Short answer: Because things at Fukushima are currently AFU, and people's idiot fears lead them to worry that it is actually SNAFU. The news media aren't helping; I thought the BBC were being a bit sensationalist (actually in light of the most recent events, maybe not), but then I caught some CNN reports ... where they were having a nice debate about ALL THE HORRIBLE THINGS THAT CAN COME OUT AND THE MANY WAYS IN WHICH THEY CAN KILL YOU.
Ngh.
This is NOT a Chernobyl type situation - at least, not yet (give it time - but, even so, that happened without warning, and with DEEP hush-hush). It's highly unlikely that the reactor is going to explode and throw bits of enriched uranium into the troposphere to spread over a whole continent. The problem is one of reducing everything that's coming out of there to that single, handy, scare-em-all phrase "radioactive material". Shit, I've got a device on my ceiling with "radioactive material" in it. It sounds a shrill alarm and stops me dying if a fire starts overnight. Am I concerned that it's going to kill me dead from radiation poisoning and/or cancer? Not really.
I've worked as a technologist for a hospital nuclear medicine service, learned the theory, procedures etc behind safely treating radioactive material at close quarters (be respectful, be swift, keep it shielded and locked away as much as possible, but don't fear it) and been quite comfortable with it, and seen the kind of work that goes into engineering plants to be safe and making sure they stay so... and usually I'd brush this stuff off as being sheer paranoia. Unless you're poledancing with a fuel rod, it's not half as bad as you think. The safe dose limits are pretty damn low, and have been successively lowered over the years as we've learned to handle things more effectively AND do more with less.
But really, looking at the situation there, I'm still getting concerned. As someone on QDB said, paraphrasing Ghostbusters "Imagine a twinkie represents the normal amount of Murphy's Law activity at a normal nuclear plant. Fukushima's twinkie would currently be 35ft long, and weigh about 600lbs". Despite the many-decades-old (in fact, not very far away from decomissioning*) plant itself pulling through JAPAN'S WORST EARTHQUAKE IN LIVING MEMORY admirably well, despite the multiple redundant systems and good adherance to (possibly questionable) procedures, there seem to be a few things that have been overlooked because they've never been encountered before (e.g. what if an earthquake is then followed by a tsunami, which knocks out the generators and local grid?) and some other events coming out of the blue with little explanation.
Every last thing is going wrong for them, and it could lead to an "accidental" release on the level of Windscale/Sellafield (we Brits know a thing or two about this sort of incident - we caused a few, back in the days where it was hushed up more effectively) or 3 Mile Island. The very greatest risk is to those in the immediate vicinity though, like within a kilometre or two. 20-30km? Probably fine. The recovery workers will have to be on strict rotations to avoid getting doses that may, possibly, have just-about-statistically-significant long term health effects. Etc.
What I'm puzzled by is the speed and narrow range of the response. By this point I'd have expected all the still-safe, still-operating plants round the country to be on skeleton crew, and a much larger emergency fight going on, with multiple fronts. Get mobile generators in to try and activate the main water pumps, if they're still operable, even just a bit (by now, the heat production should be less than 0.5% of normal... which is still a hell of a lot, but it means if you can get 1% of normal circulation you can have effective cooling). Find some way of dumping a crapload of boric acid and other neutron poisons into the reactor and storage pond water. Investigate ways of extracting and seperating the rods (at least in the pond) so they avoid further accelerated heat production and possible criticality (which will be VERY hard to recover from without a Chernobyl-style concrete sarcophagus ... balance of risk is on the side of doing it ASAP). Get some those forest fire water tanker planes flown over from California (greater water capacity and faster turn-around time, much less pilot risk). Etcetera.
And where, for the love of all that's holy, are the freakin' robots? I know they don't actually have Gundams and animated love dolls, but are there no ROVs available to do SOME of the hot work with and get things moving quicker?
A thing to keep in mind here though, as previously mentioned, is this is a very old reactor. Presumably pre-Chernobyl. They're unlikely to repair and start it up again after all this, because there wasn't much of it's service life left anyway. It's held up remarkably well to extreme, pretty much unpredictable stress, and so far - almost a week later - there's been no serious leak of material. Some radioactive byproducts, sure, and the dose rate on the ground is pretty damn high, but that might as well be from unshielded rods as from contamination. We have somewhat safer designs these days. My particular favourite in all of it would be the "pebble bed" and similar, where it's pretty much impossible to get a meltdown because of the use of uranium-alloy toruses not rods, and even if you did, the fuel is in such small chunks it wouldn't do much, and effectively has built-in control rods (I think you actively have to put neutron accelerators near it - may water itself? - to get useful power production)**. It's apparently not as efficient, so it's been largely shunned til now. But it is a lot safer. I'm not up on the fine details, but I kind of get the impression that if the shinola hits the ventilator, you could just dump the whole lot into some kind of quenching media instead of having to deal with the whole control rod + cooling water business.
* Yeah, it was only two days from retirement when it was shot or whatever.
** Man I really shoulda gone back and re-researched this instead of relying on 2-3 year old memories of doing so... but, time...
