Fukushima's surfers riding on radioactive waves
aljazeera.com
aljazeera.com
Moreover, water is a good radiation shield, so you don't get the radiation from the whole sea, but the radiation from the nearby water. See https://what-if.xkcd.com/29/
[I'd recommend not drinking the water there, just in case there is some isotope that may accumulate. But I'd prefer to get a good analysis of this part before being to worried.]
Radiation dosages are also difficult to calculate and Sv's have a weighting factor for where the radiation is taken in. The Wikipedia article [1] has a decent introduction to how the unit works, but you should really consult a higher grade text.
Mind your units.
1) radiation is heavy, so it sinks, but slow enough that the water would disperse it quickly.
2) Water is a FANTASTIC radiation shield. See above as well as any nuclear reactor.
3) The main concern are the bone seekers (isotopes that deposit within bones). Which have short half lives and aren't absorbed well. A rough number (towards upper bound) is that a fish eating it (directly it) would absorb 10% of it. A fish eating that fish would absorb 10% of that, and so on. And there wasn't much of those isotopes released in the disaster in the first place. So combine that with the good mixing from ocean currents and I'd say fine.
I would happily eat tuna caught in Japan.
Side note: short half-lives generally equate to more danger. That's because they are releasing their energy at a much faster rate (typically). Long half lives generally means they are decaying slowly (otherwise it'd be gone). I know this makes sense, but we frequently think the opposite. That isn't to say that you shouldn't be wary of long half life materials, but that the dangers are different. Radiation is a fairly complicated subject (unsurprisingly).
That is a good point about half lives. I believe since most of the conversation in peacetime so to speak is around waste management, longer half lives seem more dangerous (problematic) than the short ones.
We do need to do long term storage, but we (the US) stopped the long term plan of Yucca Mountain.
What worries me though is that we need nuclear more than ever. The IPCC agrees, it's the only current technology that we have to address (not solve) the issue.
What we know about the release and status of disasters like Fukushima, is dependent on interested first and second parties (utilities, governments etc). I am fairly confident that most/all of the information is incomplete or inaccurate.
Nuclear may well be safer. But there are more unknown unknowns with nuclear than there are with coal- driving fear and also legitimate cause for concern/caution, as a citizen.
> 1) radiation is heavy, so it sinks,
Most radioactive atoms (found in Uranium reactors) are heavy (but heavy means https://en.wikipedia.org/wiki/Heavy_metals ).
Most of the compound of these atoms are insoluble, they probably precipitated as oxides or carbonates a long time ago and are at the bottom of the sea. They are probably very dense and go to the bottom.
Some atoms are soluble in water, I think that Cesium 137 is be the main concern, but now it will be mixed by the water and distributed in the whole sea (or at least a big part of the Pacific) so the concentration should be tiny.
Also, Iodine 131 has some soluble forms, but the half life is only 8 days, so it's completely gone now. (There are probably some natural sources.)
Soluble or insoluble ocean currents are fairly strong and there is strong mixing. Solubility also means more mixing and thus more dilution. The amounts of 137Cs were fairly low, but this was one of the most dangerous materials because it is does distribute within the body, but that half life is 30 days. And consider the food chain. That actually depletes the 137Cs much faster than the 30yr half life would. Same goes for I. Also consider that the ocean currents will take that material away from Japan and into the open ocean (not towards another near by landmass).
But I want to be clear, I'm not saying that this stuff is completely safe. But that there's good reason to think that concentrations in the ocean around the area have plummeted, and should faster than on land.
On the other hand, the water is not tied to a place, it must be a billion times diluted by now. The walk from the car could be the most harmful part of surfing there.