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Fukushima: Radiation Exposure

(Updated September 2014)

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.

Shinji Tokonami et al., Thyroid doses for evacuees from the Fukushima nuclear accident, Scientific Reports, 2:507, DOI: 10.1038/srep00507

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.

Return of evacuees

Supplement to information in main paper:
From April 2012 part of the 20-km radius area and the portion of Minami Soma city extending north from it, were recategorised by the Environment Ministry: below 20 mSv/yr, evacuation called off; 20-50 mSv/yr "restrict residency", allowing entry for specific purposes with no protective equipment required and remediation action to be completed in March 2014 (now 2017); and over 50 mSv/yr "difficulty of return", with restricted entry and remediation deferred. These restricted areas, comprising about half of the 20-km radius evacuation zone, are not expected to drop below 20 mSv/yr before about March 2016. Such areas add to those devastated by the tsunami, where rebuilding is very uncertain.

In July 2012 this zoning was extended by METI to Iitate Village, an area 28-45 km northwest of the Daiichi plant and contiguous with the northern part of Minami Soma city. Most of Iitate’s residents can now return without protective gear or monitoring but not stay overnight, since annual exposure on a continuous basis would be no more than 20 mSv in some parts and 20-50 mSv in others. However, one area of Iitate (about 10 sq km), and a part of Minami Soma joining it and extending into the 20-km radius, remain fully evacuated. In August the Naraha town area south of the plant was added to the minimally-restricted category, below 20 mSv if continually occupied. In December parts of Okuma-machi southwest of the plant and close to it were de-restricted on the same basis. Thus more than half of the original evacuated area (20 km radius plus Iitate and Minami Soma) was then accessible without protective gear or monitoring. The area of Namie town and also Katsurao village outside the 20 km radius remain uncategorised. In March 2013 the government reopened Tomioka and Namie towns, making nine areas to secure redesignation.

From July 2012 to August 2013 this zoning was extended by METI to all municipalities affected by radioactive fallout, both within the 20 km zone and extending beyond it to about 45 km northwest. The extended area includes Iitate, Minami Soma, Namie, Tomioka, Katsurao and Kawamata. Within the 20 km zone, Futaba, close to the plant, was the only municipality still closed to any return of evacuees, but the government relaxed restrictions for the town in May 2013. Most of the houses were destroyed in the tsunami, so return of evacuees is limited by that. Of the total evacuees from around the Fukushima Daiichi plant, some 72,800 lived in the towns and villages of Futaba district. The Futaba district was heavily dependent economically on the plant, with much of its industry geared towards the power sector.

Japan's Reconstruction Agency < http://www.reconstruction.go.jp/english/> reviewed the human toll of the evacuation and reported in August 2012. The stresses of personal involvement in the evacuation, management and clean-up emerged as the biggest factors in ill health for the people affected. Transfer trauma - the mental or physical burden of the forced move from their homes was the cause of 34 early deaths, almost all elderly, reported then. This figure compares with 1916 people from Fukushima, Iwate and Miyagi prefectures that died during evacuation from areas hit by the tsunami and the earthquake. (The figure is additional to the 19,000 that died in the actual tsunami.) The leading causes of most of those early deaths were disruption to the smooth operation of hospitals, the exacerbation of pre-existing health problems, and the transfer trauma or general 'mental fatigue' from dramatic changes in life situation.
Evacuees dying after over a year of fatigue and despair, Japan Daily Press, 13 July 2012

Managing contaminated water, marine effects

Supplement to information in main paper:
A four-year international survey assessing radiological pollution of the marine environment near the plant commenced in July 2011, under IAEA auspices and led by Australia, South Korea and Indonesia. In September 2011, researchers at the Japan Atomic Energy Agency, Kyoto University and other institutes estimated that about 15 PBq of radioactivity (I-131 and Cs-137) had been released into the sea from late March through April, including substantial airborne fallout. In August 2013 Tepco estimated that 20 to 40 TBq of tritium might have leaked into the sea over 28 months since May 2011, which it compared with 22 TBq/yr discharge limit from the six-unit plant normally. The nine-month estimated releases from December 2012 for Sr-90 and Cs-137 were 0.7 and 1.0 TBq respectively, compared with 0.22 TBq/yr combined discharge limit. This is going into the 30 hectare inner harbour area, which is barricaded from the open sea. The radioactive contamination in the sea adjacent to the plant has remained much the same since early 2012, however, at harmless levels. Beyond the barricaded inner harbour, sampling out to 15km has indicated no detectable contamination since December 2011. (In 2013, Cs-134 levels of 0.9 Bq/m3 from Fukushima – 8000 times less than drinking water standards – were detected offshore Vancouver, enabling helpful study of ocean currents.) Radioactive Isotopes from Fukushima Meltdown Detected near Vancouver, Scientific American, 25 February 2014

In July 2014 Tepco began coating 18 ha of sea bed in the plant’s port using cement with bentonite or sand to prevent contaminated sediments moving.

In August 2013 a leak of partly-treated water was discovered and rectified. The water concerned in the puddle on the ground (concentrated by evaporation in hot weather) had 80 MBq/L, and it was initially considered that about 300 m3 (24 TBq) had leaked into the soil in the immediate vicinity of the tank and some possibly moved further. Tepco said that it was the most serious event at the plant since the March 2011 accident, and that "There is a possibility that contaminated earth and sand flowed into the drainage. We cannot rule out the possibility that part of the contaminated water flowed into the sea." The NRA classified the incident as a Level 1 ‘Anomaly’ on INES scale, but a week later raised that to provisional Level 3. At the end of June 2014 Tepco reported to the NRA that it had recovered 80% of the leaked radionuclides by removing contaminated soil, and the other 20% remained deeper but in situ. Tepco said that the leaked water had contained about 45 TBq of strontium activity.