Wednesday, March 16, 2011

On Radiation

So, I think perhaps hysteria over the nuclear plant issue is getting a little out of hand in some places. Some people are leaving Tokyo - even leaving the country - over the fear of radiation. And I just recently read that the Swedish nuclear authority has been getting hundreds of calls from people worried about the effect of fallout in Sweden. Which is not ridiculous since people's fears are very real, and fear needs to be taken seriously, but the fear is misplaced and uninformed.

First, and most important, we have tens of thousands of people dead in Tohoku, and many tens of thousands still in dire need of assistance. People still miss basic shelter and water in many areas. This is the real disaster, far worse than any effect of a broken-down reactor. The nuclear thing is a noisy sideshow, nothing more.

Leaving Tokyo: Good idea - but not for the situation at Fukushima. The Tokyo area has rolling blackouts, disrupted communications and a lack of supplies, as both power and other resources are funnelled to the disaster-stricken areas. Chances are your workplace or your school is shut down anyhow, and your company may be shifting operations to branch offices out west for the time being. If you can visit relatives in Kansai or Kyushu for a few weeks that may help relieve stress in the Kanto area a little bit, not to mention relieve some stress for yourself.

Radiation: First, to be absolutely clear, I'm not an expert. I am a researcher, but not in radiomedicine, not in nuclear engineering and not in anything connected to it. Don't take my word for things - but don't take the word of other people without expertise either.

"Sievert" is a measure of a dose of radiation, like liter or cups for liquid, meter for lengths or kilogram for weights. Sievert per hour tells you the rate over time - like kilometers per hour for speed. I'll give all numbers below in the same unit, microsievert per hour (shortened uSV/h).

Peak radiation at the Fukushima I plant have been high, well into medically unsafe levels. It is truly dangerous for the workers at the plant, and people in the area have been evacuated for good reason. But the strength quickly diminishes with distance.

Highest measured radiation so far in Ibaraki prefecture, near Fukushima was 5 microsievert (uSv) per hour. Tochigi, halfway between Tokyo and Fukushima has had a peak of 1.3 uSv/h. In Tokyo the peak was 0.8 uSv/h. All these quickly dropped to near normal again. Note how the peak is lower the further away the place is. Here in Osaka there was never any detectable difference. Sweden will never see any effect from this accident at all.

Here is a live radiation counter in Tokyo. At the time of writing, you can see a slow hump of activity over last night and morning, on average around 0.1 uSv and at most 0.2 uSv/h more than usual (100 cpm is very roughly 1 uSv/h), but back to near normal again. The lower graph is the typical level.

Normal total background radiation ranges from 0.15 to 0.5 uSV/h. Exactly how much depends on where you live - Scandinavia, for instance, tends to have relatively high background radiation, with about 0.45 microsievert per hour, and there are some places in high mountain areas that naturally give you over 5 uSv/h. Tokyo, on the other hand, lies at the lower end of the range, as you can see at the link above.

Flying exposes you to more cosmic radiation, simply because you're above much of the atmosphere. While you're chewing on a rubbery chicken and watching last years hit movie on a grainy monitor you're getting about 7 uSv every hour, more than the peak value in Ibaraki.

Let's say you decide it's a good time to escape home to Sweden. The entire peak gave you around 1 uSv extra radiation, the nightly hump also totals around 1 uSv (an average of 0.1 uSv for ten hours). The constant background level in Tokyo is about 0.2 uSv/h now. You want to leave Tokyo and get home to safe, dependable Stockholm. You hop on the airplane, which gives you about 75 uSv during the trip - 75 times the peak, and 75 times the slow hump last night - and arrive in Sweden.

Sweden has a constant background radiation rate at 0.45 uSv/h - more than twice what you have in Tokyo, and higher than during that hump of activity last night. If you live in an old stone house the rate is higher still. So, leaving Tokyo for Sweden means increasing your radiation exposure, not decreasing it.

This doesn't matter, of course, as all these values are far below any unsafe levels. What is unsafe? Around 100 000 microsievert over a year - that is 11 uSv/h for a year. Occupational limits are about 2.2 uSv/h for a year, but that's work-related exposure over and above any other sources. At about 0.2 uSv/h in Tokyo you'd need five times that level to reach workplace limits and up to fifty times current levels for a whole year to get into real unsafe territory.


  1. Great with yet another post putting all this radiation talk in perspective. I do believe that for us in Tokyo, a new massive earthquake is a larger threat than radioactivity from Fukushima.

    Still, it's somewhat unnerving to follow what's going on at the plant. Looking forward to the day when it's just the plot of a movie, not a real-time disaster.

  2. Thank you; your posts are very useful and clearly written

  3. Thank you for the well-written article. It helps since I am living in Sendai and this fear is real.

    The problem here is that there are so many different opinions on the subject that it is hard for someone who knows nothing of it to understand what is happening. I continue to hear to stay out of the rain. If the rain is "bad", then the water I am collecting is also bad and I can't use it.

  4. Excellent, level-headed, explanatory post. Many thanks

  5. Just remember that I wasn't kidding about not being an expert. If an actual expert without an obvious axe to grind tells us I'm wrong, then listen to them.

  6. Interesting and accurate, but perhaps a bit overconfident. These repeated fuel pool fires are clearly spreading radiation around at the 20km perimeter, with levels of 220 to 330uSv/hr, well above the 11uSv/hr safe value you mentioned.

    Maximum observed radiation of 25uSv/hr in the 30-60km range is troubling also. These fires seem more dangerous than the chance of a criticality excursion.

  7. Good analysis of the present. Yet, I think there's one problem with the overall argument - it pertains to the current widely known situation. Should the situation escalate for the worse, the next step will be higher levels of radiation hitting some metropolitan area. At that point it will be too late to act. Even if the information reaches you before the cloud (a big if given the recent past), it will be next to impossible to leave as lots of people will be trying to do the same and the transportation system will grind to a halt.

    As for the radiation comparison itself, it seems to me one big difference between x-ray / flying type of radiation and radioactive isotopes in the fallout is that x-ray / flying is over when it is, but isotopes can be absorbed by your body and continue exposure long time after the passing cloud is gone. Furthermore, if the source of the radiation is inside the body the effects are quite different. Finally, there are different radiation types differing in the ionization strength at various distances. I am far from being a toxicology expert, but even the experts seem to be saying that full effects are poorly understood except in severe cases.

  8. More experty people talking to UK embassy here:

    Very little cause for alarm in Tokyo area.

  9. Thank you so much for this post. I live in Osaka too as an exchange student, and to be honest, I am getting sick of the mass gaijin/parent panic. My parents are asking me to leave, I refuse, and it's getting very problematic. I just hope media starts playing it low instead of what's going on right now.

  10. What about the powerline that is supposed to help fix the problem???

  11. And what if the reactors explode? Would the fear still be misplaced and uninformed?

  12. @drrobot: local effects are bad. They may well get even worse. But they're local effects; we're not talking about anything like the devastating effect of the tsunami for instance. Major centers like Tokyo are safe.

    @Gleb: Strength dissipates over distance. There just isn't going to be enough local activity that people in, say, Tokyo or Sendai can get hurt.

    And you're right that differant types of radiation have very different effects. But the Sievert unit actually weighs the radiation according to the effect it has. It's specifically made so you can compare radiation amounts for their effect on people.

    @Anonymous: this reactor type can't explode. The containment can rupture, and fires can create radioactive clouds. But you can't get the kind of wide spread of material that happened in the explosive fires in Tjernobyl.

    Just to make clear: I generally think fission reactors are a bad idea. They're far too expensive an energy source (nobody would build a reactor without heavy subsidies), the possible downsides are great, and the system is too brittle to be a dependable energy source in emergencies.

    But no matter what I think of them, over-the-top hysteria doesn't help anybody. Especially when it can actively harm rescue efforts for the true current disaster.

  13. Jason H-J (Kobe)17 March, 2011 17:51

    Quite frankly some of the Western news reporting on this unfolding tragedy has made me cringe. Never let the facts get in the way of a good story!!

    EU officals especially Merkel have within a matter of days politicised this tragedy for their own gain/votes...I feel ashamed!!

    May those in need recieve aid as rapidly as possible; and to those who have lost their life RIP

  14. Thanks for the post. I've been planning to move to Kobe on a working holiday visa for over a year now and have been wondering how much I should delay because of this disaster. It seems like I don't really need to delay at this point.

  15. Hello,
    thanks for that great post!
    Are there any news about radiation levels in Osaka from independent measurements?

    Are there any independent sources of radiation measurements on the internet in English?

    I am concerned and hope that there is still no radiation in Osaka.

    Thanks in advance!



  16. Michael, there is no excess radiation in Osaka from Fukushima. There has never been, and there will never be. It's a bit like asking how New York is coping with the Mississippi flooding, or how Paris is dealing with avalanches in the French Alps.

    That said, there is radiation in Osaka. There is always radiation everywhere, including where you are now. so "no radiation in Osaka" would of course not be true either.

  17. Thank you very much, Janne. That was helpful information. With "no radiation" I meant radiation caused by the Fukushima damage, of course.
    I just feel uneasy to rely on Western sources of information alone about Fukushima, and not being able to read Japanese ...
    Again, thanks very much!

  18. There is radiation present in Osaka from the Fukushima plant accident. It's measurable. But it's of no consequence as far as I know. I also happen to live in Osaka, so I would worry if it were higher than it is. The biggest problem that I see is that vegetables and meat produced closer to the accident could have some isotopes in it, and as a previous person said, it has a totally different effect on the body. Also, they have found Plutonium on the Fukushima site, witch makes me believe that it could have spread further that Fukushima. You have to do chemical tests to be able to detect this, so it's not as easy to find as other isotopes. I think it was Janne who said that these reactors can't explode. This is of course false. I think that it's easy to find videos of both 1-3 as they explode. (I may be mistaken on the reactor numbers though.) They showed this on Japanese TV, so it's no secret. I'm not worried as much as for my sake as I am for my kids though. I think it's safe to live in Japan, but I'm a bit worried about the food and the water.


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