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Directly comparing Fukushima to Chernobyl

Zoom out to view Chernobyl’s radiation over Fukushima. Rotate to the Ukraine to see Chernobyl in context. Download File (source: UNSCEAR/MEXT)
This embedded version of Google Earth may have limited functionality on some browsers.

This Sunday (11 September) marks the six-month anniversary of the triple meltdown at the Fukushima Daiichi nuclear power plant in Japan. The accident has slipped from the headlines, but new data are coming out all the time. Some of the most recent findings are allowing the best comparison yet of Fukushima with Chernobyl.

A lot of media outlets (ourselves included) first made the Fukushima-Chernobyl comparison back in April, when the Japanese revised their estimate of the Fukushima accident—rating it a seven on the seven-point international INES scale. The conclusion most reached at the time was that, although the rating was the same, Fukushima was a much smaller accident.

A couple of things have changed since those first reports. First, the Japanese doubled their estimate of the radiation released by Fukushima in June to 7.7×1017 Becquerels (Bq). Then, on 30 August, they released the first maps of radioactive caesium-137 (Cs-137) contamination from the plant. Cs-137 has a half-life of 30 years, and it’s considered the major long-term contaminate for both accidents.

With the new Cs-137 data, we can now directly compare the fallout from Chernobyl to Fukushima. Check out the Google Earth mashup above (zoom out to see Chernobyl on top of Fukushima, and rotate over to the Ukraine to see Chernobyl in context).

The first thing that you can see is that Chernobyl is indeed quite a bit bigger. In fact, the permanent exclusion zone (red) encompasses most of the Fukushima fallout map (download the .kmz) to toggle the overlay on and off). If Fukushima had been a Chernobyl-scale crisis, significant amounts of radiation would have spread all the way up to Iwate Prefecture, and depending on the winds, it’s not inconceivable that Tokyo might have been hit with serious levels of fallout.

Fukushima Chernobyl.jpg

But that’s not the whole story. If Chernobyl had happened over Japan, much of its Cs-137 contamination would have ended up in the Pacific. Similarly, a good deal of the Fukushima fallout isn’t seen here because it has blown out into the ocean. Indeed, the total estimate delivered to the International Atomic Energy Agency in June states that Fukushima has released 1.5×1016 becquerels (Bq) of Cs-137—about a fifth of the Cs-137 from Chernobyl. The total radioactive release from Fukushima is currently estimated at about 5.5% of Chernobyl, which spewed an incredible 1.4×1019Bq.

The Fukushima fallout is notable for what it doesn’t contain. Some very nasty contaminants like strontium-90, americium-241, and various plutonium isotopes are all absent in any significant quantity because the concrete vessels around the reactors appear to be largely intact. In Chernobyl, the explosion and subsequent fire spewed these extremely dangerous isotopes far and wide.

The bottom line here is that Fukushima and Chernobyl are comparable, and a comparison really helps underscore the differences. Fukushima’s heavy containment vessels limited the spread of some dangerous isotopes, but the coastal location makes marine contamination a much bigger issue than it ever was for Chernobyl. The latest maps suggest that there will be a permanent exclusion zone to the northwest of Fukushima, but it will likely be quite a bit smaller than the one at Chernobyl.

For a quick update on what’s been happening at Fukushima, check out our latest video:

For continuing coverage of the Fukushima crisis, check out our Japan quake special.

For a selection of our coverage in Japanese, visit Nature Asia Pacific.


  1. Report this comment

    Ossi Mantylahti said:

    Very well written blog article. One point of note:

    the colour scale of both graphics is same, but numeric scales are different. It would be a good idea to syncronize scales and colours.

  2. Report this comment

    Geoff Brumfiel said:

    I’m glad you pointed that out Ossi. It’s true that the scales are different, and without the raw data (and a lot of time) it would be impossible to synch them.

    The permanent exclusion zone at Chernobyl was set at 1480kBq (hence its use in the scale). Looking at aerial surveys of Fukushima’s radiation levels, it’s clear that anywhere over 1000kBq will be well above the government’s annual 20mSv/year exposure limit. So in my opinion, it’s a reasonable comparison.

  3. Report this comment

    Mike Bohan said:

    Nice blog, but your use of the terms “radiation” and “radioactivity” need to be corrected. Radiation consists of electromagnetic waves (radio waves, light, UV, gamma rays, x-rays, etc) or ionizing subatomic particles (alpha or beta particles, positrons, neutrons, etc.) Radioactivity consists of unstable atoms like Cesium-137, Strontium-90, etc. which give off radiation as they decay and become more stable.

    When you say the Japanese doubled their estimate of the radiation released to 7.7×10^17 Bq, it should say they doubled their estimate of the radioactivity released to 7.7×10^17 Bq. Radioactivity is measured in unit of Becquerel. Radiation exposure, dose and dose equivalent are measured in units of J/kg, Grays and Sieverts, respectively.

    Also, in the video, you can filter out the radioactivity from the water, but you can’t filter out the radiation! As a science blog, you need to be more precise in your usage of these terms. The mainstream media makes this mistake all of the time. You need to uphold a higher standard.

  4. Report this comment

    Frangible said:

    Is there any data on the total absorbed dose release from atmospheric nuclear testing in the US to compare to this?

    I could find the total dose equivalent for I-131 between the US nuclear testing and Fukushima but that’s a limited data set.

  5. Report this comment

    James Aach said:

    Clear and well-written.

    The Fukushima / Chernobyl comparison on radionuclide dispersal is important. Another thing this event highlights again is the need among both reporters and the public to better understand how nuclear plants actually operate. They are too often treated as black boxes which occasionally spew out toxic goo which kills all that it touches. I’ve worked in the US nuclear industry over 20 years and am constantly amused/appalled at the poor coverage of this issue. (And yes, Fukushima was a total mess.) With over 400 nuclear plants around the world, and constant debates regarding how our future energy needs will be met, it would be a good idea to better understand electricity production in general and nuclear in particular.

    One learning option I would (obviously) recommend is my novel “Rad Decision”, which is available online free (no adverts, no corporate sponsors, no $$ for me). Just Google the title. The event depicted is a lot like Fukushima, oddly enough – same reactor type, same initial problem. The book also provides a detailed recounting of the Chernobyl event, to allow for comparsion. I know of nohing else like it that can give a realist inside picture of daily nuclear life and an “unpleasant” happening in a western reactor. Reading reports produced by outsiders with limited access is one thing — hearing what an insider says is another experience entirely.

  6. Report this comment

    Chris Kerr said:

    I agree with Mike Bohan. It’s bad enough that mainstream journalists make basic mistakes in their use of scientific units without Nature doing the same.

  7. Report this comment

    Gennady Zebrev said:

    An obvious confusion in numbers :

    0.055*14*10^19 = 7.7*10^18

    not 7.7*10^17 Bq allegedly. Be careful please.

  8. Report this comment

    AJ said:

    While Fukushima is due to nature havoc Chernobyl is man made.

  9. Report this comment

    Geoff Brumfiel said:


    I’m not sure where you’re getting your numbers from, but the official number from TEPCO is 770,000 TeraBq. That is 7.7×10^17 Bq.



  10. Report this comment

    Jenny Capone said:

    So the numbers were supplied by TEPCO (TEEPCOO ???) and IAEA (International Atomic Energy Agency) ? The very ones who would promote atomic energy against all odds and reasoning ?

    And you want us to believe THEM ??? HA ha ha …

    What a joke !!!

    PS. Why not ask BP about the recent disaster in the Gulf of Mexico. I am sure they will say that no harm was done !

  11. Report this comment

    Laila Maeyama said:

    I am from Japan.I agree with Mike, the unpreciseness makes science blogs not very credible to be honest. AND I agree with Jenny. I do not trust the number. TEPCO is lying all the time. The maximum level allowed to sell (of radioactivity in food was raised up to 2000 Bq/KG from 100. The population in Japan ist mostly ignorant, but the ones who are not do not trust anything coming from TEPCO or the government. By the way there was Strontium-90 found as far away as 60 KM from the plant, as it is meanwhile not a meltdown but a melthrough. This means all this material is now in bare earth. Can somebody explain me, what will happen with all this radioactive material, will it come up in Chicago some years later?

  12. Report this comment

    Robert Schneider said:

    I’m still confused about the numbers regarding total radioactive release. For Chernobyl, here, the number 14*10^19 Bq is given. The more recent article about current estimates of Fukushima radioactive release quotes Chernobyl with 1.4*10^19 Bq – which would also resolve what Gennady pointed out further up. ( And a quick Wikipedia lookup yields “total atmospheric release” as 5200 PBq, i.e. 5.2*10^18 Bq ( Do we have a consensus figure?

  13. Report this comment

    Stephen Church said:

    The figure for Chernobyl is stated as 14 × 10^19 but is that a mistake for 1.4 × 10^19 or 1.4 × 10^20? Require an answer as soon as possible. What is the source for the data please.

  14. Report this comment

    James Roberts said:

    Does anyone know if the large version of the comparison map is still available somewhere. I get a 404 error when trying to click on the large version of the map.

    1. Report this comment

      Lou Woodley said:

      James – you should now be able to see the larger version of the map by clicking on it. Thanks.

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