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How Fukushima is and isn’t like Chernobyl

Fukushima radiation 07 apr.jpg
Chernobyl CS-137.jpg

This morning, the Japanese government officially upgraded Fukushima on the International Nuclear Events Scale to a 7, or “Major accident”. The new rating is the highest on the scale, and puts Fukushima on a par with the worst nuclear accident in history—Chernobyl. Understandably, the press has made quite a big deal out of new rating, but the reality is that Fukushima is a very different accident than Chernobyl.

The maps on the right do show a passing similarity between the two accidents. The top one shows overflight measurements of radiation in the region around Fukushima. The bottom one shows Caesium-137 measurements from Chernobyl. The data are not completely analogous, but I think the maps give a sense of how both accidents have contaminated large areas and created regional hotspots that will require additional evacuations.

UPDATE: Several people have pointed out that there are no scales on the maps provided. A colleague of mine pointed me towards this site, which (sort of) compares the two events.

But there are very important differences between Fukushima and Chernobyl. The biggest, in my mind at least, is the timescale over which the accident occurred. When Chernobyl’s reactor number 4 exploded in 1986, it scattered debris over a wide area and sent radioactive fallout high into the atmosphere. Entire villages near the reactor had to be evacuated in a matter of hours, and many residents had to leave personal effects behind. A fire burned at the site until 5 May, spewing tones of radioactive material over 200,000 square kilometres. By November, workers had successfully completed a concrete sarcophagus around the core, effectively sealing it off. In the short period following the explosion, the accident spewed some 14 million terabecquerels of radiation into the environment.

The Fukushima accident has unfolded much more slowly. The damaged reactors exploded over a period of days, and after a modest initial release, radiation has fallen off. So far, the reactors have spread about half-a-million terabecquerels into the air. I haven’t been able to find hard data on the first month after Chernobyl, but I’m willing to bet my lunch that it put out a lot more in that period.

The problem is that Fukushima’s slow bleed of radiation is going to continue for a good period of time to come. Reactors are normally kept cool by recirculated water, but at Fukushima, the circulation system has been heavily damaged, and the only solution is to simply dump tons of water onto the cores. The water absorbs radioactive isotopes like caesium-137, and itself becomes a big waste problem. Moreover pictures from as recently as 10 April show steam continuing to rise from the reactors.

This seepage in the form of water, dust and steam is creating slow-motion Chernobyl at Fukushima Daiichi. Yesterday the government announced evacuations from several villages outside the current exclusion zone. Unlike the dramatic evacuations from the Chernobyl reactors, these will take place slowly over a matter of a month or so. That’s because radiation levels in the region are low enough to be safe in the near term, but not in the long-term. As ground-contamination data continues to be collected, I suspect we’ll see more localized evacuations over the coming weeks and possibly even months.

Time is important, especially in nuclear accidents. Fukushima’s slower burn makes it easier for officials to respond to radiation risks and protect the population from contaminated food, water and air. Yet the slow release of radiation into the environment could still have great long-term economic and environmental consequences. As we’ve just written, the clean-up of Fukushima will probably resemble Chernobyl in many ways, and could take longer.

For full coverage of the Fukushima disaster, go to Nature’s news special.

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



  1. Report this comment

    Nicolau Werneck said:

    Great article. But I just wanter to point out that there were (still) no exploding reactors in Fukushima. The explosions were outside the reactors. I don’t even know exactly where are the leaks in Fukushima, where exactly are the damages and what is being spilled “on purpose”, but it’s still different from Chernobyl where there was indeed a reactor that exploded.

    One thing is to measure the scale of the accident in terms of radiation and contamination. Another thing is to measure the impact and the damage. That is the scale where it’s hard to beat Chernobyl. Here we would talk about number of workers, firefighters and population killed, and raise in the number of cancer cases in the following years. As far as I know that is not the main concern in this IAEA scale.

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    hsm said:

    This is an international tragedy. I do not remember contaminated milk found in every country of the northern hemisphere after Chernobyl.

  3. Report this comment

    Geoff Brumfiel said:


    Thanks for your comment. You’re right that the explosions at Fukushima are different than the one at Chernobyl, but I think it’s still too early to say definitively where they occurred. In this case, I meant “reactors” generally as a term that included their containment.

    In terms of the explosions themselves, the real difference is that the Fukushima reactors didn’t use flammable graphite to moderate their nuclear processes and had containment vessels that prevented a much larger radiation release.


    That’s a good point, and so far anyway, the dangerous levels of contamination have been confined to Japan. This is another important difference between Fukushima and Chernobyl.

  4. Report this comment

    eddie said:

    We are all entitled to have our own opinion, so they say. I beg to differ with the authors assessment.

    Plutonium is extremely toxic.

    We do not know what exploded. I would not exclude the possibility that a reactor core did explode.

    We do know that thanks full of ‘spent’ fuel rods exploded.

    I do not believe that the explosions were not substantial; it does not take much to reach the higher atmosphere.

    Four reactors, three fuel tanks. A lot of material.

    Pollution of the ocean – very significant.

    And worst of all – no end in sight.

    This will be an international disaster of greatest proportions. It is not radiation, but contamination. “How many bullets can you take” ? This stuff does not go away.

    The best possible outcome might be achieved by detonating nuclear bombs in each of these reactors. At least you would have a stop after that.

    A concrete sarcophagus will do some good, hopefully – but not cure the problem.

    The solution will be that we will have less information in the media. The safety levels will be weakened and the governments will claim that all are safe. Cancer rates will increase. That is part of life now.

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    Uncle Al said:

    5×10^17 Bq = 14 megacuries.

    One presumes Pacific ocean contamination is concomitantly greater. A billion people will not be eating from the Pacific. It is a splendid opportunity for the lethally over-harvested Pacific fishery to recover, Alaska to Hawaii, and evolve.

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    Rick said:

    Big difference between your two maps is scale. For reference the distance between kiev and minsk is 400km. Also colours arent comparable. The bottom diagram is cesium deposition around chernobyl. The large red areas are above about 1 megabecqueral/ sq metre. These levels have only been reached in spot samples around iliate in Japan.

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    Yoshi Mizuno said:


    I disagree that the time scales are different. The largest emission of the radiation happened on May 13 when the reactor buildings blew up. I do agree that the lower level emissions will continue in near future.

    Please see my map of radiation measurement when I took a trip to Fukushima:

    You will see that the radiation measured on the highway is variable. I did not see smooth variation of the radiation as we approached Fukushima. That fact suggests that very sudden emission has caused the radiation values in the area. If the spread were to happen over long time, I would expect to see more uniform distribution of radiation values.

    Following chart (some one plotted radiation values April 5 to 7) suggests the initial north west distribution of the radiation, then the plume turning left near the city of Fukushima toward the city of Koriyama. This sort of very directional distribution would not happen with over long period of time, with a lots of wind variation.


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    Matt J. said:

    Don’t we also have good reason to believe the composition of the radioactive fallout is also very different in the two cases? According to the early TEPCO press releases, at least, most the the radioisotopes released as the volatile ones, not the heavy ones released only by burning fuel. But at Chernobyl, fire and explosion scattered fuel and fission products.

    What else has been detected or is expected to be found in the fallout in the evacuation zone other than I-131 and Cs-137?

  9. Report this comment

    Web Identity said:

    If even the Japanese can’t control their power plants then I have absolutely no hope that Americans who love deregulation, profit first & under paying employees would ever be able to keep our own nuclear plants from melting down one day. It is time to get away from nuclear power.

  10. Report this comment

    Dr.M.R.Iyer said:

    The total radioactivity release in Fukushima would be comparable to that from Chernobyl, estimates vary from 10% to 80%. The pathway of spread of activity at Chernobyl was air spreading even to stratosphere so its impact was worldwide. In Fukushima it seems to be slow and through the ocean which offeres a large dilution. Neverthless the radioactivity released to the biosphere is comparable. It looks that the Japanese are going to have a tough time identifying and containing the releases!

  11. Report this comment

    Carol said:

    Interesting comparison, Geoff. But I believe the major difference here is that the Fukushima plant has safety barriers that although not completely, it keeps the harmful materials in. On the other hand, the Chernobyl plant does not have this safety barrier that when it exploded, the harmful materials immediately mixed in the air. It is going to take a long time before the Japanese citizens could rebuild and move on from this catastrophe. I’m wishing them well in their continued positive outlook and efforts.

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    Stephan said:

    There are different ways to describe the differences. The Chernobyl reactor exploded while nuclear fission was still going almost fully. The neutron absorbing rods were manually released, but too late, the heat from nuclear fission had already deformed the mechanics so much, that the rods got stuck after one third of their way. Nuclear fission was only stopped by the explosion of the reactor. In Fukushima nuclear fission was stopped by automatic release of the rods, but the afterheat from radioactiv decay could not be cooled off. It is thinkable, that a strong Earthquake could mechanically prevent a shutoff of the reactor (rods get stuck when falling down), then Fukushima would have become more like Chernobyl.

  13. Report this comment

    Lisa said:


    Just curious about the credit you attribute to “USNNSA/UNSCEAR.” Could you be more specific about the information provided to you from this organization?

    Thank you.

  14. Report this comment

    prasad said:

    Every country and every one knows that earthquakes are common in Japan so why did they built nuclear power plants? they know very well if they blasts what will be happened. Now they facing that situation it is very bad and unfortunate. Most powerful countries in this world like Russia, America, China and other European countries should help Japan to come out from this situation as soon as Japan come out from this situation they will fulfill their needs as well.

  15. Report this comment

    Prasad said:

    The people where the Nuclear Plant blast occurred should be shifted to safety zone where they can live without any deceases without radiation. Japan government take the help from other countries like America, Russia so they can come out as early as possible.

  16. Report this comment

    Prasad said:

    All the people must be shifted to safety zone and take the necessary action to stop the radiation as early as possible they do not pour the water (radio active) into the sea and think another alternative to drop the water.

  17. Report this comment

    Vidyut said:

    I think it is too early to compare. While Chernobyl seems larger at this time, Fukushima is far from over, and no one knows what we are going to end up with. It seems true that no radioactive core exploded yet, but the fire in the reactor 4 is not exactly reassuring. What we essentially have here is radioactive material under the sky soaking in a bath tub of dubious integrity.

    The current situation seems to be one of battling emergencies rather than any stabilization or recovery. This is a far, far way from over.

    A few other things these comparisons miss are that Chernobyl exploded and was done. Fukushima’s simmering status is going to complicate everything.

    Each reactor in Fukushima contains more radioactive material than what exploded in Chernobyl. Thus, even without an explosion, with 4 reactors in various stages of instability, it is a large amount of radiation, particularly with time.

    Even saying 4 reactors is a euphimism, because three reactors are critical, PLUS four spent fuel tanks with differing statuses of integrity. Out of which, one containing plutonium is also not completely spent fuel, since the fuel that should have been in the reactor is outside – no containment, no nothing. Directly open to the outside. It is known that it has spent an unknown amount of time outside the protective water.

    It is too early to say, but Fukushima seems to be the kind of thing that is already massive and will accumulate. Call me a pessimist, but I am hoping that we don’t need to invent a level 8 on the scale for Fukushima.

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