Radiation Exposure at Fukushima

Jonathan Tran
June 13, 2012

Submitted as coursework for PH241, Stanford University, Winter 2012


On March 11, 2011 the 9.0 (MW) Tohoku earthquake and ensuing tsunami struck Japan and caused major problems at the Fukushima Daiichi Nuclear Power Plant. The force of the tsunami swept away the emergency diesel generators designated to provide AC power to Units of 1,2, and 3 of the Fukushima Daiichi Nuclear Power Plant. As a result, hydrogen explosions began damaging the facilities because Units 1, 2, 3 could not be adequately cooled via water injection. [1] Damage to the Fukushima Daiichi Nuclear Power Plant via the explosions and inadequate cooling has resulted in the release of large amounts of radioactive material into the areas surrounding the plant.

Of great concern are the many potential negative health effects on those living around Fukushima. On March 15th 2011, Tokyo Electric Power Company (TEPCO) measured radiation spikes of 10,000 millisieverts of radioactivity per hour at the plant, which, according to Japan's science ministry, is a fatal dose to humans and is enough to radiation to kill an individual within 1-2 weeks of exposure. [2] Oddly, however, Al Jazeera's claim that an exact measurement of the radiation spikes inside the plant could not be gauged because the measuring device's maximum reading is only 10,000 mSv does not agree with a radiation level graph released by TEPCO the day of the accident. Although the graph has been pulled from TEPCO's website for reasons unknown, it details radiation measures of greater than 10,000 millisierverts with no trace of detector saturation. For this reason, claims of maximum of 10,000 millisierverts radiation measurements maybe false although the evidence supporting such a claim no longer exists.

Furthermore, the explosive nature of the accident suggests radioactive dust fallout near Fukushima could have been a possibility. Although no solid evidence can be found detailing radioactive dust fallout, Figure 2B of Anzai et al. may suggest radioactive dust was released. [1] The pattern with which radiation spread, with a dip in levels 50-150 km away from the accident and sudden rise in levels 150-200km away from the accident suggest a radiation dust cloud of some sort being lofted by Southeastern winds. A similar pattern of radiation dust distribution can be seen from the Chernobyl accident. Radiation levels were highest at the site of Chernobyl and in Vyetka, cities separated by about 140 km of land not heavily impacted by radiation. [3] The possibility of gas can be ruled out since as radiation gas is released it is quickly dispersed, similar to Three-Mile Island where no health impacts in areas surrounding the accident were detected. [4]

Although research studies and data from TEPCO does exist about Fukushima, data is still limited. Such a lack of details on the Fukushima incident could result in Japanese individuals not knowing how to protect themselves properly from the accident at Fukushima.

Radiation Exposure

In order to determine what type of health risks those near Fukushima may experience, radiation exposure for these individuals must be determined first. Examining Figure 2A from Anzai et al. one can see that within a radius of 62 km of Fukushima individuals had an exposure of at least 10 µGy h-1 (0.01 mSv h-1). [1] The measurements of such radiation levels were done using car-borne surveys with a 1'' 1'' NaI (Tl) scintillation survey meter that took measurements every minute. To put such a finding in perspective, one should examine Figure 2B from Anzai et al. Since individuals were getting at least 0.01 mSv h-1 between the day of the accident (3/11/11) and the day measurements were taken (3/16/2011), a rough calculation of radiation exposure can be done. In addition, similar radiation absorption calculations can be done between 3/16/2011, 4/11/2011, and 4/25/2011 using the data from Figure 2B. [1] These results are summarized in Table 1.

Cross referencing the 1.531 mSv of radiation individuals within a 62 km radius of Fukushima are receiving at the least with Table 3 from Anzai et al. one finds individuals are receiving from Fukushima about 1/3 of their radiation intake per year, at the least. There is reason to believe, however, individuals within the 62 km radius may have received more radiation than 1.531 mSv. Examining Figure 2A from the Anzai paper, one can see Anzai et al. did not take any measurements within a 62km radius of the accident. Secondly, examination of Figure 2B from the Anzai paper clearly demonstrates radiation levels were not beginning to saturate at any certain µGy h-1 level at the 62km radius. Although Anzai et al. were able to only measure up to a radiation level of 10 µGy h-1, graph trends indicate higher levels of radiation exposure cannot be completely ruled out and more information could have been gathered by the study.

Date Radiation Exposure mSv
3/11/2011- 3/16/2011 24 Hours × 6 Days × 0.01 mSv = 1.44 mSv
3/17/2011 - 4/11/2011 24 Hours × 25 Days × 0.0001 mSv = .06 mSv
4/12/2011 - 4/25/2011 24 Hours × 13 Days × 0.0001 mSv = .031 mSv
Total: 1.531 mSv
Table 1: Calculations detailing the potential radiation exposure of those within the 62 km radius circle. Calculations are done between points in which radiation levels are measured.


Although only a brief calculation was done here to examine the levels of radiation and health consequences of the Fukushima incident, these efforts required combing of information from many scientific journals. Furthermore, documents and research studies pertaining to Fukushima are not as extensive and comprehensive enough to allow full evaluation of the radiation threat. Although the claims made here on the potential radiation impact of Fukushima were derived from educated guesses on existing data, sound evidence for support for these claims cannot be currently found. The low level of transparency and difficulty of access to information does not allow for ease of health and damage assessments of Fukushima and may make many documents on the subject incomplete.

© Jonathan Tran. The author grants permission to copy, distribute and display this work in unaltered form, with attribution to the author, for noncommercial purposes only. All other rights, including commercial rights, are reserved to the author.


[1] K. Anzai, "Fukushima Daiichi Nuclear Power Plant Accident: Facts, Environmental Contamination, Possible Biological Effects, and Countermeasures," J. Clin. Biochem. Nutr. 50, 2 (2012).

[2] D. Jamail, "Fukushima Radiation Alarms Doctors," Al Jazeera, 18 Aug 11.

[3] Radiation from Chernobyl, "Chernobyl Radiation Map, International Atomic Energy Agency: The International Chernobyl Project: Surface Contamination Maps, 1991.

[4] J. G. Kemeny et al., "Report of the President's Commission on the Accident at Three Mile Island," Office of the President, October 1979.