Japan Nuclear Incident 15th March Fukushima Daiichi; radiation dose comparisons.

After reading a Tweet from endless_psych questioning the relation between exposure in Japan and that of living in Aberdeen, I decided to do some “back of a cigarette packet” calculations.

Well, the fire at Fukushima Daiichi involving the spent fuel is, according to IAEA update page, releasing 400 μSv h-1 into the atmosphere.  The Sievert is a unit of radiation dose equivalent, so we shall convert all other comparison quantities into Sieverts.  If you happened to live in the Granite City – a.k.a. Aberdeen – then you would, in the average home, be exposed to 60 Bq m-3 from Radon gas leaching from the Granite bedrock, from Scottish Government data.  This quantity needs conversion and using the “Working Level” rationale for Radon as outlined rather concisely by the Canadian Centre for Occupational Health and Safety, here, we can see that:

60 Bq m-3 ~= 60 . 0.0044 = 0.264 WLM (at home assuming 7,000 hours a year)

0.264 WLM ~= 0.264 . 4 = 1.056 mSv annual dose equivalent.

Now the original expectation was that the exposure in Japan would be significantly less than that of living in the average house in Aberdeen.  Well, that is not the case: you would only need to be at the Fukushima Daiichi site for 1.056 / 0.4 = 2.64 hours to reach the same exposure.  However, from the same data source, the worst houses in Aberdeen receive 1600 Bq m-3 which would be over 28 mSv a year, so you would have to stand about outside at the site in Japan for 3 whole days to receive the same equivalent dose.

In real terms, it still is not too bad. I expect the problem is highly localised and we know little about the half-life of the isotopes involved.  For a final comparison, an hour at Fukushima Daiichi in Japan is equivalent to a spine X-Ray, data from Health Physics Society.

Again, these are exceedingly rough examples but were, well, worse than I had predicted.

P.S. I’m rather tired right now, so you may want to double-check my figures… I’ve got a habit of missing “powers of ten” when tired :-)


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