Safety regulations of food and water implemented in the first year following the Fukushima nuclear accident
Nobuyuki HAMADA
Haruyuki OGINO
Yuki FUJIMICHI
An earthquake and tsunami of historic proportions caused massive damage across the northeastern coast of Japan on the afternoon of 11 March 2011, and the release of radionuclides from the stricken reactors of the Fukushima nuclear power plant 1 was detected early on the next morning. High levels of radioiodines and radiocesiums were detected in the topsoil and plants on 15 March 2011, so sampling of food and water for monitoring surveys began on 16 March 2011. On 17 March 2011, provisional regulation values for radioiodine, radiocesiums, uranium, plutonium and other transuranic emitters were set to regulate the safety of radioactively contaminated food and water. On 21 March 2011, the first restrictions on distribution and consumption of contaminated items were ordered. So far, tap water, raw milk, vegetables, mushrooms, fruit, nut, seaweeds, marine invertebrates, coastal fish, freshwater fish, beef, wild animal meat, brown rice, wheat, tea leaves and other foodstuffs had been contaminated above the provisional regulation values. The provisional regulation values for radioiodine were exceeded in samples taken from 16 March 2011 to 21 May 2011, and those for radiocesiums from 18 March 2011 to date. All restrictions were imposed within 318 days after the provisional regulation values were first exceeded for each item. This paper summarizes the policy for the execution of monitoring surveys and restrictions, and the outlines of the monitoring results of 220 411 samples and the enforced restrictions predicated on the information available as of 31 March 2012.
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1. THE FUKUSHIMA NUCLEAR ACCIDENT
AND RADIONUCLIDE RELEASE
A magnitude 9.0 earthquake occurred off the northeastern
coast of Japan on 11 March 2011, triggering an ensuing
deadly tsunami with waves reaching as high as 40.5 m.
This disaster caused massive destruction across a wide area:
there have been 15 854 confirmed fatalities with 3089
people missing as of 28 March 2012 [1].
On 11 March 2011, a nuclear emergency situation was
declared due to the accident at the Fukushima nuclear
power plant (NPP) 1 (referred to hereafter as the
Fukushima accident), and Nuclear Emergency Response
Headquarters (NERHQ) were established. All operating
nuclear reactors underwent automatic shutdown upon the
quake, and the emergency diesel generators successfully
started to supply power for nuclear fuel cooling systems.
However, the tsunami swamped the reactors afterwards,
and the generators became inoperable. Elevation of
temperature and pressure inside the reactors resulted in a partial
meltdown and hydrogen explosions. Eventually,
radionuclides were discharged from the stricken reactors. A
preliminary estimate made by the Nuclear and Industrial Safety
Agency of Japan (NISA) indicated that 160 PBq of 131I,
18 PBq of 134Cs and 15 PBq of 137Cs were spewed into the
atmosphere between 11 and 16 March 2011 [2]. The
radioactivity dispersed across the whole northern
hemisphere [35]. The Tokyo Electric Power Company
(TEPCO) estimated the outflow of contaminated water into
the open sea as follows: 520 tons of water containing
4.7 PBq (a total level of 131I, 134Cs and 137Cs) between 1
and 6 April 2011, 10 393 tons of water containing 150 GBq
between 4 and10 April 2011 and 250 tons of water
containing 20 TBq on 11 May 2011 [6]. On 12 April 2011, the
Fukushima accident was provisionally rated as Level 7 on
the International Nuclear and Radiological Event Scale [7],
the same level as the Chernobyl nuclear accident in 1986.
Following the declaration of a nuclear emergency
situation, NERHQ defined evacuation zones, the ranges of
which were expanded depending on the situation. On 12
March 2011, a central circle of 20 km radius from the
Fukushima NPP1 was designated as the stay-away
evacuation zone. On 15 March 2011, its surrounding annular
area between 20 and 30 km was designated as the indoor
evacuation zone, and large-scale atmospheric radionuclide
releases occurred. On 16 March 2011, NERHQ instructed
evacuees under 40 years of age leaving the stay-away
evacuation zone to take pills or syrup of stable iodine to
reduce heath risks to the thyroid [6]. Upon this instruction,
stable iodine (1.51 million pills for 750 000 people and
6.1 kg powder for 120 000180 000 people) was
distributed in Fukushima Prefecture on 16 March 2011, but no
evacuees actually took it because the evacuation had
already been completed. As an exception, the local
governments of Futaba, Tomioka, Miharu towns and Iwaki City
of Fukushima Prefecture had distributed the stable iodine
pills without awaiting the instructions by NERHQ, and
some of those pills were taken ( precise information
unavailable). Surveys of 1149 children living in Iwaki City,
Iitate Village and other areas of Fukushima Prefecture were
conducted late in March 2011 to examine the levels of dose
posed by radioiodines, among which a maximum level
detected was a committed equivalent dose to the thyroi (...truncated)