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Comment by gus_massa | Hacker News Reader

It's not difficult to get a Geiger detector and measure the radiation level in the water, and compare it with the radiation level of water far away. IIRC the additional radiation level is tiny.

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.]

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Here's a map of Japan's radioactivity [0]. For those unfamiliar 1 Sv (Sievert) of ionizing radiation equates to a 5.5% chance increase of eventually developing cancer. It is also the maximum allowed dosage to NASA astronauts over their career.

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.

[0] https://jciv.iidj.net/map/

[1] https://en.wikipedia.org/wiki/Sievert

For those also unfamiliar, a nano Sievert is one billonth a regular Schedule, and a reading of 8500 nSv/h, or 8.5 µSv/h, would take 4860 days of constant 24 hour exposure, or a bit over 13 years, to reach a single Sv of radiation exposure. 8.5 µSv is also equivalent to 85 bananas, or 1/5th the exposure of flying from NY to LA.

Mind your units.

Here's the visual!

https://xkcd.com/radiation/

All that weighting is for external exposure though, surfing will include much more involuntary ingestion than other activities. Even if you somehow managed to never dip your head, there would still be heavy breathing right inside the spray.

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.

Great point. You do definitely ingest water when surfing. Weighting still applies, but you get a high weighting (because everything is now soft tissue). But also, you are right about the water mixing (and also being a good rad shield). To make any accurate statements we'd need a map similar to the land one that I posted, but in the ocean. I have yet to find such a good map.

Nice map. How about the water or the fish?

I don't have a map of the water, but I'd wager they are doing far better than those on land. For a few reasons.

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).

I agree, but nitpicking:

> 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.)

If we're going to nit pick, there's a difference between heavy and heavy metals. All heavy metals are "heavy" but not all metals that are heavy are heavy metals. And as you probably know, this term is vague and when talked about it is discussed in very specific ways. Though some of the metals are heavy metals.

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.

Thanks for the info, I have not seen anything like it in the news.

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.

Radiation is a strange subject to get from the news. There's a quote I heard from a nuclear scientist "Those that know the most fear the least" (note, that he didn't say "don't fear"). A lot of this is reminiscent of cold war era and nuclear weapons (a VERY real fear). And because radiation is such a difficult to understand subject, and since scientists aren't the greatest communicators to the average person, things get fuzzy. And lastly, humans are bad at understanding risk. Like that more people die per year from coal production in the US than have ever (or ever will) from any (current) nuclear disaster (see linear no threshold models). That's a crazy stat to me.

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.

We know that black lung and air pollution are things, and can be verified by disinterested third parties.

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.

Indeed. In fact, at a working power plant the spent rods are stored underwater because it's so good at blocking radiation.

I would say the main reason they are stored underwater is mostly because they need a place to transfer heat to lest they melt and cause a critical mass of spent fuel.

They do it for both reasons. The hydrogens in the water molecules are good at absorbing neutrons. The control rods are also typically made of carbon, and will release x-rays, which the water is also fairly good at blocking. Not as good as gold, but who's got that kind of money.

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