4.7 Kilograms of Cesium 137

Professor Hiroaki Koide speaks at the Foreign Correspondents’ Club of Japan (FCCJ), Tokyo
April 25, 2014
(1:13:51, in Japanese with an English interpreter)

Nuclear energy expert Professor Hiroaki Koide was recently invited to speak about the Fukushima Daiichi catastrophe at the Foreign Correspondents’ Club of Japan. Professor Koide is known for being one of the few dissident nuclear experts in Japan who defected from the infamous nuclear village. He has now become famous, as much as one can become famous while being largely ignored by mainstream society, for his expert critiques of the nuclear establishment and the way that the Fukushima Daiichi catastrophe has been handled.
During his talk on April 25, 2015, Professor Koide reviewed the history of the Fukushima meltdowns for the benefit of the journalists in the room who might not have been familiar with it. He emphasized how badly the public has been deceived all along about the severity of the disaster. Radiation levels inside the damaged reactors are so high that there is no way yet conceived (nor is there likely to be a way conceived in the future) for man or machine to move the lost nuclear waste to a safer location. There is no way to stop the leaking of radiation into the ocean, and there is a finite limit on how much radioactive water can be stored. He suggested the use of air or liquid metal cooling systems, but thought that eventually the Japanese authorities will concede defeat and just entomb the whole site, somehow.
The only development that gave him a small sense of relief was that the spent fuel from Unit 4 had been removed to a “less dangerous” place. Until that operation was concluded, there had been a constant danger that the damaged building containing the spent fuel would collapse in an earthquake and leave a burning heap of radioactive waste that would have forced the population of Tokyo to evacuate.
These circumstances are all familiar to people who have been following the aftermath of the catastrophe over the past four years. The unique and most interesting thing Professor Koide related was the information at the end of his talk about exactly how much Cesium 137 (according to what can be derived from TEPCO's data) was released in the meltdowns of the reactor cores and the fires in the spent fuel pools. He stated that this isotope was the one of most concern to him, even though there were many others to worry about. There was also heavy metal contamination caused by the release of non-radioactive materials in the fuel rods, but he limited his discussion to Cesium 137 because it is an abundant, long-lasting isotope (half-life of 30 years) which has a significant impact on biochemical processes.
He mentioned that the numbers tossed about when referring to the disaster are so astronomical as to be meaningless to most people. It is difficult to impress upon people the significance of peta and tera becquerels and so on. What do these mean? When should we worry? He asked rhetorically for the audience to guess how many kilograms of Cesium 137 were actually released in the catastrophe, then he answered that, remarkably, the total was only 4.7 kilograms, of which 0.75 kg. fell on Japan. The rest drifted eastward over the ocean, or directly into it. He mentioned too that this calculation was based on only the amounts that TEPCO admits to. The actual amount of Cesium 137 released might be much higher, but according to TEPCO all of the decontamination efforts are being done to recover this 0.75 kilograms that fell on Japanese soil. Even if it were ten times as much (7.5 kilograms) that would still be a very small amount of material to try to recover from a large territory.
In mentioning these figures, Professor Koide drove home the point that it is extremely difficult for humans to conceive of the danger that radioactive materials pose relative to their size and weight. It is the enormous hazard-per-gram ratio that makes nuclear energy so easy to ignore when reactors operate normally, and so difficult to manage when they don’t.
Since the catastrophe struck, communities all over northern Japan have frantically tried to “decontaminate” by scraping off topsoil and storing it in plastic bags in “temporary” storage sites. The photos of these sites, some of them stretching out for hundreds of meters, are now famous symbols of the catastrophe. As the bags of soil were full of seeds, they are now sprouting weeds and grasses, so they have effectively become new radioactive plantations partitioned meaninglessly by decomposing plastic. All this dirt was moved in a desperate attempt to collect 750 grams of a fine mist of radioactive particles spread over thousands of square kilometers.
When people say that a small soda can of uranium could give you all the energy you need for your lifetime, it is important to know that such people are exploiting your intuitive but misguided sense of how size and weight relate to danger. When it comes to the threats posed by radiation, we are led astray if we rely on our evolved instincts for judging threats in our surroundings. As Professor Koide pointed out, if a person were able to hold an amount of Cesium 137 large enough to be tangible, that person wouldn't be alive much longer.
There are some scientists on the pro-nuclear side who have made the radical claim that it is precisely these miniscule quantities of cesium that make the response to the Fukushima catastrophe an extreme over-reaction. They insist that there would be no noticeable impact on health far into the future if there were no evacuations and no attempt at decontamination. Professor Koide was asked about this in the question period after his talk and he dismissed such minimizing. He spoke with typical polite Japanese understatement, but it was clear that he was implying that these scientists should shut their mouths and stop making people doubt their sensible decision to minimize exposure to radiation as much as possible. He reminded everyone that the measures taken after the disaster were made according to laws based on the standards set by the nations that use and promote nuclear energy. He suggested that the minimizers should focus their energies on changing these laws (good luck with that, knock yourselves out, he seemed to imply), but in the meantime they should shut up and stop distracting the public with the suggestion that everyone should just suck up the extra radiation and be happy.


  1. Big no go on those estimates of release. Not 4.7 kilograms

    But 3000 kilograms in inventory, of which probably half was aerosolized

    Just by using uranium in air, found by EPA to comprise 200,000 lbs, and comparing that to the total source, it looks like half of everything was "liberated"


  2. He guessed 4.7kG released. My estimates are the 750kG are now being measured in the Pacific Ocean.