Going back to the issue of news reports, I know it's unwieldy, but even interviewed experts are failing to distinguish between releases of radiation and releases of radionuclides.
There are different issues with each. When it comes to the people working on site, if there's an actual radiation spike you still need to be behind as much concrete (or at as far a distance) as you can manage given your job. The civilian population and all those not needed to be on site are almost certainly going to be safe due to distance. And once the immediate crisis is over, with everything nicely settled (or entombed in concrete[1]) the evacuation and exclusion can be lifted and there are no more problems[2].
The issue of the actual, physical isotopes being spread around is another case. In turn emitting all the different types of actual radiation, in various quantities, proximity alone isn't an issue and you can protect yourself with pretty much any NBC-suitable suit/vehicle/building from direct on-skin and in-lung exposure to dangerous particulates and gasses (although that doesn't help civvies), but the quantities flying around shouldn't be anything like as much of a problem as being within a few tens of metres of a naked nuclear pile, like as from the perspective of those firefighters at Chernobyl. Instead, the problem is the particles getting onto skin, into the lungs and generally stuck on or in the human (and wildlife!) body. Whatever the particles are, and whatever their radiation (even alpha, which famously gets stopped by a good sheet of paper or two) they can then directly and unobstructively give an extended dose of radiation to the cells they are adhered to, or near, as increasing numbers of them do what comes natural and decay to various other isotopes which may or may not have chance to further decay, before becoming stable. And that's not even including the chemical effects of the heavy metal and other elements (and compounds thereof) that this dust or gas is at various stages of its decay cycle.
The fact that the current effort appears to be concentrating on keeping things cool means that they are most likely working towards minimising the potential for radionuclide emission, although they will of course be displacing some in their steam-generating process. Also that they're still working towards cooling. There's nothing known (other than directing more radiation at a sample, to change the nucleus's internal configuration) that will speed up or slow down radiation emission and decay. Which is why various isotope dating techniques are (for suitable samples of historic materials) very good, and which is why we know that nuclear waste products are going to have to be stored for so-many hundred or thousand years.
Excessive heating the materials will not cause (on its own) increased radiation emission, although material disbursement due to the burning of the material (and/or its otherwise mundane casing) or in a particularly badly-designed container the pooling of melted fuel into a larger unit would be a problem.
The most recent bugbear report I've been hearing is today is "If the ponds dry out, the spent fuel rods will emit more radiation". The real problem is most likely about their burning and releasing isotope-laden oxides into the air, not directly irradiating the surroundings more. Direct radiation exposure, given some very basic assumptions about the way that storage is laid out, wouldn't be much of an issue to the surrounds anyway, as long as current or future workers weren't in the habit of peeking over the top of the pond walls. (Arguably that wouldn't be something you could say about the pilots of the water-dumping pilots, but I suspect they've been given heights to work from where the situation on/in the ground is within limits that are prepared to be risked exposure to. This might mean they're not as efficient at delivering their cooling water, of course.)
I think that as long as the authorities do manage to prevent a 'burning stack' of fuel rods (within either reactors or ponds, and last I heard the only actual fires were ones generally around the building, although there were naturally concerns about the spent-fuel pools), the biggest danger to the population in the greater "stay in or get out" zone, and possibly even significantly within the evacuation zone, is going to be the chill winds, snow and general lack of supplies. Including fuel for the infrastructure which would normally bring the supplies that exist in the other parts of the nation into the entire tsunami-hit zone, assuming they don't still have problems with debris-blocked highways and other rescue effort issues.
However, I have made a few assumptions, above. It's so hard to get good facts, given the mix-up of details that this post was initially all about, various different news organisations relaying possibly spurious facts from similar mis-understandings or sheer hype, or possibly even believing unwarranted down-playing by those who are supposed to pass on details! Please treat this as a general exposition, not in any way authoritative of the true situation on the ground.
[1] A bad choice, in general, because of the lack of ability to monitor and deal with the situation at later leisure. OTOH, the 'leaky sarcophagus' of Chernobyl might be considered a strange way of doing it too. I think the thought process there was that they were keeping people out of the area, anyway, so they'd allow it to cool itself by air blowing through it.
[2] Yes, high radiation levels could make otherwise safe materials in the area radioactive in their own right. But compared to the radionuclide problem this would really be just like a few more cosmic rays striking down upon the Earth's atmosphere and ground.
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Topic: Holy shit Japan.... (Read 71442 times)