Fukushima: Radiation Exposure

(updated June 2013)


No harmful health effects were found in 195,345 residents living in the vicinity of the plant who were screened by the end of May 2011. All the 1,080 children tested for thyroid gland exposure showed results within safe limits, according to the report submitted to IAEA in June.  By December, government health checks of some 1700 residents who were evacuated from three municipalities showed that two-thirds received an external radiation dose within the normal international limit of 1 mSv/yr, 98% were below 5 mSv/yr, and ten people were exposed to more than 10 mSv.  So while the was no major public exposure, let alone deaths from radiation, there were reportedly 761 victims of "disaster-related death", especially old people uprooted from homes and hospital because of forced evacuation and other nuclear-related measures.  The psychological trauma of evacuation was a bigger health risk for most than any likely exposure from early return to homes, according to some local authorities.* 

* eg Dr Shunichi Yamashita, VP Fukushima Medical University. 

In July 2012 a Hirosaki University study reported on I-131 activity in the thyroid of 46 out of the 62 residents and evacuees subject to detailed investigation in April 2011. The median thyroid equivalent dose was estimated to be 4.2 mSv and 3.5 mSv for children and adults respectively, much smaller than the mean thyroid dose in the Chernobyl accident (490 mSv in evacuees). Maximum thyroid equivalent doses for children and adults were 23 mSv and 33 mSv, respectively.  This is consistent with health authorities' screening tests on 1149 children under 15 in March 2011.  Working from these data to estimated maximum doses in the worst-exposed areas in the first week after the accident it was estimated that some children could have received more than 50 mSv dose, still only about one tenth of Chernobyl evacuees.

The residents of Minamisoma town, on the coast 23 km north of Fukushima Daiichi, were found to have very low levels of radiation contamination.  In a study of internal radiation dose, measurements were taken of the full-body contamination from caesium exposure of 9498 residents who had returned to the town and stayed there between September 2011 and March 2012. The study found that two-thirds of the residents had no detectable levels of caesium. Of the rest, only one appeared to have received an equivalent dose more than 1 mSv, and that was 1.07 mSv. The current ambient dose rate in the town is about 3 mSv/yr from external sources, well within the government's 20 mSv/yr limit for returnees.  Some 1500 of the town's 70,000 residents lost their lives in the tsunami.  The internal dose results were published in the Journal of the American Medical Association.

In October 2012 the new Nuclear Regulatory Authority (NRA) released new emergency preparedness guidelines.  Its new emergency planning zones, in line with International Atomic Energy Agency standards, call for 'precautionary action zones' 5 kilometers around nuclear energy facilities and 'urgent protective action planning zones' 30 km around the plants.  NRA then drew up specific evacuation criteria, which local municipalities will use to formulate emergency response plans.

Japan's health ministry set up a special office to monitor the health of workers at the plant. The new office compiles data on radiation exposure for workers for long-term monitoring purposes, and inspects daily work schedules in advance. To March 2013 Tepco has employed some 25,837 workers at the site since the accident, keeping records of their radiation exposure as clean-up and remediation proceeded. Of these, over 95% received less than 50 mSv during the 25 month period; 4% received 50-100 mSv and fewer than 1% received over 100 mSv.