Jun 9, 2011
Radiation problems caused by the partial explosion of Fukushima Daiich Power Plant (FDPP) that were triggered by the Great Eastern Japan Earthquake and Tsunami have no doubt caused you considerable anxiety. Presented in a Q&A format, this short article is intended to deal with the questions that you may have with regards to radiation issues at APU.
Q1. Has Oita been affected by the events at the FDPP? If so, what is the level of radiation now?
A. No, Oita has not been affected by the FDPP incident. You may notice from the following diagram (see fig 1) that the level of radiation in Oita has been stable at approximately 0.050 microsieverts per hour (µSv/h) for the last several months. If Oita were affected, the level of radiation in Oita would have shown a major spike in mid March, as has been observed in other cities, but this did not happen.
Q2. With two months having now passed since the earthquake of March 11, what is the current situation in Japan with regards to radiation? Has the situation stabilized or worsened?
A. While a series of partial explosions and fires have occurred at the FDPP, the overall situation is now under control and the operational focus has shifted toward getting the nuclear reactors stable and cool. This overall situation appears also to have been reflected in the radiation statistics of major cities across Japan (see fig 1). For example, the level of radiation prior to the earthquake in Yokohama (located 250 km [150 miles] away from the FDPP) was between 0.021 and 0.029µSv/h. This suddenly shot up to 0.100-0.150 µSv/h on the 15th and 16th of March. The level of radiation began to decline again toward the end of March and continued to fall in April and in May to the current level 0.032 to 0.034 µSv/h or 25% of its peak level.
A. similar trend has been observed in Shirakawa City, Fukushima Prefecture, which is located 80 km (50 miles) away from the FDPP. Shirakawa City registered 7.70 µSv/h on the 15th of March but the radiation has since fallen to its current level of 0.057 µSv/h, or 13% of the peak level. This clearly indicates that the worst period is now over in terms of Japan's radiation problem.
Q3. Then why is the level of radiation in Oita higher than some other cities in Japan?
A. Yes, as you pointed out, the level of radiation of Oita (0.050 µSv/h) is higher than Yokohama (0.030µSv/h,) and Shizuoka (0.035 µSv/h), but this is due to natural radiation and not due to the impact of the FDPP. Humans are constantly exposed to certain levels of natural radiation which occurs mostly from radon gases from soil, other terrestrial sources (uranium, thorium and other radioactive materials) and also from cosmic rays from the sun and outer space. The level of such terrestrial and cosmic radiation differs from place to place which would explain the difference between levels found in Oita and Yokohama/Shizuoka. According to Bloomberg, for instance, in Kerala (India) where thorium is found in abundance, the level of radiation is as high as 3.420 µSv/h.
Q4. How would you compare the levels of radiation in Japan (in Tokyo and Oita) with that of other cities in the World?
A. You can see in the table below that the level of radiation in Tokyo (Shinjuku Ward) is 0.063 µSv/h, and 0.049 µSv/h in Oita (as of May 17, 2011). The table below shows that the level of radiation of these Japanese cities is much lower than many other cities around the world. For instance, radiation in Tokyo is 58% lower than Hyderabad of India (0.150 µSv/h), 52% lower than King's Park, Hong Kong (0.140 µSv/h), 43% lower than Seoul (0.110 µSv/h), 42% lower than Guangzhou (0.108 µSv/h), 21% lower than London (0.080 µSv/h), and 19 % lower than Beijing (0.077 µSv/h). It is ironic to see expatriates fleeing from Tokyo to escape the radiation only to land in cities with even higher levels of radiation.
Q5. What level of radiation presents a health risk to humans?
A. The following table indicates the levels of radiation that are harmful to the human body. This demonstrates that the current level of radiation in Oita is nothing to worry about. In fact, the annual naturally occurring radiation level in Oita is 429 µSv which is less than a single abdominal X-ray (600 µSv).
|Cause of radiation and/or symptoms||Level of exposure (µSv)|
|Light radiation poisoning (mild to moderate nausea, fatigue, 10% risk of death after 30 days)||1,000,000-2,000.000 µSv|
|Mild radiation sickness (headache, risk of infection)||500,000-1,000.000 µSv|
|Lowest dose for any statistical risk of cancer||50,000 µSv|
|Criteria for designating the evacuation zone at the FDPP (annual level)||20,000µSv|
|Full body CT scan||10,000 µSv|
|Typical background radiation from natural sources in North America||3,000 µSv|
|Abdominal X-ray||600 µSv|
|Annual radiation level at Oita||429 µSv|
|One round trip flight between Tokyo and New York||200 µSv|
Source: World Nuclear Association, National Post (Canada), Nikkei (May 11, 2011)
We hope that this information has helped you to understand that the level of radiation at Oita Prefecture is nothing to worry about. Located in the middle of Oita Prefecture, about 1,000 km (625 miles) away from the FDPP, APU is completely safe and remains unaffected by the recent nuclear crisis. In addition, the University is situated on top of a hill some 300 meters high above sea level making it totally safe from the threat of tsunamis. We hope that the above Q&A has provided you with helpful and informative data that will help to put your mind at ease.
Table: Radiation level of various cities in the world (PDF)