It was Saturday today, and I spent most of the day at home. I could therefore pay close attention to NHK's news podcast as it was broadcast.
Today, NHK broadcasting provided specific quantitative information about radiation levels near the Fukushima reactors, as well as radiation doses that people working at the Fukushima nuclear plant could expect to be exposed to. Inside the plant, radiation emission levels were reported to be at 10 to 15 milli-Sieverts per hour. It was reported that workers at the plant would not be allowed to be exposed to more than 100 to 150 milli-Sieverts of radiation. These values are high. Under normal circumstances, employees in nuclear power plants are exposed to 20 milli-Sieverts per year, and a lifetime total radiation exposure of 350 milli-Sieverts is considered high. In my opinion, this shows that people working to stabilize the situation at Fukushima are taking considerable risks, all in the name of minimizing further hurt to their country and fellow citizens. Their bravery and sacrifice in the cause of public safety should be properly recognized after the crisis passes.
The disclosure of specific radiation levels near the Fukushima plant comes after the international community criticized Japan for not providing clear information about these levels. The Japanese government should be commended for this honest and transparent disclosure of radiation levels, whether or not it has chosen to do so as a result of international pressure. Only honest and transparent disclosure of this information can ensure that the public has trust in the government as it continues to deal with the crisis at Fukushima.
Radiation levels about one kilometer away from the Fukushima plant were reported to have reached approximately 800 micro-Sieverts per hour on Saturday, but then fell to 300 micro-Sieverts per hour. Assuming that the radioactive materials are escaping from the plant uniformly in all directions, radiation levels should follow a (1 / distance-squared) relationship, where the distance is the shortest separation of a point at which a radiation level is measured from the source of the radioactive materials. Assuming that the radiation level 1 kilometer away from Fukushima is 1000 micro-Sieverts per hour, the radiation level 100 km away from Fukushima should be approximately 1 milli-Sieverts per year. Tokyo is some 200 km away from Fukushima, and 1 milli-Sieverts per year is a level comparable to natural background radiation everywhere on Earth. (It was recently reported that radiation levels of 0.6 micro-Sieverts per hour were measured in Tokyo. This is equivalent to 5 milli-Sieverts per year, a value that is consistent with my calculation above, and that is lower than exposure rates experienced by airplane pilots.) Radiation levels 1000 km away from Fukushima should be 10 micro-Sieverts per year. Seoul is approximately 1000 km away from Fukushima, and 10 micro-Sieverts per year is a very small radiation level. It is equivalent to the radiation dose that is absorbed by eating 100 bananas. Of course, higher radiation levels could occur in specific locations if radioactive material is carried by wind.
NHK also reported today that the WHO has stated that radiation levels are low outside a 30 km radius from the Fukushima nuclear plant. The WHO has also stated that radiation levels in Tokyo pose little public health risk, and that there is no public health reason to avoid travelling to Japan, except for the region near Fukushima. The calculations reported above give me confidence in these statements.
It was also reported that some countries want to screen food from Japan for radiation contamination. The Japanese government has also screened foods and, sadly, has found that some foods produced near Fukushima have higher than normal radio activity. Again, the Japanese government should be commended for undertaking such screening and for honestly reporting the results. Only in carrying out such tests in a transparent manner can the safety of foods produced in Japan be verified.
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