Alexander's

Let me start off by putting a reactor accident in perspective:[^1]
The Chernobyl explosion put 400 times more radioactive material into the Earth's atmosphere than the atomic bomb dropped on Hiroshima.[^2]

Do I believe pressure vessel -- the core of the reactor that contains all the nuclear fuel elements -- of the Fukushima reactors will hold?
Sure I do.

Am I 100% sure they will hold?
No I'm not![^3] And herein lies the problem.

Those pressure vessels are build very sturdy and the chances of them really blowing up are very slim. The small amounts of radioactivity that got released in the Hydrogen explosions will most likely not have a significant effect on the humans in the vicinity.

So one could wonder why I told my girlfriend to get the hell out of Tokyo on the first flight she could get -- no matter how expensive.

Risk management is not about the most likely case, it's about the worst case scenario. I really do not believe this will turn into a second Chernobyl, but if there is only a one in ten-thousand chance that a full core meltdown with a subsequent explosion might happen, then people that have no obligation to be in the area should leave.

The students at Todai -- at least the ones I know -- are currently not even allowed to go to their labs, so why should they stay in Tokyo, with power outages and stores depleted of food and bottled water?

It's not only me that thinks like this. Most European countries are telling their citizens to get out of Tokyo now, but -- and this brings me to the reason for this post -- there are always people who think they know better than the real nuclear experts.

That's why I decided to reprint an e-mail that a student, who got his information only from following the news, sent to a mailing list for the foreign students studying at Todai.

Dear HOME members,

I hope you and your family and friends are fine.
As a student in Nuclear Engineering and following the Japanese TV and Internet news almost non-stop since Friday night I would like to write more specifically about the situation with the nuclear power plants of Fukushima-1 and 2. I wish I could bring you information and an analysis of the situation which would help you feeling a little bit safer and also help you act calmly and wisely.

Concerning the current situation, the scenario of yesterday might possibly be repeated with a second reactor: Fukushima I-3. It means an explosion of a maintenance building[^4] which gradually fills with hydrogen gas, which reacts violently with oxygen in the air. It won't be in any case, a nuclear explosion. There might be emission of radioactive products but at a comparable level to those of yesterday and therefore no emission of dose presenting a harm for human health.

The first and the most important thing I want to ask you is not to panic.
In the current situation, there is nothing to fear in Tokyo. There are some English chain-mails talking non sense about the current situation. Please do not spread these mails. Please trust the official sources. Maybe some of you think that part of the truth is not revealed by the officials. I would like you to think rationally about this idea. Do you think that there would be any gain for officials to hide the truth after such earthquakes and tsunamis disasters ? Do you think officials wish to increase the number of casualties ? We have to trust the officials and their instructions if necessary. In the current situation Japanese experts and operators are acting calmly, and consider the safety of all of us as their first priority.[^5]

Then I imagine that some of you might want to go back to your countries, buying tickets at really high prices. Please consider that the money you put in an airplane ticket could be used to help people who have lost their home, their families, their friends. I remind you there is currently no risk related to the plants incidents in Tokyo. Based on the current weather forecasts, even if there were emissions from the plants, most of the radioactive products would be flown in the direction of the wind which is currently North East.[^6]

Finally in the case you really do not feel safe, you can take the following measures :

• try to stay at home
• close doors and windows and try to avoid circulations of air through ventilating fans.
• cover your skin with long sleeves clothes and trousers
• if there is any risk of irradiation, please cover your mouth with mask or a wet towel

I remind you these are safety measures just in case, and that these measures are not currently necessary. On the other hand, based on the Japan meteorological agency, there is a 70% chance of earthquake of magnitude 7 in the next 3 days so it might be more careful to avoid any unnecessary movement.[^7]

So stay calm, please watch/read the news (if possible not the translated versions because they give less accurate information) and let us have a thought for people who have lost everything with the earthquakes and tsunamis. Please take care.

Jonathan MAISONNEUVE
Department of Nuclear Engineering and Management
The University of Tokyo

Again I really hope and also expect this crisis to end without a major nuclear incident, but advising people to stay, when the government experts tell them to leave is more than just a bit arrogant.

[^1]: The Fukushima daiichi reactors are not that easily comparable with the one that exploded in Chernobyl, but it can give you a sense of the scale we are talking about. [^2]: Ten Years after Chernobyl published by the International Atomic Energy Agency [^3]: Some experts even think that there has already been a partial meltdown. [^4]: I'm pretty sure it was not a maintenance building that exploded, but I could be wrong. [^5]: While I too believe that the radiation levels will never get strong enough to kill anyone right away, they could increase the cancer rates further down the road. A mass panic in an already dire situation would definitely be worse. So if they can get away with downplaying the situation they just might. [^6]: The weather forecast said the wind would start blowing towards Tokyo within 48 hours. [^7]: To translate this: There are three reactors with severe problems and two others have minor problems and another strong earthquake might hit the area.