Fukushima meltdown and glow-in-the-dark Californians?

I’m a big fan of recycling and this is a re post of something I wrote in 2012 but which is still worth reading as a reminder that chicken little syndrome can be combated by a little background reading.

It seems people are getting all bent out of shape about this report.

http://iopscience.iop.org/1748-9326/7/3/034004/article?v_showaffiliations=yes

Temporal evolution of absolute peak concentrations (in Bq m−3, logarithmic scale; grey shaded) and within individual regions (see figure 4(d)) from the 0.1°-model simulation, assuming a total input of 10 PBq of 137Cs. Regions: western Pacific (I, black), off North America (II, green), Hawaii Islands (III, light blue), off Baja California (IV, blue), Aleutian Islands (V, red). The inset is a zoom into the part of the figure with levels below 2 Bq m−3 (pre-Fukushima values) on a linear scale.

Caesium isotopes coming our way are not a good thing and there may be a problem but not based on this report.


The peak level of isotope on the US pacific coast is projected to rise to double the current background radiation, which sounds bad but even at the peak, it will be less than 4Bq/m^3. To put that in perspective, you would need to drink over 250m^3 of the contaminated seawater (that’s well over 250 metric tonnes) to exceed the maximum safe contamination level of a single kilo of food (WHO recommendation, which assumes consumption of 750kg of food contaminated to that level per year) so unless you plan to drink 250 tonnes of seawater twice a day for a year you shouldn’t experience any problems.


The other statistic (gleefully misreported by the press) is that excess contamination levels on the US pacific coast six years from now will be ten times the level experienced in Japan; a truthy little factoid which has been seized on by a number of eco-bloggers who are in major panic mode that we are all going to start glowing in the dark.

Now, ten times sounds bad, but only if you think that, by some miracle of concentration, they mean ten times the peak level immediately after the fukushima meltdown but what they actually mean is that, by the time the excess radiation level here reaches the same level as existing background radiation (doubling the total), the excess radiation in Japan will have fallen to only 10% higher than background. So our excess radiation will be 2Bq/m^3 when theirs is down to 0.2Bq/m^3; that’s 10x sure enough but the TOTAL radiation levels will be 4Bq/m^3 vs 2.2Bq/m^3 which is less than twice and our level will never come within four orders of magnitude (1/10,000) of the levels seen in Japan.


By the way, the biological half life of C-137 (ie: after it has been ingested by an animal) reduces from >30 years to about 30 days so this is not something which is going to persist in the food chain.
So I think I can say that I feel pretty reassured that there will be no water borne problems in California as a result of the Fukushima meltdown.

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12 Responses to Fukushima meltdown and glow-in-the-dark Californians?

  1. Tom says:

    Another fine article. Thx.

    Like

  2. Rad Guy (SD Diver) says:

    Do not forget about the 19.2 Bq per banana!

    Also, please do not mix biological half-life with isotopic half-life. One is related to the body dwell time before being excreted and the other is related to the decay of activity concentration in a static reservoir of a particular radioactive species. Both are important in understand total dose and dose rates of ionizing radiation, but are distinctly different.

    -Rad Guy (SD diver)

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    • pyjamaslug says:

      Hi Doug, Not sure what you mean about the bananas but thanks for the comment. Yes, that half life thing was a boob, wasn’t it? A caution against throwing in random extras. It doesn’t affect the main argument, though.

      Like

    • pyjamaslug says:

      OK, Now I found it: http://en.wikipedia.org/wiki/Banana_equivalent_dose it must be a radiation groupie’s in-joke!

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      • Rad Guy (SD Diver) says:

        Yes, bananas are naturally high in potassium (that is why they are good for helping avoid muscle cramps, improved electrolyte balance) natural potassium is mostly K-39, but is 0.012% K-40 which is radioactive (and gives off a rather high energy gamma ray at 1461 keV, much more energetic than the x-rays in a dentists office (~25 keV)). The half-life of K-40 is 1.2 billion years (long by most measures), but this still results in about 19.2 bq in each and every banana. By the way, this is 19.2 decays/second (definition of a bq-becquerel). 10.6% of the K-40 decays result in the emission of the high energy gamma ray so (to do the math) for 39.1 grams of potassium (1 mole, remember chemistry)

        1 mole * 6.02×10^23 atom/mole * 0.00012 (K-40/K atoms) * 1.8×10^-17 (decays/atom/sec) * 0.106 gamma/decay = 138 high energy gamma/second for 1 mole of potassium (much more than is in a banana)

        This is what is referred to at NORM — naturally occurring radioactive material, others to look out for are kitty litter, granite certain beach sands in India (high in thorium) and a older ceramics with orange (uranium containing) glazes

        PS the high energy gamma ray from K-40 is a convenient signal for the calibration of spectroscopic gamma ray instruments. You can use it without having to carry any licensed/controlled radioactive source materials. Also thorium containing Coleman lantern mantles.

        Have fun

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  3. Rad Guy (SD Diver) says:

    The mantra of the ecologist geologist is “Dilution is the Solution to Polution!”

    I read it on the internet, it must be true!

    Like

  4. Rad Guy (SD Diver) says:

    I read parts of the ENVIRONMENTAL RESEARCH LETTERS 7 (2012) 034004 (10pp) article referenced here. There are a few interesting things to note.

    1) This is a computer model study. It is evaluating the model results of the short term (weeks) injection of a Cs-137 source term and the development of radionuclide activity concentrations over a decade or more. Although there are an industrial (the nuclear plant remains) and terrestrial (the contaminated areas around the plant) that continue to release into the sea, these are not accounted for.

    2) the spatial resolution of the models run are 0.5, 0.25 and 0.1 degrees (assume this is degrees latitude for simplicity) this means that the smallest scale feature the model addresses is 60, 30 or 12 km squares of ocean (the depth profile is then broken into 46 layers) for each of these. That does make up to 25 million voxels that are being modeled, Still there must be very considerable assumptions about the mixing that occurs within each of these volumes.

    3) The Cs-137 is treated as a non reactive “dye” in the mixing models, This completely ignoring the rather complex chemistry of caesium (UK spelling for Pete).

    4) The results are presented without a discussion of their uncertainty (possible sources of error are discussed, but not quantitatively). This is often a sign of poorly designed experiments.

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