Characteristics and Significance of Decontamination
2.1. Characteristics of Radioactive Contamination and Decontamination
Characteristics of Radioactive Contamination

As a result of analysis by the Nuclear Safety Authority, the total amounts of radioactive substances
released from the TEPCO Fukushima Daiichi NPS were estimated at about 1.1 × 1019 Bq for xenon 133,
1.6 × 1017 Bq for iodine 131, 1.8 × 1016 Bq for cesium 134, 1.5 × 1016 Bq for cesium 137, 1.4 × 1014 Bq
for strontium 90, 1.9 × 1010 Bq for plutonium 238, 3.2 × 109 Bq for plutonium 239 and 3.2 × 109 Bq for
plutonium 240 26,27 , a large amount of radioactive materials was dispersed into the atmosphere. The
dispersed radioactive materials descended to the ground with rainfall, etc., and contamination wasobserved in a wide area, mainly in Fukushima Prefecture.

TEPCO
Fukushima
DaiichNPS

LegendSpace dose rate (μSv / h) 1 m
high from the ground surface[Convert to the value
as of November 5]

TEPCO
Fukushima Daiichi NPS

LegendSpace dose rate (μSv / h) 1 m
high from the ground surface[Convert to the value
as of November 5]

A area where measurement
results are not obtained

Background Map: Electronic
Countries
Background
Map:
Electronic Countries
results are not*This map contains air dose rate by natural radionuclides.

Area where measurement
results are not obtained

Background Map:
Electronic Countries
results are not

Figure 2-1 Results of 4th aircraft monitoring by MEXT (October – November, 2011)
Source: Measurement results of 4th aircraft monitoring by MEXT (December 16, 2011)

Radioactive substances released included cesium 134, 137 and iodine 131, as well as xenon 133, tellurium
129, strontium 89, 90 and plutonium 238, 239, and 240. In subsequent soil surveys, cesium 134, 137,
NERHQ, ”Report of the Japanese Government on the IEAEA Ministerial Conference on Nuclear Safety"(June 2011)
27
MOE, NIRS, "Unified basic data on health effects etc. by radiation FY2016 edition"
26

38

iodine 131, tellurium 129, silver 110, strontium 90, plutonium 238, 239, 240 were observed. 28
Soil surveys conducted by MEXT in June 2011 and January 2012 found plutonium 238, 239, and 240 within
the range of atmospheric nuclear test impacts observed nationwide before the accident from 1999 to 2009,
except in one location where plutonium 238 deposition was detected (at about 1.4 times the maximum valueof plutonium observed before the accident). The strontium 90 was also within the range of the impacts ofpast atmospheric nuclear tests. 28 The 50-year cumulative execution dose of plutonium and radioactive
strontium are very small compared to cesium 134 and 137 at each place where the highest deposition amounts
were detected. 29
Furthermore, since the half-life is as short as about 8 days for iodine 131, about 5 days for xenon 133, andabout 3 days for tellurium 132, there is little medium- to long-term radiation exposure impact, and at thetime of the establishment of the Act on Special Measures (August 26, 2011), the abundance ratio of iodine131, for example, was 0.0001% or less than the ratio immediately after the accident, and it was not detected.
Based on these facts, two nuclides deposited were important for considering human exposure caused by
the TEPCO Fukushima Daiichi NPS accident. These were cesium 134 (half-life of about 2.1 years) andcesium 137 (half-life of about 30.2 years).

In the International Nuclear and Radiation Event Scale (INES) evaluation, which is an international
indicator of the magnitude of accidents and trouble at nuclear power stations, etc., the TEPCO Fukushima
Daiichi NPS accident is at the Level 7 (serious accident), the same as the Chernobyl nuclear accident.
When comparing the amount of radioactive materials released to the atmosphere, the TEPCO Fukushima
Daiichi NPS accident is estimated to be about 10% of the Chernobyl nuclear accident. In other major
accidents, the Three Mile Island nuclear accident was Level 5 (accident with wider consequences),
Tokaimura JCO criticality accident was Level 4 (accident with local consequences). 28
In accidents that occurred in the former Soviet Union, such as the Chernobyl nuclear accident and theSouth Ural nuclear facility accident, the information disclosure and the response of the government, was
not done sufficiently due to information regulations. Also, they occurred in a country with a vast land area
called the former Soviet Union, and accident responses were based on resettlement. Meanwhile, theTEPCO Fukushima Daiichi NPS accident occurred in Japan, a country with a more limited land area
occupied by many inhabitants, and there was an expectation that the accident response would involve
having them return to live. In addition, government announcements and media reports disclosed a lot of
information right from the beginning of the accident, and much information also circulated via the internet,
etc. Meanwhile, the response to radioactive contamination proceeded with a lack of adequate sharing of
knowledge and information between experts and the public about the health effects and risks of radiation. 30

MEXT, “On analysis results of MEXT, (1) analysis results of gamma ray emitting nuclides, and (2) analysis
results of strontium 89, 90 (secondary distribution survey)” (September 12, 2012)

28
29

MEXT, “On the results of nuclide analysis of plutonium and strontium by MEXT” (September 30, 2011)
Prime Minister's Official Website "Enhancement of science education on health risk of radiation - Japan Science Council
Recommendation - " (http://www.kantei.go.jp/saigai/senmonka_g72.html)

30

39

Table 2-1 Comparison of Estimated Emission of Representative Radionuclides of Chernobyl and
TEPCO Fukushima Daiichi NPS
Amount released to the environment
PBq (1015 Bq)
TEPCO
Chernobyl
Fukushima
Daiichi NPSTEPCOFukushima
Daiichi NPS/
Chernobyl

Radionuclide

Half life

Xenon (Xe) 133

About 5 days

6500

11000

1.69

Iodine (I) 131

About 8 days

～1760

160

0.09

Cesium (Cs) 134

About 2 years

～47

18

0.38

Cesium (Cs) 137

About 30 years

～85

15

0.18

Strontium (Sr) 90

About 29 years

～10

0.14

0.01

Plutonium (Pu) 238

About 88

1.5×10-2

1.9×10-50.0012

1.3×10-2

3.2×10-6

0.00024

1.8×10-2

3.2×10-6

0.00018

Plutonium (Pu) 239
Plutonium (Pu) 240

About 24,100
years
About 6,540
years

Source: Ministry of the Environment and Radiological Medicine Research Institute “Unified basic data on health effects,
etc., from radiation. Fiscal year 2016 edition.”

In Japan, about 66% of the country is occupied by forests, about 12% by agricultural land and about 5%
by residential areas, and population density of inhabitable areas tends to be high. 31 Fukushima Prefecture
received the strongest impacts of the TEPCO Fukushima Daiichi NPS accident; the total population before
the earthquake was about 2 million people, and the total area is large at about 14,000 km2, with forests at
about 71%, farmland at about 11%, water surfaces, rivers, waterways, etc., at about 3%, roads at about 4%,
residential areas (including industrial sites, etc.) at about 4%, and other uses (parks, green spaces, resorts
and recreation facilities, abandoned cultivation areas, etc.) at about 7%.32 Also, because the eastern side
faces the Pacific Ocean and the western side is surrounded by mountains, the situation is quite different in
the east and west during the four seasons. There is a lot of snow in the Nakadori (middle) region, and in
Fukushima City, the average number of snow days in the decade from 2005 to 2014 was 74 days a year;
this region is characterized by having many snowfall days compared to the rest of the country. 33 (Figure
2-2)
Furthermore, it is an important point that the accident occurred at the facility for supplying electricity not
for residents in Fukushima area, but for those in Tokyo metropolitan area.

Fifth National Land Use Plan (National Plan) Overview
Fukushima Prefecture, "Fukushima Prefecture Position Manual in FY2016"(https://www.pref.fukushima.lg.jp/sec/11045b/28youran.html)
33
Meteorological Agency, “AMeDAS Fukushima Observatory, Onahama Observatory Observation Results for 10 Years of
2005-2014”
31

32

40

（×10mm）

(Day)

（日）

Fukushima (Naka-dori)
福 島（中通り）

Precipitation
降水量

Snow days
降雪日数

Temperature
気温

30

（℃）

（×10mm）(Day)（日）

Onahama (Hama-dori)
小名浜（浜通り）

Precipitation
降水量

Snow days
降雪日数

Temperature

気温

（℃）

30

30

25

25

25

25

20

20

20

20

15

15

15

15

10

10

10

10

5

5

5

5

0

0

0
1月 2月 3月 4月 5月 6月 7月 8月 9月 10月 11月 12月

30

0
1月 2月 3月 4月 5月 6月 7月 8月 9月 10月 11月 12月(Month)(Month)Figure 2-2 Weather conditions in Fukushima Prefecture (average over the past 10 years)
Source: Meteorological Agency AMeDAS at Fukushima Observatory and Onahama Observatory Observation Results for 10
Years, 2005 to 2014

Fukushima Prefecture borders on six prefectures of the Tohoku (northeastern) region (including Niigata
prefecture) and metropolitan area, has the third-largest area in Japan after Hokkaido and Iwate Prefecture,and is divided into three zones (“Hamadori,” “Nakadori” and “Aizu”). Seven habitable areas are formedon the nodules of six connected axes, with three in the vertical north-south direction and three in thehorizontal east-west direction, making this a multi-polar, decentralized prefectural structure with cities
dispersed on each axis.
It is located in near to the Tokyo metropolitan region, about 200 km from Tokyo, making it a point ofcontact between the Tohoku and the metropolitan regions. It has advantageous geographical conditions forbecoming a base for exchanges of people and goods, for locating businesses and expansion of a mobile
population, via the Tohoku Expressway, Joban Expressway, and Tohoku-Yamagata Shinkansen connecting
the Tohoku area and the Tokyo metropolitan area, as well as the BanEtsu Expressway connecting the
Pacific side and the Japan Sea side of the country, plus Fukushima Airport, Onahama Port, Soma Port andother infrastructure.
Before the disaster, this prefecture was the top power producer in Japan, supplying about one-third of
the electricity consumed in the metropolis and three prefectures in the metropolitan region centering onTokyo. In FY2010, manufactured goods shipments amounted to about 5.1 trillion yen (ranking 20th
nationwide and 1st in the Tohoku area including Niigata Prefecture), agricultural output was valued atabout 233 billion yen (ranking 11th nationwide), and Fukushima was in the top class for agricultural
products capacity nationwide.
It is blessed with the natural environment, and with attractions such as Lake Inawashiro, Mount Bandai
and the Oze Marshland, is well-suited as a place for green tourism and people with two homes, and hasabundant tourism and recreational facilities such as hot springs, golf course and ski resorts. In addition, it
is a place colored by history and tradition, with many cultural assets such as Tsuruga Castle and the41

Shiramizu Amidado Buddhist chapel. 34
Characteristics of Decontamination after the TEPCO Fukushima Daiichi Nuclear Power Station
Accident
The decontamination projects associated with the TEPCO Fukushima Daiichi NPS accident are influenced
by the contamination conditions, geographical factors, and the approach to deal with residents, etc., and havethe following characteristics.

As mentioned above, pollution caused by the TEPCO Fukushima Daiichi NPS accident is mainly causedby radioactive cesium. Radioactive cesium released into the atmosphere by the accident descends to theground with rain, etc., adheres to buildings, soil and plants, etc., and accumulates in rainfall tracks, gutters,
puddles, and depressions, etc. In the environment, cesium is generally more likely to adsorb to soil that
contains clay minerals than to be dissolved in water, and it adsorbs near the surface layer of the soil, suchas in household gardens or farmland.
Also, the locations of radioactive cesium became patchy with the passage of time after the accident,
resulting in some “hotspots” having high doses, due to the fact that radioactive cesium migrates with soil
and other adsorbent materials, influenced by rain and other factors over time, and the tendency toaccumulate depends on the shape and material of the affected structure.
Decontamination work, such as the cleaning of buildings and removal of topsoil, was implemented basedon these characteristics of radioactive cesium and the characteristics of contamination that varied
depending on the target of decontamination.
In general, it is most effective to implement decontamination starting with locations that have high doses,
in order to prevent the spread of contamination by fallout of radioactive substances that have descended to
the ground. However, since cesium tends not to spread much after it has settled in soil, etc.,
decontamination work was implemented with a priority on inhabited areas in order to restore living
conditions.

Under the IAEA’s international rules on measures for decontamination and other environmental
remediation, organizations responsible for contamination countermeasures are expected to formulate
implementation plans and implement decontamination, and regulatory bodies are to approve the plans.
These international rules were not in mind at the time of the establishment of the Act on Special Measures,
but as the TEPCO Fukushima Daiichi NPS accident resulted in extensive contamination and would requirelarge-scale decontamination work, rapid responses would be difficult if it was the polluter implementing
the decontamination. As a result, it was considered to be appropriate to have a framework in which thenational and local governments would be implementing decontamination projects, while also ensuring that
34
Fukushima Prefecture, "Regarding Fukushima's Present Condition and Efforts toward Reconstruction" (5th Symposium of
Decontamination and Waste Technology Council, November 16, 2016)42

the polluter bears unambiguous responsibility.
Also, one issue in the extensive evacuation area was the prompt return of evacuees, who peaked at about
165,000 people, as well as quickly promoting safety and security measures, so decontamination activities
were given the priority, whereas reconstruction plans were not considered. At this time, considering theindication that life under evacuation should be limited to three years, it was assumed that their returnshould occur within three years of the disaster, so original policies stated the goal of completing
decontamination work in Areas under Evacuation Orders within just over two years, by FY2013.

Because of the extensive area contaminated by radioactive substances, the area targeted fordecontamination was extremely large, and according to the Act on Special Measures, the SDA where the
Ministry of the Environment (MOE) was to implement decontamination contained 11 municipalities(population about 80,000 people, area about 1,150 km2), and the Intensive Contamination Survey Areas(ICSA) where municipalities and others were to implement decontamination contained 104 municipalities(population about 6.9 million people, area about 24,000 km2), which included four municipalities in the
SDA. These areas contained many populated areas such as urban areas as well as agricultural lands.
The decontamination projects were unprecedented in the history of public works in Japan and in the world
due to the extensive area involved in large-scale work being done simultaneously in multiple municipalities
over a short period of time. In the SDA alone, a cumulative total of 13.6 million workers were involved
over a period of four years and seven months to the end of January, 2017. The scale of the effort is evident
from the number of workers involved over a short period of time compared with other major civilengineering projects in Japan. (Figure 2-3)（億円）
(Billion yen)
29,00030,00025,00020,000

Total
cost
総工費
（万人）
(Ten thousand people)
3,500

3,160

Decontamination of
Municipalities

市町村
除染

3,000

Decontamination of

14,0002,500

Municipalities

2,000

15,00010,0005,000

Decontamination of

11,300直轄
Government
除染

6,900

Seto Ohashi
瀬戸大橋
Bridge

1,800

1,000

Decontamination
of
直轄

500

1,360

15,000Decontamination
除染

市町村
除染

1,400

1,500

513
0

Total
number of（延べ）workers
作業員数

KurobeDam
黒部ダム

0Seikan Tunnel
青函トンネル900

1,000

Government
除染Decontamination
除染

Seto Ohashi
瀬戸大橋
BridgeKurobeDam
黒部ダム

Seikan Tunnel
青函トンネルFigure 2-3 Decontamination and other major projects in Japan
Note: The total cost of decontamination work is as of September 2017, and the total costs of other civil engineering works
are as of the time of each project.
The numbers of workers for decontamination work under the Ministry of the Environment are as of the end ofJanuary 2018, and the numbers of workers for decontamination work by municipalities are as of the end of
November 2017.
Construction period of each project
Decontamination: July 2012 - March 2017 (4 years and 9 months)

43

Seto Ohashi Bridge: October 1978 - April 1988 (9 years 6 months)
Kurobe Dam: April 1956 - June 1963 (7 years 2 months)
Seikan Tunnel: May 1964 - November 1987 (23 years 7 months)
Source: Bridge and Offshore Engineering Association “Document of Seto Ohashi Bridge Construction” (October1988), Kansai Electric Power Company “Kurobegawa Fourth Power Station Construction History” (September1965), Hokkaido Railway Company “Seikan Tunnel in Numbers”

In addition, the area targeted for decontamination is also characterized by having many places that
suffered damage from the earthquake and tsunami. Particularly in places with significant damage causedby the earthquake or tsunami, it was a challenge to balance the remediation work with the disposal ofresidue and decontamination where housing and infrastructure were damaged. Notably, it was necessary
to consider decontamination work without the benefit of a clear recovery policy in coastal areas that had
ground subsidence, saltwater intrusion, and tsunami deposits, and extensive areas where housing had beenlost. The circumstances differed depending on whether or not it was an evacuation area.
In SDA which were also Areas under Evacuation Orders, residents had evacuated and business activities
were also restricted. As a result, the restoration work of infrastructure, etc., tended to be delayed, but it
was still necessary to proceed with the decontamination work. Actions such as obtaining consent fromstakeholders and explaining decontamination results were to be carried out with cooperation ofmunicipalities at various places where evacuees were located. Since this region, particularly mountainous
areas, did not have well-developed transportation networks and access and accommodation were restricted,
it was necessary to devise the means to transport large numbers of decontamination workers and equipment
to the area, and to secure workers to do the decontamination. Furthermore, because living and farming
were now impossible, houses and roads deteriorated with the passage of time, and agricultural land
converted to grasslands and became overgrown with bushes, which hindered subsequent decontamination
activities.
Meanwhile, in ICSA outside of evacuation areas, decontamination activities were carried out even whilepeople went about their daily lives and farming.

Environmental pollution from a nuclear power station accident had not been expected to occur in Japan,
so the legislative system and framework for responses were not sufficiently developed. For this reason, it
was an urgent task to develop the legislation and a practical framework of procedures for emergency
responses.
Also, as it was necessary to proceed in a situation of insufficient technical knowledge and systems,
decontamination work was carried out in stages using the technical knowledge as available from
Decontamination Model Projects, etc.; first, small-scale “preliminary decontamination” work was done on
facilities that could be used as a base for decontamination, restoration and reconstruction work (municipal
offices and public facilities, etc.); after that, work progressed on to large, full-scale decontamination.
In addition, as MOE was to conduct decontamination work based on the “Basic Policy for the Act on
Special Measures concerning the Handling of Environment Pollution by Radioactive Materials ,” MOE
developed common specifications and standards for cost estimation necessary for decontamination work44and gradually improved them through trial and error in response to the actual situation at thedecontamination sites. In that effort, MOE made use of the existing rules and mechanisms established by
the Ministry of Land, Infrastructure, Transport and Tourism (MLIT) and the Ministry of Agriculture,
Forestry and Fisheries (MAFF), with the assistance of the MLIT and the MAFF, etc., which have abundant
experience in public works projects.
Also, similar to large-scale construction projects, the mobilization of a large number of workers andappropriate command and management are also required under certain radiation environments. Therefore,
large general construction contractors with expertise in large-scale construction and know-how of
construction management such as worker management were used for decontamination works. In
decontamination works by municipalities, depending on the situation, general construction contractors
were used in some cases and local construction companies or other contractors were used in other cases.

Due to the urgency of securing safety as quickly as possible, as well as recovery and reconstruction, there
was no choice but to begin the decontamination work without sufficient time to prepare adequate policies.
Therefore, as mentioned above, the PDCA (Plan-Do-Check-Act) cycle was emphasized, and informationthat was not available or grasped at the preparatory stage was incorporated over time make up for time
constraints that existed at the preparation stage.
Also, it was decided that the scope of decontamination work would include living areas such as residential
areas, schools, parks, large facilities, roads and farmlands, and the forests around residential areas, anddecontamination work then advanced from the perspective of reducing impacts on the living environment.
To carry out decontamination smoothly, it would be preferable to secure disposal sites for removed
materials in advance of decontamination work. However, as it is difficult to secure large-scale disposalsites quickly in advance, decontamination is proceeding by securing a large number of small-scale
temporary storage spaces, referred to as Temporary Storage Sites. It is difficult to secure temporary storage
space in municipalities with ICSA where residents live and farmland is being used. For that reason, after
obtaining consent from the relevant persons, work was also carried out using “on-site storage” and othermeans with temporary storage in yards in decontaminated residential areas, with the aim of completing
decontamination as soon as possible.

In order to enable residents to return to their original lives as soon as possible, it would not be enough tosimply proceed with decontamination, but rather, to proceed with consideration of their subsequent living
so as not to destroy local communities. For this reason, it was decided to proceed with decontamination
focused on community units, such as a neighborhoods or administrative districts.
This was because, besides the fact that decontamination would not be effective unless it was done area
wide, community unit such as neighborhoods and administrative districts are important units for local
decision making and programs in Japan. The same is true when establishing temporary storage sites andevacuation areas, so consideration was given to these units of division.
45

In the ICSA, attempts were made to minimize scraping and wiping so as to avoid destruction of residents’property, etc. Also, for agricultural and other lands, if farmers requested, attempts were made to choose
decontamination methods that would avoid removing the soil surface, so as to maintain the functions ofagricultural soil.
In carrying out decontamination, based on the Act on Special Measures, to the extent possible,
decontamination was done after obtaining consent from residents. It was decided not to forcibly conductdecontamination against residents’ wishes, and rather, in collaboration with residents to comprehensively
judge the situation based on the extent of contamination and the importance from the residents’ perspective,and decide whether or not to conduct decontamination, as well as details of decontamination methods, etc.
Decontamination implementation plans were shared and agreed with residents.

46

Column“Case Study on Overseas Environmental Restoration Work and Lessons”
Mr. Tadashi Inoue,

member of committee

There are several cases of overseas environmental pollution caused by radioactive substances, as
happened centering in Fukushima this time. They are largely divided into pollution of the living
environment of the general public caused by the accident, and contamination of soil and groundwater innuclear facilities (facilities used for manufacturing nuclear materials, etc.). As for significant
environmental pollution caused by an accident, in 1957, at the MAYAK (former secret facility) nuclear
power complex north of the city of Chelyabinsk in the former Soviet Union, there was a failure of thecooling system for storage tanks of high-level radioactive liquid waste generated from the reprocessingof spent fuel. As a result, the liquid waste dried up, the temperature rose, and some components of thedried waste caused a chemical explosion. As a result, contamination of 3.7 × 10 9 Bq/km2 or more spreadover a width of 30 to 50 km and a length of 300 km. The tank that exploded had contained various
radioactive substances, but strontium-90 had the greatest effect on environmental pollution, anddecontamination was done for soils, roads, vehicles, etc. There were more than 200 population
settlements in this contaminated area, more than 1,300 people were evacuated from four villages
immediately after the accident, and later, about 1,200 people moved from 24 villages. I visited this areain 1992, but even then I was required to wear a white coat and protective shoes. (Currently entry into thisarea is severely restricted). I have heard that there are still areas where entry is prohibited.
The next major environmental pollution case was due to an accident at the Chernobyl nuclear power
station in the former Soviet Union (currently Ukraine). However, since many reports (see note) havebeen published about this, I will only briefly describe it here.
In April 1986, the core of Chernobyl Nuclear Power Station Reactor No. 4 exploded and radioactive
materials was dispersed broadly into the environment. The major difference of environmental pollution
between the Chernobyl accident and the TEPCO Fukushima Daiichi NPS accident is that in the formercase the burning continued for 10 days in the reactor, so that the radioactive materials scattered included
not only radioactive iodine, cesium, and strontium, but also such as plutonium and other constituents ofnuclear fuel. (In the latter case was a core melt, so the main materials scattered included volatile iodine
and cesium.) Also, the contaminated area in the case of Chernobyl was much greater than in Japan,
affecting not only the former Soviet Union but also more distant countries such as Finland and Swedenon the Scandinavian peninsula, as well as Austria. Although decontamination of soils, buildings, roads,
water sources, etc., was carried out there from 1986 to 1989, even today entry is prohibited into areas
with high concentration contamination, and in the 30 km no-entry zone, pollution by transuranic elements(plutonium, americium, etc.) will makes agricultural production impossible for the next 1,000 years.
Although decontamination was carried out in the above two examples, the current situation is that in
Chernobyl it was not done as precisely as in Japan, because of the large scale of the country and the low
population concentration.
Based on this experience in Chernobyl, international organizations have played a central role in creatinginternational standards for environmental remediation after an accident. The International Commission47

on Radiological Protection (ICRP) has established the fundamental principles of radiological protection
after an accident (ICRP Pub. 103 (2007) Fundamental Recommendations), the Application of theCommission’s Recommendations for the Protection of People in Emergency Exposure Situations (ICRP
Pub. 109 (2009) Emergency Situations) and the Protection of People Living in Long-term Contaminated
Areas after a Nuclear Accident or a Radiation Emergency (ICRP Pub. 111 (2009) Post-Accident
Recovery). In addition, the International Atomic Energy Agency (IAEA) has issued reports on exposure
dose standards for environmental remediation (e.g., IAEA Safety Guides) and environmental remediation
strategies, etc. These are undergoing revisions currently based on the Fukushima accident. In addition,
the European Commission led the EURONOS project in preparation for the case of an accident like
Chernobyl in the future, and prepared four kinds of guidebooks, including “Residential area management
handbook in Europe,” “Drinking water management handbook,” and “Food production management
handbook.” Meanwhile, the UK has been operating the Windscale Nuclear Power Complex for many
years, and Public Health England published the “Environmental Recovery Handbook” (2009). Also, in
June 2015, the “UK Recovery Handbooks” for radiation and chemical incidents were published.
Next, I will introduce two very particular examples. In September 1987, a Cs-137 capsule that was leftin an abandoned hospital in Goiania, Brazil, was stolen. Due to rumors that there were useful metals in
it, the capsule was opened, Cs-137 spread around the city, and 1 km2 was contaminated. This incident
caused great concern for local residents. In order to restore this area, pollution was removed by
evacuation of about 200 residents, dismantling houses, covering soil with concrete, and removing thesurface soil. Another case was that in 1966, a US military aircraft carrying four nuclear bombs crashedin the air above Spain, plutonium from two bombs was released, causing environmental pollution in the
Palomares region. Four sites and a total of approximately 50,000 m3 of soil were contaminated. As soil
was removed, sieving was carried out as soil decontamination. Again, the concern of the residents was
great, and environmental remediation work and dialogue with the residents were carried out to dispel
them.
Finally, in the UK, France, and the US, some nuclear power complexes have been in use since the1950s, and some soil contamination countermeasures have been done. For example, soil and groundwater
have been contaminated at the Hanford facility in the United States, and the world’s largest cleanup
program has been in progress there since 1989 with target completion in 2050. (The entire facility has anarea of about 2.4 times that of Tokyo’s 23 wards, and access and inhabitation by the general population
are prohibited.)
In all of these cases, as well as experience in Fukushima, the utmost effort was needed for local
understanding, and it has been pointed out that it is important to explain the accident and have theinvolvement of stakeholders (residents, local representatives, business operators, regulatory bureaus,
government, etc.) in environmental remediation. For any repair, this has been raised to be a top priority,
and without it we cannot effectively restore the environment. A woman who was in charge of dialogue
with residents at the Savannah River facility in the United States made an impression when she told methat the US has long experience in communicating with the community, but Japan is still relatively at theentry level, so there is a need to learn from the example of Fukushima in the future.
48

As mentioned above, standards and guidebooks on environmental remediation have been created so far
due to accidents. However, in many countries, when such an accident happens, in many cases strategies
have not yet been established how to evacuate the residents, establish restricted areas, and restore theenvironment, etc. Therefore, it is necessary to create the legislation in advance and prepare frameworks
that ensure the safety of residents and restore the environment as quickly as possible right after an
accident.
Note: One example is “Environmental Consequences of the Chernobyl Accident and their Remediation:
Twenty Years of Experience,” Radiological Assessment Reports Series, IAEA 2006.

49

2.2. The Significance and Objectives of Decontamination
The Significance and Necessity of Decontamination

The decontamination work associated with the TEPCO Fukushima Daiichi NPS accident was the removalof radioactive materials, and shielding, etc., in order to reduce the radiation dose in living areas, based on
the following three methods. 35① Remove (removal)
Remove radioactive materials from living areas by scraping the top soil, removing branches and leaves,washing the building surface, etc., where radioactive materials were attached.
② Block (shield)
Covering the radioactive materials with soil, concrete, etc., can shield the radiation, making it possible tolower air doses and radiation doses.
③ Keep away
The intensity of radiation weakens as one moves away from the radioactive material. Therefore, if you
move the radioactive substance away from people, you can lower the exposure dose to humans. Also,
shortening the time spent near radioactive materials will function as “keeping away.”
RemoveInterrupt

Keep away

Ex) Scraping of top soil /removal of branches and leaves /removal of fallen leaves /washing etc.

Ex) Surrounded by soil andconcrete / Replacement of soil
and lower soil etc.

Ex) Inhibition etc.

Measuring
instrument

Figure 2-4 Methods for reducing exposure doses due to radioactive substances in the environment

How to reduce radiation dose from accident(physical attenuation) and the decay effect due tonatural factors such as wind and rain (weathering),
theradiationdose

decreases

even

if

Radiation dose

Since radioactive substances decrease with time

decontamination work is not done, but it takes a
long

time

to

reduce.

For

this

Before decontamination
Implement decontamination

Before decontamination

reasondecontamination is necessary in order to reduceTimeradiation doses of residents living in contaminatedApproximately 40% will be reduced after two years, about 60% will
decrease after five years, compared to August 2011.*2 In addition, byremoving radioactive materials by decontamination, radiation dose canbe reduced more quickly.

areas, enable the early return of evacuees andrestoration of livelihoods.

Figure 2-5 Natural decay of radiation
35

MOE, “The Decontamination Information Site” (http://josen.env.go.jp/about/method_necessity/index.html)

50

Concepts of Radiation Protection and the Objectives of Decontamination

ICRP is an international organization composed of scientists and experts from around the world who areknowledgeable about radiation protection measures and its recommendations are widely accepted as aninternational standard for radiation protection. Governments in each country implement specific protective
measures based on the basic concepts presented in ICRP recommendations, IAEA guidelines for radiation
protection, and so on.
According to the ICRP’s 2007 recommendations (ICRP Publication 103), 36 if the source of exposuredue to an accident or other cause cannot be controlled, as an “emergency exposure situations ,” anappropriate reference level is set according to the situation in the range of 20 to 100 mSv for annual or
single exposure, and this is used as a measure for planning and implementation of protective measures.
Thereafter, during recovery and remediation (referred to as an “existing exposure situations”), since thelong-term goal is “to lower the exposure to a level that is close to the level considered to be normal, or anequivalent level,” the reference level should be selected from the lower region in the range of 1 to 20
mSv/y.

In the initial protection measures of the TEPCO Fukushima Daiichi NPS accident, evacuation areas
were determined by referring to the disaster prevention guidelines stipulated in “Emergency Preparedness
for Nuclear Facilities” (Nuclear Safety Commission, June 30, 1980) . However, the disaster prevention
guidelines are supposed to be evacuation in a short period of time and indoor evacuation, and there were
no indicators for long-term protection measures in Japan. For this reason, 20 mSv/y which is the lower
limit of the reference level range of 20 to 100 mSv/y that is supposed to be applied to emergency exposure
situations under the ICRP recommendations, and corresponds to the most stringent value, was applied asa reference level for requiring evacuation. 37

Regarding the use of schools, on April 19, 2011, MEXT announced a “Preliminary approach in deciding
how to use school buildings and schoolyards in Fukushima Prefecture,” in accordance with the upper limitof the reference level for existing exposure situations in the ICRP recommendations (1 to 20 mSv/y), anda policy was adopted setting the dose criterion for the use of schoolyards at the air dose rate of 3.8 μSv/h.
(An exposure dose of 20 mSv/y corresponds to 3.8 μSv/h with an outdoor air dose rate assuming a patternof spending 16 hours indoors (wooden building) and 8 hours of outdoor activities, and shielding factor ofwooden houses of 0.4). Later, on August 26, 2011, “On the reduction of doses of school buildings andschoolyards in Fukushima Prefecture” was announced on a more safety-oriented basis, stating that the
government aims for less than 1 mSv/y for the radiation dose that children and students in Fukushima

36

The 2007 Recommendations of the International Commission on Radiological Protection ICRP Publication 103 (August
2009)
37
NERHQ, "Standards for the review of the Areas under Evacuation Orders (Standard 20 mSv/y)" (July 2012)51

Prefecture receive at school.
Regarding concepts of radiological protection of general residents, a statement “About the Basic Conceptof Radiation Protection for Recovery and Release of Emergency Evacuation” released on July 19, 2011 by
the Nuclear Safety Commission, stated that “We will select a lower dose of 1 to 20 mSv annually for range
applied to existing exposure situations. An intermediate reference level can be set to gradually improve
the situation, but in the long term, we aim for 1 mSv/y.”

Even in areas where the estimated annual exposure dose (excluding medical exposure, same hereinafter)is less than 20 mSv/y, the “Basic Concepts for the Promotion of Decontamination” (August 26, 2011,
Nuclear Emergency Response Headquarters) indicated aiming at effective decontamination with anestimated annual exposure dose approaching 1 mSv/y, with the cooperation of municipalities and residents.
This principle was carried over to the basic guidelines based on the Act on Special Measures.
The basic guidelines based on the Act on Special Measures indicate targets for measures such as
decontamination, and in areas where the annual additional exposure dose as of August 2011 was 20 mSv/yor more, the goal was to reduce the dose in stages and quickly. In areas with less than 20 mSv/y, the goal
was 1 mSv/y or less per year in the long term.
The annual additional exposure dose of 1 mSv/y as this long-term goal was originally targeted for the
additional exposure dose to humans, and it was not only for decontamination work, but also governmental
objectives to be achieved including other protective measures. Nonetheless, regarding these basic
guidelines, due to simple quotation of this numerical value, opinions were received that this target wasperceived to be achieved only by decontamination.

In the “Basic Policy for Emergency Response on Decontamination Work” (August 26, 2011 Nuclear
Emergency Response Headquarters) the long-term goal was that the additional exposure dose will be lessthan 1 mSv/y in areas of 20 mSv/y or less. Also, as the approach to decontamination, decontamination wasconsidered necessary in areas with relatively high doses where doses were between 1 and 20 mSv/y, but
in areas with relatively low doses, considering physical attenuation due to natural factors such as wind andrain (weathering effect), radioactive substances basically do not require surface decontamination, althoughdecontamination of places that show high doses locally such as roadside drains and rain gutters (building
eaves) was regarded as important.
Based on this, at the 2nd Investigative Committee on Remediation (September 27, 2011), the criterion
for designation as an ICSA was set as areas where the exposure dose exceeds 1 mSv/y, and actually the air
dose rate of 0.23μSv/h was set as the criterion for designation. This conversion method refers to the method
used when converting 20 mSv/y to 3.8 μSv/h in the “Preliminary approach in deciding how to use schoolbuildings and schoolyards in Fukushima Prefecture,” (April 19, 2011, MEXT Release No. Monka-Su-134).
Regarding the criterion for designation, on November 22, 2011, in “Radiation hazards based on the52

provisions of the Special Measures Law concerning the handling of pollution of the environment byradioactive substances released by nuclear power station accidents caused by the Tohoku Region PacificOffshore Earthquake that occurred on March 11, Regarding the formulation of technical standards
concerning prevention (consultation),” 38 the Minister of the Environment consulted the Chairman of the
Radiation Council, and on December 13, 2011 the Chairman indicated that the decision was appropriate.
39

Based on this, on December 14, 2011, “Ministerial Ordinance that specifies requirements fordesignation of contaminated waste disposal areas” (Ministry of the Environment Ordinance No. 34, in2011) was promulgated.
When considering the standards, numerical values were calculated on the safe side, as there had not yet
been a sufficient accumulation of knowledge for converting radiation doses from air dose rates in the caseof wide area contamination by radioactive substances. Opinions were voiced that for calculations on thesafe side, the shielding effect should not be considered, while other opinions were voiced that more realisticcoefficients should be used and therefore to include the shielding effect and staying time.

In specifying ICSA, it was thought that the additional exposure doses can be estimated by measuring
the air dose rate if certain assumptions are made. For radiation protection in the TEPCO Fukushima Daiichi
NPS accident, under certain assumptions, additional exposure doses of 1 mSv/y are assumed to be 0.23
μSv/h when converted to the air dose rate per hour. The concepts behind this assumption are as follows. 40
・Unrelated to any accident, radiation already exists in nature, and the radiation dose from the Earth is0.38 mSv/y (0.04 μSv/h). 41
・Assuming a daily life pattern of a person who is in an area with a constant air dose rate both spatiallyand temporally, with the person staying outdoors for 8 hours and indoors for 16 hours (assuming awooden house with a shielding coefficient of 0.4), the person’s additional exposure dose will be 1
mSv/y, which corresponds to 0.19 μSv/h for the air dose rate.
※ 0.19 μSv/h × (8 hours + 0.4 × 16 hours) × 365 days = 1 mSv/y・In measurements of the air dose rate using NaI scintillation type survey meter , the radiation dosefrom the Earth is measured within the radiation from nature in addition to the additional exposure
dose due to the accident, 0.19 μSv + 0.04 μSv = 0.23 μSv/hour corresponds to an additional exposure
dose of 1 mSv/y.
The above description is a simple estimation method based on assumptions on the safe side (i.e.,
conservative) in order to determine the scope of ICSA. Some opinion were expressed that the external dose
received by an individual in actual life will be different from the estimated value, and generally can be
38

MOE, “Radiation hazards based on the provisions of the Special Measures Law concerning the handling of pollution of
the environment by radioactive substances released by nuclear power station accidents caused by the Tohoku Region PacificOffshore Earthquake that occurred on March 11, Regarding the formulation of technical standards concerning prevention(consultation)” (November 22, 2011)
39
Radiation Council, "Radiation hazards based on the provisions of the Special Measures Law concerning the handling ofpollution of the environment by radioactive substances released by nuclear power station accidents caused by the Tohoku
Region Pacific Offshore Earthquake that occurred on March 11, Regarding the formulation of technical standards concerning
prevention (Report)" (December 13, 2011)
40
MOE, " Additional radiation dose "1 mSv per year" concept " (October 10, 2011)
41

MOE, NIRS, "Unified basic data on health effects etc. by radiation FY2016 edition"53

lower than the estimated value. The reason is that the time spent outdoors is often shorter than the
hypothetical 8 hours in many cases, the indoor shielding rate differs depending on the type of building, etc.
(e.g., coefficient of 0.2 in concrete construction), the air dose rate attenuates with the lapse of time, and it
depends on where the individual stays and move around in daily activities.

Commentary

Air dose rate and additional exposure dose received by an individual

In Fukushima Prefecture, since FY2011, municipalities have measured the radiation doses using
individual dosimeters, mainly for children and pregnant women. Looking at the correlation between the
air dose rate (average) and individual additional exposure dose (average) in Soma City and Date City,
even in areas where the average air dose rate exceeds 0.23 μSv/h, the average individual exposure dose
may not exceed 1 mSv/y. (See the figure below.)
In addition, the radiation doses from the individual dosimeters measured in each municipality in
Fukushima Prefecture in FY2012 were as follows: Hama-dori municipality A 0.4 mSv/y (estimated value
by area air dose rate 2.9 mSv/y), Hama-dori municipality B 0.7 mSv/y (estimated value by area air dose
rate 2.1 mSv/y), Naka-dori municipality F 0.6 mSv/y (estimated value by area air dose rate 2.4 mSv/y),Aizu district municipality P 0.2 mSv/y (0.7 mSv/y). These values are lower than the exposure dose
estimated from the air dose rate, and it has been confirmed that there are large variations due to personal
lives and behaviors.
<Distribution of average value of air dose rate and annual additional exposure dose>

Average annual
additional
exposure
dose (mSv/y)Soma City
Date City

Air dose rate (μSv/h)* Based on the measurement of Soma City (elementary school students) and Date City (all ages)* The dashed line shows the annual additional exposure dose estimated from the air dose rate.
Source: Discussion meeting with experts on decontamination - thinking from the past findingsin the country and the four cities ~ Fact Book (August 1, 2014)

54