is as easily available. as the time that this happened.
I'll have to stop for now but I hope to respond to your other questions when I get a chance.....