REPORT

Fukushima, one year later
Initial analyses of the accident and its
consequences
Report IRSN/DG/2012-003 of March 12, 2012

% of deposit surface area

Spent Fuel Pool

Cesium 137 surface activity (in KBq/m2)

Editorial
Starting on March 11, 2011, IRSN mobilized to assist in the analysis of developments and probableradiological consequences of the nuclear accident caused by the earthquake and tsunami at the
Fukushima Dai-ichi site some 200 km northeast of Tokyo. IRSN’s analyses, performed in real timeusing data provided by the facility operator and Japanese authorities, gave French authorities,
including the French president and his administration, the French Nuclear Safety Authority (ASN),
elected officials, and the French ambassador to Japan vital information during the critical phaseof the accident to help protect the French expatriate community of several thousand people
residing in Japan. IRSN provided perspective and forecasts with total transparency bysystematically publishing the results of its analyses and facilitating media access to thisinformation.
A year later, this mobilization continues on several fronts. First, by monitoring the situation in
Japan, whether it concerns what will become of the damaged reactors, the radiologicalconsequences of radioactive releases for workers, the environment and the population living incontaminated regions. This report covers what has been done in this area, often in close
coordination with IRSN's scientific partners in Japan and other countries.
The conclusions to be drawn from this accident, which demonstrated for the first time that a
cataclysmic natural event could cause a major nuclear accident, constitute another element of
the IRSN’s ongoing mobilization. With this in mind, IRSN in the framework of the European “stresstest” approach has formulated ambitious proposals, which have now been adopted by the ASN, toincrease the protection of nuclear installations from severe risks which until now had been
considered too unlikely to be considered. These discussions on the need to improve risk
prevention have also led to identifying the need for new research programs, which will be
undertaken as part of an international framework, and seeking on European level to strengthen
management in the event a major nuclear emergency, which would inevitably have majorrepercussions for most of the continent. The report submitted by IRSN to ASN on the results andproposals following the stress tests has been made public. With the same concern fortransparency, IRSN will also publish the results of its research on additional means to prevent therisks of nuclear accidents.

Jacques Repussard

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Abstract
The earthquake of magnitude 9 of March 11, 2011 with an epicenter 80 km east of the Japanese island of Honshu,
and the subsequent tsunami, severely affected the region of Tohoku, with major consequences for its populationand infrastructure.
Devastating the site of the Fukushima Dai-ichi nuclear power plant, these natural events were the cause of thecore meltdowns of three nuclear reactors and the loss of cooling of several spent fuel pools. Explosions also
occurred in reactor buildings 1 through 4 due to hydrogen produced during fuel degradation. Very significant
radioactive releases into the environment took place. The accident was classified level 7 on the International
Nuclear Event Scale (INES).
This report provides an assessment and perspective on the information gathered by IRSN during the first twelve
months following the disaster in an effort to understand the condition of the installations, evaluate the releases
and analyze and evaluate the consequences of the accident on workers and the impact on the population and theenvironment.
On the basis of available information, the report provides an initial analysis of the chain of events. It should be
noted that a year after the accident, the full sequence of events is still not understood. Operating experience
feedback from the 1979 Three Mile Island accident in the United States, in which reactor core damage was notconfirmed until 1986, suggests that it may be several years before a detailed scenario can be constructed of theaccident that led to radioactive releases. It will require access to the damaged installations.
The situation at the site remains dangerous (reactor pressure vessels and containments are not leaktight, diffuse
releases, etc.). If it has significantly improved as a result of the significant resources deployed by the Tokyo
Electro Power Company (TEPCO) to regain control of the installations, this effort must continue over the long term
to begin evacuation of fuel from pools (in two years) and remove degraded fuel from reactors (in ten years), as has
been announced.
An assessment of quantities of radioactive releases to the air and water as well as their dispersion is given here
but must be considered provisional. It should be noted that a significant effort has been made in Japan tocharacterize environmental contamination, which has greatly diminished in the weeks and months following theaccident due to the virtual disappearance of short-lived radionuclides. The highest risks for the population wereconcentrated in the initial months. Today and for years to come, the environment remains contaminated byradioactive cesium that will complicate the return of evacuated residents to the most contaminated regions.
Removing residual deposits will be a difficult, long and waste-producing process. Another long-term impact may
remain for the agricultural production in the most contaminated regions; it may be reduced using appropriate
practices and close monitoring. Natural environments (forests) will remain the most vulnerable over time, also
because of cleanup difficulties.

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With regard to the health aspects of the disaster, IRSN’s work concerned initial assessments of doses the Japanese
population may have received during the release phase and external exposure to radioactive deposits during thefirst year after the accident. The various epidemiological monitoring studies on the Japanese population carriedout locally are presented. According to Japanese authorities, received doses are less than 100 mSv. Although it is
not certain that at this dose level an excess of the risk may be detected by epidemiological studies, these studies
are nevertheless indispensable because they respond to a legitimate demand by the population. They also provide
new information about exposure to low doses of ionizing radiation. There is however a lack of measurements for
exposed persons, especially children exposed to radioactive iodine.
To date, the Japanese authorities have not provided any report on health consequences observed in workers. The
only currently available information on doses received by workers is that provided by TEPCO for its employees andsubcontractors involved in operations at the Fukushima Dai-ichi nuclear power plant. No precise information
concerning the other categories of exposed workers (firemen, police officers, municipal employees, civilian
security personnel) has been obtained, even though at least some of these workers have undergone dosimetricmonitoring. To date no deterministic effect attributed to acute exposure to radioactivity has been observed,
however it is very difficult at present to obtain precise information about worker exposure and its health effects.
The present report also describes work launched in 2011 by the United Nations Scientific Committee on the Effectsof Atomic Radiation (UNSCEAR) with a view to producing an initial report on assessing exposure levels in theenvironment and populations related to the accident at the Fukushima Dai-ichi nuclear power plant and theconsequences for human health.

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TABLE OF CONTENTSFOREWORD..........................................................................................8
1. IRSN’S EMERGENCY RESPONSE CENTER ....................................................8
2. INTRODUCTION TO BOILING WATER REACTORS ........................................ 10
2.1. GENERAL DESCRIPTION ........................................................................................102.2. CONTAINMENT BARRIERS ......................................................................................10
2.3. SAFEGUARD SYSTEMS ..........................................................................................122.3.1. Isolation condenser - IC ..................................................................................122.3.2. Reactor core isolation cooling system – RCIC.........................................................13
2.3.3. High Pressure Core Injection system - HPCI ..........................................................142.3.4. Safety relief valves – SRV ................................................................................142.3.5. Hardened Venting System - HVS ........................................................................15

3. TOHOKU EARTHQUAKE OF MARCH 11, 2011 ........................................... 16
4. CONSEQUENCES ON THE FUKUSHIMA DAI-INI, ONAGAWA, TOKAI, HIGASHIDORIAND HAMAOKA REACTORS ..................................................................... 21
5. FUKUSHIMA DAI-ICHI ACCIDENT ........................................................... 225.1. ACCIDENT SEQUENCE, MARCH 11-25, 2011.................................................................23
5.1.1. Reactor 1 accident sequence ...........................................................................25
5.1.2. Reactor 2 accident sequence ...........................................................................27
5.1.3. Reactor 3 accident sequence ...........................................................................29
5.1.4. Spent fuel pools ...........................................................................................31
5.1.5. Atmospheric releases.....................................................................................35
5.2. ACCIDENT SEQUENCE: MARCH 25-APRIL 17, 2011 .........................................................37
5.3. FROM APRIL 17, 2011, ONWARD .............................................................................37
5.3.1. Gradual regaining of control of the facilities ........................................................37
5.3.2. The mid- and long-term roadmap ......................................................................38
5.4. REMEDIATION MEASURES ......................................................................................39
5.4.1. Damage suffered by the cores of reactors 1, 2 and 3 ...............................................39
5.4.2. Status of the SFPs.........................................................................................40
5.4.3. Containment of the facilities ...........................................................................40
5.4.4. Protection of the facilities from future earthquakes and tsunamis ..............................41
5.4.5. Current radioactive releases ............................................................................41

6. ENVIRONMENTAL IMPACT IN JAPAN ...................................................... 43
6.1. ATMOSPHERIC DISPERSION OF RADIOACTIVE RELEASES ..................................................44
6.1.1. Characteristics of the radioactive materials released into the air by the accident............44
6.1.2. Modeling of the atmospheric dispersion of releases in Japan .....................................49
6.2. CONTAMINATION OF JAPAN'S TERRESTRIAL ENVIRONMENT..............................................55
6.2.1. General comments on the deposition of radioactive fallout in Japan............................55
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6.2.2. Map of the radioactive fallout in Japan ...............................................................57
6.2.3. Isotopic composition of the fallout, changes over time and spatial variations .................68
6.2.4. Interpretation of the source and distribution of radioactive fallout in Japan ..................80
6.3. IMPACT OF RADIOACTIVE FALLOUT ON AGRICULTURE IN JAPAN .......................................83
6.3.1. How did crops and animal-source foods become contaminated? .................................83
6.3.2. Overall assessment of contamination of foodstuffs in Japan ......................................85
6.4. CONTAMINATION IN THE MARINE ENVIRONMENT..........................................................99
6.4.1. Description of the marine area exposed to discharges ............................................ 100
6.4.2. Characteristics of marine radioactive pollution around the fukushima dai-ichi power plant..................................................................................................................... 101
6.4.3. Estimate by IRSN of the quantities of cesium 137 released into the sea ...................... 105
6.4.4. Simulation of the dispersion of cesium 137 in seawater off the coast of Japan.............. 110
6.4.5. Comparison of the evaluations of radioactive releases at sea................................... 112
6.4.6. Radionuclides in sediments ........................................................................... 116
6.4.7. Radionuclides in marine and river–marine species ................................................ 118
6.5. FORESEEABLE IMPACT ON THE TERRESTRIAL AND MARINE ECOSYSTEMS ............................ 122
6.5.1. Basic principles for assessing the ecological impact of a nuclear accident ................... 123
6.5.2. Impact analysis for terrestrial ecosystems around the Fukushima Dai-ichi power plant .... 126
6.5.3. Impact analysis for marine ecosystems ............................................................. 128
6.5.4. Projects initiated by irsn on the ecological consequences of chronic exposure to low doses
following a nuclear accident .................................................................................. 129

7. ACTIONS TO PROTECT POPULATIONS AND POST-ACCIDENT MANAGEMENT IN
JAPAN .............................................................................................134
7.1. EVACUATION OR PROTECTION.............................................................................. 134
7.1.1. Emergency protection actions ........................................................................ 134
7.1.2. Additional protective actions implemented from april 2011 .................................... 135
7.2. MANAGEMENT OF FOODSTUFFS IN JAPAN ................................................................ 137
7.3. PREPARATION FOR THE RETURN OF POPULATIONS AND DECONTAMINATION ACTIONS ........... 139
7.3.1. Population return strategy announced in Japan ................................................... 139
7.3.2. Decontamination actions .............................................................................. 139

8. DOSIMETRIC AND HEALTH IMPACT IN JAPAN ..........................................145
8.1. GENERAL CONCEPTS ......................................................................................... 146
8.2. EXPOSURE OF WORKERS AND OTHER PARTICIPANTS ON THE FUKUSHIMA DAI-ICHI SITE .......... 147
8.3. EXPOSURE OF THE JAPANESE POPULATION .............................................................. 148
8.3.1. The various population exposure pathways for radioactive substances released into theenvironment...................................................................................................... 148
8.3.2. Estimate of the doses likely to have been received by the local population during theatmospheric release phase..................................................................................... 151
8.3.3. Estimate of the doses likely to have been received by the local population from external
exposure to radioactive deposits ............................................................................. 154
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8.3.4. Risks associated with internal exposure from ingestion of contaminated foodstuffs ........ 159
8.4. RESULTS OF CHECKS CARRIED OUT BY IRSN ON FRENCH NATIONALS ................................ 162
8.5. HEALTH EFFECTS AND MEDICAL MONITORING OF EXPOSED WORKERS ............................... 166
8.5.1. Health effects ........................................................................................... 166
8.5.2. Medical monitoring ..................................................................................... 167
8.6. EPIDEMIOLOGICAL MONITORING OF EXPOSED POPULATIONS IN JAPAN .............................. 167
8.6.1. Principle of the studies conducted................................................................... 167
8.6.2. Progress and initial results ............................................................................ 168

9. VERY LONG-RANGE IMPACT ...............................................................172
9.1. IMPACT IN FRANCE AND IN FRENCH OVERSEAS DEPARTMENTS, REGIONS AND COLLECTIVITIES . 172
9.2. ATMOSPHERIC CONTAMINATION IN EUROPE.............................................................. 173
9.2.1. Scope of the analysis ................................................................................... 174
9.2.2. Air monitoring stations................................................................................. 174
9.2.3. Results and discussion.................................................................................. 175

10. CONCLUSION ................................................................................182
10.1. AT THE INTERNATIONAL LEVEL ........................................................................... 182
10.2. AT THE NATIONAL LEVEL .................................................................................. 186
10.3. NEED TO CHANGE RESEARCH PRIORITIES................................................................ 187

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FOREWORD
On the basis of information made public about the condition of the Fukushima Dai-ichi nuclear power plant, thisreport provides a summary, a year after the accident, of information gathered by IRSN on what is known about theaccident and its health and environmental consequences.
Initially, during the weeks following the earthquake and tsunami that led to the accident, IRSN's emergency
response center analyzed the situation to assist the French embassy in Japan and French public authorities inunderstanding the situation, its issues, scenarios and possible consequences, to inform the public at large andassist firms (French industrial firms in Japan, airlines, etc.) dealing with the consequences of the accident. In late
April 2011, at the end of the emergency, a project structure was set up at IRSN to pursue the work of analyzing
the accident and its consequences. The objective is to draw lessons from this disaster and advance scientific andtechnical knowledge, reconsider technical policies to help prevent the recurrence of such accidents, and better
manage emergency and post-accident situations.
It should be noted that one year after the accident, the complete sequence of events is still not clear. Operating
experience feedback from the Three Mile Island accident that took place the United States in 1979, in which
reactor core damage was not confirmed until 1986, leads to the conclusion that it may take several years toreconstitute a detailed scenario of the accident that led to radioactive releases. This will require access to thedamaged installations.

1. IRSN’S EMERGENCY RESPONSE CENTER
Operation of the emergency response center during the Fukushima accident
At 6:46 am Central European Time on Friday, March 11, 2011, a very high magnitude earthquake occurred east of
the Japanese island of Honshu, resulting in emergency shutdown of some ten Japanese nuclear power plants. The
earthquake was followed by a tsunami.
In response to the news from Japan, IRSN decided to activate its emergency response center at 11:00 am. At
11:52, the first conference call to assess the initial situation was organized by Météo France1 (which had been
alerted by the International Atomic Energy Agency, IAEA), Department of Civil Defense and Emergency
Preparedness of the Interior Ministry and Nuclear Safety Authority (ASN). The emergency response center remained
operational for six weeks, including four weeks with round-the-clock staff, until 11 am on April 29.
The emergency response centre initially included units for administration, installation assessment, assessment ofradiological consequences, communication, and support and logistics. A general administrative unit was quickly
added, as well as a health unit on Monday, March 14, responsible for handling outside requests concerning people
that may have been exposed to releases from the accident or worried about their health, and an environment unit
was set up on Saturday, March 19, to organize increased environmental monitoring of radioactivity in France andits overseas departments, regions and collectivities. On Tuesday, March 15, engineers from AREVA and EDF who
could speak and read Japanese joined the emergency response center, where they served in shifts over the next
four weeks. On Sunday, March 13, in coordination with the emergency response center, IRSN dispatched one of its
experts to Tokyo as part of a civil protection mission assisting the French Ambassador. His mission lasted one
month.

1

French national meteorological service, French representative at the World Meteorological Organisation
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During its four weeks of round-the-clock operation, the center numbered at least 30 experts during the day,including three spokespeople, and at least 20 at night. In total, 200 people were mobilized from IRSN’s staff of
1,700.
IRSN’s leaders participated in daily meetings organized by the secretary general of the presidency and the prime
minister’s cabinet director, as well as meetings with the Quai d'Orsay2's emergency response team and theinterministerial emergency response committee chaired by the secretary general of national defense and security.
IRSN’s emergency response center was in permanent contact with the ASN’s own emergency response center andparticipated in a daily conference call with the French embassy in Tokyo.
The need for information by the media and the public required adapting to communication resources and tools.
Three representatives were quickly named for specific fields: facility safety, environment and health. IRSN's
website was modified to handle the increased traffic, and the database of radioactivity measurements in France
and its regions and collectivities abroad were made available to the public. Information bulletins for Frenchnationals living in Japan were also issued regularly.
Lessons from operation of the emergency response center
The first operating experience feedback on the operation of the IRSN’s emergency response center shows that thetechnical support center performed well (thanks to its tools and the training of the experts) and IRSN’s work overthe past several years in preparing post-accident situations (research on the Chernobyl accident) and its active
involvement in the work of the steering committee for the management of the post-accidental phase of a nuclear
accident (CODIRPA) have enabled it to anticipate health and environmental issues reasonably well.
Lessons, both technical and methodological, were however learned about atmospheric dispersion, the impact ofradionuclides on the marine environment, deposits, radioactivity measurements, etc., as well as the need tointernationalize IRSN's assessment tools to extend their use to the various types of nuclear facilities found abroad.

From an institutional perspective, IRSN fully performed its role as a public expert by supporting numerous publicauthorities that were involved in managing a major nuclear emergency, even if it took place abroad. This includes
ASN, to which IRSN provides ongoing technical support, as well several ministries involved in various aspects ofemergency management, including products imported from Japan, the embassy responsible for protecting andinforming French nationals in Japan, and several large French firms working in Japan. In total, IRSN produced 58
information reports for French authorities and responded to more than 94 requests from various ministerial
departments, including 36 from ASN.

2Minister of Foreign Affairs
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2. INTRODUCTION TO BOILING WATER REACTORS
2.1. GENERAL DESCRIPTION
The boiling water reactor (BWR) is one of two types of light water reactors (LWRs); the other, used in France, isthe pressurized water reactor (PWR).
BWRs (Figure 2-1) differ from PWRs in that water turns into steam when it passes through the reactor core and thesteam goes directly to the turbine without use of an intermediate cooling system (“secondary system”) in PWRs. In
this sense BWRs closely resemble a traditional forced recirculation boiler.

1 Reactor Pressure Vessel (RPV)
2 Nuclear Fuel Rod
3 Control Rod
4 Circulating Pumps
5 Control Rod Motors
6 Steam
7 Feedwater
8 High Pressure Turbine
9 Low Pressure Turbine
10 Generator
11 Exciter
12 Condenser
13 Cold Water
14 Pre-reheater
15 Feedwater Pump
16 Cold Water Pump
17 Concrete containment (or container)
18 Connection to electric grid

Figure 2-1 – Diagram of general operation of a BWR

2.2. CONTAINMENT BARRIERS
As with PWRs, there are three containment barriers between radioactive materials and the environment, withsome differences:a)

Fuel element cladding. Fuel element cladding contains radioactive products. In BWRs, leaktightness isparticularly important to avoid contaminating the turbine, as seen in the cladding being 50% thicker
than that found in PWRs.

b)

Main cooling system. In contrast with PWRs where water circulating in the system must remain liquid,water in BWRs boils and is not kept at the same high pressure (operating temperature for the tworeactor types is similar). Consequently, parts making up the BWR reactor coolant system are not as
thick.

c)

Reactor containment. It has evolved over time. At Fukushima Dai-ichi, the containment for reactors 1
to 5 is the MarK I type (Figure 2-2) and MarK II for reactor 6 (Figure 2-3).

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BWR reactor containments are very specific, but in general include:-

drywell, the upper part of the containment, the reactor pit; the drywell is made inert withnitrogen;-wetwell, the lower part of the containment (which is toroidal in shape on the Mark I); thewetwell is half filled with water (suppression pool) and its free surface area is topped withnitrogen.

The drywell and wetwell are connected by several vents through the water contained in the wetwell.
The wetwell is mainly used in two situations:-in the event of pipe rupture, the water/steam mix is directed to the suppression pool where it
condenses through sparging in the water, which limits the pressure increase in the reactor
containment, designed to resist a pressure of approximately 3.5 bars;-

if the containment pressure becomes too high, releases to the outside may occur. Lines withvalves are connected to the wet- or drywell for this purpose;-

if necessary, water in the reactor pressure vessel (RPV) can be drained using pipes connecting
the RPV and suppression pool.

In both cases, the suppression pool must be cooled using a dedicated system, which is one of the roles of the
Residual Heat Removal System (RHRS).

Wetwell,including
Suppression Pool

Figure 2-2 – Mark I reactor containment

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11/188Figure 2-3 - Mark II Reactor Containment
The reactor building includes the reactor containment as well as the spent fuel pool (SFP) in which new andirradiated fuel assemblies are stored. The building is not considered leaktight.

2.3. SAFEGUARD SYSTEMS
Only a limited number of systems were challenged during the initial phase of the accident since the others were
unavailable due to the lack of electrical power or cooling. These include:
1)

Isolation Condenser (IC), which is only found on reactor 1, which is a BWR/3 model;

2)

Reactor Core Isolation Cooling (RCIC), which is only found on reactors 2 and 3, which are BWR/4 model;

3)

High Pressure Coolant Injection (HPCI), which is installed on the three reactors, but briefly functioned
only on reactor 3;

4)

Steam Relief Valves (SRV);

5)

Hardened Venting System (HVS).

This chapter presents the operating principles of these systems using the acronyms given above.

2.3.1. ISOLATION CONDENSER - ICThis system (Figure 2-4) cools the core when the main condenser is not available to remove heat (12 in Figure 2-1).
Steam flows through pipes located in the upper part of the RPV to a heat exchanger located in a water reserve.
There, steam condenses and the heat exchanger/reserver serves as a condenser. Gravity forces condensed waterto return to the RPV through pipes connecting the condenser and the lower part of the vessel. Natural forces
provide for circulation without the need for pumping as long as valves are open. Nevertheless, the heattransmitted to the condensers is removed as water evaporates to the atmosphere, with the water reserve
requiring makeup.

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12/188Figure 2-4 - Fukushima Dai-ichi – Schematic diagram of IC system (reactor 1)

2.3.2. REACTOR CORE ISOLATION COOLING SYSTEM – RCIC
This system (Figure 2-5) cools the core when the reactor is at shutdown or when normal feedwater systems areunavailable (steam isolation valves to the turbine are closed or the feedwater pump is unavailable). The steam
produced in the RPV by residual heat runs a turbine that activates a pump which injects water from several
possible sources (including the suppression pool and condensate storage tank) in the RPV. The steam in this turbine
is then returned to the suppression pool where a dedicated system cools it (see section 2.2).

Figure 2-5 – Schematic diagram of
RCIC system (reactors 2-5)

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2.3.3. HIGH PRESSURE CORE INJECTION SYSTEM - HPCIThe system (Figure 2-6) injects water into the core using a spray ring located above the assemblies. The water
comes from the condensate storage tank or suppression pool if no water is available from the condenser. The
name of the system and the type of pump that ensure water circulation in the system vary by BWR type (for all
reactors at Fukushima Dai-ichi, the system is HPCI and uses a pump supplied by a dedicated turbine).

Figure 2-6 –Schematic diagram of HPCI system

2.3.4. SAFETY RELIEF VALVES – SRVThis system controls pressure in the RPV (Figure 2-7). There are two types of valves:
1)

safety valves, three per reactor, open at relatively high pressure and release directly into thedrywell,2)

main steam safety relief valves release water into the suppression pool. The valves arepneumatic, using compressed air. Air is provided to each valve through an air line using asolenoid valve (zig-zag). If electrical power is lost, the solenoid valves are unloaded and thesafety relief valves are closed.

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14/188Figure 2-7 – Schematic diagram of safety release valve (SRV) on reactor 1

2.3.5. HARDENED VENTING SYSTEM - HVS
The pressure relief system for emergency situations is a recent modification. Before Chernobyl, these reactors had
only a venting system for normal operation. The system was not designed to operate in severe accident conditions.
Following the Chernobyl accident, the US Nuclear Regulatory Commission chose to modify General Electric’s BWRs
in the US by adding a Hardened Venting System for emergency situations. The HVS was installed on the Fukushima
reactors between 1999 and 2001.
The pressure relief system for the MARK-I reactor containments in Fukushima 1, 2 and 3 is shown below.

Figure 2-8 - Schematic diagram of containment pressure relief system – reactor 1

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3. TOHOKU EARTHQUAKE OF MARCH 11, 2011
Throughout its history, Japan has known numerous deadly earthquakes. The most recent include Zenkoji (May 18,
1847, magnitude 7.4, 34,000 dead), Sanriku (June 15, 1896, magnitude 7.6, 22,000 dead), Tokyo (September 1,
1923, magnitude 8.3, more than 100,000 dead) and Kobé (January 16, 1995, magnitude 7.2, 5,502 dead).
At 2:46 pm local time on Friday, March 11, 2011, a powerful earthquake of magnitude 9.0 struck Japan. It was thestrongest quake ever recorded in Japan and ranks as the fourth strongest quake recorded since the eighteenth
century (Figure 3-1). The earthquake was centered 80 km off the coast east of Honshu and 370 km northeast ofTokyo. A very large tsunami (ranging in size from several meters to some ten meters) quickly ensued, striking theeast coast of Honshu and producing a very large number of victims (some 20,000) and very significant material
damage. Two days before, a strong temblor of magnitude 7.2 and three with magnitudes over 6.0 had alreadyshaken the region without suggesting the subsequent catastrophe. In hindsight, the events are considered
precursors to the March 11 earthquake.
Year
1960
1964
2004
2011
1952
1868
1700
2010

Location
Magnitude
Chile
9,5
Prince William Sound, Alaska
9,2Sumatra-Andaman Islands
9,1
Near the East Coast of Honshu, Japan
9,0Kamchatka
9,0
Arica, Peru (now Chile)
9,0Cascadia Subduction Zone
9,0
Offshore Bio-Bio, Chile
8,8

Figure 3-1- Highest magnitude quakes recorded
since 1700 (USGS/NEIC).
The Japanese archipelago is located in an area where
three major tectonic plates converge and form acomplex geodynamic structure (Figure 3-2). In thesouth, the Philippine plate slides under the Eurasianplate, while in the north (off the coast from Tokyo), the Pacific plate slides under the Philippine and Eurasianplates. The rapid convergence of these plates (~8-9 cm/year) makes the area highly seismic, primarily in areas
where plates come into contact. The earthquake of March 11 took place at a depth of 32 km, where the Pacificand Eurasian tectonic plates are in contact.

Earthquake ofMarch 11

Figure 3-2 - seismotectonic situation of Japan (according to L. Jolivet).

The zone of the fault that ruptured during the earthquake of March 11, 2011 extends over more than 500 km,
while slipping on the fault exceeded 25-30 meters in some points (Figure 3-4). Such exceptional dimensions explain
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16/188the long duration of the earthquake (more than two minutes in Tokyo). The colossal energy liberated during the
rupture resulted in very significant movements of the ground over much of Japan. The Japanese earthquake
recording network, the world's densest, maps the distribution of the maximum accelerations (Figure 3-3). In somelocations, the accelerations exceeded that of gravity.

Figure 3-4 – Map of slip during the Tohoku

Figure 3-3 – Map of distribution of maximal

earthquake (color scale, Wei et al., 2011)

accelerations recorded by the Kik-net and K-

and aftershocks (gray dots). The surface

networks at ground level. For reference, anprojection of the fault zone active during

acceleration of 980 gal equals that of gravity

the principal shock is represented by a(1g) (source: USGS/NEIC).

black rectangle.

Analysis of data recorded by the many GPS stations of the Geospatial Information Authority of Japan (GSI) on thenorthern part of Honshu reveals that the north coast of the country shifted east by 2.4 meters on average, and by
more than 4 meters in some places. Likewise, geodetic data indicates that the east coast subsided 50 cm onaverage, with the greatest subsidence occurring in East Miyagi prefecture, which reached 1.1 meters (USGS).
The relative displacement of the Pacific and Eurasian plates that took place in the Earth’s crust during the Tohoku
quake considerably modified the distribution of forces throughout the zone (change in state of stress). The
readjustments required for a new equilibrium resulted in several thousand aftershocks (Figure 3-4), including
several of high magnitude (four over 7.0 and more than 500 with a magnitude in excess of 5.0). Most of theaftershocks occurred along the subduction plane. It should nevertheless be noted that some aftershocks wereobserved in other geological structures activated over a great distance by the changes of the state of stress
reacted over a greater distance. Major aftershocks occurred on land, resulting in significant damage and surface
movements. The most important took place on April 11, 2011 (magnitude 7.1, see Figure 3-5). It will last several
years before seismic activity related directly to the Tohoku earthquake subsides.

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17/188Figure 3-5 - Surface displacement following aftershock of
04/11/2011 (Hamadoori earthquake). Vertical scarp due to fault
movement between 1-3 meters (Ishiyama et al., 2011)

An earthquake followed by a tsunami…

Less than an hour after the earthquake, beginning at 3:27 pm, a series of tsunamis affected the Fukushima Dai-ichi
site, with some overtaking the seawalls protecting the site. The height of the first wave, which occurred at 3:27
pm, is estimated at four meters. At 3:35 pm, a second tsunami of unknown height rolled over the site.
In the end, the installations were submerged up to 14-15 meters above sea level, doubling the maximum forecast
adopted by TEPCO over the past decade. Reassessment of the flooding risk led to a maximum level of 5.7 meters
above sea level (1.3 meters for the tide and 4.4 meters for the tsunami). The Japanese tsunami warning system
was activated, but the height of the wave predicted to hit Fukushima was only three meters. The platforms ofreactors 1 through 4 are located at +10 meters from the reference level while the platforms for reactors 5 and 6
are located at +13 meters. Four meters of water thus submerged the platforms of reactors 1 through 4. Figures 3-6
and 3-7 illustrate the violence of the event and the extent of flooding.

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18/188Figure 3-6 - Inundation of area of plant units 1 to 4 at Fukushima Dai-ichi site (source: TEPCO)

Figure 3-7 - Submersion of seawall at the Fukushima Dai-ichi site (source: TEPCO)

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One year later…
Scientists worldwide have pored over the data recorded during the Tohoku earthquake and will continue to do sofor years to come in an effort to understand its nature. The subduction megathrust earthquake or megaquake isthe event that provides the greatest variety and quantity of high-quality observations. These data should improve
the knowledge of physical mechanisms that govern the seismic behavior of rapid convergence zones and help tobetter assess associated earthquake hazards and related risks.

Another aspect deserves examination. It is clear that the Japanese scientific community was anticipating a major
earthquake in the region over the medium term. Nevertheless, the knowledge acquired up until then had led amajority not to consider the possibility of a megaquake and an associated tsunami of such scale. The challenge
today is to understand why the latter assumption was not given priority and to identify signals that could haveobliged the scientific community to consider the possibility of such an event (Figure 3-8).

Figure 3-8 - Evaluation of coupling between
Pacific and Eurasian plates. The results(obtained from data acquired over a periodof 15 years) indicate that the contact zonethat yielded during the Tohoku megaquake
was significantly coupled. Elastic
deformation (which is the motor ofseismicity and the result of plateconvergence) added to this, which a
posteriori could have been the basis for
anticipating a major event. Such results
contradict hypotheses proposed until then
to explain the deficit between the quantityof energy liberated by historically known
quakes and that related to the convergenceof tectonic plates. In effect, research
considered that a significant part of thedeformation brought on by convergence
was dissipated aseismically (according to
Avouac 2011).

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4. CONSEQUENCES ON THE FUKUSHIMA DAI-INI, ONAGAWA,
TOKAI, HIGASHIDORI AND HAMAOKA REACTORS
Eighteen BWR nuclear power plants were in operation at five sites along the east coast of Honshu (Figure 4-1).
None of these reactors is currently operating (March 2012).

epicenter

Figure 4-1- Location of Japanese nuclear power reactors

The four reactors at the Fukushima Dai-ini site (Fukushima prefecture) were at power at the time of the quake,
which caused an emergency shutdown. At reactor 1, the tsunami led to the inundation and unavailability ofelectrical systems. In addition, cooling resources using seawater were considered unavailable following flooding.
As a result, the equipment dependent on them, including emergency diesel generators (EDGs), were unavailable.
Cooling to the spent fuel pool (SFP) was also unavailable. Removal of residual heat from the reactor core was
ensured by water makeup in the reactor pressure vessel (RPV) by dedicated systems. Injected water, heated as it
passed through the core, could not however be cooled. Nevertheless, gradual restoration of cooling and electricalsupply—usually with temporary systems—avoided degradation of fuel assemblies. A similar scenario occurred inreactors 2 to 4, but the loss of electrical and cooling systems using seawater was only partial.
The three reactors at power or in restart mode at the Onagawa site (Myagi prefecture) shut down automatically asa result of the earthquake. They did not experience loss of off-site power (LOOP). However, failure of atransformer on reactor 1 led to switching to an EDG. On reactors 2 and 3, flooding of certain rooms housing cooling
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resources using seawater had a limited impact since it was only partial. The situation was rapidly controlled at thethree reactors and no core degradation was reported. The same was true for the SFPs for which cooling, lost
following the earthquake, was restored the same day.
At the Tokai nuclear power plant (Ibaraki prefecture), the single reactor3, which stopped automatically,
experienced LOOP after the earthquake. Nevertheless, one of the EDGs whose cooling systems were not flooded
remained operational. The EDG was used to supply electricity to the SFP the day after the earthquake.
In Aomori prefecture, the reactor at the Higashidori nuclear power plant, which was shut down for periodic
inspection at the time of the quake, experienced LOOP. Power was restored during the night and an EDG supplied
power in the interim.
Finally, some 500 km for the quake’s epicenter, the three reactors4 at the Hamaoka nuclear power plant (Shizuoka
prefecture) encountered no special difficulty, with the two reactors in operation at the time of the quake
remaining at power. Nevertheless, a decision by the government in May 2011 prolonged the outage of reactor 3(which had been shut down for inspection at the time of the quake) and shut down reactors 4 and 5 to strengthen
protection at the site.

5. FUKUSHIMA DAI-ICHI ACCIDENTThe Fukushima Dai-ichi (or Fukushima I) site includes six reactors. Figure 5-1 shows the site before the accident.
Reactor buildings 1, 2, 3 and 4 can be seen at the center of the photo with reactors 5 and 6 off to the side on ahigher platform. The site also includes a shared spent fuel pool that contained 6,400 fuel assemblies at the time of
the accident.

5

Piscine de stockage
Spent Fuel Pool (SPF)des combustibles usés

4

3

2

6

1

Bâtiments
TurbineBuildings
turbineFigure 5-1 - Fukushima Dai-ichi site before the accident (photo: Google maps)

Located in the districts of Okuma and Futaba in Fukushima prefecture, the Fukushima Dai-ichi site is operated by
the Tokyo Electric Power Company (TEPCO).

3
4

Reactor 1, which is gas-cooled, was decommissioned in 1998.
Two other reactors– 1 and 2 (BWR) – were shut down in the last decade and decommissioned in 2009.
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It includes six BWRs with the following electrical output: 460 MWe (reactor 1), 784 MWe (reactors 2 to 5) and 1,100
MWe (reactor 6).
Reactors 1 to 5 are Mark 1 containment type. Reactor 6 is Mark II containment type. Table 5-I gives data about thereactors at the Fukushima I site, and their status and core inventories before the accident.

Table 5-I: Fukushima I facility datareactor types and core inventories (PN* nominal power)
Plant Unit 1

Plant Unit 2

Plant Unit 3

Plant Unit 4

Plant Unit 5

Plant Unit 6

460

784

784

784

784

1,100

BWR-3

BWR-4

BWR-4

BWR-4

BWR-4

BWR-5

March 1971

July 1974

March 1976

October 1978

April 1978

October 1979

400

548

548

0

548

764

100% PN*

100% PN*

100% PN*

unloaded core

shutdown

shutdown

UO2

UO2

UO2

UO2

UO2

Electrical Output(MWe)
Reactor Type
Commissioning
Date
Number of fuelassemblies incore
Reactor state
before theaccident
Fuel typeUO2 and 32
MOX

Reactors 1, 2 and 3 were operating at full power at the time of the earthquake. Reactor 4 had a scheduled outagethat started on November 30, 2010. The core was completely unloaded and assemblies are stored in the SFP.
Reactors 5 and 6 also had scheduled refueling outages which began respectively on January 3, 2011 and August 14,
2010. Fuel assemblies were loaded in the cores.

5.1. ACCIDENT SEQUENCE, MARCH 11-25, 2011
Note: The following information was taken from reports published by the IAEA and Japanese organizations
analyzing the accident. Uncertainties remain about the precise accident sequence. Damage to the installations
and core states due to the earthquake is poorly known since the radioactive environment renders certain areas of
the reactor buildings inaccessible. The following information may be revised and should be consideredpreliminary.
The earthquake that occurred at 2:46 pm JST5 on March 11 caused a LOOP at the Fukushima Dai-ichi site.
Following the earthquake, reactors 1, 2 and 3 were shut down automatically by inserting control rods in the core
to stop the chain reaction. Residual heat removal systems started up (two per reactor). EDGs supplied electrical
power. While the earthquake does not appear to have directly called into question the operational character ofsafety functions, damage to facilities and effects of any damage on the accident sequence are not accurately
known at present.

5

Japan Standard Time
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23/188Less than an hour after the quake, facilities at the site were flooded by a series of waves. The most devastating,with a height of 14-15 meters above sea level, was recorded at 3:42 pm JST.
The seawall at the site was submerged. The pumping stations for the six reactors were severely damaged and thecooling pumps, which were not protected from flooding, were under water, so that the reactors and the SFP no
longer had a source for cooling. Water then penetrated the buildings of the nuclear islands, causing the loss of allor part of the EDGs and electrical switchboards that supply power to reactor safety systems and SFPs. With the
exception of reactor 6, all of the reactors at the site experienced total loss of the emergency power supply system
and loss of ultimate heat sink (LUHS).
The air-cooled EDG of reactor 6 alternately supplied power to reactors 5 and 6 to cool cores and SFPs.
Only the batteries of reactor 3 remained operational after the tsunami. The control rooms of reactor 1 and 2 thus
had no lighting. Power supply to the control room of reactor 2 was not restored until March 22.
Battery loss also led to losing valuable data on the state of the facility, including the operation state of certain
systems and parameters for monitoring facility state (RPV water level and reactor containment pressure). Data was
obtained periodically using small generators.
Lastly, loss of electrical supply led to loss of communications resources included in the on-site emergency plan for
updating emergency response teams. All of these aspects greatly disrupted accident management.
In reactor 3, the control room and part of instrumentation and control remained operational.

Figure 5-2 - Area inundated after the tsunami

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5.1.1. REACTOR 1 ACCIDENT SEQUENCE
In the event of total loss of the emergency power supply system, reactor 1 has two cooling means to remove
residual heat from the core after the nuclear reaction has stopped:-a heat exchanger or isolation condenser (IC) that condenses steam that forms in the RPV from evaporation- removal of residual heat from the core - and using gravity to re-inject water in the RPV. It is an aircooled heat exchanger. There are two redundant trains, i.e., two heat exchangers (cf. section 2.3). The
pipes connected to the vessel are equipped with battery-operated isolation valves;-a high pressure core-injection system (HPCI) injects water into the vessel from the condensate storagetank or the suppression pool using a turbine-operated pump run by steam produced in the vessel.

Following emergency shutdown of the reactor and closure of the isolation valves of the steam pipes, the IC systemstarted up automatically shortly after the quake at 2:52 pm JST. In order to observe the cooldown gradientrequired by the operating procedures, i.e. 55°C/hour, the operators manually shut down the system at 3:03 pm on
March 11. Then, from 3:10 to 3:30 pm, the operators operated the train 1 isolation valves on the IC system tocontrol pressure and regulate water level in the RPV.
At the time of the tsunamis, valves on both IC trains were closed (trains A and B). Loss of electrical power
prevented confirming operation state of the system.
The operators noticed the valves were in open position after 6 pm on March 11 after the power supply was
restored. At 6:18 pm, the IC isolation valve reopened before closing again at 6:25. It opened again at 9:30 pm. The
assessments show that at that time, the core was severely degraded; the system was not able to operatecorrectly, due either to the configuration of the isolation valve or the presence of hydrogen that blocked
exchange. This issue remains to be confirmed.
At 5:12 pm on March 11, due to doubts surrounding IC operation and the lack of information about the water levelin the RPV, TEPCO began to consider alternative sources of water supply. Use of a pump from the fire protection
system connected to the spray nozzle assembly and taking water from an underground tank was considered.
Assembling these resources on the site, given the damage caused by the earthquake and the tsunami, took time.
Without cooling, water in the RPV heated upon contact with the hot fuel assemblies and evaporated. Residual heatto be removed exceeded some ten MW when cooling was lost. Steam produced led to an increase in pressure in the
RPV and the opening of relief valves of the main cooling system (RPV) in the wetwell.
Without any means to remove heat transferred to the suppression pool, the temperature of the water in thewetwell reached the boiling point. Pressure in the reactor containment then increased, causing it to exceed its
design basis (4-5 bars), necessitating repeated implementation of a procedure of containment venting to avoid
rupture. A pressure of 6 bars was measured in the containment of reactor 1 at 23:50 pm on March 11. Operations
to prepare venting of the reactor containment were accelerated.
Confirmation of the evacuation of the village of Okuma was expected prior to venting. Evacuation was completed
at 9:03 am on March 12. Operations to open the valves and relieve pressure in the reactor containment started at
9:15 am. The operators encountered a number of difficulties in opening the valves to align the venting system. The
containment was not opened until 2:00 pm.
Considering the time required before venting could take place, it is possible that leaks formed in the reactor
vessel head from the pressure, which may explain the presence of hydrogen in the superstructure of the reactor
building.
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After water in the RPV evaporated, the water level gradually diminished until the level no longer ensured removalof residual heat and cooling of fuel assemblies. This level was reached some two hours after the tsunami.
RPV level (mm in relation to height of fuel assembly)

Train A
Train B

Figure 5-3- Change in water level in the pressure vessel of reactor 1(from measurements available during the accident)
The melting point of fuel is approximately 2,800°C while zirconium cladding deteriorates around 800°C andruptures around 1,200°C. The oxidation reaction between the zirconium cladding and water produces significant
quantities of zirconium oxide and hydrogen, which mixes with steam and accumulates in the upper part of themain cooling system and the reactor containment. The higher the temperature, the faster the Zr+H2O reaction,
which accelerates significantly above 1,200°C. It is an extremely exothermic reaction.

UO2 FUSIONZIRCONIA FUSION
Release1’of fission products fromcladding gap

700°-900°C
1
CLADDING SWELLING
AND RUPTURERELEASEof fission products fromfuelFigure 5-4 – fuel assembly behavior in severe accident conditions
Presumed leaks in the reactor vessel head and operations to release the pressure in the containment while coredegradation had already begun caused very significant releases into the environment and the release of asignificant quantity of hydrogen resulted in an extremely violent hydrogen explosion in the upper part of thereactor building over the SFP. The explosion destroyed the upper part of the building.
It should be stressed that the operations to relieve the pressure in the containment involved opening valveslocated in the wetwell, which significantly limited releases since radioactive aerosols remained in the water(radioactive aerosols were retained by a factor of approximately 1,000).
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26/188Figure 5-5 – 3:36 pm on March 12: Explosion in reactor building 1

Figure 5-6 – Schematic diagram of the explosion in reactor building 1

At 5:46 am on March 12, despite increasingly difficult radiological conditions, the operator was able tointermittently inject fresh water from available reserves and, beginning at 7:04 pm, borated sea water to cool thecore using fire extinguishing pumps (pump discharge pressure on the order of 4-5 bars), which stabilized thesituation.
Beginning on March 25, fresh water from naval barges was injected.
Overall, injection of water into the RPV was interrupted for approximately fourteen hours. Under these conditions,complete core meltdown, ex-vessel progression and the interaction between corium and the concrete of thereactor building are highly probable.

5.1.2. REACTOR 2 ACCIDENT SEQUENCE
In the event of total loss of the emergency power supply system, reactors 2 and 3 are also equipped with two
cooling resources for injecting water in the RPV after shutdown of the nuclear reaction: Reactor Core Isolation
Cooling (RCIC) system and the High Pressure Coolant Injection system (HPCI). The systems rely on turbine-driven
pumps using steam from the RPV. They are equipped with isolation valves that run on emergency batteries.
After the earthquake, operators in plant unit 2 started the RCIC system manually at 2:50 pm on March 11. It
stopped automatically several times due to the high level of water in the RPV and was restarted by the operators.
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The injected water was initially taken from the condensate storage tank, and when it was empty, from thewetwell. The steam that is used to run the turbine pump then condensed in the wetwell. Since the cooling
resources of the wetwell water were unavailable, the water heated and inevitably caused the system to shut
down.
It should however be noted that the RCIC ensured heat removal from the core for approximately three days until
1:25 pm on March 14, a significant delay compared with the assumptions usually adopted for design studies, which
are on the order of several hours.
Prepared for the loss of RCIC, TEPCO planned an alternative water supply. Firefighting equipment was readied to
inject water if RCIC shut down. At 11:01 am on March 14, the explosion in reactor building 3 destroyed thefirefighting pumps and pipes which had been prepared.
Following loss of RCIC and lacking a substitute resource (HPCI was unavailable and emergency firefighting
equipment was destroyed in the explosion), the water level in the RPV decreased to the level where it was nolonger possible to remove residual heat from the assemblies. Core meltdown of reactor 2 took place on March 14,
generating, as for reactor 1, the release of a significant quantity of hydrogen fission products in the RPV and thereactor containment.

Train A
Train B

Figure 5-7 – Change in water level in RPV of reactor 2

TEPCO then began injecting seawater into the RPV. The injection requires that pressure be reduced in the reactor
coolant system. The operation was made very difficult by the loss of the emergency power supply system,
conditions at the site and aftershocks which interrupted work. Seven hours and twenty-four minutes passed
without water being injected. At 7:54 pm on March 14, seawater was injected in the RPV using mobile emergency
equipment. The injection stabilized the situation.
At the same time, as with the other reactors, the issue of venting the reactor containment arose. The operators
prepared for venting operations by opening necessary valves. Nevertheless, containment pressure at this time was
not sufficient for the rupture disk (see Figure 2-8) in the system to burst. As a result, the isolation valve in theventing system closed. After the explosion in reaction 3, the valve could not be reopened.
At 6:10 am on March 15, a significant increase in pressure occurred in the drywell. Efforts to vent the drywell were
unsuccessful.
Since efforts to open discharge valves located in the drywell and wetwell failed, a rupture took place in theannular torus.
It is thought that a hydrogen explosion occurred following contact with air. As a result, highly contaminated waterin the torus entered the reactor building.

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Train A

Figure 5-8 – Pressure change in the containment of reactor 2

Figure 5-9 - Explosion in the lower part of reactor building 2 – 6:10 am, March 15

A connection to an outside source of electrical power was not re-established until March 22, 11 days after the startof the accident (restoring lighting to the control rooms). Previous efforts to establish an electrical supply,
particularly for safeguard systems, had all failed due to the flooding of certain switchboards and short cuts on theswitchboards.
Beginning March 25, clear water was injected into the RPV to replace the seawater.

5.1.3. REACTOR 3 ACCIDENT SEQUENCE
Reactor 3 is identical to reactor 2 (BWR/4 model). It is also equipped with RCIC and HPCI systems.
After the earthquake RCIC was started manually at 3:05 pm on March 11 as a preventive measure. At 3:25 pm, it
was shut down since the water level in the RPV was too high.
At 3:38 pm, the two EDGs and the electrical switchboards became unavailable after the tsunami. In contrast, thebatteries remained available, making it possible to regulate valves in these two systems from the control room andcontrol RPV water pressure and level.
The RCIC started up again at 4:03 pm on March 11 and shut down at 11:36 am on March 12. At 12:35 pm, the highpressure core injection (HPCI) system started up automatically with a low level of water in the RPV. In preparation
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for the batteries losing power, TEPCO planned alternative resources for injection. It required using emergency
firefighting resources from reactors 5 and 6 as well as the Dai-ini nuclear power plant. Transport of this equipment
to reactors 1-4 was difficult6. At 2:42 am on March 13, the HPCI system failed.
The water level in the RPV decreased, causing core meltdown.
3000

2000

1000

0
11/3/11 12:00

12/3/11 0:00

12/3/11 12:00

13/3/11 0:00

13/3/11 12:00

14/3/11 0:00

14/3/11 12:00

15/3/11 0:00

15/3/11 12:00

16/3/11 0:00

16/3/11 12:00

Voie AA
Train
Train
Voie BB

-1000

-2000

-3000

-4000

Figure 5-10 – Change in water level in RPV of reactor 2
Use of firefighting equipment required reducing the pressure in the RPV, which took time. The batteries lost powerso that the RPV discharge valves could no longer be controlled. Batteries from the cars of TEPCO's employees werethen collected and installed in the control room to supply the safety relief valves (SRVs).
The valves open at 9:08 am on March 13 so that pressure could be reduced in the RPV. Nearly seven hours after
the loss of the HPCI, at 9:25 am on March 13, fresh water was injected. The water level in the RPV continued todecrease. At 12:20 pm, with the reserve of fresh water depleted, the decision was made to inject seawater. The
task of switching the water intake was disrupted by aftershocks which forced workers to seek shelter in a
protected area. At 1:12 pm on March 13, seawater was injected into the RPV and the situation stabilized.
The operations to reduce pressure in the reactor containment, necessary in the absence of a heat sink for thecontainment, started at 8:41 am on March 13. TEPCO made significant efforts to open the valves to implement theprocedure. A new operation to vent the containment was needed at 5:20 am on March 14.
The explosion, which occurred in reactor building 3 at 11:01 am on March 14, had a consequential impact on the
structure of the reactor building. Debris was scattered around the building, damaging water injection systems forreactors 2 and 3. At 4:30 pm on March 14, injections of seawater recommenced.

6

For example, the road connecting reactors 1-4 and reactors 5-6 was no longer fit for use after the tsunami.
Roadclearing and safety work was necessary before transporting the equipment.
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30/188Figure 5-11 – 11:01 am on March 14: explosion in reactor building 3

5.1.4. SPENT FUEL POOLSThe total loss of the emergency power supply system and heat sink that affected reactors 1-4 also affected thespent fuel pools (SFPs). Since cooling resources were not restored quickly, water temperature in the SFPs, on theorder of 20-25°C before the accident, increased with a kinetics that depended on residual heat and thus on thenumber and age of the stored fuel assemblies.

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Table 5-II gives an inventory of SFPs and an estimate of the residual power to be removed at the time of theaccident.

Reactor 1

Reactor 2

Reactor 3

Reactor 4

Reactor 5

Reactor 6

994 (including

940 (including

1,531
Number of fuelassemblies in
SFPs

392 (including
100 new
assemblies)

615 (including

566 (including

28 new

52 new

assemblies)

assemblies)(including 783
spent, 548
recentlyunload and 20

48 new

64 new

assemblies)

assemblies)

1.07 Mw

0.86 Mw

new)

Residual heat in
the SFPs7

0.18 Mw

0.58 Mw

0.51 Mw

2.39 Mw

Table 5-II – Inventory of SFPs at the time of the accident

The SFP with the largest inventory is that belonging to reactor 4, which had the equivalent of three cores,
including one recently unloaded from the reactor (reactor 4 had a maintenance outage beginning on November 30,2010). IRSN estimated the residual heat of the fuel stored in the pool to be 2.4 thermal MWs. TEPCO confirmedthat the residual heat of the stored assemblies was 2.26 MW on March 11.
At the time of the accident, a gate separated the reactor cavity, which held a significant volume of water, and the
SFP. It is quite possible that due to the gradual draining of the SFP, the water was transferred from the reactor
cavity by partial elimination of the gate. TEPCO is now considering this hypothesis, which was put forward by
IRSN’s experts during the accident. This would explain the lack of dewatering of the assemblies stored in SFP 4.
There was thus a delay of several days before the start of dewatering of the assemblies in the storage racks (after
March 18), as long as the pool and connected pipes remained intact. On March 15, several fires or hydrogen
explosions took place in reactor building 4, causing extensive damage. Several hypotheses have been presented
regarding the causes of these fires or explosions.
On November 8, TEPCO inspected reactor building 4 using remote-controlled robots (cf. Figure 5-12). This
inspection confirmed the hypothesis that the explosion in the building was related to hydrogen that originatedwith a ventilation duct from reactor building 3.

7

IRSN estimate of March 21 based on cooling time for various assemblies.
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32/188Figure 5-12 - Visual inspection using remote-controlled robots in reactor building 4 (2nd floor)
Gas treatment system pipes leading to the ventilation stack for reactors 3 and 4 have a common section throughwhich part of the hydrogen produced during the degradation of core 3 passed on March 14. Released in significant
quantities during operations to relieve the pressure in the reactor containment, it could have been transferred toreactor building 4 (cf. Figure 5-13).

Plant Unit 4

Ventilation Stack
Plant Unit 3

Figure 5-13 – Gas treatment system of reactors 3 and 4

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It also appears that there was no significant degradation of fuel assemblies in this pool (films of the pool interior,measurement of water radioactivity).

Figure 5-14 - Spent fuel storage racks in pool 4 after the accident (source: TEPCO)

Water temperature in the other SFPs also increased, sometimes to the boiling point. In all cases, makeup to thepools was restored before stored assemblies were dewatered. Makeups to SFP 3 began on March 17 with drops
from a helicopter, then with a fire truck (using a pump normally used to inject concrete). Makeups to SFP 2 began
on March 20. Daily makeups were later necessary to compensate for the loss of water from vaporization (reactors
1-4).
The first significant makeups to SFP 4 were carried out using fire hose nozzles starting on March 20, then, on March
22, by a truck with a concrete pump for injecting water using an articulated arm.
The most notable point is without a doubt the impact of hydrogen explosion on the SFPs. Overall, it appears thatthe pools resisted the hydrogen explosions but a significant loss of leaktightness in the pools and dewatering of thefuel assemblies may have occurred, seriously aggravating the situation in terms of radiological conditions at thesite and releases into the atmosphere. Figure 5-15 shows the extent of the destruction to reactor 4.
The water temperature of the shared pool also increased gradually following loss of cooling resources. It washowever possible to inject water and to start up the cooling system before boiling occurred. Available time wasquite significant.

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East

West

South

North

Figure 5-15 – Reactor building 4 after fires and explosion on March 15

5.1.5. ATMOSPHERIC RELEASES
During the fuel degradation process, hydrogen production from cladding oxidation is concomitant with the releaseof the most volatile core products. Operations to reduce pressure in the containments or supposed leaks in reactor
vessel heads that took place after core degradation thus resulted in significant releases into the environment, notonly of noble gases and gaseous iodine, but of radioactive products in the form of aerosols such as cesium 137. A
significant share of the aerosols was however trapped in the water in the wetwells in reactors 1 and 3.
Atmospheric releases were produced initially in the form of puffs that could be identified by changes in dose
measurements at site monitoring posts.
Figure 5-16 gives dose rate measurements at monitoring posts. Correspondence between dose rate peaks andoperations to reduce pressure in containments was confirmed.

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35/188Dose rate from Dai-ichi monitoring posts

Explosion atreactor building 1

Venting ofreactorcontainment 3
West Gate
PointsMain Gate
Gymnasium (side)
Main Office North

Venting ofreactorcontainment 2

Japanese Standard Time

Figure 5-16 – Dose rate measurements in μSv/h at site monitoring posts

Monitoring post locations are given in the following figure.

Figure 5-17 Location of fixed and temporary monitoring posts at the Fukushima Dai-ichi site

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36/188IRSN’s assessment of releases from the start of the accident were confirmed by estimates published in June by the
Nuclear and Industrial Safety Agency (NISA). This point is described and discussed in section 6.1.

5.2. ACCIDENT SEQUENCE: MARCH 25-APRIL 17, 2011
On March 25, TEPCO announced that contaminated water had accumulated in the basements of the turbine
buildings at depths varying from 40 cm to 1 meter. The water, which had most likely been in the basements since
the tsunami, had been contaminated by water from the containment vessels when they lost their structural
integrity during the accident. The highly contaminated water measured in the turbine building of reactor 2 mostprobably came from the wetwell that was damaged by the March 15 explosion. It is worth noting that thiscontamination demonstrates the effectiveness of the wetwells to retain air releases.
With the loss of the structural integrity of the containment vessels of reactors 1, 2 and 3, the contaminated water
spread first to the reactor buildings, flooded the turbine buildings and ultimately flowed into the cabling trenches(see Figure 5-18).

Figure 5-18 - Path of the water leaks

Managing effluent and the releases of radioactive water became a top priority in remediating the crippled site.
TEPCO was forced to "intentionally" dump effluent (mildly contaminated water) in order to free up the storage
tanks. Very highly contaminated water also leaked into the sea over a few days in late March. IRSN estimated thata total of 27 1015 Bq of cesium-137 was released into the sea up to mid-July (see section 6.4.3 of this report), withmost being released before April 8 as planned. The releases estimated after this date make up only 18% of thetotal amount released.

5.3. FROM APRIL 17, 2011, ONWARD
5.3.1. GRADUAL REGAINING OF CONTROL OF THE FACILITIESOn April 17 TEPCO issued a two-phase, short-term plan to bring the Fukushima Dai-ichi plant back under control.
The first phase had three goals: reduce the amount of radiation that was still being released (albeit at much lower
levels than at the start of the accident); maintain and enhance cooling of the reactors and pools; and provide
additional containers to store contaminated water. The first phase, which was estimated to last for 3 months, wascompleted by TEPCO on July 19.
A system to pump, decontaminate and desalinate the water in the turbine buildings was started up in June.
Decontamination plants were built on site in record time with the assistance of foreign companies, including
French firms Veolia and Areva. The decontaminated water was stored in tanks installed for such purpose and fed
back into the vessels (see Figure 5-19).

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Reactor building

Turbine building

Storage

Closed-loop
Closed-loopsystemsystemFiltration

Figure 5-19 - Schematic diagram of treatment of the contaminated water

The second phase, scheduled to last for 3-6 months, had three goals: make the buildings secure in order to bring
the radioactive releases under control; maintain stable cooling of the reactors (i.e. ensure that the water flowing
in the core remains below 100°C so as to prevent the generation of steam); and reduce the amount ofcontaminated water on the site. Six months after the accident, the target of maintaining the vessels at below
100°C was met.
TEPCO's roadmap also called for covering reactor buildings 1, 3 and 4 in order to limit further radioactive releases
into the atmosphere and raised the possibility of building an underground barrier to reduce the amount ofcontaminated water flowing into the ocean through the soil and groundwater.
Lastly, major efforts have been undertaken to improve work conditions on the site, which remain very difficult.
Very high dose rates have been measured at various points on the site.

5.3.2. THE MID- AND LONG-TERM ROADMAP
A document titled Mid- and Long-term Roadmap on Decommissioning of Fukushima Dai-ichi Nuclear Power Plant
was adopted on January 23, 2012. Divided into three phases, the roadmap for the decommissioning of reactors 1-4
will be implemented once the plant has been brought back under control:The main goal of Phase 1 is the removal of the fuel assemblies from the SFPs. TEPCO estimates that thisphase will start within the next 2 years;The main goal of Phase 2 is the removal of the molten fuel from the cores of the reactors. The aim is tobegin this phase within 10 years. The vessels will also be reinforced during this period;

In Phase 3, the plant will be decommissioned over a period of 30-40 years.

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5.4. REMEDIATION MEASURES
5.4.1. DAMAGE SUFFERED BY THE CORES OF REACTORS 1, 2 AND 3
TEPCO published the results of simulations of the accident performed using a thermal-hydraulic transientcomputer code that also made it possible to simulate the progression of the accident after the core meltdown. It
confirmed that reactor 1 had suffered a complete meltdown and that its vessel has been breached. According to
the analysis, the entire mass of corium dropped to the bottom of the reactor containment vessel and came into
contact with the concrete of the foundation basemat, initiating a corium-concrete interaction. Although thecorium ate away a 70 cm-deep hole into the basemat, TEPCO states that it would have had to melt through morethan 1 m more of concrete before reaching the metal wall of the containment vessel. For TEPCO, the injection ofwater is enough to cool the corium.
IRSN considers that these results should be interpreted with precaution as a number of assumptions, including themass of corium that dropped onto the basemat and how it ate through the basemat (radial or axial erosion), canhave a very significant influence on them. In particular, the raft could be eroded more extensively than announced
by TEPCO.
As for reactors 2 and 3, TEPCO considers that their cores also sustained heavy damage but that only a small
amount of corium dropped onto the basemat, eating through a depth of just around 20 cm.

7,6 m
Réacteurs
Reactors
2 &n°2&3
3

Réacteurn°1
Reactor1

Figure 5-20 - Diagram illustrating the condition of the cores of reactors 1, 2 and 3 according to theanalysis

Freshwater is continuing to be fed into the cores. As a result, the water temperature in the RPVs and PCVs of thethree reactors remains below 100°C.

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39/188Figure 5-21 - Evolution of the temperatures in the RPVs and PCVsof reactors 1, 2 and 3 (measurements)

Nitrogen gas is continuing to be injected into the PCVs of all three reactors to prevent the risk of hydrogen
combustion (hydrogen is produced in large quantities during a corium-concrete interaction and, in lower
quantities, water radiolysis).

5.4.2. STATUS OF THE SFPS
Operations to desalinate the water in the SFP of reactor 4 in order to mitigate the risks of corrosion were started
on August 20, 2011, and have proven their effectiveness. Operations to desalinate the water in the SFPs ofreactors 2 and 3 are underway.
The water temperature in the pools is being maintained at between 20°C and 30°C.

5.4.3. CONTAINMENT OF THE FACILITIESWork on covering the reactor 1 building ended on October 28, 2011 (see Figure 5-22). The buildings of reactors 3
and 4 are scheduled to also be covered. The purpose of these covers is to limit, filter and measure radioactive
releases into the atmosphere and protect the buildings from the elements (flooding of the basements and trenches
by heavy rain).

Figure 5-22 - Construction of the cover around the reactor 1 building

A system to control the pressure in the containment built to mitigate radioactive releases, as well as an air
sampling system, have been or will be installed in reactors 1, 2 and 3.

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5.4.4. PROTECTION OF THE FACILITIES FROM FUTURE EARTHQUAKES ANDTSUNAMIS
Measures have been taken to reinforce the SFP of reactor 4. The earthquake resistance of the reactors' pools has
been checked and the anti-tsunami seawall was raised first opposite reactors 1 to 4 and then reactors 5 and 6.

Figure 5-23 - Protection of the facilities from tsunami risks

5.4.5. CURRENT RADIOACTIVE RELEASESRadioactive materials are still being released into the atmosphere, but at levels incommensurate with those frommid-March 2011.
Contaminated water is continuing to be treated in order to mitigate the risks of radiation being released into theocean. The sludge storage tanks are filled to 75% capacity. TEPCO plans to concentrate the sludge more in order toreduce its volume. In other respects, seepage related to rain and the leaks from the containment vessels havemade it impossible to dry out the site's buildings.

Figure 5-24 - Volumes of contaminated water treated since June 17, 2011

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In addition to the measures taken to mitigate and control radioactive releases into the atmosphere and limit theamount of contaminated water on the site, on October 28, 2011, TEPCO began building a wall to limit the amountof radioactive water reaching the ocean through permeable layers of soil around the site (see Figure 5-25).

Shielding wall

Existing seawall
Permeable
layersSlowlypermeable layers

Figure 5-25 - Wall designed to limit releases of radioactive water

TEPCO has made very substantial efforts to regain control of the site, employing between 2,000 and 3,000 people
since July 2011. Work to clear away debris, particularly with the use of remote-controlled heavy equipment, is
continuing. The ambient dose rate outside the site's buildings remains low due to regular spraying of a polymer
resin on the ground and structures. These agents also prevent the radioactive materials from being dispersed by
the wind and rain.

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6. ENVIRONMENTAL IMPACT IN JAPANThe accident that occurred at the Fukushima Dai-ichi plant on March 11 and the following days resulted in therelease of radioactive substances:

into the atmosphere, in the form of radioactive gases or very fine radioactive particles dispersed into theair (aerosols), of which a portion settled on the surfaces of the soil in Japan, forming residual radioactive
fallout;

into the marine environment, directly in the form of water releases into the sea and indirectly due tofallout on the sea's surface from radioactive aerosols dispersed over the ocean.

Figure 6-1 shows maps of the northern portion of Honshu island and Fukushima prefecture to help you to locate theplaces mentioned in this section.

Figure 6-1 – Maps of the northern portion of Honshu island (left) and Fukushima prefecture (right).

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6.1. ATMOSPHERIC DISPERSION OF RADIOACTIVE RELEASES

6.1.1. CHARACTERISTICS OF THE RADIOACTIVE MATERIALS RELEASED INTO THE
AIR BY THE ACCIDENT
6.1.1.1 Work conducted by IRSN to estimate the radioactive releases into theatmosphere
Even one year after the accident, reconstructing the various sequences of releases of radioactive substances into
the air and determining the characteristics of these releases remains a difficult task. The reason is that there are
no direct measurements of these releases. Only indirect estimates have been able to be made by interpreting thedata available during the emergency, namely: the chronology of the events at the facility (explosions, venting of
the containments, smoke emissions, etc.), the parameters of the damaged reactors (pressure, water level in thevessels, etc.) and on-site dose-rate measurements taken by TEPCO (stationary and portable monitors) or taken by
the automatic monitors in the SPEEDI network (System for Prediction of Environmental Emergency Dose
Information).

• IRSN's initial estimates
As soon as it received news of the accident, IRSN began assessing the radioactive releases into the atmosphere andupdating these assessments as new events occurred on the site and new data became available. IRSN's initial
estimates on March 12 were very rough as they were based primarily on its knowledge of the inventory ofradionuclides in the nuclear reactors and of how these radionuclides behave during a core meltdown. In particular,
the lack of sufficient data on the state of the safety systems of the three damaged reactors at Fukushima Dai-ichi
and on the measures taken by TEPCO made it difficult to predict the degradation kinetics of the cores anddetermine when future releases would occur. Despite these difficulties, with each day IRSN was able to constructa more and more accurate picture of the releases since the start of the accident and updated its findings as new
events took place. On March 22 IRSN published its initial estimate of the "source term" (Table 6-I), or theatmospheric releases likely to have occurred since March 12, when the containment vessels were vented for the
first time and the first hydrogen explosion occurred in reactor building 1. This estimate was based on:a diagnosis of the state of the three damaged reactors (understanding of the situation, state of thecooling systems, etc.);knowledge gained by IRSN through its research programs on the behavior of nuclear fuels during accident
situations;

information provided by the Japanese authorities concerning deliberate venting of the reactor
containment vessels to protect the containments from the risk of degradation due to overpressure.

The assessment’s conclusions were reinforced by comparing atmospheric contamination values calculated using amodel with the results of field measurements taken in Japan.
The release kinetics as a function of time were reconstructed based on the interpretation of the dose-rate peaks
observed along the site's boundary. Before March 17 the releases were related to ventings and explosions for which
the timeframe is now well known. It is assumed that after March 17 the releases coincide with observations ofsmoke.

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44/188• Update of the estimate of atmospheric releases
After the events of March 2011 IRSN continued to estimate the releases from the Fukushima accident byanalyzing a greater amount of available environmental data and by using its local- and regional-scaleatmospheric dispersion models to interpret this data. The dose-rate measurements are the most abundant (Figure6-2). The vast majority of the available readings was obtained by the automatic monitors in the SPEEDI network.
However, because the earthquake and tsunami had rendered the SPEEDI monitors in Fukushima prefecture
inoperative during the period of the releases, the data from the SPEEDI network was used only for comparison
purposes with the results of the regional-scale model (several hundred kilometers). IRSN also used this data toestimate the source term using the tracer method, which involves modeling the dispersion of the individual"tracer" releases and correlating the passage of the resulting plume with the dose-rate peaks measured by themonitors at various locations throughout Japan. Furthermore, MEXT8 published dose-rate readings taken in eachprefecture, particularly Fukushima prefecture, and which were compared to the results of the local-scale model(under 100 km).

Figure 6-2 - Locations of the dose-rate monitoring stations: stations in the SPEEDI network (left) andmonitors in Fukushima prefecture (right)
To date, very few atmospheric activity concentration measurements taken throughout Japan have been madepublic. The few results of genuine interest (because they span the entire period of the major releases) wereobtained by the following monitoring stations:Tokyo-Shinjuku, located 250 km south-southwest of the plant;

Tsukuba (Ibaraki Prefecture) located around 170 km from the plant in the direction of Tokyo,

Takasaki (Gunma Prefecture) located 250 southwest of the plant.

However, because these monitoring stations are located in the same area, their readings are redundant. The only
exception is that of the noble gas measurements taken by the Takasaki monitor.
IRSN's assessment after the accident made it possible to piece together a tentative overall picture of thesubstances released by each reactor into the atmosphere during the accident (Table 6-I and list in Appendix 61) and distributed across time (Figure 6-3). It is important to emphasize that, due to the lack of monitoring
stations (particularly on March 13-14 and March 16-19), this reconstruction carries a high degree of uncertainty as
to the releases that could have occurred as they spread across the Pacific Ocean. The releases from reactors 1 and3 therefore remain highly uncertain. Another major source of uncertainty is the composition of the releases(isotopic composition and chemical forms, particularly for iodines). The main measurements available are doserate measurements, which give an overall picture of all the gamma-emitting radionuclides. However, this picture
is not sufficient to deduce the composition of the releases. Furthermore, the activity concentration measurements
8

Ministry of Education, Culture, Sports, Science & Technology, http://radioactivity.mext.go.jp/en/
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of the airborne radionuclides are very few in number and generally cover the periods after March 17. For example,
looking solely at the activity concentration measurements taken in Ibaraki Prefecture, it is assumed that thequantities of gaseous radioactive iodines were double those of iodine particles.
Other research agencies or teams published their own estimates of the atmospheric releases from the Fukushima
accident based on different methods (Table 6-I). The source terms published in 2011 by NISA9 and the NSC10 inJapan were based essentially on an analysis of the events and phenomena in the damaged facilities; the source
term estimated in the paper by Stohl et al. (2011) is based on measurements taken in Japan and at a very long
distance and relate solely to xenon-133 and cesium-137.

Table 6‑ I – Estimates, made in 2011 by IRSN (during and after the accident) and various Japaneseagencies and scientific teams, of the activities (× 1015 Bq) of the main categories of radionuclides
released during the Fukushima accident. Releases from the Chernobyl accident are also provided forcomparison.

Noble gases(incl. Xe-133)

IRSN ERS - March 22, 2011

Xe-133

Iodines(incl. I-131)

I-131

Cesiums(incl. Cs-137)

Cs-137

Total

2,080

2,000

182

90

26

10

Reactor 1

1,920

1,530

42

13

3

1

Reactor 2

2,270

2,180

114

57

17

6

Reactor 3

2,350

2,240

253

126

38

14

Total

6,550

5,950

408

197

58

21

Reactor 1

-

3,400

-

12

-

0.6

Reactor 2

-

3,500

-

140

-

14

Reactor 3

-

4,400

-

7

-

0.7

Total

-

11,000

-

160

-

15

Total

-

-

630

150

-

12

Total

-

-

-

150

-

13

Stohl (Stohl et al. (2011))

Total

-

-

-

-

Morino et al. (2011)

Total

-

-

-

142

-

9.94

Chernobyl (IAEA 2005)

Total

6,533

6,500

4,260

1760

168

85

IRSN - 2011 research

NISA (June 2011)

NSC (April 2011)
Chino et al. (2011), JAEA,
NERH report

16,700(13,400-20,000)

35.8(23.3-50.1)

9
Nuclear and Industrial Safety Authority - "Regarding the Evaluation of the Conditions on Reactor Cores of Unit 1, 2 and 3 related
to the Accident at Fukushima Dai-ichi Nuclear Power Station, TEPCO"
10
Nuclear Safety Commission – "Trial estimation of emission of radioactive materials (I-131, Cs-137) into the atmosphere from
Fukushima Dai-ichi Nuclear Power Station"

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Release rate (×1014 Bq/s)

Reactor 1
Reactor 2
Reactor 3

Date in 2011 (JST)Figure 6-3 - Evolution in the per-reactor release rate for all the radionuclides released into theatmosphere during the Fukushima accident(blue: reactor 1; red: reactor 2; green: reactor 3).

6.1.1.2 Comment on the atmospheric releases
Altogether, IRSN estimates that nearly 15 release events occurred between March 12 and 25, with the largest
releases probably occurring before March 17 (venting of the three damaged reactors' containment vessels). Given
the extent of damage suffered by the facilities and the heavy contamination of the nuclear site, atmosphericreleases must have continued over the course of the following months but at much lower levels not easily
detectable in the environment.
IRSN's estimate of the distribution of the releases among the reactors is uncertain. For example, reactor 3 appears
to be responsible for the largest releases (65% of cesiums and 62% of iodines). However, most assessments seem toagree that reactor 2 is responsible for most of the releases on account of the damage suffered by the containment
during the hydrogen explosion. Moreover, there is no easy way to attribute releases to a specific reactor after themain release period ending on March 17.
Although the results of the various estimates of the atmospheric releases made by IRSN and other teams areinconsistent, they lie within the same ranges of value and reveal the following major trends:


The releases of radioactive noble gases, the main one of which is xenon-133 (133Xe, half-life of 5.3 days),
are estimated at between 6,500 and fewer than 20,000 PBq (petabecquerels, 1015 Bq). The latter value isprobably overestimated since the activity concentration of 133Xe indicated in the paper by Stohl et al.
(2011) is higher than the total activity concentration of 133Xe in the three reactors before the accident.
Releases of radioactive noble gases from the Fukushima accident may be of the same order of magnitude,
if not higher, as those from the Chernobyl accident. Of these gases, krypton-85 (85Kr) has the longest
half-life (10.8 years). IRSN estimates that 33 PBq of 85Kr were released. As 85Kr is present only as a gas
and is not very chemically reactive, it will remain in the atmosphere (no deposition) and be diluted in the
air across the planet;

The releases of radioactive iodines are estimated in the order of a few hundred PBq, which is around tentimes lower than the Chernobyl accident. Of the radioactive iodines, iodine-131 is one of the mostsignificant in terms of environmental and dosimetric impact. Current IRSN estimates place its release at
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by IRSN on March 22 during the emergency. Iodine-132, and to a lesser extent iodine-133, were alsosignificant constituents of the radioactive iodines released (activity concentrations of 168 PBq and
42 PBq, respectively, according to IRSN estimates) but their impact on the environment was lower due totheir short half-lives (2.3 hours and 20.8 hours, respectively);

The releases of radioactive cesiums are estimated in the order of a few dozen PBq. They consist primarilyof equal parts of cesium-137 and cesium-134 and, to a lesser extent, cesium-136 (estimated release of
9.8 PBq), which has a short half-life of 13.2 days. As regards cesium-137, which will persist the longest in
the Japanese environment (half-life of 30.1 years), IRSN's current estimate of 21 PBq – twice as high as
the March 22, 2011, estimate – accounts for around one-fourth of the cesium-137 released by the
Chernobyl accident.

The study by Stohl et al. (2011) ascribes a portion of the releases to the pool of reactor 4 on account of the highwater temperature (84°C) and the apparent correlation between the start of spraying of the pool and the loweringof the ambient dose rates on March 19. At present, IRSN considers that pool 4 was not a source of significant
releases because the water level measured seems to indicate that the assemblies remained submerged and thus
were not damaged. This analysis is confirmed by an American report published in November 2011 (INPO (2011)).
Altogether, IRSN estimated the radioactivity released for 73 radionuclides (135, counting their radioactive
progeny), making this the most extensive source term ever published. Besides the three aforementioned maincategories of radionuclides, these include the radioactive isotopes of tellurium, also released in significant
quantities (145 PBq, all its radioactive isotopes combined), particularly tellurium-132 (half-life of 3.2 days;
estimated release of 108 PBq) and its decay product iodine-132, a radionuclide with a very short half-life (2.3
hours), and tellurium-129m (12 PBq) associated with its decay product tellurium-129 (8 PBq). According to IRSN
estimates, the releases from the other radionuclides account for a total radioactivity of 28 PBq. Not all of theseradionuclides have been detected in Japan's environment for one of two reasons: their overly short half-lives (afew minutes for some) or the excessively low amount of radioactivity released. Of those that have been measured
in the environment (see section 6.2.3) barium-140 (estimated at 1.12 PBq) and strontium-89 (0.043 PBq) andstrontium-90 (0.003 PBq) were released in lower quantities than the others because they are less volatile. Thatsaid, estimates of the radioactivity released for these radionuclides remain rough due to the lack of a sufficientbody of measurements and information on the actual condition of the damaged reactors. The case is the same forplutonium and other transuranium elements. Their presence in the environment due to the accident has not been
easy to detect on account of possible confusion with residual plutonium from atmospheric nuclear tests conductedin the 1960s. However, the detection11 of neptunium-239, which has a short half-life of 2.4 days, in soil andplant samples collected on April 10, 2011, along the boundary of the Fukushima Dai-ichi site and in the villageof Iitate proves without doubt that transuranium radionuclides were released by the Fukushima accident. Thisis also confirmed by the interpretation of certain results of plutonium measurements taken in the soils northwestof the Fukushima Dai-ichi site and published by MEXT (see section 6.2.3.3). The decay product of neptunium-239,
which has completely disappeared due to its short half-life and can no longer be measured, is plutonium-239 (halflife of 24,000 years). However, since its specific activity is much lower than that of neptunium-239, it is highly
unlikely that it will be able to be detected and distinguished from the plutonium left from atmospheric nuclear
tests.

11

Article by Shozugawa et al, published in the January 2012 issue of Environmental Pollution (No. 163).
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6.1.2. MODELING OF THE ATMOSPHERIC DISPERSION OF RELEASES IN JAPANAs soon as the accident occurred, IRSN developed a model of the atmospheric dispersion of the releases that it had
estimated, on a local and regional scale, using the codes from its C3X calculation platform installed at theInstitute's emergency response center. These assessments were updated regularly as new data became available.
However, the local-scale assessments (a few dozen kilometers around the site) were very rough on account of
insufficient data on the release conditions and the local weather. On the other hand, the regional-scale (a few
hundred to a few thousand kilometers) and global-scale results yielded by these assessments were satisfactory
overall thanks to the better meteorological data.
Over the course of 2011, IRSN used environmental data available to continue modeling the atmosphericdispersion of the releases at local and regional scales. Its work allowed it to more realistically estimate theconsequences of this dispersion, particularly in terms of doses potentially received by the population exposed to
the radioactive plume (see Section 8).

6.1.2.1 Regional-scale modeling of the atmospheric dispersion (Japan)
IRSN used the three-dimensional ldX model of its C3X platform to model the atmospheric dispersion at the regional
level (several hundred to several thousand kilometers). Developed over the past few years, ldX was validated bymany comparisons with experiments (particularly ozone-pollution episodes) and the reconstruction of thecontamination of the air in Europe after the Chernobyl accident. The model's spatial resolution is that of theweather data used, i.e. around 12 km. ldX is a Eulerian model, meaning that, at the scale of a unit cell (element
volume of the atmosphere used in the modeling), the calculated activity concentration (as well as the deposition)
is homogeneous. The results yielded by ldX are thus comparable with measurements only when the width of theplume was substantially larger than that of the cells. In practice, the results yielded by ldX are usable at a
distance of around 5-8 cells from the discharge point. In the case of Japan, this is around 50-80 km. Below
this distance, the model does not make it possible to calculate the concentration gradients of airborne
radionuclides, which persist near the discharge point. A local-scale modeling tool should therefore be used (seeSection 6.1.2.2).
The reliability of the results obtained with ldX depends largely on the quality of the data on the releases from theaccident and the weather.
• The initial estimates made by IRSN in March 2011
On March 16, while the Fukushima accident was still taking place, IRSN began developing its first models with ldXusing the release estimates it made between March 12-20 and regularly updating its models throughout the rest of
the month. The calculation results obtained for cesium-137 and iodine-131 in Tokyo were compared with theresults of air contamination measurements taken in the same city. Both showed good consistency (Figure 6-4).

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Evolution in the activity concentration of cesium-137 and iodine-131 measured in the air over Tokyo
between March 15-17 (local time)

March 16, 2011

March 17, 2011

Air concen tration in Bq/m3

March 15, 2011

Air concentrations of cesium-137 and iodine-131 over Tokyo,
calculated by IRSN by means of long-range atmospheric dispersion
modeling

Cesium-137

Measurements

Iodine-131

IdX model

Figure 6-4 – Comparison of the results of the calculation of the air concentration of cesium-137 andiodine-131 over Tokyo, obtained by IRSN on March 19, 2011, using the ldX model (right) and resultsfrom measurements taken in Tokyo during the same period(left: SPEEDI monitoring station).
• Update of the modeling of the dispersion of atmospheric releases
Over the course of further work in 2011, IRSN reconstructed the history of radioactive contamination of the air inJapan during the Fukushima accident at the same time as it was estimating the source term described in Section
6.1.1.1. The results of the regional-scale model are generally consistent with the readings made by the ambient
dose rate monitors in Japan and were used to identify the main air-contamination events in Japan:


The first releases, occurring between March 12-14, spread mainly northward along the eastern coastof Honshu island, then toward the northeast and east, over the Pacific Ocean (Figure 6-5);

On March 15 and 16, the radioactive releases from reactor 2 spread over Japan, but the weather
conditions were changing rapidly (Figure 6-6);

On March 16 and the following days, the releases spread eastward, moving over the Pacific andsparing most of Japan (Figure 6-7);



Between the afternoon of March 20 and March 23, the radioactive releases again spread over Japan(Figure 6-8). After March 23, the contaminated air masses moved toward the Pacific. The subsequent
releases have been too low to cause a significant increase in the radioactivity in Japan's terrestrial
environment.

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5:00 pm on March 12, 2011

5:00 am on March 13, 2011

12:00 pm on March 14, 2011

Figure 6-5 - Model of the ambient dose rate due to atmospheric dispersion of releases from the
Fukushima accident between March 12-14 (excluding the contribution of radioactive fallout – IRSN's ldXmodel).
5:00 am on March 15, 2011

7:00 pm on March 15, 2011

6:00 am on March 16, 2011

Figure 6-6 - Model of the ambient dose rate due to atmospheric dispersion of releases from the
Fukushima accident on March 15 and the morning of March 16 (excluding the contribution of radioactive
fallout - IRSN's ldX model), illustrating the first air contamination event on Honshu island.
11:00 a.m. on March 16, 2011

2:00 p.m. on March 16, 2011

3:00 a.m. on March 19, 2011

Figure 6-7 - Model of the ambient dose rate due to atmospheric dispersion of releases from the
Fukushima accident between midday, March 16, and March 19 (excluding the contribution of radioactive
fallout – IRSN's ldX model) illustrating the second dispersion event over the Pacific Ocean.

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6:00 p.m. on March 20, 2011

5:00 p.m. on March 21, 2011

3:00 p.m. on March 22, 2011

Figure 6-8 - Regional-scale model of the ambient dose rate due to atmospheric dispersion of releases
from the Fukushima accident on March 20 and 22 (excluding the contribution of radioactive fallout IRSN's ldX model), illustrating the second air contamination event on Honshu island.

6.1.2.2 Local-scale modeling of the atmospheric dispersion (Fukushima prefecture)
In order to model the atmospheric dispersion of the releases at the local scale (a few kilometers to a few dozen
kilometers), IRSN used the pX model of its C3X calculation platform, which is suited to local-scale studies. Because
pX is a Gaussian burst model, the choice of the law of standard deviation is crucial. IRSN's tests on the Fukushima
accident led to the use of Pasquill standard deviations. The pX model takes into account the spatial heterogeneityof the wind across its range of calculation. In the case of Japan, it was applied to a circular area measuring 80 km
in diameter around the Fukushima Dai-ichi plant.
During the Fukushima Dai-ichi emergency, IRSN had neither sufficient nor adequate data to allow it to construct a
reliable local-scale model. In particular, it did not have the necessary meteorological data for the Fukushimaregion and had to rely on results from local observations. In France, this data is usually provided by Météo France
using suitable meteorological models. Moreover, the layout of the environment near the Fukushima plant made it
hard to model the wind. The coastal effects and the effects due to the complex orography (valleys, mountains)mean that the wind changes direction very often and is therefore hard to simulate. As a result, the work
performed subsequently by IRSN in collaboration with Météo France showed that some meteorological events werevery hard to model, even a posteriori. This was especially the case of the first release event in the direction ofJapan on March 15-16: the meteorological models were unable to reproduce the wind directions observed. Thesedifficulties also affected the regional-scale simulations, but less noticeably than at the local scale, where theplume was highly concentrated.
Various meteorological observations, made at the Fukushima Dai-ichi and Daini sites (TEPCO) or at various
meteorological stations in Fukushima prefecture (available on the site of the JMA [Japan Meteorological Agency12])were used by IRSN for analysis and comparison purposes with the meteorological models. However, the loss of
power following the tsunami made them intermittently available or unavailable during the period of releases fromthe accident. Rainfall radar images available on the JMA's website were therefore used in order to best reproduce
the wet deposition event of March 15-16 associated with the heavy localized rainfall.
The combination of the meteorological observations and the data from the CEP meteorological model yielded
generally consistent simulations with the available environmental measurements (Figure 6-9 to Figure 6-12). The
results of these simulations made it possible to obtain a more accurate picture of certain dispersion events
described previously using the regional-scale model:

12

http://www.jma.go.jp/jma/indexe.html
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the initial releases that occurred on March 12, 2011, first passed over a small portion of Japan northof the Fukushima Dai-ichi plant (particularly Minamisōma, the only place in Japan where this release
event was detected by a monitor) then moved out to the Pacific Ocean over the course of the evening(Figure 6-9);

11:00 p.m. on March 12, 2011

7:00 p.m. on March 12, 2011

Figure 6-9 - Model of the ambient dose rate due to atmospheric dispersion of releases from the
Fukushima accident over the course of March 12, 2011 (excluding the contribution of radioactive fallout– IRSN's pX model).

-On the morning of March 15, the radioactive releases moved southward while those that had
occurred the previous evening moved northwest of the plant (Figure 6-10);

10:00 p.m. on March 15, 2011

5:00 a.m. on March 15, 2011

Figure 6-10 - Model of the ambient dose rate due to atmospheric dispersion of releases from the
Fukushima accident over the course of March 15, 2011 (excluding the contribution of radioactive fallout– IRSN's pX model).

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53/188-On the early morning of March 16, the plume released during the night of March 15-16 continued tomove towards the northwest then gradually turned southwest inland. The following releases moved due
south then southeast as the day progressed (Figure 6-11);
11:00 a.m. on March 16, 2011

3:00 a.m. on March 16, 2011

Figure 6-11 - Model of the ambient dose rate due to atmospheric dispersion of releases from the
Fukushima accident over the course of March 16, 2011 (excluding the contribution of radioactive fallout– IRSN's pX model).
-Finally, on March 21-22, several releases moved toward the south or southwest in the direction ofTokyo (Figure 6-12)
1:00 a.m. on March 22, 2011

6:00 a.m. on March 21, 2011

Figure 6-12 - Model of the ambient dose rate due to atmospheric dispersion of releases from the
Fukushima accident on March 21 and 22 (excluding the contribution of radioactive fallout – IRSN's pX
model).

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6.2. CONTAMINATION OF JAPAN'S TERRESTRIAL ENVIRONMENT
6.2.1. GENERAL COMMENTS ON THE DEPOSITION OF RADIOACTIVE FALLOUT IN
JAPANDuring the air-contamination events, a portion of the radionuclides released into the air in the form of very fineparticles (aerosols) or soluble gases (a portion of the radioactive iodines) were deposited onto surfaces on the
ground. This process is caused by two complementary subprocesses that are illustrated in Figure 6-13.

Dry deposition
Wet deposition

Figure 6-13 – Figure illustrating dry deposition and wet deposition of radioactive materials from aradioactive plume.
All surfaces of all types and directions (horizontal, vertical or reversed) were contaminated by dry deposition, i.e.
the transport of airborne contaminants to surfaces by means of turbulence. The extent of this fallout depended
especially on the concentration of airborne radionuclides at ground level and the duration of contamination of theair. Dry fallout was deposited inside buildings as the air inside them became contaminated.
Certain areas were contaminated by wet deposition, i.e. the removal of radioactive particle or soluble gases (caseof iodine) from the radioactive plume by precipitation (rain or snow). This fallout did not affect building interiors.
The distribution of the contamination of ground-level surfaces receiving these radioactive particles obviously
varied across short distances based on whether the rain (or melting snow) flowed across the ground or infiltrated
into the soil.
Both types of fallout led to contamination of Japan's terrestrial environment that persisted after the air
contaminated by the accidental releases had been blown away. The geographical distribution and themagnitude of this contamination depend both on the subsequent trajectories of the radioactive plume created by
the radioactive releases that lasted for several days and the location and extent of the rainfall at that time. This
fallout had two main consequences:-a permanent rise in the ambient dose rate due to gamma radiation emitted by the radionuclides
contained in the fallout and which gradually lowered with time based on the radioactive decay of theradionuclides that were first deposited;-contamination of agricultural products, more or less immediate and more or less long-lasting.

As will be later shown, the impact of radioactive fallout on the environment and health varies with time and is at
its highest in the weeks following the deposition of this fallout. This is why it is important to gain a quick (andeven rough) understanding of the geographical distribution and characteristics (radioactivity and isotopic
composition) of this fallout in order to implement, as quickly as possible, early countermeasures to protect
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populations from the two main routes of exposure: external exposure from fallout and the ingestion ofcontaminated foodstuffs.
Two additional methods are used to estimate the fallout from an accidental release of radioactive materials:-

atmospheric dispersion modeling of releases and ground-level radioactive fallout;
measurement surveys involving the use of airborne measuring instruments or field teams collecting soil
samples or taking in situ measurements.

The first method makes it possible to quickly obtain initial estimates. However, these estimates can be very roughin the case of insufficient understanding of the radioactive releases and weather conditions.
The second method gives a more representative and multiscale picture of reality. However, it has the major
drawback of being long, especially in the case of vast distances, and can thus delay the implementation of theappropriate countermeasures.
The distinctive feature of the Fukushima accident is that it led to the overlap of a release phase – primarily over adozen days (with the threat of new releases lasting for at least several weeks) and creating an immediate risk of
exposure to radioactive plume (external exposure and inhalation) – with a fallout phase that became significant
starting on March 16 while the radioactive releases were still occurring (Figure 6-14).

Ambient dose rate measurement in Ibaraki Prefecture (Mito)(in microsieverts per hour)

March

April

Figure 6-14 – Timeline of the measurement of the ambient gamma dose rate in Ibaraki showing theoverlap of the release phase and the fallout phase from the Fukushima accident. c: ambient dose rate
before the accident; d: first event of atmospheric contamination; e: dose rate from residual
radioactive fallout deposited during the first event of atmospheric contamination; f: second event of
atmospheric contamination; g: dose rate from the residual radioactive fallout deposited during thesubsequent events of atmospheric contamination.

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56/188Series of ambient dose rate measurements comparable to those illustrated by Figure 6-14 and taken at various
points throughout Japan show similar events but at times and with intensities that occasionally differ (Figure 615). Readings by most of the monitors that were still operational after the accident show that the ambient dose
rate began rising on March 15 or 16, except in Minamisōma, located some 20 kilometers north of the damaged
nuclear power plant, where the measurements taken by the monitor show that the first events of atmosphericcontamination started on March 12.

Dose rates measured in Fukushima prefecture

Figure 6-15 - Evolution in the ambient dose rate measured at several municipalities in Fukushima
prefecture. The difference in the level of background radiation (nearly a factor of 100 between Iitate
and Minamiaizu) is due to the variable magnitude of the radioactive fallout. The general downward
trend during this observation period is caused by the gradual disappearance of the short-lived
radionuclides.
The complexity of the Fukushima accident, with multiple release events and changing weather conditions, and thelack of sufficient data in IRSN's possession at the time of the accident made it very difficult to estimate the extent
and geographical distribution of the fallout with the help of modeling tools. The measurement surveys conductedin Japan are therefore what made it possible to gradually gain a clearer understanding of the radioactive fallout.

6.2.2. MAP OF THE RADIOACTIVE FALLOUT IN JAPAN
Many measurement surveys have been conducted in Japan since late March 2011 to map the radioactive fallout
from the Fukushima Dai-ichi accident, primarily by means of airborne techniques. These maps are of the ambient
dose rate caused by the fallout as well as the surface activities of cesium-134 and cesium-137. Coordinated andorganized by the Japanese Ministry of Education, Culture, Sports, Science, and Technology (MEXT), these airborne
measurement surveys have been conducted with the JAEA13 and NUSTEC14 with the technical support of the U.S.
DOE/NNSA15).
In addition, soil samples (first 5 cm) were collected for laboratory analysis by a consortium of Japanese
universities under the auspices of MEXT in order to better understand the fallout and check the consistency of theJapan Atomic Energy Agency
Nuclear Safety Technology Center
15
U.S. Department of Energy, National Nuclear Security Administration
13
14

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results obtained with the results of the airborne surveys. The first collection surveys took place between June 6
and July 8, 2011, at 2,200 points throughout Fukushima prefecture. Similar surveys, including one in December
2011 involving the participation of an IRSN team, were subsequently conducted in order to monitor changes in thecontamination. These surveys also provided the opportunity to compare the results obtained with various
measurement techniques, such as in situ gamma spectrometry or radiation meters onboard vehicles circulating
within the contaminated areas.
The data from these surveys is presented in a general map of radioactive fallout in the northern portion of Honshu
island.
Due to the conditions under which the airborne measurements were taken (see Appendix 6-2), the resulting mapsof the northern portion of Honshu island only provide an indication of the average level of ground fallout at thescale of 1 kilometer. They do not make it possible to better characterize local variations in the fallout fromsources such as the runoff or accumulation of fallout-laden rain or the melting of fallout-laden snow. This
characterization was made possible only by measurement surveys conducted in the field with radiation meters,
particularly in urban areas.

6.2.2.1 Map of the ambient dose rate from the radioactive fallout
Following a number of initial reconnaissance surveys in March, in particular during a mission carried out with thesupport of the U.S. DOE from March 30 to April 3, 2011, the first three airborne measurement surveys were limited
to an 80-km radius around the Fukushima Dai-ichi plant. They took place from April 6 to April 29, from May 18 to
May 26, and from May 30 to July 2.
By way of illustration, Figure 6-16 shows the map of the ambient dose rate measured at 1 m above groundpublished by MEXT after the first survey in April.

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Ambient dose rate at 1 m above ground, normalized toApril 29, 2011 (in µSv/h)

Figure 6-16 - Map of the ambient dose rate at 1 m above ground (in µSv/h, normalized to April 29, 2011)
published by MEXT after the first airborne measurement survey conducted from April 6 to April 29
within an 80-km radius around the Fukushima Dai-ichi nuclear power plant.

This map shows a main zone of radioactive fallout extending more than 50 kilometers northwest of the Fukushima
Dai-ichi plant. The ambient dose rates measured in this area ranged from greater than 2 µSv/h (i.e. 20 to 40 times
higher than the level due to naturally occurring radiation) to more than 20 µSv/h in its worst-affected portion.
Southwest of the plant is an area of less fallout where the dose rate was greater than 1 µSv/h. At the time of thisfirst survey, the deposition must have been made up of nearly 75% cesium-134 and cesium-137, in more or lessequal amounts, and the rest consisting essentially of iodine-131 (half-life of 8 days) and tellurium-129m (half-lifeof 33.6 days). After the third survey (July 2), the Japanese authorities indicated that the ambient dose rate within
the same area of the map had decreased by around 20%. This decrease is consistent with the continued radioactive
decay of iodine-131 and tellurium-129m, and to a lesser extent, cesium-134 (the activity ratio of 134Cs/137Cs musthave been near 0.85 at this date, versus 0.9 to 1 on March 15, the date on which the bulk of the fallout was
deposited in Japan).
Starting in late June, MEXT began implementing airborne measurement surveys across a much wider area in orderto verify the absence of extensive fallout beyond the main fallout zone already identified. As of December 1, 22
prefectures in the northern half of Honshu island had been mapped. MEXT has published an overview of this map(see Figure 6-17).

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Ambient dose rate
(in microsieverts per hour µSv/h)>19
9.5 to 19
3.8 to 9.5
1.9 to 3.8
1 to 1.9
0.5 to 1
0.2 to 0.5
0.1 to 0.2≤ 0.1

Figure 6-17 - Map of the ambient dose rate at 1 m above ground (in µSv/h, normalized to November 1,2011) published by MEXT after the various airborne measurement surveys conducted since late June
2011 for 22 prefectures within the northern end of Honshu island.
Apart from Fukushima prefecture, the location of the aforementioned main fallout zone, this expanded map raises
the following comments:-

the areas where the ambient dose rates are less than 0.1 µSv/h (in dark blue on the map) can beconsidered to be free of significant fallout from the Fukushima accident. This level is comparable to theambient dose rate due to the radiation of cosmic or terrestrial origin – between 0.05 and 0.2 µSv/h
depending on the altitude or the geological nature of the ground – that makes up natural "backgroundnoise";-

a number of prefectures located far from Fukushima contain more or less extensive zones with dose rates
of between 0.1 and 0.5 µSv/h, and between 0.5 and 1 µSv/h locally (Gunma, Tochigi). As these levels are
significantly higher than the natural background noise from gamma radiation, they attest to residual
fallout from the Fukushima accident deposited over long distances from the damaged plant aftermaterials released by the accident were dispersed into the atmosphere. The prefectures where theselevels were recorded over at least a significant portion of their areas are Tochigi, Gunma, Ibaraki,
northern Chiba, western and northeastern Tokyo, western Saitama, eastern and northeastern Niigata, as
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well as other, less affected prefectures (southern and northern Miyagi et southern Iwate, Yamagata,
Nagano, northern Shizuoka, eastern Toyama).
MEXT also published prefecture-specific maps. Figure 6-18 shows the maps of the ambient dose rates at 1 m above
ground for the Gunma and Tokyo Metropolis Prefectures.

Ambient doserate
(in microsieverts
per hour - µSv/h)

0.5 to 1
0.2 to 0.5
0.1 to 0.2
≤ 0.1

Tokyo
Metropolis

Figure 6-18 – Examples of the maps of the ambient dose rates at 1 m above ground (in µSv/h) publishedby MEXT for the Gunma and Tokyo Metropolis Prefectures (the list of surveys and their start and end
dates is provided in Appendix 6.2).

The map of the ambient dose rates in the eastern portion of Fukushima prefecture was published in late April; themap of its western portion has since been made available (Figure 6-19). Apart from a drop in the dose rate due tothe disappearance of short-lived radionuclides, this new map does not significantly differ from the map publishedat the end of the April survey (Figure 6-16). However, its scale of values has a higher level of detail.

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Ambient dose rate at
1 m above ground(µSv/h, normalized toAugust 28, 2011)>19
9.5 to 19
3.8 to 9.5
1.9 to 3.8
1 to 1.9
0.5 to 1
0.2 to 0.5
0.1 to 0.2≤ 0.1

Figure 6-19 – Updated map of the ambient dose rate at 1 m above ground (in µSv/h, normalized toAugust 28, 2011) published by MEXT for Fukushima prefecture.

Many detailed maps showing the results of dose rate measurements taken during field surveys have been publishedin Japan. Conducted under the auspices of various ministries or at the initiative of prefectures or local
associations, they show variations – at times significant – in radioactive fallout at the local scale. The detailed dose
rate maps published on February 24, 2012, by the Japanese Ministry of the Environment merit pointing out. These
maps were created using measurements taken between November 2011 and January 2012 by instruments installedon vehicles circulating in the most heavily contaminated areas, including in the vicinity of the crippled site (seeFigure 6-20. This map shows measurement points located close together in areas accessible by vehicle; there are
no readings for the mountainous areas. At this level of detail, a lobe of fallout extending in a north by northeast
direction can be distinguished from the main lobe heading towards the northwest. This lobe was probably formed
during a different release event.

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Ambient dose rate

Fukushima
Dai-ichi site

≤ 1.0 µSv/h
1.0 to 1.9 µSv/h
1.9 to 3.8 µSv/h
3.8 to 9.5 µSv/h
9.5 to 19 µSv/h>19 µSv/h

Figure 6-20 - Detailed map of the ambient dose rate northwest of the Fukushima Dai-ichi plant,
produced using the results of measurement taken by instruments installed on cars between November
2011 and January 2012 (source Japanese Ministry of the Environment). The arrows show the directionsof the main cloud of radioactive fallout (headed northwest) and a secondary cloud headed in a north bynorthwest direction.

6.2.2.2 Map of the surface depositions of radioactive cesium
As of late April 2011 cesium-134 and cesium-137 became the two prevailing radionuclides in the radioactive fallout
from the Fukushima accident. As indicated in Section 6.2.3.4, their proportion in the total fallout increased as theshort-lived radionuclides gradually disappeared. After December 1, the activity of these two radionuclides
accounted for nearly 99% of the total activity of the residual fallout.
After continuing the airborne measurement surveys mentioned previously, MEXT published an updated version of
the map of the cumulative surface activities of cesium-134 and cesium-137 in the northern portion of Honshu
island (Figure 6 21-a). Similar maps have been produced for just cesium-134 and cesium-137 (Figure 6 21-b) since,
within a few years, cesium-137 will make up the vast bulk of the residual fallout in Japan (94% of the activity of
the residual fallout in 2020)
Because radioactive cesium emits gamma radiation and is predominant in the fallout, it is the main cause of therise in the ambient dose rate mapped in Japan (see Figure 6-17). The results of in-field measurements conductedin June and July in order to check the representativeness of the fallout maps produced using airborne
measurements enabled MEXT to draw a relatively satisfactory correlation between the ambient dose rate and thetotal surface activity of cesium-134 and cesium-137. Fallout of 276,000 Bq/m2 would therefore correspond to anincrease in the ambient dose rate of 1 µSv/h (July 2011). Due to the 20% decrease in the ambient dose rate
between April and July, caused by the gradual disappearance of the short-lived radionuclides (see Section

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6.2.2.1), this correlation value published by MEXT is consistent with what IRSN had estimated in its report16
published on May 23, 2011, i.e. 300,000 Bq/m2 for 1 µSv/h in late April.
These maps also confirm that, outside the main fallout zone (located less than 80 km from the Fukushima Dai-ichi
plant), significant amounts of lower-level fallout also formed along the direction of the main fallout zone and evenbeyond, in the form of isolated spots (leopard-spot distribution). Outside Fukushima prefecture, the surface
activity of cesium-134 and cesium-137 is generally below 100,000 Bq/m2, except in a few areas where it can be as
much as 300,000 Bq/m2. These levels are comparable with those observed in Sweden, Austria and other countries
in Europe after the Chernobyl accident. These secondary fallout zones are located primarily in Tochigi, Gunma and
Ibaraki prefectures, northern Chiba, and the borders Miyagi prefecture shares with Fukushima and Iwate
prefectures.

Deposits of 134Cs+ 137Cs(in thousands of Bq/m²)
>3000
>3000
1000 toto 3000
3000
1000
600 toto 1000
1000
600
300 toto 600
600
300
100
to
300
100 to 300
60 to
to 100
100
60
30 to
to 60
60
30
10 to
to 30
30
10
10
≤≤ 10

Deposits of137
Cs(in thousands of Bq/m²)
>3000
>3000
1000
to30003000
1000 to600
to10001000
600 to
300
to600
600
300 to
100
to300
300
100 to
60
to100
100
60 to
30
to60
60
30 to
10
to30
30
10 to
≤
10
≤ 10

Figure 6-21 – Map of the cumulative deposition of cesium-134 and cesium-137 (a) and cesium-137 (b)published by MEXT following airborne measurement surveys conducted since late June 2011.

At the scale of the available maps, it appears that the other mapped prefectures either were spared from any
fallout or received low amounts of fallout containing radioactive cesium with a surface activity of no more than
10,000 Bq/m2 (as was the case in most of France, except for its eastern part, after the Chernobyl accident).
The airborne surveys conducted over the summer also made it possible to refine the map of cesium deposition in
Fukushima prefecture (Figure 6-22). As for the neighboring prefectures, this map shows secondary fallout zones in
the west, also in the form of leopard spots, with surface activities of several dozen becquerels per square meter.

Rapport IRSN DRPH n°2011-10 « Évaluation au 66ème jour des doses externes projetées pour les populations vivant dans la zone
de retombée nord-ouest de l’accident nucléaire de Fukushima »16

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Deposition of
134Cs + 137Cs(in thousands of Bq/m²)>3000
1000 to 3000
600 to 1000
300 to 600
100 to 300
60 to 100
30 to 60
10 to 30
≤ 10

Figure 6-22 - Updated version of the map of the cumulative deposition of cesium-134 and cesium-137 in
Fukushima prefecture published by MEXT.
In late August 2011 MEXT also published maps of radioactive cesium-137 fallout (Figure 6-23) which superimpose
the map of the surface activities of cesium-137 determined from airborne measurements of the gamma radiation
emitted by the fallout (colored zones in the background) and the results of the measurements of the activity in soil
(first 5 cm) obtained during sampling surveys conducted at 2,200 points by a consortium of Japanese universities
between June 6 and July 8 (colored dots). The results of these measurements have been normalized to June 14,
taking into account the radioactive decay of the radionuclides.
Superimposing these two sources of results shows a good overall consistency of the mapping of fallout at thisscale.
These maps also raise the following comments:
Inside the 20-km zone that was evacuated immediately after the accident occurred, the surface activities ofcesium-137 measured on the soil samples vary between less than 30 kBq/m2 and 15,000 kBq/m2, or a difference ofa factor of 500 between the extreme values. Of the more than 100 sampling points in this zone, 11 measured asurface activity of cesium-137 of more than 3,000 kBq/m2. The highest activities were observed immediately westof the plant (dot inside of a black circle on the map in Figure 6-23): 14,000 kBq/m2 of cesium-134 and15,000 kBq/m2 of cesium-137.
In the planned evacuation zone set up on April 22 (pink area on Figure 6-23, and spanning the municipalities of
Iitate, Katsurao and portions of Namie, Kawamata and Minamisōma), the surface activities of cesium-134 andcesium-137 range between less than 60 kBq/m2 and 8,000 kBq/m2. Of the more than 100 sampling points in thiszone, three measured a surface activity of cesium-137 of more than 3,000 kBq/m2.
Apart from these two zones, the cumulative surface activities of cesium-134 and cesium-137 do not exceed
600 kBq/m2, except 20-30 km to the southwest (Figure 6-22).

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evacuation zone

Emergency
evacuation zone

Cs-137 (in thousands of Bq/m²)>3000
1000 to 3000
600 to 1000
300 to 600
100 to 300
60 to 100
30 to 60
10 to 30
≤ 10
Highest value(15 million Bq/m²)

Figure 6-23 - Map of the surface activities of cesium-137 published by MEXT (normalized to June 14, 2011). Colored zones: based on airborne measurementsof ambient gamma radiation (MEXT). Colored dots: based on measurements of samples (first 5 cm of soil). Black circle: highest cesium-137 reading.

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Using the cesium-137 fallout maps published in the fall of 2011 by MEXT, IRSN estimated the surface areas of theaffected areas based on the extent of the fallout. It excluded the area nearest to the Fukushima Dai-ichi plant(within a 9-km radius and with an area of 133 km2), which was not mapped at this scale. Under to its estimates :-altogether, the surface area of the areas where cesium-137 fallout from the Fukushima accident has been
identified (surface activity exceeding 10,000 Bq/m2) is estimated to be in the region of 24,000 km2. 420 km2
of this zone is located 250-300 km away from the crippled plant, corresponding to the maximum spread of
the radioactive fallout;-

the surface area of the zones with the highest amount of fallout (surface activity of cesium-137 exceeding 1
million Bq/m2) is estimated to be 262 km2 (and nearly 400 km2 if the 9-km zone is assimilated with a highdeposition zone) northwest of the crippled plant. The fallout in at least 60 km2 of this zone is estimated to
exceed 3 million Bq/m2;-

all the zones where the cesium-137 fallout exceeds 300,000 Bq/m2 are less than 50 km from the plant. As aresult, the cesium-137 fallout is between 600,000 and 1 million Bq/m2 across a 225 km2 area and between
300,000 and 600,000 Bq/m2 across a 379 km2 area;-

the chart in Figure 6-24 shows, by amount of surface activity, the surface area proportions that wereaffected by the fallout. As expected due to the atmospheric dispersion of the releases that deposited this% of total surface area of the fallout

fallout, the larger the surface area, the less the amount of fallout.

Surface activity of cesium-137 (in kBq/m2)

Figure 6-24 – Proportion of surface area affected by the cesium-137 deposits as a function of the amountof this fallout (assuming that the fallout in the 9-km area is highest overall)

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Table 6-II below compares the surface areas contaminated after the Fukushima and Chernobyl accidents. For thesame level of contamination, clearly smaller surface areas were affected in Japan than in Ukraine. This is explainedin particular by the fact that a major portion of the releases from the Fukushima accident drifted over the Pacific
Ocean, leaving no residual fallout. Compared to the 13,000 km2 of land around Chernobyl, only around 600 km2 ofland in Japan – or 20 times less than in Ukraine – is contaminated by more than 600,000 Bq/m2 of cesium-137(including the land located within the 20-km zone). However, as IRSN indicated in May 2011, in addition to the
80,000 residents evacuated as an emergency measure in the 20-km zone, a population of 70,000 lives in these areas.
In all, this amounts to more than half the number of people who were living in the most heavily contaminated areas
around Chernobyl (270,000 people for cesium-137 fallout measurements greater than 555,000 Bq/m2).

Table 6‑ II – Comparison of surface areas contaminated in Japan (IRSN assessments, based on MEXT maps)
and in Ukraine after the Chernobyl accident.
Chernobyl accident
137

Cs fallout measured in

Fukushima accident

Surface area by country

137

Cs fallout measured in

1986-87

Surface areas

summer 2011
Exclusion zone

Circle with a 30 km radius

Exclusion zone (20 km)

around 2,800 km2

Semi-circle with a 20 km around 600 km2
radiusoutside exclusion zone
More than 1,480 kBq/m²

Russia: 300 km

Outside exclusion zone (20 km)²

Belarus: 2,200 km

More than 1,000 kBq/m²

Japan: 170 km²

600 to 1,000 kBq/m2

Japan: 150 km²

30 to 600 kBq/m²

Japan: 8,200 km²²

Ukraine: 600 km²
Other countries: /555 to 1,480 kBq/m²

Russia: 2,000 km²
Belarus: 4,000 km²
Ukraine: 1,000 km²
Other countries: /37 to 555 kBq/m²

Russia: 56,000 km²
Belarus: 40,000 km²
Ukraine: 40,000 km²
Other countries: 45,000 km²

6.2.3. ISOTOPIC COMPOSITION OF THE FALLOUT, CHANGES OVER TIME ANDSPATIAL VARIATIONS
The isotopic composition of the radioactive fallout from the Fukushima accident kept changing on account of the fast
radioactive decay of the short-lived radionuclides (from a few hours to a few days). As illustrated by the series ofmeasurements taken 30 km northwest of the Fukushima Dai-ichi plant (along the limits of Namie and Iitate) fromMarch 18 to April 5 (Figure 6-25), this fast decay had a direct effect on the trend toward a decrease in the ambient
dose rate from radioactive fallout. The decay began to slow down in mid-April when the radionuclides with very shorthalf-lives, initially abundant in number, had virtually disappeared.

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April 15, 2011

May 16, 2011

June 16, 2011

July 17, 2011

Figure 6-25 – Evolution in the ambient dose rate due to radioactive fallout, measured in Namie (Akougi
Teshichiro), 31 km northwest of the plant (MEXT measurement point #32).
For this reason, measurements taken on soil samples (or samples of plants that had received fallout) during thesecond half of March or throughout April are what provided the most complete information on the initial isotopic
composition of the radioactive fallout. In order to compare the measurement results obtained on samples collected
at different dates, the values should be corrected by the radioactive decay of each identified radionuclide bynormalizing them to the same date. Given that the main fallout formed during the night of March 15-16, 2011 (seeSection 6.2.4), the convention adopted for the purposes of comparing the results was to normalize all values toMarch 15.
The results obtained from soil samples collected in Japan were regularly published by MEXT in 2011. IRSN also
analyzed samples sent to it. In France, ACRO17also performed many measurements on samples from Japan.

6.2.3.1 Measurements taken by IRSN on a soil sample from Iitate Maeta
IRSN analyzed a topsoil sample (first 2 cm) collected on March 31 in Iitate Maeta, located some 40 km northwest of
the Fukushima Dai-ichi plant (50 g sample provided by ACRO; see map in Figure 6-26 for the location). Gammaemitting radionuclides as well as strontium-90 (a pure beta source) were quantified in these samples. The results are
given in Table 6-III below. Iodine-131 is the most abundant radionuclide, followed by cesium-137 and cesium-134,
which have similar activities. Generally speaking, volatile radionuclides (iodines, cesiums and telluriums)
predominate. Semi-volatile elements (barium, lanthanum, silver, strontium) account for less than 1% of the total
activity of the sample. The reason for this is that the conditions of the releases during the accident (depressurizationof the containments of the three damaged reactors) were very different from those during the Chernobyl accident(the explosion of the reactor released significant quantities of semi-volatile or non-volatile elements).
By adjusting the isotopic composition of the analyzed sample in order to normalize it to the date of the formation of
the radioactive fallout, which was estimated at March 15, it became clear that iodine-131 and the18 tellurium132/iodine-132 pair were largely prevalent. At that time, their activity accounted for more than 80% of the total
activity of the initial fallout at this point (also see Figure 6-29), with around eight times more iodine-131 and six
times more tellurium-132/iodine-132 than cesium-137. These values are consistent with the isotope ratios deduced
from the source term estimated by IRSN for reactor 2 (responsible for the bulk of the contamination in this area) andwhich are 9 for iodine-131, 8 for iodine-132 and 5 for tellurium-132.

Association pour le Contrôle de la Radioactivité dans l’Ouest (Association for Radioactivity Monitoring in Western France).
Because iodine-132 is produced by the radioactive decay of tellurium-132 and has a half-life that is much shorter than that of its
parent, both radionuclides are always found together in the environment at relatively similar levels on account of the quasiequilibrium between their activities. The same is true of the barium-140/lanthanum-140 pair and the tellurium-129m/tellurium-129
pair, although, in the case of the latter, the equilibrium activity of tellurium-129 accounts for only 63% of the activity of its parent
element (tellurium-129m), which has two modes of radioactive decay.
17
18

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Table 6- III - Results of measurements of the specific activity of radionuclides found in a topsoil sample
collected on March 31 in Iitate Maeta (at point [Acro] on the map in Figure 6-26) and estimation of thecorresponding activities on the assumed date of formation of the radioactive fallout.

Radionuclide(half-life)

Specific activity on the sampling
date (March 31, 2011) (Bq/kg)

Specific activity normalized tothe assumed date of formation of
the fallout (March 15, 2011)(Bq/kg)Iodine-131 (8 days)

86,680345,345

Iodine-132 (2.3 hours)

7,084≈’250,000

Cesium-137 (30.1 years)

44,36244,407

Cesium-134 (2.1 years)

45,34346,003Cesium-136 (13.2 days)

4,442

10,317

Tellurium-129m (33.6 days)

34,472

47,953Tellurium-129 (1.2 hours)

21,692≈’30,000

Tellurium 132 (3.2 days)

7,961

253,652

Barium-140 (12.7 days)

859

2,057

Lanthanum-140 (40.2 hours)

1,128≈’2,000

Silver-110 m (249 days)

309

323

Strontium-90 (29.1 years)

33

33

6.2.3.2 Measurements regularly taken at various locations around the Fukushima powerplant
In early June 2011 MEXT published the results of measurements of radioactivity in soil samples collected at morethan 100 points located within 20-62 km of the Fukushima Dai-ichi plant (a few are depicted on the map in Figure 626).
The point where the highest specific activities were measured was in Namie (place name: Akougi Kunugidaira; seepoint on map [83]), around 24 km from the power plant. The chart in Figure 6-27 shows the evolution in the specificactivities measured in soil collected in Namie (approx. first 5 cm). The activity of cesium-134 and cesium-137 is very
high (several hundred thousands of Bq/kg). The activity of iodine-131 was at the same level in early April, but
steadily decreased to reach, as expected, a 100 times lower value in late May. At this measurement point, there may
have been around seven times more iodine-131 than cesium-137 in the initial fallout (March 15 estimate). The results
published by MEXT for samples collected in May also provide indications for tellurium-129m (activity slightly lower
than 100,000 Bq/kg) and cesium-136 (activity around 1,000 Bq/kg), and reveal the presence of semi-volatile
radionuclides (strontium-89 and strontium-90, silver-110m, lanthanum-140, niobium-95) with activities ranging froma few hundred to nearly 1,000 Bq/kg.

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70/188Figure 6-26 - Locations of a few of the points where soil samples were regularly collected and sampled by
Japanese laboratories ([1], [3-1], [3- 12], [83], [n5] and [3-7]) and of the soil sample analyzed first by
ACRO then by IRSN.

March 18, 2011 April 2, 2011

April 17, 2011

May 2, 2011

May 17, 2011

June 1, 2011

Figure 6-27 – Evolution in the specific activity in topsoil samples collected in Namie (point 83).
A soil sample collected on June 13 in Namie at location [n5] and measured on June 14 by the JAERI19 yielded thespecific activities indicated in Table 6-IV. At this date, the radionuclides with very short half-lives (tellurium-132,
iodine-132) were no longer detectable and the ambient dose rate due to the gamma radiation emitted by theresidual radioactive fallout was 34 µSv/h (i.e. more than 500 times the normally measured value). The specificactivities estimated for the assumed fallout formation date (March 15) are virtually 10 times higher than those of thesample collected in Iitate Maeta (identified as [Acro]) and analyzed by IRSN. The isotope ratios normalized to cesium137 are similar for these two sites: 8 for iodine-131 and 0.87 for cesium-134.

19

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Table 6‑ IV - Results of measurements of the specific activity of radionuclides found in a topsoil sample
collected on June 13 in Namie at point [n-5] and estimation of the corresponding activities on theassumed date of formation of the radioactive fallout.

Radionuclide (halflife)

Specific activity on the sampling
date (June 13, 2011) (Bq/kg)

Specific activity normalized tothe assumed date of formation of
the fallout (March 15, 2011)(Bq/kg)Iodine-131 (8 days)

1,300

3.096 152

Iodine-132 (2.3 hours)< detection limit

Inestimable

Cesium-137 (30.1 years)

420,000

422,397

Cesium-134 (2.1 years)

340,000

368,808

Cesium-136 (13.2 days)

510

58,383Tellurium-129m (33.6 days)

78,000499,373

Tellurium-129 (1.2 hours)

50,000≈’315,000

Tellurium 132 (3.2 days)< detection limit

Inestimable

Barium-140 (12.7 days)

Undetermined

Inestimable

Lanthanum-140 (40.2 hours)

220≈’30,000

Silver-110 m (249 days)

1,600

2,056

Niobium-95 (35 days)

430

2,556

The other sampling points northwest of the plant show evolutions comparable to those observed at the Namie
station, but with different specific activities (in reference to cesium-137): several tens of thousands of Bq/kg at
points [3 1] in Iitate (place name: Nagadoro) and [3 12] in Namie (place name: Tsushima), and around 10,000 Bq/kg
in Fukushima City (place name: Sugitsuma, point [1]). In this last place, strontium-90 was measured at aconcentration of about 10 Bq/kg; in early June, the iodine-131 concentration in the same place was around
100 Bq/kg.

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6.2.3.3 Case of plutonium
In late September 2011, MEXT published a memo reporting the results of plutonium (and strontium) measurements insoil samples collected between June 6 and July 8 within an 80-km radius around the Fukushima Dai-ichi plant. The
results (expressed in surface activity in the soils, in Bq/m2) were plotted on a map (an excerpt is provided in Figure6-28). These results relate to plutonium-238 (238Pu; half-life of 87.7 years) and plutonium-239 and plutonium-240
combined20 (239+240Pu; half-lives of 24,100 years and 6,564 years, respectively).
Interpreting the results obtained is not task, for these plutonium isotopes were already present in Japan's soil before
the Fukushima accident. According to MEXT, the mean surface activities throughout Japan, estimated using
measurement results obtained between 1999 and 2008, were 0.498 Bq/m2 and 17.8 Bq/m2 for 238Pu and 239+240Pu,
respectively, with peak values of 8 Bq/m2 and 220 Bq/m2, respectively. Despite a certain degree of dispersion ofthese values, the activity ratio of 238Pu/239+240Pu, which is 0.0261 in Japan, can be considered as characteristic of thepersistence of fallout from atmospheric nuclear weapons tests (however, the Japanese data shows that, before the
Fukushima accident, this ratio could be up to 10 times higher for some results).

Figure 6-28 – Locations of the plutonium measurement points around Fukushima Dai-ichi (adapted map
taken from the map published by MEXT on September 30, 2011). For each point, the top result refers to238

Pu and the bottom result to 239+240Pu. The surface activity values in Bq/m2 are normalized to June 14,
2011.

The numbers in the green circles indicate points where the measured surface activity of 238Pu exceeded
the detection limit; the results are given in Table 6-IV.

The map published by MEXT shows 64 measurement points within an 80-km radius. Six of these points show a surface
activity of 238Pu above the detection limit of the measurement technique used, which, according to MEXT, is
0.5 Bq/m2. These six points are shown on the map in Figure 6-28 and the results are given in Table 6-V.

As 239Pu and 240Pu emit similar levels of alpha radiation, the alpha spectrometry measurements do not make it possible to quantify
the activity of these radionuclides separately. This is why the results are provided for both radionuclides combined.

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Table 6-V – Results of the surface activity measurements of 238Pu and 239+240Pu for the six points shown on
the map in Figure 6-28. The result at point 5 for 239+240Pu is below the detection limit (< DL) of around
0.5 Bq/m2. Under these conditions, the 238Pu/239+240Pu ratio for this point is necessarily above 1.

Point No.

238

239+240

Pu in Bq/m²

Pu in Bq/m²

238

Pu/239+240ratio

1

0.82

2.5

0.328

2

0.77

0.6

1.283

3

4

1.8

2.222

4

2.3

1.8

1.278

5

0.57

< DL

>1

6

0.55

0.66

0.833

For all 64 measurement points, the results for 239+240Pu range between 0.44 (or the detection limit) and 7 Bq/m2,
corresponding to the residual background noise from fallout from nuclear testing. For the six points where 238Pu wasdetected, the surface activities range from 0.55 to 4 Bq/m2 and the 238Pu/239+240Pu ratio is between 0.33 and 2.2, farhigher than the characteristic ratio for fallout from atmospheric nuclear weapons tests. To confirm this observation,
IRSN measured the plutonium in the soil sample from Iitate Maeta provided by ACRO (see above). The specificconcentrations of 238Pu and 239+240Pu are 0.33 and 0.41 Bq/kg fresh weight, respectively, yielding a 238Pu/239+240Pu
ratio of 0.8 that is fully comparable to those determined using the results published by MEXT. These results
therefore show that plutonium was released during the Fukushima accident. More specifically, the fact that allthese values were obtained at points located within the main fallout zone extending to the northwest makes it
possible to attribute this plutonium to releases from reactor 2 after its containment was damaged by the hydrogen
explosion on March 15. It should be noted that the environmental impact of this release of plutonium is low, as no
more than a few Bq/m2 of fallout have been measured in Japan. This is much lower than the fallout measured
around Chernobyl, where the surface activity of 239+240Pu exceeds 3,700 Bq/m2 over a distance of more than
30 km and is even as high as several hundred thousand Bq/m2 within a few kilometers of the plant.
The highest values for 238Pu were measured more than 20 km from the Fukushima Dai-ichi plant, at points 3 and 4
northwest of Namie and south of Iitate. They are most likely due to the wet deposition that must have been heavy inthis area, as shown on the fallout map in Figure 6-23.

6.2.3.4 Change over time in the activity and isotopic composition of radioactive fallout inJapan
The activity and isotopic composition of the fallout are influenced by two main phenomena:-

radioactive decay of the radionuclides;-

deposition of fresh atmospheric fallout of radionuclides due to continuing small releases from the Fukushima
Dai-ichi plant.

Other phenomena, such as migration into deep soil layers and surface erosion caused by wind or runoff, may havealso come into play. However, their influence on the temporal evolution of the fallout must have been generally low
during the first year. As a result, it is difficult to quantify.

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As shown by the results in Tables 6-III and 6-IV as well as the chart in Figure 6-25, the radionuclides making up thefallout decayed at a particularly fast rate in the first few weeks after their formation. To illustrate, the chart in
Figure 6-29 shows the decrease in activity of a contaminated soil having the same isotopic composition as the Iitate
Maeta sample analyzed by IRSN (Table 6-VI).

activity of the initial fallout, in percent

Tellurium-132 + iodine-132
Iodine-131
Barium-140 + Lanthanum-140
Cesium-136
Tellurium-129m + Tellurium-129m

Cesium-134
Cesium-137

Figure 6-29 – Evolution in the activity of the main radionuclides in the fallout, deduced from the analysis
performed by IRSN on a topsoil sample collected on March 31, 2011, in Iitate Maeta (Table 6-III).
This chart shows the same kinetics of radioactive decay for the fallout as that for the ambient dose rate measured in
the same sector (Figure 6-25). As of April 5, the total radioactivity of the residual fallout amounted to less than 20%of the initial activity on March 15. This rapid decrease is a clear illustration of the fact that the bulk ofradioprotection measures in Japan were carried out in the first month after the accident in order to protect the
public as much as from doses potentially received through external exposure to the fallout as from the risk ofcontamination of plant-based (leafy vegetables) and animal-based (milk) foodstuffs produced in the areas thatreceived the radioactive fallout (see Sections 6.3 and 7).
This chart also shows the respective contributions of the various radionuclides in the fallout. The tellurium132/iodine-132 pair initially accounted for nearly 49% of the activity of the fallout, but disappeared from theenvironment very quickly (less than 5% of the total activity of the residual fallout as of early April). Iodine-131 was
the second main contributor to the activity of the fallout, accounting for as much as 40% of the activity at thislocation on March 23 (it will be seen later that the proportion of iodine-131 in the fallout varied by location), while
the tellurium-132/iodine-132 pair accounted for just 21%. As of May 1, iodine-131 accounted for less than 5% of theactivity of the fallout. In the following weeks, it virtually disappeared from Japan's environment except in areas withthe highest fallout, where it remained measurable until summer 2011 (in late June, the residual activity of iodine131 was 10,000 times lower than its initial activity)
The contribution of the tellurium-129m/tellurium-129 pair to the fallout increased with time, from 8% on March 15 to
26% on April 15, before itself dropping to less than 5% of the residual activity of the fallout August 1, 2011.

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Although cesium-136 and the barium-140/lanthanum-140 pair were detected in the environment in the weeks
following the accident, their contribution to the total activity of the fallout never rose above 1.7% and 0.7%,
respectively, in early April. More generally, all the radionuclides detected in small amounts, regardless of theirradioactive half-life, contributed – and will contribute – only marginally (less than 1%) to the activity of the fallout
and thus the exposure of the population.
Although they accounted for just 9% of the initial activity combined, cesium-134 and cesium-137 make up most of theresidual fallout in terms of time. As of May 20, they accounted for 80% of the activity of the fallout in Japan, which
explains why they were the only radionuclides that appeared on fallout maps published in Japan. Due to its shorter
half-life, cesium-134 decays at a noticeable rate. Its contribution to the fallout was at its maximum around midSeptember 2011 (46%). Since then, it has continued to slowly decrease (43% one year after the accident) and will
drop below 5% in March 2020, or nine years after the accident.
• Deposition of fresh radioactive fallout
Monitoring of the deposition rate continued in each prefecture in the months following the March phase of significant
atmospheric releases responsible for the bulk of radioactive fallout found in Japan. MEXT published the results of thismonitoring for three radionuclides (iodine-131, cesium-137, and cesium-134). These results show the persistence of
low atmospheric deposition probably due to continued low-level releases from the Fukushima Dai-ichi plant andpossibly resuspension in the air of previously deposited surface contamination. As a result, the deposition rate
recorded on April 18-19 in two prefectures south of Fukushima prefecture rose to:-

290 Bq/m2 of 131I and 160 Bq/m2 of 137Cs in the town of Hitachinaka (Ibaraki prefecture);-

368 Bq/m2 of 131I and 137 Bq/m2 of 137Cs in the town of Saitama (Saitama prefecture).

At its highest, the daily deposition rate of iodine-131 was around a dozen Bq/m² in early May in the various towns
where this radionuclide was being monitored. No traces of iodine-131 have been detected in any prefecture sincelate May (even with a detection limit lowered to 7 Bq/m²/month, or 0.02 Bq/m²/day).
The total daily deposition rate of cesium-134 and cesium-137 in Fukushima (Fukushima prefecture) varied greatly
from day to day between May 2011 and February 2012, regularly reaching a few Bq/m²/day and occasionally
exceeding 100 Bq/m²/day. IRSN considers that these values and their variations may be due to resuspension ofpreviously deposited cesium, which can lead to air concentrations of a few mBq/m3, followed by fresh surface
deposition of variable amounts depending on the weather conditions of the day (higher fallout levels with rainfall).
These variations in resuspension are too low to be observed by ambient dose rate measurement monitors.
The monthly deposition rates of cesium-134 and cesium-137 during fall 2011 were:•around 4,000 Bq/m2/month in Futaba (Fukushima prefecture) in the immediate vicinity of the plant;•a few dozen Bq/m²/month in Hitachinaka (Ibaraki prefecture) and Saitama (Saitama prefecture);•a few Bq/m²/month in seven other prefectures (Iwate, Yamagata, Tochigi, Gunma, Chiba, Tokyo,
Kanagawa).

These deposition rates are low compared to the rates recorded in March. Due to the decay of the short-lived
radionuclides described above, they do not compensate for the general decrease in the total surface activity initiallydeposited in March 2011.

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6.2.3.5 Spatial variations in the isotopic composition of the fallout
Outside the main fallout zone located northwest of the plant, the fallout is lower and its isotopic composition isdifferent. The activities measured on a soil sample collected on May 3 in the town of Hirono, 23 km south of theplant, are as follows:
-

131

-

134

-

137

-

89

-

90

I: 2,600 (Bq)/kg
Cs: 3,900 Bq/kg
Cs: 4,700 Bq/kg

Sr: 30 Bq/kg
Sr: 1.9 Bq/kg

The ambient dose rate measured at this point was 0.2 µSv/h. The fallout (in reference to cesium-137) is nearly
100 times lower than at station 83 in Namie, which is located at a comparable distance from the plant. On the other
hand, projecting these results at the date of March 15 yields an iodine-131/cesium-137 ratio of 38, well above thatobserved at the high-fallout spot located northwest of the nuclear site (near 8). Further away, some 30 km south ofthe plant, the iodine-131/cesium-137 ratio on March 15 is estimated to be around 50.
IRSN collected and interpreted the results of specific activity measurements of iodine-131, cesium-134, cesium-136,
cesium-137, tellurium-129m and silver-110m performed on soil samples collected starting in mid-March 2011.
Published by MEXT, these results came from nearly 160 sampling points unevenly distributed within a semi-circle
having a radius of 20-80 km around the crippled plant. Starting in mid-March 2011, one or more samples consisting of
the first 5 cm of soil were taken at more or less frequent intervals at each point, yielding several hundred – if notseveral thousand – values for each of the six radionuclides. By adjusting the measured activities in order to normalize
them to March 15 (date of formation of the main fallout), in view of the radioactive decay of the radionuclides, IRSN
was able to estimate the initial specific activities for each radionuclide with a specific degree of uncertainty at eachsampling point. These specific activities (Bq/kg fresh soil) were converted into surface activities (Bq/m2).
IRSN used geostatistical analysis to estimate the spatial distribution of these specific activities within a spatial
domain containing all the sampling stations and was able to deduce their activity ratios (in relation to cesium-137,
the reference radionuclide) on March 15. The activity ratio values for each radionuclide were presented in the formof a statistical distribution in order to determine their mode or modes (i.e. the value or values most frequently foundin the area being studied) and the standard deviations (Table 6-VI).
Table 6‑VII - Law of distribution (mode±standard deviation) of the activity ratios (in reference to cesium137) on March 15, 2011, within the 20-100 km radius around the Fukushima Dai-ichi site. The distributionsof the isotope ratios for iodine-131 and tellurium-129m present two modes corresponding to two different
geographic sectors.
134

Cs/137Cs

136

Cs/137Cs

0.89±0.05

0.39±0.2

131

I/137Cs

129m

Te/137Cs

11.7±4.6 (northwest)

1.56±0.62 (northwest)

48.2±7 (south)

6.1±1.4 (south)

110m

Ag/137Cs

0.05±0.06

The most frequent values of the 131I/137Cs ratio range between 10 and 15 (11.7 mode) and relate to the heaviest
fallout that formed on March 15 northwest of the crippled site. This means that the initial surface activities ofiodine-131 within this zone were able to rise past 30,000 kBq/m² on March 15 (red area in Figure 6-23).
The map in Figure 6-30 shows significant variations in the 131I/137Cs activity ratio (on 15 March 15) based on thelocation. The ratio rose to its highest level south of the Fukushima Dai-ichi plant, ranging between 30 and 80(corresponding to the second mode shown in Table 6-VII for iodine-131). In this sector, where the radioactive fallout
was lower than in the northwest, the higher proportion of radioactive iodine could be explained by:

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77/188-different fallout formation conditions (predominance of dry deposition)-differences in the physicochemical forms of iodine (gas or aerosol) in the air at the time of deposition;-or differences in the isotopic composition of the subsequent releases emitted by the stricken reactors(the accident caused several puff releases from three different reactors; see Section 6.1.1).

This also means that if the residual fallout south of the Fukushima Dai-ichi plant is relatively lower, it is possible thatthe concentrations of radioactive iodine in the air may have been as high as in the northwestern sector in the hours
following the radioactive releases, as IRSN's 2001 model of the atmospheric dispersion of releases also seems to show(see Section 6.1.2).
In late September 2011, MEXT published a map of the surface activity ratios of 131I/137Cs normalized to June 14(Figure 6-31) based on the new soil surface activity measurement results (first 5 cm) obtained from samples collected
at 2,200 points by a consortium of Japanese universities between June 6 and July 8, 2011. The colored dots on themap show the sampling points where iodine-131 was detectable on the analysis date. As expected, due to theradioactive decay of iodine-131, the values of the 131I/137Cs ratio are much lower than those estimated by IRSN for
March 15, 2011. However, the geographic variability of these ratio values is consistent between both data sources.

131 137
I/ Cs activity ratio estimated on
March 15, 2011

Figure 6-30 – Map showing the distribution of the ratio of the specific activities of 131I/137Cs in the soils
around the Fukushima Dai-ichi plant on March 15, 2011 (date of formation of the main fallout) obtainedby IRSN through geostatistical analysis of the measurement results published by MEXT. The pink dots show
the soil sampling stations.

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131I/137Cs ratio on
Extrapolation
On June 14, on March 15,
2011
2011

Figure 6-31 – Ratios of the surface activities of 131I/137Cs in the soils around the Fukushima Dai-ichi planton 14 June 2011 (MEXT, from a survey conducted in June-July) and extrapolation on March 15, 2011.
In late October 2011, MEXT published two similar maps (Figure 6-32 and Figure 6-33), one for tellurium-129m andanother for silver-110m, based on the same samples collected by the Japanese universities in June and July. Bothmaps also use cesium-137 as the reference and were normalized to June 14. As for iodine-131, the 129mTe/137Cs ratio
is higher on along the coast south of the plant. In the case of silver-110, the ratio is higher along the entire coastboth north and south of the plant.

129Te/137Cs ratio on

June 14, 2011

Figure 6-32 – Ratios of the surface activities of 129mTe/137Cs in the soils around the Fukushima Dai-ichi
plant on 14 June 2011 (MEXT, from a survey conducted in June-July).

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79/188Figure 6-33 – Ratios of the surface activities of 110mAg/137Cs in the soils around the Fukushima Dai-ichi
plant on 14 June 2011 (MEXT, from a survey conducted in June-July).

6.2.4. INTERPRETATION OF THE SOURCE AND DISTRIBUTION OF RADIOACTIVEFALLOUT IN JAPANThe two main events of dispersion of releases from the Fukushima Dai-ichi plant, on March 15-16 and March 21-23,
coincided with more or less heavy rainfall (or snowfall in high-altitude areas). Thus, after interpreting the evolution
over time of the ambient dose rate measured by the various monitors installed in Fukushima prefecture, IRSN
considers that the main fallout zone northwest of the Fukushima Dai-ichi plant may have been created by the releaseof radioactive materials somewhere between 1:00 p.m. and 11:00 p.m. on March 15, 2011. These materials may havebeen carried towards the northwest during the period of heavy rainfall or snowfall, particularly over the village of
Iitate (Figure 6-34 and Figure 6-35).

Locallyobserved wind

Direction of the rain front

March 15 at 9:00 p.m. (local time)

March 16 at 12:00 a.m. (local time)

March 16 at 3:00 a.m. (local time)

Figure 6-34 - Movement of the rain/snow front during the night of March 15-16, 2011, in the Fukushima
area (radar images).

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Total precipitation between 6:00 p.m. on March 15, 2011, and3:00 a.m. on March 16, 2011 (JST)In the form of rain

Total precipitation (snow) between 6:00 p.m. on March 15,
2011, and 3:00 a.m. on March 16, 2011 (JST)In the form of snow

Figure 6-35 - Estimation of the total rainfall (map on left) and snowfall (map on right) during the night ofMarch 15-16, 2011 (data from the European Center for Medium-Range Weather Forecasts [ECMWF]
provided by Météo France).
Moreover, the scattered spots of fallout observed at a distance from the Fukushima Dai-ichi plant, in Fukushima
prefecture and the other prefectures listed in section 6.2.2, corresponding to areas where the precipitation musthave been heavier than elsewhere, with the total rainfall exceeding 100 mm locally when the releases weredispersed across Japan. The distribution of the fallout is also influenced by the conditions under which theradionuclides were dispersed in the air, particularly in the sector closest to the crippled plant, where the deposition,
both dry and wet, reflects the footprint of the radioactive plume with a high concentration gradient.
In addition to these regional variations in the fallout, clearly illustrated by the maps obtained after the airborne
measurement surveys, the local distribution of fallout can also be highly variable between the plant cover and thesoil, as illustrated by Figure 6-36.
Total activity deposited (Bq. m 2)

Wet deposition

Dry deposition

Dry depositionon leavesWet depositionon leaves

Deposits carried away by runoff

Deposits carried in by runoff

Wet deposition
on soilDry deposition
on soil

Residual activity in the soil

Figure 6-36 - Diagram illustrating the distribution of wet and dry deposition between the plant cover andsoil, as well as the redistribution of wet deposition under the influence of surface runoff of rainwater.

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81/188Thus, when the plant cover is dense and very leafy (such as with a forest), dry deposition tends to be higher andaccumulate primarily on plants. Conversely, wet deposition (contaminated rain) tends to drip from the plant coverand either seeps into the soil (thus contributing to continual soil contamination, known as "residual fallout") or runs
along its surface depending on its impermeability and slope (particularly if the runoff is heavy). This results in a local
redistribution of wet radioactive fallout, resulting in higher amounts of residual fallout forming, for example, aroundtrees (from the dripping of contaminated rain from leaves), under rain gutters, in storm sewers, and in naturalaccumulation zones (impluvium) at the foot of more or less extensive catchment basins. Inversely, it can lead to theformation of lower amounts of residual fallout on impermeable or sloped surfaces. Some of this wet deposition may
also be carried away by the river system.
In the case of wet deposition by snowfall, the contamination temporarily stored in the snow cover may be moved by
the wind (snowdrifts) and then drip into the soil during the thawing season, creating small yet heavily contaminated"spots" (Figure 6-37).

Figure 6-37 - A thawing firn dripping water. The radioactive materials contained in the firn converge at
the point where the drops fall, forming a spot of contamination in the soil just below.
All these phenomena can therefore lead to high local differences in residual fallout that can vary by a factor of 10 ormore. Points where rainwater accumulates or infiltrates the soil can thus become "hot spots", with local surface
activities that are much higher than in the rest of the area.
These local differences in radioactive fallout do not appear on the maps obtained from the airborne measurement
surveys, which are not precise enough. Only field surveys with radiation meters or portable spectrometers, or soil
samples analyzed in the laboratory, make it possible to identify hot spots. The various measurements published by
the Japanese authorities thus revealed these differences, particularly in urban areas.
There are always differences in fallout levels in urban areas because air turbulence from buildings creates
accumulation points in areas where the air is recirculated. Moreover, the adherence of fallout depends on the type of
surface (horizontal, slanted, etc.) and its material (hard or soft, smooth or rough, impermeable or porous, etc.). The
rougher the surface, the better dry fallout will adhere; the smoother and more impermeable the surface, the easier
wet fallout will flow. In addition, the ground directly under downspouts is particularly conducive to the accumulationof radioactivity and thus the creation of hot spots.

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6.3. IMPACT OF RADIOACTIVE FALLOUT ON AGRICULTURE IN JAPANIn order to monitor variations in the contamination of plant- and animal-based foodstuffs in Japan, IRSN collected theresults of measurements performed on these foodstuffs and published on the website of the Japanese Ministry of
Health, Labor and Welfare (MHLW).

6.3.1. HOW DID CROPS AND ANIMAL-SOURCE FOODS BECOME CONTAMINATED?
Generally speaking, radioactive fallout resulting from the dispersion of the radioactive plume contaminated the partsof plants exposed to the air and, consequently, crops for human and animal consumption.

Leafy vegetables (salads, spinach, leeks, etc.) were most directly affected by this contamination. The level ofcontamination depended not only on the intensity of the fallout, but also on its wet or dry deposition. As Figure 6-36
above shows, only a portion of wet deposition (rain) is retained by leaves; the rest flows down the leaves andinfiltrates the soil or runs along its surface. The wet deposition capture efficiency of the leaves of a given type ofplant depended on the depth of the rainfall that deposited this fallout: the heavier the precipitation (high rainfall
depth), the lower the capture efficiency of the leaves. Thus, although the wet deposition may have been muchhigher than the dry deposition at the same location, the contamination of the leaves did not increase proportionallyto this deposition and reached a saturation level during heavy rains.

Leaf contamination was highest immediately after the deposition of the fallout but decreased rapidly as newleaves produced by the plants did not receive any radioactive fallout (typically, salads harvested 50 days after an
accident are 100 times less contaminated than salads that reach maturity immediately afterward). Furthermore, as
shown previously (Figure 6-29 in Section 6.2.3.4), the short-lived radionuclides, which predominated immediately
after the deposition of the fallout, decreased at a fast rate in the following days. This was observed in Japan after
the Fukushima accident, including more than 100 km away from the stricken plant, as is illustrated by the case ofspinach harvested in Ibaraki prefecture between mid-March and late April (Figure 6-38). The models of radionuclidetransfer in land environments (plants and animals), such as those used by IRSN (ASTRAL or SYMBIOSE), accurately
simulate this effect of radioactive decay and biological dilution through plant growth, as illustrated in Figure 6-38.

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Measurements (spinach from
Ibaraki prefecture)
Model with dry deposition of
30 kBq/m2
Model with wet deposition of
1 kBq/m2

Figure 6-38 - Evolution of cesium-137 (top) and iodine-131 contamination (bottom) measured in spinach21
grown in Ibaraki prefecture (MHLW data). Comparison with the model results obtained by the SYMBIOSE
software (for leafy vegetables) with various scenarios of radioactive fallout deposition on
March 15, 2011.

The evolution in the contamination of leafy vegetables was calculated with SYMBIOSE using extreme, yet realistic for
Ibaraki prefecture, assumptions on the surface activity deposited on March 15, 2011. The red lines in the chart in
Figure 6-38 correspond to a maximum dry deposition (30 kBq/m² of cesium-137 and 30 times more iodine-131). The
blue lines correspond to a minimum wet deposition (1 kBq/m² of cesium-137 and 10 times more iodine-131).
The contamination deposited on the leaves of plants was rapidly absorbed and carried by their sap to their otherparts, particularly the storage tissue that they formed in the weeks following the accident (fruits and fruit-type
vegetables, cereal grains, tubers, wood, etc.). Called "translocation", this type of contamination through uptake andstorage in plants leads to persistent contamination, even of new shoots, primarily during the first year and, to alesser extent, the following years (variable depending on the type of plant). As a result, the contamination levels ofsome crops harvested in Japan several weeks and even several months after the Fukushima accident were high,although not as much as immediately after the accident. This was particularly the case of Japanese apricots, bamboo
shoots and tea leaves (see Section 6.3.2).

In light of the absence of precision, some of this data may relate to greenhouse spinach (nonetheless, most of this data relates tofield-grown spinach). On the other hand, the protective effect of greenhouses is not included in the SYMBIOSE calculations.

21

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If surface-deposited radionuclides penetrate into soil, they can be partially absorbed by plant roots. This is
known as root uptake. For the same amount of fallout, plant contamination by root uptake is always much lower(around 100 times lower) than initial contamination from fallout on foliage. Moreover, given the soil migration timeof radionuclides, root uptake is significant only for radionuclides with sufficiently long half-lives, such as cesium-134
and cesium-137. Rice crops in Japan's contaminated areas are what risk being most susceptible to contamination byroot uptake. Moreover, given that rice is grown in paddies, uptake can occur directly through contact withcontaminated water. It is probably this mode of uptake that explains why significant yet low levels of cesium
contamination have been observed in some rice harvests in Fukushima prefecture since 2011 (see Section 6.3.2).
Unlike contamination via foliage, which is transient and especially high in the weeks following an accident,
contamination by root uptake will last for years, albeit at lower levels, if no human intervention is taken to mitigate
it. This can create a risk of chronic contamination of some crops and is the reason why, in 2011, the Japanese
authorities prohibited the cultivation of land where the soil contamination exceeded 5,000 Bq/kg of radioactive
cesium per kilogram of earth22. When a root uptake factor (plant/soil concentration ratio) of 0.1 (a conservativevalue) is considered, the cesium contamination of crops growing in soil with 5,000 Bq/kg might reach 500 Bq per kg
of fresh produce. This corresponds to the marketing or consumption standard laid down in 2011 by Japan forfoodstuffs.
The contamination of animals or animal-source foods (meat, milk, eggs, etc.) was caused primarily by theingestion of contaminated fodder and, to a lesser extent, drinking water. Animals fed with foodstuffs not directly
exposed to the radioactive fallout, imported (a frequent case in Japan), or harvested prior to the accident andsufficiently protected from its fallout, therefore could not have high levels of contamination. Conversely, herds thatwere given grass in their feed might have become rapidly contaminated. Like all other foliage plants, grass isimmediately affected by radioactive fallout and is the most susceptible type of fodder.
A portion of radionuclides contained in ingested foods remains in the blood after digestion. There, they spreadthroughout the body and contaminate animal products before being eliminated. The intensity and persistence of thisuptake depends on the biokinetics (metabolization) of the radioactive element absorbed into the body. For example,
iodine is absorbed by the mammary glands, where it contaminates milk. Cesium spreads throughout the body,particularly muscles (meat), and can contaminate milk. The iodine content of milk is highest three days after
contaminated fodder is first ingested. If the quantity and quality of subsequent fodder remain the same, the iodine
activity in milk drops quickly over a period of around 4-5 days under the combined effect of radioactive decay andthe metabolic elimination of iodine-131 from the animal's body. Under the same conditions, the cesium content inmeat is highest only after a few weeks of gradual accumulation. If cesium continues to be absorbed, thecontamination of meat stabilizes at a balance point between ingestion and elimination. If cesium ingestion is
stopped, the contamination of meat decreases slowly and is completely eliminated in around 3 months (decrease in
the contamination of meat by half in 3 months).

6.3.2. OVERALL ASSESSMENT OF CONTAMINATION OF FOODSTUFFS IN JAPAN
Between mid-March 2011 and 8th February 2012 (the date of writing of the present report), the Japanese Ministry of
Health (MHLW) published test results on its website (specific activity in iodine 131, cesium 134, and cesium 137) from104,318 food samples (whatever their origin). Of those 104,318 samples, 1111 showed signs of contamination
exceeding the standard limits for sale or consumption in Japan23. For the Fukushima district alone, 18,350 products
were tested, of which 642 exceeded the limits.
These products found to be outside the limits belonged to the following categories:
22
Guideline. Assuming that the cesium is evenly distributed in the first 10 cm of soil, which has a density of around 1,500 kg/m3,
soil contamination of 5,000 Bq/kg corresponds approximately to a surface deposition of cesium of 750,000 Bq/m2, a level that is
virtually unseen in Japan except in the main contamination zone northwest of the Fukushima Dai-ichi plant and within less than
30 km southwest of it (see Figure 6-23).
23
The standards for sale or consumption of foodstuffs were adopted in Japan in the days following the accident. For iodine 131, thelimits were 300 Bq/liter for milk and other liquids for human consumption, and 2 000 Bq/kg for other foods. For the cesiums(134Cs+137Cs), they were 200 Bq/liter for milk and other liquids for human consumption, and 500 Bq/kg for other foods.

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Leafy vegetables (e.g., spinach), flower vegetables (e.g., broccoli), and root vegetables (e.g., turnips),-

Fruit from fruit trees (Japanese apricot, fig, pomegranate, persimmon, yuzu, loquat, kiwi) and chestnuts,-

Tea leaves and the leaves of medicinal plants,-

Bamboo shoots,-

Cereals (wheat, rape, rice),-Mushrooms,-

Farmed meat (beef) and game (boar, pheasant, etc.),-

Cow's milk,-

Sea and river fish,-

Shellfish and crustaceans,-

Marine algae.

The specific activities attained and how they change over time vary greatly from one category to another. They arelisted below.
IRSN has no information concerning the details of the sampling protocols used to obtain the measurements publishedin Japan. These data were probably not obtained with a view to conducting a scientific study of the environmental
contamination caused by the accident, but rather for the operational purpose of monitoring, to manage theboundaries within which the sale of foodstuffs produced in the contaminated territories should be banned, or toguarantee quality for certain sectors deemed to be sensitive by the producers or consumers (such as rice and beef).

It is important to note that, as is customary, the measurements were all expressed in becquerels per kilogram of‘raw’ product as sold, which is not necessarily the same as the contamination of products as consumed. Tea, forexample, is normally consumed as an infusion, after processing (refer to the inset below concerning themeasurements performed by IRSN). In the list above, products may be consumed raw or following some type ofprocessing. There is no way to predict whether such processing would be likely to concentrate or to dilute theradionuclides present in the raw products.

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Radioactivity measurements performed by IRSN on tea imported from Japan and on the infusion madewith this tea
The IRSN performed measurements on tea from the municipality of Omaezaki (Shizuoka district), takenfrom a batch imported into France and intercepted by the French customs authorities at Charles de Gaulle
Airport (Paris) in June. This tea, which contained significant cesium 134 and 137 contamination, wasprepared by infusion, using 50 grams of tea leaves per liter of water (the dosage recommendations range
from 10 to 40 g/L according to the type of tea). The results of the measurements (on 21st June 2011) are
given in the table below.
Results of the measurement of specific activity of the radionuclides present
in the tea sample from Omaezaki (Shizuoka district)
Tea leaves (Bq/kg)

Infusion (Bq/L)

Rate of transfer into
the infusion

Cesium 137

480

22

92%

Cesium 134

450

18

80%

Cesium 136

1.2< 0.248-

Potassium 40

560

23

82%

The sum of the specific activities of the cesiums (931 Bq/kg) in the tea leaves exceeds the maximum
allowable level stipulated in European regulation No. 297/2011 dated 25 March 2011, modified on 11 April
2011, which is 500 Bq/kg for foodstuffs other than liquid foods and dairy products. Note that potassium 40,
a naturally-occurring radionuclide always present in food, has 560 Bq/kg of specific activity, which is nottaken into account under the regulations. This high value is due to the fact that the tea leaves are
dehydrated, which tends to concentrate the radionuclides in the dry mass.
More than 80% of the cesium contained in the tea leaves is transferred to the infusion. The same applies topotassium 40, which is an alkaline element like cesium, and has the same chemical properties. The
radioactive cesium concentration in the infusion is 40 Bq/L, which is below the upper limit specified by themodified European regulation dated March 25th (200 Bq/L).
Assuming that this tea infusion is consumed at the rate of 1 liter per day, the effective dose taken would be
0.6 microsievert (µSv) per day, and 220 µSv/year (i.e., approximately 0.2 mSv per year). Considering a lessconcentrated infusion prepared using 6 g of tea in 30 cL of water (the dose usually recommended for thistype of tea), and applying the same rate of transfer of the cesium into the infusion, the effective dosetaken in for daily consumption of one liter would be 0.24 microsievert (µSv) per day, and 90 µSv (orapproximately 0.1 mSv per year).

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6.3.2.1 Report on plant-based foods•

Vegetables

Of all data transmitted by the MLHW on edible goods, with all categories mixed together, leafy vegetables
demonstrated the earliest and highest-level contamination:-

54,100 Bq/kg wet of iodine-131 in a sample of spinach taken on 18 March in Hitashi (Ibaraki district),
approximately 120 kilometers south of the plant;-

41,000 Bq/kg wet of cesium-134 and 41,000 Bq/kg of cesium-134 in a kukitachina sample (a local leafy
vegetable) taken on 21 March in Motomiya (Fukushima district), approximately 60 kilometers west of theplant.

During the month of March, many vegetable samples from the Fukushima, Ibaraki, Chiba, and Tochigi districts
contained cesium and/or iodine 131 contamination exceeding the standards for sale or consumption; most of thesesamples were spinach, but there were also other local leafy vegetables (komatsuna, kukitachina, shinobuhuyuna,
Japanese parsley, etc.) and broccoli (flower vegetables). In April and May, occasional overshoots of these standards
were still being observed (for the cesiums only). Until the end of June, cesium activities that were detectable but
below sales and consumption standard limits were still found. This fast transition is illustrated by the example ofspinach from the Ibaraki district, as already seen (Figure 6-38), and spinach from the Fukushima district (Figure 639).

cesium 134 + 137 (spinach, Fukushima district)iodine 131 (spinach, Fukushima district)

Mar. 16Mar. 31

Apr. 15

Apr. 30

May 15

May 30Jun. 14

Jun. 29

Figure 6-39- Change in iodine-131 and cesium-134 and -137 contamination in spinach from the Fukushima
district (MHLW data, Bq/kg wet)

For root vegetables such as turnips and wasabi, the edible part was not directly contaminated by the radioactive
fallout. As already indicated (Para. 6.3.1), they were contaminated via translocation of the foliar deposit. The
specific activity measurements are much lower than those for leafy vegetables, with the maximum values concerninga sample of turnips from April 3rd 2011 (Fukushima district), at 1000 Bq/kg wet iodine 131, and 4100 Bq/kg wet
cesiums 134+137. In mid-November, samples of wasabi (the root part) taken from the Fukushima district stillcontained cesium in excess of the standards for sale or consumption.
Fruit vegetables (such as tomatoes and melons) suffered very little contamination, with no cases of overshooting thestandards. For tomatoes, the maximum activity levels reached were in March 2011, with about twenty Bq/kg wet
iodine, and about a hundred Bq/kg wet cesium.

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From May 2011 until the fall, detectable contamination, sometimes exceeding the standards for sale or consumption,
were detected in tree fruits.
The first fruits in which significant activity was observed, from late May onwards, were Japanese apricots. Japanese
apricots (umé) are the fruit of a very early-flowering tree, which had probably already blossomed by mid-March. This
fruit tree is comparable to something between a plum tree and an apricot tree. It seems to flower like French apricot
trees: the blossoms bloom early in the spring (March or April), and sometimes even in January or February, according
to the climate. The leaves appear much later, and the fruit reaches maturity around the end of May. The most recent
measurements obtained from Japanese apricots picked in the Fukushima district vary from 137 to 700 Bq/kg wet ofcesiums 134+137. The highest levels of contamination observed in the spring of 2011 were the result of very large
deposits.
The maximum specific activities on fruits were observed on yuzu fruits: up to 2400 Bq/kg wet on August 26th in
Minamisoma and, later, 860 Bq/kg wet on October 11th in Date (Fukushima district). Yuzu fruit grows on a mediumsized prickly tree. The yuzu looks like a small grapefruit, and its color ranges from green to yellow according to its
degree of ripeness. The fruit has little flesh and many large seeds. It has an acidic taste. The yuzu originated in
China, but nowadays it is most commonly grown in Japan. In Japan, an ornamental version of the yuzu tree is grown
for its flowers (flower water) rather than its fruit. Yuzu is also used, for its zest, in Japanese cooking. Since the yuzu
tree is related to the lemon tree, it probably produces flowers and fruit throughout the year, as many citrus trees do(a lemon tree yields 200 to 600 fruits per year).
High values were also reached in kiwis picked in the fall, with specific cesium activity of up to 1100 Bq/kg wet on
November 14 in Minamisoma.
Figs also turned out to have relatively high cesium contamination, up to 520 Bq/kg wet on July 19th in
Minamisoma. In September 2011, specific activity of a few tens to a hundred Bq/kg wet of cesium was still being
recorded in figs. In October 2011, the values were less than 10 Bq/kg wet. Specific activity in cesiums of 560 Bq/kg
wet was also measured on pomegranates sampled in Date (Fukushima district) on October 13th.
With regard to nuts, high specific activity in cesiums was also observed in chestnuts, with one sample in Minamisoma
on September 6th (2000 Bq/kg wet) and another in Kashiwa (Chiba district) on October 11th (200 Bq/kg wet).
Most other fruits from fruit trees (apples, pears, peaches, plums, etc.) might have reached specific cesium activity ofa few tens of Bq/kg, without exceeding the standard limits for sale or consumption.
•

Bamboo shoots and tea leaves

In May and June 2011, raw or refined bamboo shoots and tea leaves had significant cesium 134 and 137
contamination, with the sum of the activities of those two radionuclides occasionally exceeding the limits for sale orconsumption in Japan (Figure 6-40).

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Japanese apricots

Raw tea leaves (in the field)
Unrefined tea leaves (1st cutting)

Raw tea leaves (2nd cutting)

Raw tea leaves
Unrefined tea leaves (2nd cutting)Bamboo shoots

Figure 6-40- Changes in caesium-134 and -137 contamination in Japanese apricots, tea leaves and bamboo
shoots harvested in different Japanese districts.
At the time of the deposit, the bamboo and tea plants had evergreen leaves, which intercepted the radioactive
deposits. The radionuclides intercepted by the leaves, particularly cesium, were assimilated by the plant, and thesap transported them throughout the tissues and organs, leading to the overall contamination of the plants(translocation effect). Because tea plants and bamboo have significant biomass (e.g. 7 to 14 kg dry matter per square
meter for tea), the interception of radioactive deposits was especially effective in March, even for slight deposits far
from the damaged power plant. Some of the foliar deposit was assimilated by the plants and transferred to the newshoots harvested from the end of April onwards, which explains the significant cesium contamination observed in new
tea leaves and bamboo shoots, even if they grew several weeks after the deposits were formed.
The specific activities measured (cesiums 134+137) managed to exceed 1000 Bq/kg wet for tea from the first
harvest (1330 Bq/kg wet in Kanagawa and 981 Bq/kg wet in Shizuoka on June 21st) and 2000 Bq/kg wet for bamboo
shoots (2060 Bq/kg in Minamisoma and 1 070 Bq/kg in Souma on June 23rd). These contamination levels could
correspond to relatively moderate cesium deposits, estimated at a few tens of thousands of Bq/m2, which could haveformed up to a few hundred kilometers from the Fukushima Dai-ichi power plant (see the map in Figure 6-21). The
measurements performed on tea leaves and bamboo shoots concerned the first harvest after the deposits.
Note that unrefined leaves from the Saitama district (harvest number not specified) still had 1300 Bq/kg wet ofcesium specific activity in November.
Rice and other cereals
In view of how it is grown, rice could have been contaminated by interception of radioactive deposits if the plant wason the ground at the time of the radioactive fallout, via water contamination, or via soil contamination alone (roottransfer). At the time of the accident in March, rice had probably not yet been planted, and therefore it did notreceive any direct radioactive fallout. To prevent excessive contamination by root absorption of the cesiums present
in soil, the Japanese government authorized rice-growing only in soils whose maximum cesium content was less than
5000 Bq/kg, leading to the assumption that the maximum cesium concentrations in raw grains of rice harvested
would not exceed the standard limits for sale or consumption in Japan (500 Bq/kg; see Para. 6.3.1).
In agricultural areas (mainly in the Tohoku and Kanto regions), where the specific concentration of cesiums in the soil
exceeded 1000 Bq/kg (whilst remaining below 5000 Bq/kg), the Japanese government instituted a two-stage
monitoring process:-Preliminary inspection of the rice one week before harvest,-

Main inspection after harvest.

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If the result of the preliminary pre-harvest inspection revealed cesium concentrations above 200 Bq/kg, the area oforigin of the samples tested was considered a priority area, and post-harvest rice tests were performed at a large
number of farms in that area. If not, there were fewer post-harvest tests. Nonetheless, whilst the preliminary preharvest tests in the Fukushima district had indicated cesium concentrations of only 136 Bq/kg, the tests carried out
after the harvest revealed a contamination of 630 Bq/kg in rice from one of the two farms tested. This was thehighest results. The insufficient reliability of the initial tests raised concerns about the monitoring protocol. Certain
municipalities therefore demanded that the central government should set up a system of screening all batches ofrice.
Several factors can affect the contamination of a grain of rice before and after it has been picked:-

Between the preliminary test carried out before the harvest and the test performed after the harvest, thematuring of the rice naturally leads to some drying of the grain. The cesium concentrations therefore
naturally increase between the tests.

-

Most of the contamination in the rice is stored in the husk that surrounds the grain. This means that theprocessing by which it is transformed into white rice (removal of the husk, bran, and germ, and polishing of
the grain) lowers the contamination levels. The rice bran, on the other hand, which can be used for humanor animal consumption, contains the largest proportion of the cesium in the rice.

Moreover, before going on sale, rice crops are usually mixed at the time of processing. It is therefore possible thatthe white rice analyzed in Japan could in fact have been a mixture of rice from several different paddy fields, which
could have resulted in a reduced level of contamination in the product placed on sale, due to dilution.
In view of the monitoring procedures implemented, rice underwent a large number of tests (approximately 3900 testsof raw or refined rice between August and January). The cesium 137 and 134 contents measured were usually below
the detection limits of the measuring instruments. Fewer than 10% of tests revealed detectable cesium
contamination (mainly samples from the Fukushima district). Three tests revealed content exceeding the authorized
limits (rice samples from the Fukushima district and rice bran from the Miyagi district).
With regard to cereals, occasional overshoots of the limits for sale or consumption were observed in wheat and rape.

6.3.2.2 Overall assessment of contamination of animal-based foods•

Cow’s milk

In general, based on the results published in Japan, the activities measured in milk seem to have been relatively
moderate in comparison to the very high levels of deposits and the contamination of grass to the northwest of
the damaged power plant. Thus, the higher activities measured in milk were 10 to 100 Bq/L, with a maximum
measurement of 210 Bq/L for each of the cesiums (in Iitate, March 19th, 2011) and 100 to 1,000 Bq/L, with amaximum measured value of 5,300 Bq/L for iodine-131 (in Kawamata, March 20th). Between March 2011 and the
beginning of February 2012, out of approximately 2000 analyses of milk and milk product samples, only 23 exhibited
iodine or cesium activities that exceeded permitted sales standards.
It is likely that the date of the accident, occurring at the end of winter, limited animal contamination (and thus milk
contamination), as animals must be fed with either local fodder harvested during the previous season or imported
fodder (the importing of animal feed seems common in Japan). Figure 6-41 presents the results of measurements
taken on weeks from the Iitate area (blue diamonds). The iodine 131 activities measured reached 2.5 MBq/kg wet
immediately after the deposits.
The simulation carried out using IRSN's ASTRAL software (blue line) shows that these activities in weeds could
correspond to iodine 131 deposits of the order of ’ MBq/m2 (estimated initial surface activity at the date of formation
as at March 15th 2011) that could have formed, mainly in wet form (contaminated rain). The change in activity
observed in these plants matches the predictions of the simulation. The same assumptions concerning the probableconditions of contamination of weeds in Iitate were applied in order to estimate the possible theoreticalcontamination of milk if the livestock had eaten these weeds: The red curve in Figure 6-41 shows that thisFukushima, one year later
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contamination could have reached 100,000 Bq/L in the first few days, during the week following the formation ofradioactive deposits, and then dropped by a factor of 100 after one month.

Cow’s milk
Measurements in milk from Motomlya

Weeds

Measurements in milk from Kawamata
Measurements in milk from Iitate
Measurements in milk from Date
Simulation (ASTRAL) of iodine 131 activity in milk
for a deposit of 3 MBq/m2 at 80% w

Measurements in weeds - Iitate

Bq/kg weeds or Bq/L milk

Simulation (ASTRAL)
of ioding 131 activity in weeds for adeposit of 3 MBq/m2 at 80% wet deposition

March-13

March-23

Apr-02

Apr-12

Apr-22

May-02

Figure 6-41- Specific (volume) activity of iodine 131 in milk samples with the highest contamination levels,from the Iitate-Kawamata-Date region, as well as Mitomiya (red symbols). Specific (mass) activity ofiodine 131 measured in weeds sampled in Iitate (blue diamonds) and simulation using ASTRAL software ofiodine 131 activities in these plants (blue line) and milk (red line) produced by cows assumed to haveeaten these plants. The model was created assuming an initial iodine-131 deposit of 3 MBq/m2 at 80% in
the form of a wet deposit.
The Iitate, Kawamata, and Date areas, from which the most highly contaminated samples came, are located in thezone that received the most deposition, to the north-west of the damaged power plant. The iodine 131 activity inmilk in those areas was a maximum of a few thousand Bq/L. This figure also shows that milk from Motomiya, which isabout forty kilometers south-west of Kawamata, outside this area of heavy deposition, was contaminated to acomparable level. This appears to confirm that the contamination of milk is not caused primarily by the regularconsumption of local grass, but rather is related to the ambient contamination in these areas (accidental ingestion of
surface contamination, or contamination in fodder or drinking water exposed to a contaminated environment).
Figure 6-41 also shows a fast decline in iodine 131 content in both weeds and milk, and great variability in theactivities observed in a single area, as shown by the significant batch of samples taken in Kawamata on March 20th.
This variability is related to the variable nature of fodder contamination, which in turn is probably more related to
the nature and origin of the fodder that the variability of the radioactive deposits in this area. The reduction
observed, corresponding to an effective decay period of the order of 4.5 to 5 days, matches that seen in French milkin 1986 after the Chernobyl accident, and is in good agreement with radioecological models. It is caused by theradioactive decay of iodine 131 in fodder and its elimination by the animal, particularly through the milk itself. After
mid-April, the iodine 131 activity levels in the milk samples fell below the detection limits, which were often of theorder of 10 to 50 Bq/L. The iodine 131 activity in milk nevertheless inevitably fell to less than 1 Bq/L before the endof May 2011 because of the radioactive decay of this radionuclide.

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Cow’s milk
Measurements in milk from Motomlya
Measurements in milk from Kawamata

Weeds

Measurements in milk from Iitate
Measurements in milk from Date
Simulation (ASTRAL) of cesium 137 activity in milk for adeposit of 2 MBq/m2 at 80% wet deposition

Measurements in weeds - Iitate

Bq/kg weeds or Bq/L milk

Simulation (ASTRAL) of cesium 137 activity in weeds for adeposit of 2 MBq/m2 with 80% wet deposition

8
.- 1
ar
M

.-2
ar
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1
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8
r.Ap

15
r.Ap

2
r.Ap

2

29
r.Ap

. -6
ay
M

.-1
ay
M

3

0
.- 2
ay
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.-2
ay
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7

Figure 6-42: Specific (volume) activity of cesium 137 measured in milk samples with the highest
contamination levels from the Iitate-Kawamata-Date region, as well as Mitomiya (red symbols). Specific(mass) activity of cesium 137 measured in weeds sampled in Iitate (blue diamonds) and simulation using
ASTRAL software of cesium 137 activities in these plants (blue line) and milk (red line) produced by cows
assumed to have eaten these plants. The model was created assuming an initial cesium-137 deposit of 2
MBq/m2 at 80% in the form of a wet deposit.

These results were interpreted in a similar way to those for iodine 131 above. Once again, the levels of cesium 137
contamination in the weeds can be explained by significant deposits of a few MBq/m2, corresponding to the cesium
137 surface activity mapped in the municipality of Iitate (see Figure 6 23 page 66). Moreover, as for iodine 131, thecesium 137 concentrations measured in milk are much lower than those that could have been reached if livestock had
been fed nothing but locally-grown contaminated plants. There is no way of knowing how the contamination of milkchanged after mid-April 2011, because the cesium 137 concentrations in the milk probably remained below thedetection limits of the measurement methods used.
Iodine 131 and cesium 134 and 137 activities in milk samples from Ibaraki, south of the damaged power plant, werealso measured at similar levels to those mentioned above. That area also received significant radioactive deposits,with a higher proportion in dry form than the area to the north-west of the power plant, which could havecontaminated plants more efficiently.

•

Meat

Like the activity detected in milk (and probably for the same reasons), the iodine and cesium activity in meatremained moderate, considering the radioactive deposits in the worst-affected areas. Iodine-131 was almost
never found in the meat: the activities remained below detection limits, which admittedly are rather high (usually 20
to 50 Bq/kg). Of some 65,000 meat sample analysis results (between March 2011 and February 2012), about 200 had
cesium activities exceeding sales limits, including 67 game samples (mainly wild boar meat) and 141 samples of beef.
Game meats are discussed in greater detail below (Para. 6.3.2.3.1).

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For the sake of comparison, if the animals had consumed grass having the same activity level as the weeds measured
in Iitate, the cesium-137 contamination in the meat could have reached 200,000 Bq/kg wet in mid-April 2011.
The cesium contamination of meat followed a very different curve from that of milk because of the far longer
persistence of cesium in muscle tissue, and possibly because feeding practices differ for different types of livestock
farming. Figure 6-43 presents the activities of cesium 134+137 measured in samples of beef between March andNovember 2011 in areas where the most testing of beef was performed because some of the highest activity levels
were found. With very few exceptions, the cesium activity in beef did not start to regularly exceed 20 Bq/kg untillate April because of the gradual accumulation of cesium. The highest activity levels (cesium 137+134), between
1000 and 4350 Bq/kg wet (Kawamata-Machi), were reached in early July.

March-12

May-01June-20

August-09

Sept.-28

Nov.-17

Asakawa (machi and cho)

Figure 6-43 presents the activities of cesium 134+137 measured in samples of beef between March andNovember 2011 in areas where the most testing of beef was performed because some of the highest
activity levels were found.
More than the location and size of these deposits, it is food production practices that are the determining factors.
Thus, two batches of meat samples were analyzed on 8 and 9 July in Minamisoma-shi, north of the Fukushima Dai-ichi
plant, on a farm located just outside the 20-km exclusion zone. The results of the two batches are drasticallydifferent: 1500 to 4200 Bq/kg for the first batch and 4 to 10 Bq/kg for the second. As pertains to the 11 bovines
involved in the first batch with the highest activities, and based on information published on July 12th in the Mainichi
Daily News, since the beginning of April, the livestock farmer had been feeding his livestock rice straw harvested theprevious autumn that had been stored outside and was consequently contaminated by atmospheric radioactive fallout
in March. A similar deviation appears in Kawamata-machi.
The fact that the contamination of beef from an area such as Obanasawa, located in Yamagata district more than 150
km north-west of the Fukushima power plant, on surfaces where the deposits should not have exceeded 30 kBq/m2, is
as high as, or higher than, that of meat from municipalities such as Minamisoma, Katsuroa, Iitate and Kawamata,which are located in, or on the edge of, the area worst affected by radioactive fallout, confirms the importance ofanimal feeding practices.
Likewise, in the period from September to November 2011, the highest cesium activities measured in beef, which
regularly reached a few hundred Bq/kg, or occasionally 1000 Bq/kg, came from places in the Miyagi district(particularly Kurihara), nearly 150 km north of the damaged power plant, where the deposits did not exceed 60
kBq/m2.

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For all meats whose activities exceeded 500 Bq/kg, the decision by the Japanese Ministry of Agriculture, Forestry and
Fisheries, dated April 14th, to limit fodder for bovine animals to 300 Bq/kg (cesium 134+137), was not complied with.
Certain sets of measurements seem to indicate that, following the discovery of these cases, which concern only avery small number of farms, decisions were taken concerning the corresponding farming practices, leading to a fall in
the levels of contamination of meat, although this was slow because of the biological elimination period of cesium(around three months).
It can then happen that new farms, which are often more distant but had not made any special arrangements
because of their remoteness and moderate levels of contamination, are stigmatized precisely because of the relative
stability of the activity levels observed. That is what happened to one farm in Fujinomya (Shizuoka district, morethan 100 km south-west of Tokyo), where activity of a few tens of Bq/kg was observed on a regular basis from July
until quite recently. At such a distance from the damaged facility and in an area where the deposits were probably
very slight, the source of this activity and the reason for its persistent nature needs to be investigated.
With regard to other meats and foods of animal origin, tests performed on chicken meat and eggs remained negative(below the detection limits, except sporadically a few very low iodine 131 readings), which is to be expected in viewof the foods they eat: often products made with cereals harvested the previous summer, and therefore prior to theaccident. The same applies to pork meat and offal, although activity levels of 100, or even up to 200 Bq/kg havebeen observed very occasionally. Unlike the tests carried out on beef, a great majority of tests on game (wild boar,
Asian black bear, deer, Japanese pheasant) produced results above the detection limits, but the cesium activities
measured remained close to those of farmed cattle: from a few tens to a few hundred Bq/kg, very occasionallyreaching 1000 Bq/kg.
In the coming years, activities in caesium-134 and caesium-137 in animal products, milk and beef in particular,
will continue to depend mainly on the practices used to feed animals. So, even though the activity levels in fodder
potentially produced in the worst-affected areas may have fallen by a factor of nearly 1000 from the maximum
values in mid-March and the observations in September, like the case of the weeds tested in Iitate, any increase in
the proportion of those local products in the animal feed could lead to an increase in the activity in milk and meat.
Therefore, a livestock practice that strictly respects the fodder contamination limit of 300 Bq/kg for the productionof beef and milk (MAFF decisions, April 14th, 2011), could lead to activities in milk that would be near the sales
standard for milk (500 Bq/L) and above-limit activities for meat.

6.3.2.3 Contamination of foodstuffs from natural and semi-natural environments
Natural or semi-natural foodstuffs such as mushrooms, berries, game, and products from rivers and lakes, such as fish
and crawfish, have special characteristics that make them more sensitive, and for a longer time, to atmosphericradioactive fallout. These characteristics are related to the environments in which these organisms live, as well as
their physiology and their way of life (nutrition in particular).

6.3.2.3.1 Forest products
There are often more significant dry deposits in wooded areas than on grassland or cultivated areas, because theleaves of trees are efficient at trapping the radionuclides present in the air. Moreover, the wet deposits (formed byrain) can vary widely on a local scale because of a specific topography or the redistribution of rain deposits bydripping (most notably along trunks or on leaves).
Since then, the cycle of organic matter in forests has maintained high availability of cesium (the only radioactive
element that has persisted in the environment after the Fukushima accident) for plants and animals. From the firstyear, the falling of leaves that intercepted the radioactive deposits will create a bed where cesium is concentrated,
and which will continue to be fed regularly by a cycle that includes the transfer of the cesium from this bed to thesoil, its absorption by tree roots, and its transfer to the new leaves, etc.
These effects will maintain the contamination of forest products at levels that will fall only very slowing, andcertainly much more slowly than farm products. 25 years after the Chernobyl accident, forest products may have

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levels of cesium 137 up to 10,000 times higher than agricultural foods subjected to an equivalent initial radioactive
deposit, and mushrooms may still exceed the limits for sale or consumption.

•

Mushrooms

The item commonly known as a ‘mushroom’, which we eat, is in fact a reproductive organ called the ‘carpophore'—
generally an above-ground and ephemeral part of the plant. The permanent part of the mushroom consists of a
network of filaments called ‘mycelium’. The mycelium usually grows underground, generally at a fairly shallow depth
although this depends on the type, or on dead wood, tree trunks, or stumps. In the event of atmospheric fallout inthe form of rain, any mycelium near the surface (at a depth of a few centimeters) can be reached quickly by thecontaminated water that penetrates the soil. Radionuclides are then transferred to the carpophore very quickly. That
is why activities in iodine-131 and cesium-134 and -137 ranging from a few dozen to thousands of Bq/kg were
measured starting in the month of April in mushrooms from the Fukushima district, demonstrating this rapid transfer.
According to the results published in Japan, more than 120
January 2012 had cesium activity (

134

Cs+

137

mushroom samples taken between April 2011 andCs) in excess of the limits for sale or consumption (500 Bq/kg), and of

those, about 15 exceeded 2000 Bq/kg. The majority of mushrooms with high contamination were dried shiitake
mushrooms (it should be noted that drying can concentrate the cesium up to tenfold), but level activity levels werealso measured in fresh mushrooms. The highest cesium (134Cs+137Cs) activity identified among the published results
was 28,000 Bq/kg; it was measured in a “weeping milk cap” (Lactarius volemus) mushroom, picked on September 1st
2011 in Tanagura-machi (Fukushima district). The highest iodine 131 activity, 12,000 Bq/kg, was measured in a(shiitake) mushroom picked on April 8th in Iidate-mura. The cesium 134+137 activity in that sample was 13,000 Bq/kg.
These highest activity levels correspond to moderate deposit areas, and it is likely that much higher cesium
contamination levels will be found in the future in the worst-affected areas.
The contamination of a mushroom depends directly on the environment in which it grows, on a very local scale. This
leads to very wide variations in cesium content. This variability is further reinforced by the differences between
species, modes of nutrition (saprophyte, parasite, or symbiont), and depth of mycelium. Thus, during the first years,
species whose mycelium is nearest the surface of the ground will be the most sensitive. As the years go by, thosewith a deeper mycelium will become more contaminated with the downward migration of cesium, slow though thismight be.
It is important to note that, as seen in the aftermath of the Chernobyl accident, mushroom contamination will
no doubt continue for a long time—years or even decades—with cesium activity levels similar to, or even higher
than, those measured in Japan in 2011, in the areas worst affects by the radioactive fallout from the Fukushima
accident.
•

Wild berries

No measurement result on wild berries (wild strawberries, raspberries, blueberries, etc.) seems to have been
published to date. Although in general, in an equally contaminated environment, berries have cesium content similar
to the least sensitive species of mushroom, their activities in the years to come should also become more and moredifferent from those of agricultural products.

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•Game

Almost 350 tests were performed on game in Japan between April 2011 and January 2012, mostly since fall 2011.
They concern boar meat (155 tests), Asian black bear (85 tests), pheasant (42 tests), and deer (65 tests). Unlike inlivestock products (beef), the cesium activities (134Cs+137Cs) were most often above detection limits. The highest
levels were observed in wild boar and bear meat. Figure 6-44 presents the specific activities measured in wild boar
meat. They are extremely variable: from a few Bq/kg wet to a few thousand Bq/kg wet (maximum recorded value of
14,600 Bq/kg wet), the highest being those from the Fukushima district.

Fe
b.

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01
2
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ct

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11

Bq/kg wet of 134+137Cs

Fukushima district
Other districts

Figure 6-44 - Cesium (134Cs+137Cs) concentrations measured in boars taken from different districts (solid
symbols: Fukushima; hollow symbols: Chiba, Gifu, Gunma, Ibaraki, Kanagawa, Miyagi, Saitama,Tochigi,
Yamagata).

The activity levels in bear meat had similar levels and variability, with a maximum value of 1850 Bq/kg.
The cesium contents of pheasant and deer meat were lower: no more than a few hundred Bq/kg.
The unfavorable context of forest environments and the way of life of wild animals explain the variable, andgenerally higher, contamination than in beef. Thus, in the case of boars, the spatially heterogeneous nature of thecontamination of the environment is combined with a large seasonal fluctuation, related to herbivorous/fructivorous
eating in the spring and summer (although the boar is a highly opportunistic omnivore), and burrowing in the autumn
and winter (acorns, roots, tubers, worms, larvae). Note that, after the Chernobyl, accident, similar seasonalvariability was observed for roe deer in relation to mushroom consumption; the meat of an animal slaughtered in thefall can be ten times more contaminated than that of an animal slaughtered in the spring.

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6.3.2.3.2 Aquatic species•

Summary of measurement results in Japan

From the end of March, various freshwater and marine organisms were analyzed in Japan. More than 3000 samples
were taken between March and November. The case of marine species is presented in Section 6.4.7.
Of the various species taken from fresh water, five frequently had higher contamination levels in the Fukushima
district, regularly exceeding the limits for sale or consumption, and were subject to regular monitoring (Figure 6-45).
These species were:dace (tribolodon hakonensis), white spotted char (salvelinus leucomaenis), ayu sweetfish(plecoglossus altivelis), cherry salmon (oncorhychus masou), and wakasagi smelt (hypomesus nipponensis). All ofthese fishes, except dace, are able to migrate between fresh water and salt water (amphihaline species), but certain
populations seem to be confined to fresh water only. The results are very variable, however what clearly stands out
is the fact that the most affected samples were all collected from rivers or lakes in the Fukushima district (shown inred) except for a few specimens fished from lakes in the Gunma district (shown in blue). The highest levels were

Bq/kg wet of 134+137Cs

found in fish caught near the town of Minamisoma in the Fukushima district.

Figure 6-45 - Concentrations of radioactive cesium (134Cs+137Cs, in Bq/kg wet) measured in five species offish caught in rivers or lakes in various Japanese districts.

Other aquatic species have been subjected to more or less regular monitoring, such as various types of freshwaterclam, crabs, crawfish, shrimps, carp, and salmon. In most cases, the cesiums (137Cs+134Cs) were detected in thosespecies at levels below 200 Bq/kg wet.

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Note that one species of salmon, the chum salmon (Oncorhyncus keta), was also monitored regularly in the districtsof Hokkaido and Fukushima. The results published are all below the detection limits (except for one sample taken on
November 11th in the Fukushima district, measured at 41 Bq/kg wet). This can be related directly to how this species
lives; only adult specimens are found in rivers, and they do not eat during that phase of their lives, which tends tohighlight the importance of food as the main source of contamination in fish.
The contamination in fish will diminish all the more slowly as water and sediment are renewed slowly, particularly inlakes and ponds. In those environments, after the Chernobyl accident, effective half-lives (the time required for
cesium contamination to be halved) of 100 to 200 days, and sometimes longer for carnivorous species, wereobserved.

•

The progress of contamination in the aquatic environment

Although surface aquatic media received atmospheric fallout directly, that contribution was often small compared tothe contributions related to trickling from neighboring surfaces when the radioactive deposits are mainly from rain,
as in the most contaminated are to the north-west of the Fukushima Dai-ichi power plant. The contamination of
bodies of water resulting from these effects must have been intermittent and almost simultaneous with thedeposition. The IRSN is not aware of any measurement results with which this initial episode of contamination of theaquatic environment may be characterized.
The levels of contamination of surface water reached during this initial contamination episode could have been
extremely variable according to the characteristics of the catchment basin, particularly the surface area, topology,
morphology, pedology, vegetation cover, and the duration of deposit formation. Smaller bodies of water locatedupstream from the river network may be more sensitive than rivers in the downstream part of the hydrographic
network because of dilution, in particular by the accompanying water table. It is important to remember thatwhatever its magnitude, this initial contamination episode only slightly affects aquatic organisms because of its
transient nature.
After this early contamination episode, continental aquatic environments are then subjected to a supply ofradionuclides, mainly cesium, related to soil drainage (supply of particles from contaminated soil and water). The
renewal of river waters causes a significant proportion of this contamination to be exported quite quickly towards
the rivers and the sea. Nevertheless, a fraction becomes fixed more or less permanently in the sediment, which thenbecomes a source of delayed contamination for water and aquatic life. The resulting activities in water in themonths following the deposits are generally 10 to 100 times weaker than those observed during the initialepisode, but will contribute to the long-term contamination of aquatic organisms. Little information is available
concerning current activities in bodies of water in Japan, except for a series of measurements taken by the Japanese
Ministry of the Environment in bodies of water in the Fukushima region in September 2011.

6.4. CONTAMINATION IN THE MARINE ENVIRONMENT
The marine environment was affected at the time of the accident and the following days by fallout of aerosols
emitted into the atmosphere at the time of their dispersion above the ocean (§ 6.1.2) as well as by the release of
liquids directly into the sea. In future, the leaching of contaminated soils will be the main source of long-term
contamination of the marine environment.

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6.4.1. DESCRIPTION OF THE MARINE AREA EXPOSED TO DISCHARGESThe Fukushima power plant is located on the coast of the island of Honshu, 200 km north-east of Tokyo. The coast
runs north-south, facing the Pacific Ocean. The seabed shelves off gently to a depth of 200 m, 50 km from the coastand then drops suddenly to more than 5,000 m, about a hundred kilometers offshore (Figure 6-46).

Depth

Figure 6-46 - Topography of the sea bed in Japan and bathymetry off the east coast.
In the zone affected by radioactive pollution, the currents are generated by the tide, wind and the general Pacificcirculation. In the short term, the tidal effect predominates. The tide moves the masses of water according to analternating movement along the coast towards the north and the south, with speeds in the region of one meter per
second and a periodicity of 12 hours. The wind influences the circulation of surface waters.
The general larger-scale circulation is the result of the interaction between the Kuroshio oceanic current, whichcomes from the south and runs along the coasts of Japan, and the less powerful Oyashio current, which comes fromthe north (Figure 6-47 and Figure 6-48). The intensity and scale of the Kuroshio are comparable to those of the Gulf
Stream. The coastal waters in the vicinity of the Fukushima Dai-ichi plant are situated in the zone where these twocurrents interact, creating weak and variable gyratory currents. It is these currents which were determining factors
in the medium-term dispersion of the radioactive pollution.

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Figure 6-47 - Surface currents in the north-west Pacific (http://www.hycom.org/)

Figure 6-48 - Observations of surface currents in the north-west Pacific. The Kuroshio (red) runs from thesouth-west to the east (http://www1.kaiho.mlit.go.jp/KANKYO/KAIYO/qboc/2011cal/cu0/qboc2011060cu0.html).

6.4.2. CHARACTERISTICS OF MARINE RADIOACTIVE POLLUTION AROUND THE
FUKUSHIMA DAI-ICHI POWER PLANT
From 21st March and in the days that followed, strong radioactive pollution was observed in the marine environment
near the Fukushima Dai-ichi nuclear power plant. This pollution was characterized mainly via measurements
performed on samples of seawater, sediments, and species living in the marine environment. The results have been
published by MEXT and TEPCO. The IRSN is not in a position to perform measurements in Japan, but has regularlycollected and analyzed these results in order to monitor the progress of the radioactive pollution in the marine
environment.
The measurement results published in Japan mainly concern gamma-emitter radionuclides, listed in Table 6-VII. The
impact of these liquid releases started to be observed on March 21st near the power plant (1484 Bq/L in 137Cs, 5066
Bq/L in 131I) (Figure 6-49). The concentrations in seawater then increased from March 25th to 28th (up to 12,000 Bq/L
in 137Cs, 74,000 Bq/L in 131I). Another increase was measured on March 29th and 30th (up to 47,000 Bq/L in 137Cs,

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180,000 Bq/L in 131I). For the sake of comparison: before the Fukushima accident, the cesium 137 concentrationlevels in seawater off the Japanese coast were just a few mBq/L (1 to 3 mBq/L) and no iodine 131 was detected.

Table 6-VIII – Main radionuclides measured in seawater
Main radionuclides detected
Radionuclide

Half-life

131I)

8 daysCesium 137 (

137

Cs)

30.1 years

Cesium 134 (134

Iodine 131 (Cs)

2.1 years

Cesium 136 (136Cs)

13.1 days

Tellurium 132/Iodine 132 (132Te-132I)

78 hours

Seawater measurements, Dai-ichi

Figure 6-49- Evolution of concentrations of iodine 131 (131I) and cesium 137 (137Cs) in the seawater lessthan 500 m from the Fukushima Dai-ichi power plant.
Iodine 131 (131I) and cesium 137 (137Cs) are the main radionuclides that were monitored in 2011 in the marine
environment. Although it was predominant at the time of the accident, the amount of iodine-131 fell sharply in the
weeks following the accident, due to its rapid radioactive decay. After the end of May, it was no longer detectable.
Other artificial radionuclides, most with a short half-life, have also been detected occasionally, at lower
concentrations. Tellurium 129m/tellurium129 (T = 33.6 days), barium 140/lanthanum 140 (T = 12.7 days), ruthenium
105 (T = 4.4 hours), ruthenium 106 (T = 368 days), molybdenum 99/technetium 99m (T = 65.9 hours), cobalt 58 (T =70.9 days). There are fewer measurements concerning pure beta-emitter radionuclides: Nine results for strontium 90
in seawater, at concentrations between 1 and 10 Bq/L, representing from 1 to 20% of the radioactivity of cesium 137
measured in the same samples, i.e. a higher proportion than that observed in the atmospheric fallout from theaccident onto land areas of Japan, which was in the region of 0.1%.
The high concentrations measured in the seawater in the immediate vicinity of the Fukushima Dai-ichi plant were theresult of liquid radioactive releases which no doubt had several origins. This would include the water used to cool thedamaged reactors, which was in contact with materials heavily contaminated by the atmospheric releases, and someof which trickled out to sea. Another part came from the water which escaped from the containments of reactors 2
and 3. In particular, a crack in the pit adjacent to the reactor 2 turbine hall led to the release of heavily
contaminated water directly into the sea. On April 6, at approximately 6 am local time, TEPCO successfully stopped
this release by plugging the leak with an injection of sodium silicate. The estimate of the release directly into thesea made by the Japanese authorities is based on the quantification of this leak.

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This coastal radioactive pollution made its way southwards between the 25th and 28th of March, with an increase in
the iodine 131 and cesium 137 concentrations of the order of a factor of 10 in Iwasawa (approximately 20 kilometers
south of the damaged power plant starting on March 28th and especially on March 29th.
The radioactive pollution in the sea was also caused by the fallout on the marine surface of some of the radionuclides
contained in the radioactive plume during the atmospheric dispersion of the releases occurring mainly from March
12th to 23rd 2011. This diffuse pollution of the surface waters occurred dozens of kilometers from the nuclear power
plant. Thus, the concentrations measured 30 km offshore from the damaged power plant before March 30th were
probably mainly caused by atmospheric deposits. They varied from 2 to 27 Bq/L for cesium 137 and 3 to 57 Bq/L for
iodine 131. After falling to a minimum on 30th March, the concentrations in the seawater rose during the first half ofApril because of the offshore dispersion of liquid radioactive releases from the power plant.
The changes in time and space of the concentrations of 131I and 137Cs are representative of those of all theradionuclides released into the sea. The results are summarized by the two figures below:-

The concentrations measured near the outfall pipe, which are representative of the flow of radionuclides
released in that location (Figure 6-50),

Source: IRS based on TEPCO – MEXT measurements

Cesium 137 in Bq/L

IR (Iodine 131/Cesium 137)

Cesium 137

IR ratio (I-131/Cs-137)

Figure 6-50– Change in 137Cs concentrations in seawater and IR ratio (131I/137Cs), within 500 m of the
Fukushima Dai-ichi power plant. The value of the IR ratio was corrected for radioactive decay andnormalized to 11th March for the purpose of making the results comparable to each other.

-

Cesium 137 concentration isovalue maps, showing the distribution of radioactive pollution in seawater at
different periods (Figure 6-51).

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Source: IRSN based on TEPCO-MEXT measurements

Figure 6-51 – Changes in the spatial distribution of 137Cs concentrations in seawater between April 11th
and July 11th 2011.

The measurements performed near the installation give a relatively uniform IR ratio (131I/137Cs) in the region of 20,
with a gently falling trend over time until April 19th. This reduction, which is not due to the radioactive decay ofiodine, and already taken into account in the calculation of the ratio, suggests a process of regular elimination of theiodine 131 measured in the seawater, with an apparent decay period (half-life) of 35 days. A similar trend wasobserved at 10 and 20 km to the south between March 27th and April 16th, but it is not detectable far from thecoast. The causes of this gradual elimination of iodine in the seawater have not yet been identified. This effect could
be a sign of a behavior specific to iodine, either in the damaged installations before discharge, or in the marine
environment. It could also result from a gradual mixing with another source that has a lower isotopic ratio.
After April 19th, the IR ratio (131I/137Cs) became highly variable, no doubt because of the increasing inaccuracy of theresults of measuring iodine 131 in seawater as its radioactivity decreases due to decay. These variations could also be
the result of fluctuations in the composition of residual discharge from the damaged site, even though this must havebeen greatly reduced from April 11th onwards, at which time a significant decrease in radioactivity in the seawater
near the power plant began.
The maps in Figure 6-51 represent the spatial distribution of the mean cesium 137 concentrations for successive
periods between 11th April and 11th July, whose duration (7 days from 11th April to 2nd May, and then 14 days for thefollowing periods) was chosen by the IRSN to provide a sufficient number of measurements spread over the scope ofthe study to perform a representative interpolation. These maps show a similar distribution of the pollution from thevicinity of the nuclear power plant towards the open sea. The concentrations fell sharply over time, and the area ofthe colored zones, corresponding to measurements above the detection limit (around 5 Bq/L), decreased
accordingly.

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After July 11th, the concentrations measured at sea were mostly below the detection limits of the measurement
methods used for monitoring. From that time onwards, it was no longer possible to perform a representative
inventory of the residual pollution at sea.

6.4.3. ESTIMATE BY IRSN OF THE QUANTITIES OF CESIUM 137 RELEASED INTO
THE SEA
6.4.3.1 Direct liquid releases
The precise quantities and the duration of the liquid releases into the sea are difficult to estimate directly. The first
IRSN estimate, using the concentrations measured in the water of the n°2 reactor turbine hall, 2.3x10+15 Bq (2.3
million billion becquerels) of cesium 137 could have been released into the sea. In addition, from April 4th to 10th,
TEPCO discharged "slightly contaminated'" water into the sea. This was 10,000 tons of liquid effluent stored in tanks.
These discharges, estimated by TEPCO at 1.5x10+11 Bq, did not significantly increase the concentrations resulting
from the previous releases.
Based on the maps in Figure 6-51, the IRSN updated its estimate of the quantities of 137Cs present at sea, in the zone
located in the blue frame shown on these maps. This estimate took the bathymetry into account, as well as the
mixing depth deduced from the salinity-temperature profiles drawn up by MEXT, when this depth is less than thedepth of seawater. The results are presented in Tableau 6-VIII and the change over time of these estimatedquantities is represented in Figure 6-52.

Table 6-IX – Quantities of 137Cs in the coastal sea zone near the Fukushima Dai-ichi power plant, estimatedfrom the interpolation of individual measurements in seawater over different periods from April 11th.

Inventory period

Number ofmeasurements

Quantity of 137Cs(Terabecquerels)

Start

End

Middle11/04/11

18/04/11

14/04/1192

11,60018/04/11

25/04/11

21/04/11

77

4,750

25/04/11

02/05/11

28/04/11

118

3,380

02/05/11

16/05/11

09/05/11

293

667

16/05/11

30/05/11

23/05/11

233

261

30/05/11

13/06/11

06/06/11

227

163

13/06/11

27/06/11

20/06/11

250

42

27/06/11

12/07/11

04/07/11

202

2.4

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82% of liquid releases
Figure 6-52 - Changes in the 137Cs quantities in seawater in the coastal area near the Fukushima Dai-ichi
power plant from April 11th to July 11th 2011. The horizontal error bars represent the periods during
which the measurements were taken into account. The vertical error bars represent the error in theestimated quantities of 137Cs. It is related to the estimate of the thickness of the mixture layer (+-50% for
all values).
This quantity follows an exponential curve, decaying with a half-life T1/2 of 6.9 days (95% confidence interval: 5.7 –8.6 days). This means that the quantity of cesium 137 present in seawater inside the calculation zone washalved every 6.9 days. This decrease was due to the dilution of the polluted seawater by sea currents thatbrought a regular supply of uncontaminated water into the zone concerned. This is an especially fast renewal
rate. It is due to the strength of the Kuroshio and Oyashio currents, which meet in this area, and their generalorientation towards the open sea. The regularity of the dilution is also remarkable, taking into account the variabilityof the turbulent flow observed in this mixing zone.

This active dilution effect tended to reduce the impact of the accident on coastal waters. Contaminated waters
were carried swiftly eastward, toward the center of the Pacific, where they continued to be diluted due to thedispersion of ocean waters.

Over the longer term, the rate of this dilution could have been modified by two effects:-

Seasonal variations in the ocean currents (Kuroshio and Oyashio),-

The return into the zone of ocean waters previously polluted by discharge from the Fukushima Dai-ichi
accident due to the recirculation of water masses in the northwestern Pacific. This phenomenon could
prevent or delay the return to cesium 137 concentrations comparable to the pre-accident levels (between
0.001 and 0.004 Bq/L)24.

24

Nakanishi, T., Zheng, J., Aono, T., Yamada, M., Kusakabe, M., 2011. Vertical distributions of 99Tc and the 99Tc/137Cs activity
ratio in the coastal water off Aomori, Japan. J. Env. Radioactivity V.102, 8, 774-779.
Povinec, P.P., Hirose, K., Honda, T., Ito, T., Scott, E.M., Togawa, O., 2004. Spatial distribution of 3H, 90Sr, 137Cs and239,240Pu in surface waters of the Pacific and Indian Oceans--GLOMARD database. J. Env. Radioactivity V.76, Issues 1-2, 113-137
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Thus, unlike in the terrestrial environment, where a residual deposit will persist for several years, the acutecontamination period of the marine environment was contained within a period of about six months. This duration is
not a general characteristic of accidental pollution in a marine environment. It is the result of especially favorablehydrodynamic conditions related to the dynamics of the currents, the fact that they are directed towards the open
sea, and the size of the receiving medium (the Pacific Ocean). If this event had taken place in an enclosed sea (e.g.,
to the west of Japan), or in a bay, the short- and long-term consequences could have been ten times worse. By way
of comparison, the half-life of the waters in the Normandy-Brittany Gulf, where the Flamanville power plant islocated, is approximately three months (twelve times the half-life observed in the Fukushima region), even though
the tidal currents in that area are very strong.
The extrapolation of the regression curve to April 8th provides an estimate of the total quantity of 137Cs discharged at
the end of the main discharge period (March 26th – April 8th). The quantity estimated by extrapolation is 22.1015 Bq(22 million billion becquerels), with a 95% confidence interval from 20.8 to 23.1 1015 Bq. The main error associatedwith this calculation is related to the estimate of the mixing depth. This uncertainty is evaluated at around 50%. Thisevaluation of the cesium 137 releases at sea produces a higher result than the first estimate mentioned above, which
was obtained using a different method, but in view of the major uncertainties in these estimates, the orders ofmagnitude can be considered to be close.
IRSN has also been able to establish an empirical correlation between the total quantity of cesium 137 estimated forthis period from March 26th to April 8th and the mean cesium 137 concentrations measured in seawater in theimmediate vicinity of the damaged power plant during the same period: for each Bq/L measured near the facility,
there are 1.06.1011 Bq released per day (Figure 6-53). By applying this correlation to the measurements taken up to
July 18th, after which the number of significant measurements became too small to perform an adequate
measurement of the released flux, IRSN was able to determine the overall quantity of cesium 137 released into
the seawater until mid-July. The value thus obtained is 27.1015 x 1015 Bq. As expected, most of the release
took place before April 8th, and the estimated release after that date accounted for only 18% of the total
release. This is the largest one-off injection of artificial radionuclides into the marine environment everobserved. After July 18th, the number of significant measurements is too low for any reasonable estimate of thereleased flow to be made.

Cesium 137 concentration (Bq/L)

Cesium 137 release flowrate (Bq/day)Figure 6-53 - Concentrations of 137Cs within 500 m of the Dai-ichi power plant (Bq/L) and the corresponding
flux in seawater (Bq/jour).
By comparison with other major sources of artificial radionuclides in the marine environment, the direct releases
from Fukushima Dai-ichi represent the largest emission recorded in such a short time in a limited area. Table 6-Xsummarizes the main sources and the conditions of their release for 137Cs.
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Table 6-X - Inventory of the main sources of 137Cs in the oceans, in PBq (1015Bq).

Atmosphericfallout from
nuclear tests
948 a

Spent fuelreprocessing
1951 -> 2010
BNFL
Areva-NC
Sellafield The Hague
41.21

1.04

Chernobyl
accident

15-20 aImmersion of solid
Fukushima Dai-ichi
waste in the sea(beta + gamma
Atmosphericemitters)
Direct releasedepositionc0.076 c27
78 - 82 a, b
(12 - 41)(80 km radius)

a: Aarkrog (2003); b: Linsley et al. (2005); c: IRSN (Bailly du Bois et al. (2011))

The highest concentrations measured in the open sea that could be compared to the concentrations measured near
Fukushima Dai-ichi are those measured in the Irish Sea in 1974 - 1976 with 137Cs levels above 10 Bq/L (Figure 6-54).
Those values were a factor of a thousand less than the maximum values observed near the Fukushima Dai-ichi power
plant, but they concerned the entire Irish Sea, and persisted for several years in accordance with the controlled
releases from the Sellafield plant. Since July 2011, concentrations above 10 Bq/L have not been measured outside
the immediate vicinity of the Fukushima Dai-ichi power plant.

Figure 6-54 - 137Cs concentrations in the Irish Sea (RIFE, 2009).
For reference, this total contribution of 27 x 1015 Bq of cesium-137, diluted at a depth of 0 to 100 meters throughout
Pacific Ocean, would lead to an added concentration of 0.002 Bq/L, which would be double the residual backgroundin the seawater due to the fallout from atmospheric nuclear tests (0.002 Bq/L). Although measurable with current
techniques, these concentrations would represent only one 3000th of the natural potassium 40 concentrations inseawater (12 Bq/L). The cesium is essentially dissolved in the seawater and will remain measurable for decades.
Thus, the cesium 137 resulting from the atmospheric nuclear tests of the 1960s remains clearly identifiable on aworldwide scale. At the time of the Fukushima accident, the radioactivity of the cesium 134 released into the sea
was at the same level as that of the cesium 137, but because these two radionuclides have different half-lives, 2 and30 years respectively, the radioactive ratio 134Cs/137Cs will fall over time, and can be used for many years to identify
and date bodies of water contaminated by discharge from Fukushima on the scale of the surface waters of the North
Pacific.

6.4.3.2 Atmospheric fallout onto the surface of the sea
There are few measurement results that can reveal the scale and extent of the atmospheric radioactive fallout on
the surface of the ocean, because the surface water that receives the atmospheric fallout is quickly mixed in withthe rest of the seawater via advection and dispersion. Only seawater measurements taken a small number of days
after the deposit can provide information about the impact of this radioactive fallout. Before March 24th, when there
was still relatively little direct liquid release, the concentrations measured in seawater more than 10 km from theinstallation could be attributed to atmospheric fallout (cf. § 6.4.2). The IR ratio (131I/137Cs) determined at that
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distance, before March 30th, is from 5 to 12, which is comparable to that observed in the terrestrial environment inJapan (see § 6.2.3).
During the same period, the measurements published in Japan revealed the presence of another polluted zone along
the coastline, more than 10 km to the south of the facility, with values from 20 to 100 Bq/L of 137Cs, and an IR ratio(131I/137Cs) from 35 to 110. This pollution can be attributed to other atmospheric fallout or to direct liquid releaseprior to that identified from March 21st onwards.
The atmospheric fallout onto the ocean surfaces was evaluated by IRSN using the updated model for atmosphericdispersion of release from the Fukushima Dai-ichi power plant (§ 6.1.2.1). According to this estimate, thecumulative deposit of cesium 137 onto the sea in an 80 km radius was 76.1012 Bq (76,000 billion Becquerels), a
value approximately 10 times lower than the value estimated in July. This supply of contamination into the sea
represents only 0.3% of the overall radioactivity from cesium 137 released directly into the sea by the Fukushima Daiichi power plant, estimated by IRSN in Section 6.4.3.1. The map in Figure 6-55 represents the spatial distribution ofthis fallout onto the Japanese marine environment. Apart from the deposit that formed in this coastal domain andthe one that formed on Japanese land, most of the atmospheric releases of cesium must have been deposited ina scattered manner on the oceans and continents of the northern hemisphere, across great distances.

Figure 6-55 - Distribution of the total atmospheric deposit of 137Cs on the sea as at March 23rd, estimatedby IRSN by simulating the atmospheric scattering of releases from the Fukushima Dai-ichi accident.

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6.4.3.3 Transport of radioactive pollution by leaching of contaminated soil
The radioactive deposits that formed in the terrestrial environment during the dispersion of the atmospheric releases
from the Fukushima Dai-ichi plant were able to be partially leached by rainwater and then transported to the sea by
run-off. The contaminated land areas thus drained can represent several thousand km2 (cf. § 6.2.2.2).
There is currently no predictive model for these exports to the sea and how they evolve that is sufficiently robust
and operational to provide reliable forecasts over a period of several years. Since the Chernobyl accident, empiricalmodels have generally been the most widely used and completed. In this context, IRSN has developed the HAMSTER
database, which collects all transfer function parameters available in the literature. The results presented in Figure
6-56 come from a first use of this database to predict the flux over ten years of cesium 137 activity at the outlet of
the Ukedo river (river from the catchment basin most contaminated by the Fukushima accident).

Initially, thecartography of the surface deposits and the variability of the parameters deduced from this database allow a (wide)
range of possible values for the flow at the outlet to be calculated. Based on the first radioactivity measurements
performed at that outlet by the Japanese Ministry of the Environment in September 2011, the second stage is to
reduce this range according to the local variability of the hydro-sedimentary parameters such as flow rate, size ofparticles in suspension, the partitioning coefficient, etc.

Bq/dayRange of 137Cs activity flux at the outfall pipe

Days

Figure 6-56 – High and low prediction of the change during the 10 years following the accident of the flux
(Bq/day) in 137Cs at the outlet of the Ukedo basin.
Although much smaller than the uncertainties of the 1st stage, the uncertainties of the 2nd stage are still high,because the shortage of local hydro-sedimentary data makes it necessary, for the time being, to associate them witha wide variability range. If flow rates were known, these uncertainties could be very significantly reduced. These
initial calculations are currently extended to all contaminated Japanese catchment basins, and they will be
continually refined as new data are obtained.

6.4.4. SIMULATION OF THE DISPERSION OF CESIUM 137 IN SEAWATER OFF THE
COAST OF JAPANIFREMER was approached by IRSN to run simulations of the dispersion of the discharge from Fukushima Dai-ichi. The
Mars 3D model is used, the hydrodynamic limit conditions come from Mercator-Ocean, and the meteorological forcing
is given by the European ECMWF model.
The cesium 137 discharge used in this simulation comes from the calculations presented in Section 6.4.3.1. The
assumption that cesium 137 was dispersed in soluble form was applied.

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The concentrations measured and simulated less than a kilometer from the installation give results in agreement; thesource term taken into account reproduces the small-scale dispersion well (Figure 6-57-a). With regard to the full setof 137Cs measurements available in July (Figure 6-57-b), although there are significant deviations, the model does not
significantly under- or overestimate the concentrations.

Model

Concentrations of 137Cs (Bq/L)

Concentrations of 137Cs (Bq/L)

Measurements

Mars simulation

Measurements

Figure 6-57 - Comparison of the concentrations measured and simulated by the Mars model. (a): Within
one kilometer of the facility; (b): For all 137Cs measurements at sea.

Figure 6-58 reproduces the results of the simulation of the dispersion of discharge from Fukushima on the scale of thenorth-west Pacific. It illustrates the complexity and variability of the currents resulting from a comparison of
Kuroshio, arriving from the south, and Oyashio, arriving from the north. The dispersion structures are comparable tothose simulated by the Sirocco model in Toulouse.
After July 1st, the simulated concentrations were generally below the detection limits applied to the monitoringmeasurements. They could have been identifiable with the classic methods used in oceanography (LD < 0.001 Bq.L -1).

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April 15

May 15

May 1

June 1

Source: IRSN-IFREMER
June 15

July 15

July 1

July 26

Figure 6-58 - 137Cs concentrations in seawater simulated by Mars 3D between April 15th and July 26th
2011 in the north-west Pacific.

6.4.5. COMPARISON OF THE EVALUATIONS OF RADIOACTIVE RELEASES AT SEA
Since the Fukushima accident, four scientific publications have presented estimates of the direct liquid releases into
the sea caused by the accident: the Japanese government (NERH), which draws on the TEPCO calculations;
Kawamura et al., (2011) and Tsunume et al. (2011) who performed comparisons of dispersion models tomeasurements at sea; and IRSN (Bailly du Bois et al. 2011), based on the interpretation of measurements at sea. The
estimates given in these publications are shown in Table 6-XI; this table also mentions the publications thatspecifically concern radioactive deposits on the sea.

With regard to 137Cs, the estimates vary in a ratio of 1 to 27.

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Table 6-XI – Estimates of the releases at sea caused by the Fukushima accident according to the various
scientific publications.
Direct release at sea

Deposit131

131

Source137

MethodCs (PBq)

I (PBq)(131I/137Cs)*

137

I in

Cs in PBq

PBq

(surface in km²)

(131I/137Cs)*

NERH 2011 (TEPCO)

Calculation of leak rate

0.94

18.7* (19.9)

4

11 (2.8)

Comparison of model (SEAKawamura et al. (2011)

GEARN) /measurements at
sea
Comparison of model

Tsunume et al. (2011)(ROMS) /measurements at(2011)

releaseQuantities deduced fromsea measurements and27 (12 - 41)

540* (20)dilution + pX simulation
Comparison of model

Honda et al. (2011)(JCOPE2) / measurements
in JapanMorino et al. (2011)

0.0076(50 x 100)

0.18

1

/measurements in Japan(600 x 600)

model /measurements inJapan

0.1* (14)(1,500 x 1,500)

Comparison of CMAQ model
Comparison of FLEXPART

Yasunari et al. (2011)57 (11.4)

Less than direct

3.5 (± 0,7)

sea
IRSN (Bailly du Bois et al.

5(1,700 x 1,700)

1(1,700 x 1,700)* When data are available, the values are corrected for decay to March 11th 2011.

The uncertainties associated with each type of evaluation are significant. They are discussed in the sections that
follow.

6.4.5.1 Release Calculated by TEPCO (NERH Report)
The calculation of the release at sea is based on an estimate of the flow rate through a hole in the containment of
Unit 2, which was discovered on April 2nd. The calculation uses the diameter of the hole (approximately 3 cm),height, drop distance, and initial concentration to evaluate the radionuclide flux. This is considered constant at 4.3
m3/h for 120 hours. With 1.8x 106 Bq/cm3 of 137Cs, TEPCO estimates a release of 0.94 PBq in 120 hours. TEPCO’s
overall estimate is 4.7x1015 Bq released, taking all radionuclides together.

Comments
Tsunume et al. (2011) IRSN (Bailly du Bois et al. (2011) indicate a period of release from March 26th to April 6th or
8th 2011 respectively (264 h – 312 h, Figure 6-59), based on measurements in seawater which show a sharp net risein the concentrations starting on March 26th. It therefore seems that the release duration indicated in the NERH
report (120 hours) is an underestimate by at least a factor of 2.

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Concentration in cesium 137 (Bq/L)

Figure 6-59 - Concentrations measured in seawater within 500 m of the Fukushima Dai-ichi power station,
detail from March 10th to April 17th 2011.
In addition, TEPCO’s estimate of the flows released was performed on the basis of a concentration measurement
taken on April 2nd downstream from the leak. However, the period from April 2nd to 4th corresponds to a minimum
concentration in the measurements in seawater in the vicinity of the facility (Figure 6-59), since the concentrations
are considerably higher before and after that period. It is possible that this mean concentration applied to the entire
duration of the release is in fact an underestimate of the mean release.
Tsunume et al. (2011) also suggest the hypothesis that the releases prior to April 1st could be explained by direct
releases with a different origin.

6.4.5.2 Release Calculated by Tsunume et al. (2011)
The marine release is evaluated by comparing simulations using a marine dispersion model (ROMS model with a 1 kmmesh), with the in situ measurements. According to Tsunume, direct release is the main source of radionuclides atsea.
The direct release taken into account lasts 11 days, from March 26th to April 6th 2011, with a constant flux of
2.2.1014 Bq/j during this period, followed by exponential decay until April 24th.
There is good agreement between the concentrations simulated and measured near the outfall pipe and along thesouth coast, until April 2nd. After that date and far from the outfall pipe, the divergences become greater andgreater, and the measurements can be up to a factor of 10 higher. 30 km offshore, the divergence between modeland measurements is even more pronounced (Tsunume et al.) (2011), Figure 6-60).

Figure 6-60 - Concentrations measured and simulated on the coast (a) and offshore (b), according toTsunume et al. (2011).

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The total direct release is estimated at 3.5 ± 0.7 PBq in 137Cs. Of the 15 PBq released into the atmosphere (NERH),
the deposition in the calculation zone is apparently weaker than the direct releases.
The main source of error associated with this calculation concerns the representativeness of the hydrodynamic model
used.

6.4.5.3 Release Calculated by Kawamura et al. (2011)
The marine release is evaluated by comparing simulations using a marine dispersion model (SEA-GEARN model with a
2 km mesh), with the in situ measurements. The model/measurements comparison is performed at two points, on
the coast and 15 km offshore.
The direct release is evaluated on the basis of daily concentrations measured near the outfall pipe from March 21stto April 30th 2011. An adjustment coefficient is used to match a radionuclide flux to the concentrations measured,by making the measured values and those simulated by the model coincide. This calculation method is very sensitive
to the size of the computational unit mesh and the dilution conditions in the vicinity of the outfall pipe.
The deposition on the ocean is calculated using the WSPEEDI-II model, based on the release figures published by
Chino et al. (2011).
The concentrations simulated and measured at 15 km are of the same order of magnitude (Kawamura et al. (2011),
Figure 6-61). There are no results at the other measurement points.

Figure 6-61 - Measured and simulated concentrations (solid line) 15 km from the coast according to
Kawamura et al. (2011).
According to Kawamura et al., atmospheric deposition represents 5 PBq deposited on the sea in the zone covered by
the model (1700 x 1700 km). Direct releases account for 4 PBq in 137Cs.
The main source of error associated with this calculation concerns the representative nature of the hydrodynamic
model used and the dilution of the release near the power plant.

6.4.5.4 Release calculated by the IRSN (Bailly du Bois et al. (2011))
The calculation method is described in Section 6.4.3.1. The main uncertainty concerns the thickness of the mixing
layer applied to extrapolate the measurements obtained on the surface to the bottom. The robustness of thiscalculation is based on: simple integration that does not require the prior validation of models, large number ofmeasurements available for the reports (from 77 to 293 for each inventory period, Table 6-IX); the regularity of therenewal of waters in the area (Figure 6-52).
The results obtained with the Ifremer model in Section 6.4.4 (Figure 6-57) are comparable to those obtained by themodels of Tsunume et al. and Kawamura et al., but with a release more than six times higher. It is currently notpossible to determine which of these three models is the most realistic. The area where the release was introducedis the seat of a variable turbulent flow that is difficult to reproduce deterministically. The representativeness of the

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whether they reproduce the fast renewal of the masses of water observed from the measurements.

6.4.6. RADIONUCLIDES IN SEDIMENTS
The materials in suspension in the seawater tend to fix some of the radionuclides dissolved in the water column
according to the levels of radioactivity in the surrounding water. These materials end up as sediment on the sea
floor, creating a contaminated superficial deposit. In a coastal environment, the contributions via leaching bycontaminated catchment basins will ultimately constitute a delayed but long-lasting source of contamination of thiscompartment.
Sediment samples were collected as far as 186 km from Fukushima Dai-ichi and 70 km offshore, at a depth from 20 to
200 m. The sampling depth and conditions, and the nature and granulometry of the samples had not been reported at
the time of publication of the km offshore, at a depth from 20 to 200 m. The sampling depth and conditions and thenature and granulometry of the samples had not been reported at the time of publication of the results. Because
these parameters can have a major effect on the mass concentrations of the measured sediments, the measurement
results published in Japan should be interpreted with caution. The results are given in kg of dry mass whenever this isspecified (one in ten times).
Of the 184 samples measured since April 29th, the main radionuclides measured in the sediments are:-Cesium 137 (183 significant results):-

Cesium 134 (178 significant results), with a 134Cs/137Cs ratio normalized to March 11th at 0.95,-

Cesium 136 (6 significant results):-

Iodine 131 (17 significant results from the end of April; no detection after June 9th), with an 131I/137Cs ratio
normalized to March 11th at 23,-

Tellurium 129 and 129m (28 and 36 significant results, from 10 to 16,000 Bq.kg-1),-

Strontium 89 and 90 (two significant results, from 10 to 140 Bq.kg-1),-

Plutonium 239 and 240 (six significant results, from 0.09 to 0.49 Bq.kg-1),-

Barium 140 (one significant result of 2,900 Bq.kg-1).

Figure 6-62 shows the development of 137Cs concentrations in all of the samples inventoried, as well as the respective
distance to the outfall pipe. Except in the vicinity of the Fukushima Dai-ichi power plant, the concentrations usually
vary from 1 to 10,000 Bq.kg-1, with on average an increasing trend over time This trend may be the result of the
kinetics of the transfer of the cesium towards the sedimentary particles and the processes by which the finerparticles are deposited. In view of the reduction of concentrations in seawater, this curve should stabilize over the
coming months. The highest concentrations are recorded near the outfall pipe (100,000 and 150,000 Bq.kg-1). Fourvalues greater than 10,000 Bq.kg-1 had been recorded at a distance greater than 38 km before April 7th, but thesehave not been confirmed by subsequent measurements.
Figure 6-63 shows a map of the distribution of 137Cs concentrations in the sediments. It was drawn up by IRSN,
excluding the six measurements near the site, which gave concentrations in excess of 10,000 Bq.kg-1. The
concentrations reached are generally less than 1,000 Bq.kg-1; they are relatively low in view of the equilibrium
distribution coefficient of cesium between the seawater and the sediments, which is usually greater than 1000. Thus,
with concentrations greater than 100 Bq/L measured in the coastal seawater, we might have expected to findconcentrations of 100,000 Bq.kg-1 in the sediments. The transient pollution of the seawater by cesium 137 probably
did not allow equilibrium to be reached with the sedimentary stock sampled. Only recently-deposited particles
contributed to the marking of the superficial sediments, and these represent only a fraction of the volume sampled.

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Cesium 137 in sediments (Bq/kg)

Source: IRSN based on TEPCO-MEXT measurements

Distance from the power plant:Less than1 km

From 1 km to 50 km

More than 50 km

Figure 6-62– Graphical representation of 137Cs concentrations measured in sediments as a function of time,with indication of the distance between the sampling point and the Fukushima Dai-ichi power plant(Bq/kg sec)

Ultimately, some of the radionuclides fixed on the sedimentary particles are likely to be remobilized in the seawatercolumn. The sediments will then behave as secondary sources of contamination, which are delayed, distant, anddiffuse. In coastal regions, the contamination of sediments was mainly the result of direct contact between polluted
seawater and the surface sediments, and could propagate by transport and mixing with deeper sediments. In the
pelagic domain, one would expect to find traces of radionuclides at the water-sediment interface following theirtransport toward the bottom via processes related to biological activity in the open sea (primary production of solid
matter by phytoplankton, grazing by zooplankton, production of feces, and direct transport toward the bottom).
According to the map in Figure 6-63, the stock of cesium 137 fixed on the sediments appears to be relatively low. It
should not lead to very high marking of the seawater by unloading in the future. The cesium unloading half-life
observed in the sediments of the Irish Sea is two years25. Under these conditions, the first ten centimeters of
sediment contaminated to 1,000 Bq.kg-1 would contribute 500 Bq.dm-2 in two years to the 20 to 200 m of water above
it. In view of the renewal kinetics of the water observed (50% renewal every 6.9 days), the resulting concentrations
would be approximately 5 to 50 Bq/L in seawater, on average. These concentrations should not have an impact onpelagic organisms in terms of radiation protection.
These concentrations could be higher in less deep zones, or zones with a lower renewal rate. Benthic organisms living
in direct contact with the sea bed, or filtering organisms, could then be directly concerned by the residual pollution
in the sediments.

25

Finegan, P., Vintró, L.L., Mitchell, P.I., Boust, D., Gouzy, A., Kershaw, P.J., Lucey, J.A., 2009. Accumulation, solid partitioning
and remobilisation of 99Tc in subtidal and intertidal sediments in the Irish Sea. Continental Shelf Research Volume 29, Issues 16,
Pages 1995-2010.
Jones, D.G., Kershaw, P.J., McMahon, C.A., Milodowski, A.E., Murray, M., Hunt, G.J., 2007. Changing patterns of radionuclide
distribution in Irish Sea subtidal sediments. Journal of Environmental Radioactivity Volume 96, Issues 1-3, Pages 63-74.
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Source: IRSN based on TEPCO-MEXT measurements
April 11 – October 14

Figure 6-63– Mapping of 137Cs concentrations in sediments (mean of values measured up to October 14th).

6.4.7. RADIONUCLIDES IN MARINE AND RIVER–MARINE SPECIES
6.4.7.1 Aquatic species that have exceeded the cesium limits for sale or consumption
The list of species for which the cesium content exceeds the limits for sale or consumption (500 Bq/kg for the sum of
cesiums 134 and 137), drawn up by the Japanese authorities, has changed over time according to the products caught(Table 6-XII). In general, the species included in this list during the summer of 2011 were:-

Either species that were very infrequently sampled before the month of June and the monitoring of which
intensified during the summer,-

Or species that were not sampled until the summer of 2011.

It is therefore not possible, with this information alone, to attribute the increase in the number of species with ahigh level of contamination to a change in the contamination of the marine environment. It is important toemphasize the fact that all of these organisms come from the Fukushima district, and that no organism fished fromthe sea outside the area near the power plant or in the open sea exceeds the standard limits for sale orconsumption.

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Table 6-XII – Lists of aquatic organisms (animals or plants) with cesium 134+137 concentrations greaterthan the maximum allowable levels for consumption since monitoring began
List as at June 7th 2011

List as at August 21st 2011

List as at January 12th 2011

Arame (algae)

Arame (algae)

Arame (algae)

Hijiki (algae)

Hijiki (algae)

Hijiki (algae)

Wakame (algae)

Wakame (algae)

Wakame (algae)

Sea urchins

Sea urchins

Sea urchins

Clams

Clams

Clams

Sandeels (Japanese sand lances)

Sandeels (Japanese sand lances)

Sandeels (Japanese sand lances)

Boe drums

Boe drums

Boe drums

Mediterranean mussels

Mediterranean mussels

Mediterranean mussels

Japanese smelts (caught in freshJapanese smelts (caught in fresh water)

Japanese smelts (caught in fresh water)water)

Ayu (caught in fresh water)

Ayu (caught in fresh water)

Ayu (caught in fresh water)

Masu salmon (caught in fresh water)

Masu salmon (caught in fresh water)

Masu salmon (caught in fresh

Tribolodons (freshwater)

Tribolodons (freshwater)water)

Char (freshwater)

Char (freshwater)

Tribolodons (freshwater)

Cyprinide fish (bred in fresh water)

Cyprinide fish (bred in fresh water)

AinameAinameFlounder (flatfish)

Flounder (flatfish)

Halibut (flatfish)

Halibut (flatfish)

Hakeling

Hakeling

RedfishRedfish

Rays

Rays

Crabs

Crabs
Bass

6.4.7.2 Concentrations observed in marine animals
Figure 6-64 shows the measurement results concerning the marine species for which data are obtained on a fairly
regular basis.

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Cesiums (Bq/kg wet)

AinameSandeel

100000CongerHalibut

10000

GurnardMackerel

1000

Ray
SardineAbalone100

Sea Orchin
Clam

10
1
0,1
3
18/0

/201

1

4
07/0

/201

1

4
27/0

/201

11
11
11
11
11
11
11
5/20 6/06/20 6/06/20 6/07/20 5/08/20 5/08/20 4/09/20
1
0
2
0
2
1
17/0

1

Figure 6-64 – Change over time of 137Cs+134Cs (Bq/kg) concentrations in some sea products.
Of the marine products sampled, those with the highest contamination levels, detected early in the fishing products
monitoring program, were the Japanese sand lances (sandeels) (Figure 6-65). Caesium-137 and -134 have been
detected in all samples of this species taken from the Fukushima and Ibaraki districts; the maximum concentrations
reached 12,500 Bq/kg wet (134Cs+137Cs) off the shore of Iwaki on 13 April. The Japanese fish and eat the sandeel, orJapanese sand lance (Ammodytes personatus) in the larval and juvenile stages, which are pelagic stages (living in thewater column) in the period from January to April. The adults, however, live buried in the sediment from May to
December, and are no longer fished, which explains why the data for this species practically vanishes from late April
onwards.

Figure 6-65 – Japanese sandeels (Ammodytes personatus (Girard)). (a) larvae, (b) juveniles.
In addition to the concentrations in sandeels, Figure 6-64 shows the concentration curves for both cesium isotopes inother species that are regularly sampled. It is difficult to identify a change in the contamination of fish over time,
given the wide spread in the results obtained. However, halibut, rays, and to a lesser extent, gurnards, all of whichhave a characteristic way of life in close contact with sediment, tend to be amongst the higher values in the cesium
concentration range observed in Japan.
Note that the measurement results obtained on samples of sea urchin, abalone and clam taken from the Fukushima
district also managed to reach some high levels.
With regard to iodine 131: this has not been detected in the organisms since mid-June, in accordance with the trend
in its levels in the surrounding environment (Figure 6-66).

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Iode131
frais)
Iodine131(Bq/kg(Bq/kgwet)

100000
10000
1000
100

AinameAinameLançons japonais
JapanesesandeelCongreseels
CongerHalibut
Flétans
Grondins
Gurnards
Maquereaux
MackerelsRay
raie
Sardines
Sardines

AbaloneOrmeaux
Oursins
Sea
Urchins
Clams
Palourdes

10
1
0,1

0 11
0 11
0 11
0 11
0 11
0 11
0 11
0 11
0 11
0 11
9/2
8/2
8/2
7/2
6/2
6/2
5/2
4/2
4/2
3/2
0
0
0
0
0
0
0
0
0
0
/
/
/
/
/
/
/
/
/
/
14
25
05
16
26
06
17
27
07
18

Figure 6-66 – Change over time of iodine 131 concentrations (Bq/kg) in some sea products.

6.4.7.3 Expected curve for marine species
With regard to filtering species such as mussels, oysters, and clams, the trend in the absence of new releases should
be a downward one. And, in fact, the changing levels over time in these organisms reflect the changes in thesurrounding environment quite well, and the trends clearly show a reduction in the concentrations over time (Figure6-67).

Bq/kg wetClams in the Fukushima /Iwaki District

Figure 6-67 Change of cesium concentrations over time in clams (Pseudocardium sachalinense) taken off
the coast of Iwaki in the Fukushima district. In red, the limit for sale or consumption (500 Bq/kg for thesum of cesiums 134 and 137).

With regard to fishes, their contamination curve does not follow the decay observed in the waters. Figure 6-68 gives
the example of the change in concentration in a species of ray (Okamejei kenojei) caught in the waters near Iwaki
like the clams (Figure 6-67).

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Spotted ray in Fukushima/ Iwa district

Bq/kg wet

Cs total

Figure 6-68 - Change of cesium concentrations over time in a species of spotted ray (Okamejei kenojei)
caught off the coast of Iwaki in the Fukushima district. In red, the limits for sale or human consumption(500 Bq/kg for the sum of cesiums 134 and 137).

In fish, variations in concentration could very well be due to their movement, for species that are not strictly
confined to the area where they were fished, but they also reflect the complex trophic regimes of these organisms,
which differ from one species to the next.
Generally speaking, fish will be the best medium- and long-term indicators of cesium contamination in the marine
domain. Cesium presents higher concentration factors in fish, and tends to increase in species that are higher up in
the trophic chain. Consequently, although in the short term the highest concentrations tend to be found in species
positioned at the beginning of the food chain, in the longer term, once the transfer to the different links of thetrophic networks has taken effect, the predators at the top of the food chain should present higher levels. Theselevels should be even higher for species whose way of life involves close contact with sediments and whose habitat isclose to the contaminated zone.
Thus, even if the cesium contamination in the sea water has fallen sharply in the vicinity of the Fukushima Daiichi power plant, there is justification for continuing to monitor the marine species fished from the coastal
waters of north-east Japan.

6.5. FORESEEABLEECOSYSTEMSIMPACT

ON

THE

TERRESTRIAL

AND

MARINEThe analysis of the ecological consequences of the Fukushima accident is very complex because these consequences
are combined with those of two other major natural events: earthquake and tsunami. To this, we must add theimpact of uncontrolled release of toxic chemical substances including metals or persistent organic pollutants (HAP,
PCB, pesticides, etc.) from a variety of industrial facilities that were damaged by the natural catastrophe. A review
article in the American journal ‘Environmental Health Perspectives’ raised awareness of this exceptional case ofmultiple pollution26. This special context heightens the uncertainties concerning the forecasting of the radiologicalimpact on ecosystems of the nuclear accident. Guidelines for evaluating the ecological impact of a nuclear accident

26

Anonymous (2011). “Chemical aftermath: contamination and cleanup following the Tohoku Earthquake and Tsunami”.
Environmental Health Perspectives 119(7): A290-A301.
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6.5.1. BASIC PRINCIPLES FOR ASSESSING THE ECOLOGICAL IMPACT OF A
NUCLEAR ACCIDENT
Following a major nuclear accident such as Chernobyl or Fukushima Dai-ichi, ecosystems exposed to ionizing
radiation because of radioactive substances released into the receiving environments (air, river, sea, etc.) reactaccording to a complex dynamic. So-called ecotoxic responses, observed at different levels of biological andecological organization, are extremely varied (Figure 6-69), particularly because of the heterogeneous exposure of
the various species that provide biodiversity.
In a given place and at a given time, the radiological dose administered can vary in quality (i.e. exposure pathway via
external or internal irradiation; alpha, beta, or gamma radiation) and quantity. This variation can cover several
orders of magnitude between species (Figure 6-70a) and between individuals of one species, for example at different
stages in its life. All of this is combined with a variability range covering six orders of magnitude to express thesensitivity to ionizing radiation of the biodiversity of fauna and flora (Figure 6-70b).

cell
molecule

Ecological
Pertinenceécologiquerelevance
Composition
Fonctionnement
Structure
Structure
Abondance
Abundance
Age distribution
Distributiond ’âgeComportement
Behavior
Croissance
GrowthReproduction
Reproduction
SurvieSurvival
Métabolisme
Metabolism
Physiologie
Physiology
Intégrité
tissulaire
Tissue integrity
Intégritécellulaire
Cell integrity
Mechanisms of defense
Mécanismes dedéfenseMolecular damage
Dommagesmoléculaires

Understanding
Compréhension
des mechanisms
mécanismestheThe response at different levels

organ individual Population Community

Variety of effects from molecules
to ecosystems

Example of dose rate–
effect relationship% effect compared to
unexposed control group

100 %

50 %

10 %
Dose rate(Gy per unit time)
Threshold from which the effect is significant(often compared to the dose rate producing
10% effect)

Figure 6-69 - Varieties of ecotoxic responses observed at different levels of organization of living things,
and example of a logistical ‘dose rate—effect’ relationship. These relationships are used to determine thethreshold beyond which the effect is significant.

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a- Range of variation of exposure between species

a- Range of variation of radiosensitivity between
speciesFreshwater life
Marine life

Vertebrates
PlantsInvertebrates

Terrestrial life
Percentage of species exposed

Percentage of species affected

Dose rate (µGy/h)

Dose rate (µGy/h)for a unit concentration in the medium(1 Bq/kg or 1 Bq/L)- Reading example For 1 Bq of 137Cs in a soil, 50% of terrestrial species

5% of species have an ionizing radiation sensitivity

receive a dose rate below 3x10-4 µGy/h.

threshold below 17 µGy/h.

For the same concentration of 137Cs in the water, theRadiation sensitivity varies over six orders of magnitude

dose rate to marine organisms varies across four orders

between species.

of magnitude.

Figure 6-70 - Ranges of variation between species (a) of the absorbed dose rate for a same unit
concentration of the medium (example of 137Cs and 131I) and (b) of the radiosensitivity.

The method for evaluating the ecological impact is based on comparing the doses or dose rates to which livingorganisms are exposed during a given period to protection criteria. The protection criteria are defined for a
specific taxonomic group or to maintain the structure and operation of an ecosystem. For example, therecommended ecological protection criterion on completion of the European PROTECT project is 10 µGy/h(0.24 mGy/d): Below that dose rate, no effect related to exposure to ionizing radiation is expected for ecosystems27.
In its publication No. 10828, the International Commission on Radiological Protection suggests dose rates for which
certain types of effect are probable according to group of species (e.g. reduced reproductive success of birds

27
Garnier-Laplace, J. et al. (2010). A multi-criteria weight of evidence approach to derive ecological benchmarks for radioactive
substances. J. Radiol. Prot. 30, 215-233.
28
CIPR (2008). Environmental Protection - the Concept and Use of Reference Animals and Plants. ICRP Publication 108. Ann. ICRP
38, 4-6.

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between 1 and 1000 mGy/day). Over the last ten years, many studies, largely guided and carried out by IRSN within
the framework of European projects (ERICA, PROTECT) have been conducted to determine the numerical values ofthese protection criteria. On an international level, the method of evaluating the radiological risk to ecosystems andthe associated criteria, which were developed in the framework of the ERICA project, are now recognized and will beapplied in particular in the context of the UNSCEAR working group on evaluating the impact of the Fukushima Dai-ichi
accident.
For non-human species, the biological effects of interest are essentially those that can be directly interpreted interms of the demographics of the species populations: survival, growth, and reproduction. They are deterministic,
appearing above a threshold according to a dose (or dose rate) / intensity of effect relationship, which is often
logistical (Figure 6-70).
As in the case of the analysis of the ecological impact of the Chernobyl accident, it is (and will be) essential todistinguish three phases in the levels and type of exposure of living organisms to understand how the effects
observed on fauna and flora unfold: acute exposure at a high dose (a few weeks), transient exposure at a medium
dose (a few months), and chronic exposure at a low dose (years).
The acute phase extends throughout the initial weeks following the accident. This phase is characterized by thepresence of a large quantity of short half-life radionuclides likely to generate high dose rates for living organisms,
mainly by external irradiation with a significant proportion of the dose delivered by beta-emitting radionuclides. For
organisms living on land, the main exposure pathways during that period are immersion in the plume, in addition tofoliar deposit for plants and inhalation for animals. These three processes are almost simultaneous with theatmospheric release. For aquatic creatures, the exposure pathway is direct exposure to water, which is the receiving
medium of the release, whether direct in liquid form or caused by the surface deposition of atmospheric release.
During this phase, the so-called ‘acute’ effects are likely to be observed. ‘Acute’ effects include any notablebiological modification occurring within a few days or weeks of absorption of a significant radiological dose, leading
to irreversible damage and, eventually, death (‘acute radiation syndrome’). For example, in the Chernobyl exclusionzone, dose rates of up to 20 Gy/day caused the appearance of the ‘red forest’, in which 90% of the pine trees (pinus
sylvestris L.) died.
The transient phase covers the few months following the accident. It is characterized by the decay of the shorthalf-life radionuclides and a redistribution of all the deposited radionuclides, which occurs to a greater or smaller
extent in the various compartments of ecosystems (initiation of the processes of dispersion, erosion, runoff, andtransfer within and between compartments). During this period of a few months, the internal contamination of livingorganisms becomes gradually predominant over the external irradiation. For example, during the three months
following the Chernobyl accident, 80% of the total dose was delivered to the plants and animals, and more than 95%
of this dose is due to β radiation. The effects that can potentially be observed during this phase are acute and appear
as of a cumulative absorbed dose threshold. The feedback from the Chernobyl accident shows the absence of harmful
effects on plants or animals for cumulative doses below 0.3 Gy29in the initial months after the accident.
The chronic phase, during which the contamination levels of the environments change much more slowly, takes
place on a scale of many years. Long half-life radionuclides such as 137Cs integrate into the biogeochemical cycles of
their stable counterparts. For example, in the exclusion zone around the Chernobyl power plant, the exposure
situation can be considered to have become chronic from the fall of 1986, when the dose rates were less than 1% of
the initial values, with a variable contribution fromand β radiation for each species, according to the location, wayof life, and intensity of the internalization flows of the dominant radionuclides, which are 137Cs and 134Cs. The effects
reported in the literature concerning that period are often contradictory or subject to scientific controversy becauseof a large number of potentially confusing factors. The reasons for these controversies are varied: the weakness orlack of a robust evaluation of the dose or dose rate (in qualitative and quantitative terms), the failure to allow for
the extreme spatial heterogeneity of the exposure for ‘mobile’ wild species in the exclusion zone, the failure to take
into account various environmental factors, such as seasonality, the lack of similar observations for true non-exposed

29
UNSCEAR (2008) Vol. II. Sources of ionizing radiation United Nations Scientific Committee on the Effects of Atomic Radiation.
Report to the General Assembly, with scientific annexe E. United Nations, New-York, 2011

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control subjects, the unsuitable statistical methods used to interpret the data, and the uncertainties inherent in theextrapolations required to interpret the ecological significance of the effects observed at different levels of
biological organization (e.g., what is the consequence on the population of an increase in cytogenetic
abnormalities?).

6.5.2. IMPACT ANALYSIS FOR TERRESTRIAL ECOSYSTEMS AROUND THE
FUKUSHIMA DAI-ICHI POWER PLANT
As far as IRSN is aware, to date no information concerning the effects observed on fauna and flora in the 20 km
exclusion zone has been reported in the scientific literature. Very recently, Shozugawa et al. (2012)30 published a
few gamma spectrometry test results concerning samples of soil and plants collected on April 10th, 2011 within 5 kmof the power plant. The radionuclide concentrations measured by gamma spectrometry in the three soil samples
collected (values in Bq/kg read on a graph: 4.9x104 for l’131I, 5x103 for each of the two cesiums (134Cs and 137Cs), 5
for l’110mAg, 100 for 132Te, 10 for each of 140Ba and 140La, 5x103 for each of 91Sr and 91Y, 7 for each of 95Zr and 95Nb),
make it possible to estimate the order of magnitude of the associated dose rates for flora and fauna. At those levelsof soil contamination, the maximum dose rates are obtained for mammals (20 µGy/h) and birds’ eggs (1 mGy/h) thatmight be present in this zone.
Although the information currently available is very sparse, it highlights the existence of a potential ecologicalrisk to the terrestrial ecosystem in the Fukushima Dai-ichi exclusion zone, particular for reproduction, which is
the most radiation-sensitive criterion. In situ studies are required in order to refine this initial rough estimate,which is based on a very small number of spot measurements.
With regard to the Japanese terrestrial environment in the 100 km around the damaged power plant, it was possible
to estimate the maximum dose rates outside the 20 km zone during the very first month following the accident,
based on the deposits on the ground. That is how the IRSN published the first estimate of the potential impact onterrestrial ecosystems31, which has been brought up again many times in the scientific literature32,33. This study
focused on the forest ecosystem and the geographical area located 25-45 km north-west of the Fukushima power
plant—one of the areas worst affected by atmospheric deposition. The dose rate, estimated according to theEuropean ERICA method34, and taking into account the main radionuclides emitted (137Cs, 134Cs, 131I, 129mTe,
129

Te, 132Te, 136Cs, 132I), extend in a range from 2 mGy/day for birds to 6 mGy/day for small mammals. These

values are ten to one hundred times higher than the ecosystem protection criterion, taken to be 0.24 mGy/day
in Europe, and are indicative of probably cytogenetic damage and altered reproduction in conifers andvertebrates (Figure 6-71). As with the observations made in contaminated territories outside the Chernobyl
exclusion zone, no acute effect has been reported to date or to our knowledge concerning non-human species inthe terrestrial ecosystems around the Fukushima site.

30
Shozugawa et al. (2012). “Deposition of fission and activation products after the Fukushima Dai-ichi nuclear power plant
accident.” Environmental Pollution 163 : 243-247.
31
Garnier-Laplace J. et al. (2011). Fukushima wildlife dose reconstruction signals ecological consequences. Environ. Sci. Technol.
doi:10.1021/es201637c
32
Schmidt C. (2011) Scientists Estimate Radiation Doses To Wildlife Near Fukushima Nuclear Disaster: Animals and plants near theJapanese nuclear plant may have received unsafe doses. Chemical & Engineering News 10 juin 2011, ISSN 0009-2347 American
Chemical Society
33
Schiermeier Q. (2011) Wildlife threatened by Fukushima radiation. News published online 27 May 2011 | Nature |doi:10.1038/news.2011.326
34
Brown, J.E et al. (2008). The ERICA Tool. J. Environ. Radioact. 99, 1371-1383.

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Bottom-dwelling fishes

Brown algae

Sedimentary invertebrates

Rodents

Birds

Ground-dwelling invertebrates

Wild herbs

Conifers

mGy/day

0.24 mGy/day
Dose rate without
effect on ecosystems

Natural background noise

Dose rates calculated for the worst-affected areas outside the 20 km zone
Maximum dose rates estimated from the concentrations in soil
Maximum dose rates estimated from the concentrations in seawater

Effects on non-human species
Mortality or reduced
life expectancy

Reducedreproductive
success

Very low
probability ofeffects

No information
available

Figure 6-71 - Scale of potential effects on marine and forest fauna and flora (outside the exclusion zone)
predicted based on the estimate of dose rates induced by exposure to the dominant radionuclides (131I,
134

Cs, 137Cs) the first month after the Fukushima Dai-ichi accident. The ranges of dose rates for the various
taxonomic groups and effects are from the studies by the ICRP 10835(adapted from Garnier-Laplace et al., 2011).

For the exposed Japanese ecosystems, the transient phase started with the arrival of spring. It therefore coincidedwith the resumption of the biological activities of the species present, and covered the first post-Fukushima breeding
season. To date, the analysis of the effects that appeared during this period for terrestrial ecosystems is mentioned
in only one article, which appeared in the journal ‘Environmental Pollution’36. It inventories the effects observed in
fourteen species of bird sampled in July 2011 at 300 capture points in the Fukushima district. At each station, thetotal number of birds seen or heard was counted and the species identified. Based on statistical processing, theauthors revealed that the bird community was significantly depleted in the most contaminated areas. Of the 14
species common to the Chernobyl and Fukushima regions, the negative correlation between ambient dose rate andabundance (number of individuals) is stronger in Japan: the birds in the Fukushima area would therefore seem to be
more sensitive to ionizing radiation than their counterparts in Chernobyl, where the species have been exposed for
25 years. Going back over this analysis, and this time considering all species, including those that are specific to eachof the regions, would show, on the contrary, a stronger correlation in Chernobyl. The authors explain this result by
the disappearance of many species in the most contaminated areas of Chernobyl. These results would need to be

35

CIPR (2009)- International Commission of Radiological Protection Environmental Protection Eds. The concept and use of Reference
Animals and Plants. Annals of ICRP; Publication 108, 242 pages, 2009.
36
Møller, A.P. et al. (2012) Abundance of birds in Fukushima as judged from Chernobyl. Environmental Pollution. 164 : 36-39.
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127/188confirmed, however, because of the lack of characterization of the dose rates received by the organisms, which are
not specified in the article, and details concerning the statistical methods used to process the data.
From July 2011, because of the physical decay of the short half-life radionuclides, it is possible to consider as a first
approximation that the exposure of living organisms was essentially due to soils contaminated by radioactive cesium(external and internal radiation from this secondary source term, whose concentration is considered to be stable overtime). Thus, ignoring the genetic adaptation processes that could take place over the course of several
generations, and based on the data in Figure 6-23 adjusted for radioactive decay, and assuming that noremediation action is undertaken, the areas with 134+137Cs surface activity above 600, 1 000 and 3 000 kBq/m2
are potential risk areas for biodiversity and terrestrial ecosystems respectively after one year, five years, andup to 30 years of chronic exposure (Table 6-XIII).
Table 6-XIII - Change over time of the exposure dose rate ranges for fauna and flora according to theaccumulated deposits of cesium 134 and 137. Prospects at one year, 5, 10, 20 and 30 years. The shaded
areas indicate that a potential risk persists (value greater than the ecosystem protection criterion). The
reference date is the date of the accident.
Range of variation of dose rates for terrestrial species (µGy/h)

Depositions
2(kBq/m )1 year

5 years

10 years

20 years

30 years

Min

Max

Min

Max

Min

Max

Min

Max

Min

Max

<=10

0.03

0.20

0.02

0.16

0.01

0.09

0.01

0.06

0.00

0.04

30

0.09

0.6

0.07

0.5

0.03

0.3

0.02

0.2

0.01

0.1

60

0.2

1.2

0.1

1.0

0.06

0.5

0.04

0.4

0.03

0.3

100

0.3

2.0

0.2

1.6

0.1

0.9

0.1

0.6

0.05

0.4

300

0.9

6.0

0.7

4.8

0.3

2.6

0.2

1.8

0.15

1.3

600

1.7

12

1.3

9.7

0.6

5.1

0.4

3.6

0.3

2.6

1 000

2.9

20

2.2

16

1.1

8.6

0.7

5.9

0.5

4.4

>3 000

8.6

60

6.7

48

3.2

26

2.0

18

1.5

13

6.5.3. IMPACT ANALYSIS FOR MARINE ECOSYSTEMSFor the transient phase, the evaluation performed by a Russian team37 reflects this drastic drop inconcentrations in the water column, leading to overall dose rate estimates in the region of 2 mGy/day for fishes
and marine mollusks, and remaining below 10 mGy/day near the shore. These values are, however, indicativeof possible damaging effects on reproduction and embryonic survival in vertebrates. Buesseler et al.38 , in theirmeta-analysis of radionuclide concentrations of seawater, also emphasize the effectiveness of the dilution caused by
the local and regional hydrodynamics of the Pacific Ocean, and they suggest that, because of this, the dose rates to
non-human species will remain very low from direct exposure and will be below the protection criteria for species.
This estimate, however, unlike that of Kryshev et al. (2011)32, does not include the possibilities of
bioaccumulation via the trophic networks, or the role of secondary release sources that can be played by
sediments, particularly coastal ones. Finally, the Pacific Ocean, whose waters had 137Cs concentrations in July 2011that were 10,000 time higher than the baseline levels measured in 2010, still receives terrestrial supplies from theerosion and runoff processes operating in the contaminated catchment basins of the Fukushima district.
Once again, the knowledge currently available does not allow the possibility of a radiological risk to the marine
ecosystem to be ruled out. This knowledge is still very limited, which creates great uncertainly concerning the37

Kryshev A et al. (2011) Evaluation of the irradiation dose rate for marine biota in the region of the destroyed Fukushima reactor(Japan) in March–May 2011 Atomnaya Énergiya 111: 41–45.
Buesseler K et al. (2011) Impacts of the Fukushima nuclear power plants on marine radioactivity. Environmental Science &Technology 45: 9931–9935.
38

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results obtained. Continued environmental monitoring and increased knowledge concerning accidental releases
are therefore two key elements that will allow us to evaluate the ecological impact of the Fukushima Dai-ichi
accident on the marine environment. Finally, any forecast of ecological risk in a context of multiple stresses(physical, chemical, radiological) is bound to be highly uncertain.

6.5.4. PROJECTS INITIATED BY IRSN ON THE ECOLOGICAL CONSEQUENCES OFCHRONIC EXPOSURE TO LOW DOSES FOLLOWING A NUCLEAR ACCIDENT
An overall analysis of the work by Møller et al. as well as other review publications on the subject of the ecologicalconsequences of the accident at Chernobyl39, has recently led the IRSN to launch a research program on the
Chernobyl area in order to:-Specify the chronic exposure level due to the radionuclides present (external and internal exposure),-

Determine whether the species are or have been capable of adapting (effect on genetic diversity) to thisnew environment. This will particularly involve an examination of whether genetic and phenotypicaldifferences between populations are observable according to the level of contamination;-

Specify the taxonomic differences in radiosensitivity in order to understand why certain authors reach the
opposite conclusions from Møller et al. (for example, the work of Baker et al.40 which shows, inmicromammals, that populations increase in the exclusion zone and that the high exposure levels (of theorder of mGy/h) do not cause any major abnormality, particularly on reproductive capabilities, growth,etc.),-

Evaluate the ecological condition of this zone by applying an integrated approach (the field of functional
ecology), for example, by studying the degradation of bedding in the terrestrial and aquatic environments(an indicator of the material and energy flows), but also by developing models to understand and dissociate
direct effects (e.g. exposure to radiation) from indirect effects (e.g. the prey/predator relationship). To
date, these aspects have not been examined by any team.

In parallel, work has also begun in the Fukushima region. The Freebird project, selected by the National
Research Agency in the context of the Flash Japan call for projects, aims to evaluate the effects of a radioactive
contamination gradient on the bird populations inhabiting the area in a 100 km radius around the damaged
power plant. The idea is to look into the effect of exposure to radioactivity on:-

The physiology of birds via (i) the quantification of oxidizing stress by the dosing of carotenoids, thepigments involved in the coloring of feathers and in anti-oxidant defense; (ii) genotoxicity, (iii)
immunotoxicity, and (iv) the effects on hormones;-

Sexual signals and maternal commitment during the mating period, looking for a possible connection
between the physiological status of birds and these two key selection processes (e.g., potential reduction of
the quantity of carotenoids in feathers under the action of ionizing radiation can lead to consequences interms of sexual attractivity).

39

Geras’kin, S.A et al. (2008). Effects of non-human species irradiation after the Chernobyl NPP accident. Environ. Int. 34: 880-897.
Baker, R. J., Wickliffe, J.K., 2011. Wildlife and Chernobyl: The scientific evidence for minimal impacts. Bulletin of the Atomic
Scientist. 14 April 2011. Web Edition.

40

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APPENDIX 6-1: ATMOSPHERIC RELEASES FROM THE ACCIDENT
RE-ASSESSED IN 2011 BY IRSN (SOURCE TERM MER5)
The tables below present the cumulative releases for the main isotopes of the source term. For iodine, the total
corresponds to the sum of iodine in gaseous form (2/3 of the total) and particulate form (1/3 of the total). The
cumulative release of all the isotopes is 7.18x1018 Bq, of which 91% rare gases, 6% iodines, 2% tellurium, 0.8%
cesiums and less than 0.5% of other isotopes. This source term has 73 released isotopes, and 135 isotopes weredispersed when progeny were taken into account.
Rare gases (period)

Total (Bq)

Kr-83m (1.83 hours)

6.37x1014

Kr-85 (10.8 years)

3.26x1016

Kr-85m (4.48 hours)

4.39x1015

Kr-87 (76.3 minutes)

4.28x1013

Kr-88 (2.84 hours)

2.16x1015

Xe-131m (11.8 days)

3.92x1016

Xe-133 (5.24 days)

5.94x1018

Xe-133m (2.19 days)

1.32x1017

Xe-135 (9.14 hours)

3.71x1017

Xe-135m (15.3 min)1.73x1016

Xe-138 (14.1 min)6.26x1003

Total rare gases

6.54x1018

Tellurium (period)

Iodines (period)

Total (Bq)I-131 (8.02 days)

1.97x1017

I-132 (2.29 hours)

1.68x1017

I-132m (1.39 hours)

2.70x1010

I-133 (20.8 hours)

4.20x1016

I-134 (52.5 minutes)

5.01x1011

I-135 (6.57 hours)

2.20x1015

Total iodines

4.09x1017

Total (Bq)

Cesiums (period)

Total (Bq)

Te-127 (9.35 hours)

9.51x1015

Cs-134 (2.06 years)

2.78x1016

Te-127m (109 days)

2.14x1015

Cs-134m (2.9 hours)

1.49x1012

Te-129 (69.6 min)7.97x1015

Cs-136 (13.2 days)

9.80x1015

Te-129m (33.6 days)

1.22x1016

Cs-137 (30.17 years)

2.06x1016

Te-131 (25.0 min)8.36x1014

Cs-138 (33.4 min)1.08x1009

Te-131m (30 hours)

3.71x1015

Total cesiums

5.82x1016

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Te-132 (3.20 days)

1.08x1017

Total tellurium

1.44x1017

Other radionuclides

Total (Bq)(period)La-140 (1.68 days)

1.66x1013

Ba-140 (12.8 days)

1.12x1015

Nb-95 (35.0 days)

1.08x1013

Sr-89 (50.5 days)

4.33x1013

Sr-90 (28.8 years)

3.27x1012

Pu-238 (87.7 years)

2.43x1009

Pu-239 (24110 years)

4.07x1008

Pu-240 (6564 years)

5.08.1008

Pu-241 (14.4 years)

1.40x1011

Pu-242 (375000 years)

1.65x1006

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APPENDIX 6-2: PRESENTATION OF AIRBORN MEASUREMENTCAMPAIGNS PERFORMED IN JAPAN
Since April 2011, MEXT has organized several airborne measurement campaigns in collaboration with the Japan
Atomic Energy Agency (JAEA) and the Nuclear Safety Technology Center (NUSTEC). As of December 1st 2011, 22
districts had been mapped.

The measurements were obtained using on-board instruments in privately-owned helicopters, emergency helicopters,
or military helicopters. The flights were carried out at an altitude from 150 m to 300 m according to the terrain,
where high reliefs were not mapped (during the first campaign performed with the DOE, the flight altitude went ashigh as 700 m).

The measurements were performed on rectilinear routes, with the flight paths spaced as far apart as 3 km (see figure
below). According to the site to be mapped, the spacing of the flight paths could be reduced. Thus, in the 80 km
zone around the facility, this space was between 1.8 km and 2 km.

Example of a measurement map for the Yamanashi district
To obtain a cartographic representation, the measurements performed were integrated spatially on disks with aradius of 300 m to 600 m according to the flight altitude.
The measurements taken concerned the dose rate equivalent 1 m from the ground (without subtracting the natural
ambient dose rate) and the surface activity in cesium 134 and cesium 137. The airborne measurements were thencorrelated with measurements carried out in situ by the Japan Chemical Analysis Center for validation.
After analyzing the results, MEXT compiled them before publishing them on its website. They were publishedapproximately three weeks to one month after each measurement campaign. The results were published later inEnglish. The results were occasionally corrected, and new maps put online. The corrections were due to errors ofinterpretation of the raw results, or better correlation with the in situ measurement campaigns.
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According to the size of the district, each campaign lasted from one week to several weeks. The following airborne
measurement campaigns were carried out in 2011:o April 6 Æ April 29: 80 km around Dai-ichio May 18 Æ May 26: 80 km to 100 km around Dai-ichio May 31 Æ July 2: 80 km around Dai-ichi

o June 22 Æ June 30: Miyagi districto July 12 Æ July 16: Tochigi districto August 9 Æ August 15: Yamagata districto July 26 Æ August 2: Ibaraki districto August 16 Æ August 28: Fukushima districto August 23 Æ Sept. 8: Gunma districto August 30 Æ Sept. 23: Niigata districto Sept. 14 Æ Sept. 28: Akita districto Sept. 14 Æ Oct. 13: Iwate districto Sept. 23 Æ Sept. 30: Shizuoka districto Sept. 24 Æ Oct. 7: Nagano districto Sept. 30 Æ Oct. 4: Yamagata districto Oct. 5 Æ Oct. 12: Gifu districto Oct. 7 Æ Oct. 9: Toyama districto Sept. 8 Æ Sept. 12: Saitama districto Sept. 8 Æ Sept. 12: Chiba districto Sept. 14 Æ Sept. 18: Kanagawa districto Sept. 14 ÆSept. 18: Tokyo districto Oct. 7 Æ Nov. 1: Aomori districto Oct. 16 Æ Oct. 20: Aichi districto Oct. 17 Æ Oct. 24: Ishikawa districto Oct. 17 Æ Oct. 20: Fukui district

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7. ACTIONS TO PROTECT POPULATIONS AND POST-ACCIDENTMANAGEMENT IN JAPANThe accident at Fukushima led the Japanese authorities to initiate actions to protect the populations, firstly from theimmediate consequence of the releases (exposure to the radioactive plume) and then concerning the radioactive
deposits formed by the atmospheric dispersion of these releases (external exposure to radiation emitted by thedeposits and risk of internal contamination by ingestion of contaminated foodstuffs).
Moreover, during the past year, in addition to radioactivity measurements aiming to characterize the environmental
contamination (mapping the deposits) or monitor the contamination of foods and the dwelling-places of persons (seeSection 6), post-accident management actions were carried out by the government bodies or local authorities toreduce contamination and prepare for a gradual return to the evacuated territories.

7.1. EVACUATION OR PROTECTION
The information sources available to IRSN, most notably the report from the Japanese government concerning the
Fukushima accident, sent to the IAEA on June 7th41, provide a record of the sequence of main population protection
decisions taken from the start of the accident.

7.1.1. EMERGENCY PROTECTION ACTIONSOn March 11th 2011, because of damage caused by the tsunami, on the Fukushima Dai-ichi power plant in particular,
the Prime Minister declared a nuclear emergency situation at 7:03 pm local time, and requested the setting up of a
emergency cell.
The same day, at 8:50 pm, the Governor of Fukushima District ordered the evacuation of the towns of Futuba andOkuma, located within a 2 km radius of the Fukushima Dai-ichi power station. At 9:23 pm, the Prime Minister
instructed the relevant local authorities to evacuate the area in a 3 km radius around the facility and to shelter any
persons outside this 3 km radius but within a 10 km radius. On March 12 at 5:44 am, the evacuation was extended toa 10 km radius.
In parallel, the problems encountered in the other nuclear power plant, Fukushima Dai-ini, located a dozen
kilometers south of Fukushima Dai-ichi, led the Japanese authorities to decide, on March 12 at 7:45 am, to evacuate
the population living within a radius of 3 km around the facility and to shelter the population beyond that radius andwithin a 10 km radius. On March 12th at 5:39 pm, the evacuation was extended to 10 km (subsequently, on April 21,
this radius was reduced to 8 km, which in practice made it the same evacuation area as the 20 km one set up in themeantime around Fukushima Dai-ichi.
On March 12 at 6:25 pm, following the explosion in Reactor Building 1, the evacuation zone around the Fukushima
Dai-ichi site was extended to 20 km (affecting approximately 78,200 persons, including those within a 10 km radius of
Fukushima Dai-ini), and then a shelter zone in a radius from 20 to 30 km around the site was set up on March 15th at
11 am (concerning approximately 62,400 persons).
On March 15th at 11:30 pm, NISA announced that the evacuation of inhabitants in a 20 km radius around Fukushima
Dai-ichi and a 10 km radius around Fukushima Dai-ini had been in effect since that day at 7 pm.

41
Report of the Japanese Government to the IAEA Ministerial Conference on Nuclear Safety - The Accident at TEPCO’s Fukushima
Nuclear Power Stations.

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The table in Figure 7-1 summarizes the emergency protection actions decided upon in Japan from 11th to 15th March
2011.
Fukushima Dai-ini

Fukushima Dai-ichi

11/03/11
7:03PM: Nuclear emergency organization
8:50PM

Evacuation
2 km

9:23PM

Evacuation
3 km

Shelter
3 to 10 km

12/03/11
Evacuation
10 km

5:44 am
Shelter
3 to 10 km

Evacuation
3 km

7:45AM

Evacuation
10 km

5:39 pm

Explosion, Reactor Building 1

6:25 pm

Evacuation
20 km

15/03/11
6:25 pm

Shelter
20 to 30 km

11:30 pm: evacuations in force since 7 pm-

Dai-ichi: 20 km
Dai-ini: 10 km

Figure 7-1– Chronology of the protective actions decided on in Japan from March 11th to March 15th 2011
around the Fukushima Dai-ichi and Fukushima Dai-ini power plants.

7.1.2. ADDITIONAL PROTECTIVE ACTIONS IMPLEMENTED FROM APRIL 2011
At the end of March, while the major atmospheric releases occurring between the 12th and 25th of March had
dissipated, the results of the initial measurement campaigns revealed significant dose rates beyond the 20 km
evacuation zone, and particularly toward the north-west. Moreover, certain inhabitants located between 20 and 30km, where the shelter instruction still remains in force because of the precarious condition of the damaged facilities
of Fukushima Dai-ichi, started to evacuate that area voluntarily because their economic and social life was becoming
increasingly difficult to sustain. In this context, local initiatives and new decisions by the government authorities
were implemented to supplement the emergency protective actions taken in March.

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For example, on April 7th, the Mayor of Iitate took the initiative of advising pregnant women and children under theage of 3 (50 persons) to go to the neighboring town of Fukushima within one week.
On April 11th, the first announcement extending the initial evacuation zone was made: the residents of Katsurao,
Iitate, Namie, and part of Kawamata and Minamisoma were asked to leave within one month (first announcement).
On April 21st, the 20 km evacuation radius became a ‘Prohibited Area’. Unauthorized entry into this area became
subject to a fine of 100,000 yen (approximately €835).
On April 22nd, the residents of Katsurao, Iitate, Namie, and part of Kawamata and Minamisoma were again asked toleave within one month. Those areas then constituted the ‘Planned Evacuation Zone’ or ‘Extended Evacuation Zone’.
In parallel, taking shelter in the 20-30 km area was lifted around the Fukushima Dai-ichi power plant, and that area
became an ‘Emergency evacuation preparation area’. This concerned the municipality of Hirono, part of
Minamisoma, part of Tamura, and part of Kawauchi. In those municipalities, the population may remain, but must be
prepared for a possible emergency evacuation in the event of a new problem arising on the Fukushima Dai-ichi site.
The map in Figure 7-2 illustrates the protective zoning in force at that time.

Extended Evacuation Zone

Prohibited Zone

Emergency evacuation
preparation zone
Figure 7-2 - Population management zones.

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On May 15th, 4000 residents of Iitate and 1100 from Kawamata (municipalities located in the extended evacuation
zone decided on in April) were re-housed in neighboring towns.
On 16th June, the Government recommended the evacuation of persons residing in ‘hot spots’ (dose greater than 20
mSv/year) located outside the Prohibited Zone: this concerned 113 homes in the municipality of Date.
On July 21st, the government recommended the evacuation of 59 homes in the municipality of Minamisoma, and on
August 2nd and 3rd, 72 homes and one home respectively in the towns of Minamisoma and Kawauchi.
On August 18th, the evacuation of residents from the extended evacuation zone was almost totally complete.
In parallel, in order to limit the exposure of children in schoolyards, MEXT indicated that schoolyards were only
accessible subject to the dose rate at 1 m in primary schools or 50 cm in nursery schools being less than 3.8 µSv/h.

7.2. MANAGEMENT OF FOODSTUFFS IN JAPANWith regard to the mechanism for monitoring foodstuffs, Japan relies on the standards for sale or consumption
defined by the MHLW on March 17th 2011 and validated by the FSC (Japanese food safety commission) on March 29th
(Table 7-I). Exceeding these standards leads to the implementation of bans.
Table 7-I – Standards for sale or consumption instituted in Japan following the Fukushima accident
Milk and dairy(Bq/kg)Baby foodiodines

100

300

2,000

-

-

Pu and transPu alpha

1

1

1

10

10

products

Vegetables

Cereals

Meat, eggs, fishuranium

20

20

20

100

100

cesiums

200

200

500

500

500

This mechanism is not comparable to a zoning system. In Japan, it is not implemented via the definition of aperimeter in which actions are applied. The controls and bans are applied on a case-by-case basis according to thespecific strategy implemented by each local government concerned by the consequences of the accident.
MEXT however issued certain general rules. The system of bans and lifting of restrictions thus operated in thefollowing way during the past year:-

Marketing authorization is granted a priori; restrictions are not implemented unless a posteriori tests reveal
values outside the limits of the standards,-

Testing is performed by sampling, but the exact protocol is never disclosed; some doubt therefore remains
concerning the representative nature of the samples on the scale of the farms, municipalities, or districts
concerned,-

The procedure for lifting bans appears to be strict:o

Select several sampling points,o

Perform weekly tests on foodstuffs products at those points,o

When the measurement results for three consecutive weeks are within the limits, it is possible tolift the ban.

This management mechanism was applied to many product categories in Japan, but the dates, duration, and areas inwhich it was applied were variable, as the example of spinach illustrates in Figure 7-3.

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Key
Restriction periods for spinach
No restriction

Figure 7-3- History of restrictions on the sale of spinach
The information currently available does not enable IRSN to fully evaluate the effectiveness of the foodcontamination management mechanism in Japan. In particular, it seems that the restrictions are sometimes
implemented rather late and non-exhaustively, which has led to part of the Japanese population losing confidence inthis mechanism. A few observations cast doubt on the effectiveness of the system implemented:-

Certain restrictions were implemented very late, after measurement results exceeding the limits had beenobtained; for example:oFor bamboo shoots, the results from samples taken on April 27th 2011 in Iwaki (Fukushima district)exceeded the limits set by Japanese standards, but the restriction on sale did not take effect until
May 9th 2012,o

For tea leaves, the first sample found to have exceeded the limits was taken on May 9th 2011 in
Kanagawa district, but the sale restriction order was not issued until June 2nd 2011; however, theleaves picked in early May 2011 might not yet have been ready for processing.

-

Certain types of produce underwent sampling whose results exceeded the limits without giving rise torestrictions on a national level, and products whose contamination exceeds the limits were detected on theJapanese market (tea leaves, algae and mussels, loquat);-

Certain municipalities were subject to restrictions although no samples were taken there or the samples all
produced results within the limits;-

The marketing restriction is not always associated with the consumption restriction,-

There is no systematic application of the three tests before release, or the information concerning therepresentative nature of the tests performed is very patchy.

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These observations do not allow us to assess whether there were major food-related health risks in Japan. The doses
received in Japan by ingestion of contaminated foods are difficult to estimate (see Chapter 8). It is important,however, to remember that the occasional consumption of foods with contamination levels slightly exceeding
authorized threshold limits does not pose a significant health risk. Only the regular consumption of strongly
contaminated foods could have led to significant doses, particularly in the initial weeks following the accident.

7.3. PREPARATION FOR THE
DECONTAMINATION ACTIONSRETURNOF

POPULATIONS

AND

7.3.1. POPULATION RETURN STRATEGY ANNOUNCED IN JAPANOn July 20th 2011, the Japanese government announced that it hoped to allow residents to return to the evacuation
zones outside the 'Prohibited Zone' and eliminate the 'Prohibited Zone' in the coming months.
On August 9th, the government announced that it had established the plan to be implemented to re-evaluate theextension of the zones.
On August 26th, the first temporary visits to the 3 km zone were organized.
On September 30th, the emergency evacuation preparation zone status was lifted. On the 58,500 persons concerned,
approximately 28,500 had chosen to leave altogether rather than live in a constant state of alert.
On January 3rd 2012, the Japanese authorities announced that they could cancel the 20 km Prohibited Zone as ofApril 2012, and create three new areas with different statuses according to radioactivity level.
The government then plans to create:-

A return preparation zone, which concerns the areas where the annual dose potentially received by external
exposure related to deposits is between 1 and 20 mSv/year. This area would be decontaminated as apriority, to achieve a dose level as close as possible to 1 mSv/year, corresponding to the legal limit for the
exposure of populations to nuclear activities under normal operation. To make the area habitable, however,
the infrastructures and economic activities would have to be restored, after nine months lying idle andbecause of the damage caused by the earthquake and the tsunami. The decontamination work in this area ispaid for by the municipalities and district governments;-

A ‘Limited Habitation Zone’, concerning the areas where the annual dose is between 20 and 50 mSv/year.
Decontamination would be carried out there to return the level below 20 mSv /year and allow residents toreturn later. The decontamination work in this zone is paid for by the Japanese government;-

A ‘Difficult Return Zone’ where the annual dose exceeds 50 mSv/year. This is essentially a strip going
north-west from the power plant, It will remain totally deserted for at least a decade. The State should
offer to buy back the abandoned land from inhabitants.

7.3.2. DECONTAMINATION ACTIONS•

Government decontamination plan

In the territories where exposure is between 20 mSv/year and 10 mSv/year, the aim is to implement actions to
reduce the contamination and reach a dose lower than 10 mSv/year at the end of 2012. In these areas, for schools,
the target figure is maximum exposure of 5 mSv/year (or 1 µSv/h).
Wherever the annual dose is between 10 mSv and 5 mSv, the aim is to reach annual doses less than 5 mSv/year in
March 2013, and close to 1 mSv/year (i.e. 0.23 µSv/h) from the end of 2014.

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To train the participants, public meetings were organized, local companies were created, and a Ministry of theEnvironment field office has now been set up in Fukushima.
To carry out these actions successfully, the government has created a guide to decontamination best practices,which was published in late November. These practices were defined after several months of experimentation,
carried out by the JAEA, amongst others, on the initiative of the government.

•

Decontamination pilot sites

In the summer of 2011, actions were undertaken by the municipalities as well as by institutes such as JAEA todecontaminate schoolyards, public swimming pools, squares, etc. The work carried out by JAEA led to the creation ofmanuals for private individuals and municipalities.
Municipalities such as Date City and Fukushima City have set up their own initiatives to conduct cleaning campaigns
42

in certain neighborhoods .
JAEA, with support from the government, set up two pilot sites in 2011, covering about 7 or 8 acres (3 ha) each, in
Minamisoma City and Date City, near 'hot spots’. These pilot sites were used to test different cleaning methods in
different environments (buildings, forests, agricultural, etc.).
Another project, supported by the government and managed by JAEA, was set up in late 2011. Its aim was to create
pilot decontamination sites in 12 municipalities of the evacuated zone. There are 16 pilot sites in all, and they
include neighborhoods, parks, schools, industrial buildings, etc. The total surface to be decontaminated is 221 ha(over 500 acres). The decontamination period is estimated at approximately three months.
The pilot sites are divided into three groups. Each group is in charge of defining the actions it will carry out. Morethan twenty companies are involved in this project. The various actions being tested include pressure jet cleaning,cleaning using sponges with cesium-absorbent properties, spray-on films that trap radionuclides after polymerization,using vacuum sweepers,
To better evaluate the effectiveness of the various actions undertaken, a precise mapping of the site is made before
and after the actions are carried out. Finally, to reduce the quantity of waste, various reduction measures areapplied before storage. These actions are, for example, are treating the water used for decontamination, crushingplants, and sorting masses of earth according to their level of contamination.

•

Example of decontamination actions• Decontamination action in a school

In April, certain municipalities decided to implement decontamination actions on schools where the dose rate levels
were above 3.8 µSv/h at 1 cm.
To limit the exposure of children in the town of Koriyama, the municipality stripped the surface of the playground or
grass to a depth of 3 cm on April 27th (see Figure 7-4). The effectiveness of this action was evaluated during theoperation (see Table 7-II). Following on from this experiment, two surface stripping campaigns were carried out
between April 27th and May 2nd, and May 24th and 28th, in all schoolyards where the dose rate was greater than 3.8µSv/h at 1 cm. The dose rates measured before and after surface stripping are presented in Table 7-III. The removed
soil was stored and then sprayed with a fixer product to make it less prone to returning into suspension.

42

Actions implemented in Date City (in Japanese) http://www.jaea.go.jp/fukushima/pdf/decon_j_11.pdf
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Figure 7-4 – Stages of surface stripping in schoolyards.

Table 7-II – Effectiveness of soil stripping carried out on April 27th
HeightDose rate in µSv/hr

fromgroundSchool 1
School 2

April 7

April 27 (before removal)

April 27 (after removal)

1cm

5.5

4.1

1.9

50cm

4.5 (measured at 1m)

3.3

1.9

1cm

4.7

4.5

0.9

50cm

3.4

3.1

0.9

Table 7-III – Effectiveness of soil stripping campaigns of April 27th to May 2nd and May 24th to 28th
Average dose rate in schools (µSv/h)
Measurements 1 cm from the ground
Before removal
Mean(min-max)•

After removal

Efficiency (%)

Measurements 50cm from the ground
Before removal

After removal

Efficiency (%)

2.1

0.7

65.3

1.7

0.7

59.1

(1.4 - 4.5)

(0.2 - 1.9)

(35.0 - 90.5)(1.1 - 3.3)

(0.2 - 1.6)

(25.0 - 88.2)

Decontamination of the Watari district43

An initial cleaning campaign was carried out in the Watari district (Fukushima). This was done to study theeffectiveness of the actions to then apply them to other neighborhoods. This campaign was carried out on July 24th.
Town employees and private individuals participated in the cleaning work. The Fukushima town website indicatesthat 3400 persons took part in this action.
The actions carried out included the cleaning of roads, sidewalks and ditches using sweepers and pressure jets, aswell as the cleaning of flower beds and certain administrative buildings open to the public. The dose rate and dose43

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were checked before and after cleaning. In the coming weeks, new actions will be undertaken to clean the publicparks. Provisional results are given in Table 7-IV and Table 7-V.
Table 7-IV : Effectiveness of the cleaning of school access routes, campaign of July 24th44

Average dose rate on school access routes (µSv/h)
Measurements 1 cm from the ground

Mean

Measurements 50cm from the ground

Before cleaning

After cleaning

Efficiency (%)

Before cleaning

After cleaning

Efficiency (%)

2.25

1.8

20.55

1.65

1.35

18.9

Table 7-V : Mean effectiveness of the cleaning of a house, campaign of July 24th
Dose rate (µSv/hr)
Before cleaning

After cleaning

Efficiency (%)

Guttering

6.8

1.6

76.5

Entry

0.9

0.8

11.1

Garden

1.5

1.2

20

Interior

0.5

0.4

20

In general, the contamination reduction actions on buildings reduce the ambient contamination only slightly, unlesscarried out in the initial weeks following the deposition, i.e. before the radionuclides have become fixed. Cleaning
and removal of vegetation that had accumulated in eavestroughs or gutters, however, eliminates a significant
proportion of the radioactivity accumulated in these hot spots. Figure 7-7 shows that, on average, the cleaning ofguttering reduced the dose rate at the deposition points approximately by a factor of four.

•

Waste processing plan

In parallel with the decontamination plan, the Ministry of the Environment has presented a plan to dispose of andstore the waste obtained from the decontamination process.
The planned storage method would be scalable over time.
For all the waste generated by the decontamination process, the decision was to set up a temporary, but monitored,
storage system for a maximum period of three years.
For longer periods—from three to 30 years—the government plans to set up temporary storage centers.
Finally, thirty years from now, the government plans to set up long-term underground storage facilities.
In any case, regular or continuous checks are planned to ensure that no contamination of the environment is caused(Figure 7-5).
The waste generated by the decontamination process that is considered to be contaminated, is waste whose activity
exceeds 8000 Bq/kg for waste other than soil.
For certain categories of waste (e.g., agricultural waste), the plan is to incinerate it and then store thecontaminated ashes.

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Allles
types
Tous
typesofdewaste
déchets

Temporarystorage<<3ans
3 years
Entreposage provisoire

Temporary
Stockagestorage
provisoire< <30
30 yearsansLong-term storage

Stockage long terme

Figure 7-5 – Steps in the storage of contaminated waste.

•

Contamination of the urban environment

In urban areas, the deposition is heterogeneous. Meteorological disturbances due to the effects of buildings cause
accumulation points in locations where air recirculates. In addition, there is more or less deposition according to theurban surfaces. A dry deposit will become better fixed on a rough surface, and a wet deposit will run off better froma smooth surface. In addition, as for an accumulation of snow, the deposition areas of the eavestroughs are locations
where radioactivity can particularly accumulate, creating hot spots.
The different measurements published by the Japanese authorities revealed these deposition disparities in the urban
environment.
Figure 7-6 presents measurements taken in late July on paths toward a school in the Watari area of Fukushima before
and after cleaning the sidewalks. Different dose rates are observed on either side of the road. The sidewalk on theright always has a higher dose rate than the one on the left.

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Figure 7-6 – Dose rate measurements taken before
and after decontamination at 1 m along theschool path

Figure 7-7 presents the dose rates measured near a house in the Watari neighborhood before and after contamination
reduction actions. The maximum dose rates are measured at the eavestroughs, i.e. at the deposition points of therunoff from the roof.

Figure 7-7 – Dose rate measurements taken before and after decontamination

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8. DOSIMETRIC AND HEALTH IMPACT IN JAPANFollowing the earthquake and tsunami that occurred on the east coast in northern Japan, the Fukushima nuclear
power plant was badly damaged, and a large quantity of radioactivity was released into the atmosphere and the sea.
The surrounding populations were evacuated, while others, who lived in more remote areas, were placed undershelter. The countermeasures taken with regard to the exposure of the population in Japan included temporary
restrictions on drinking water and certain foods produced in several districts, ordered by the Japanese authorities.
During emergency operations undertaken in the power plant, workers and other participants were exposed tosignificant levels.
The health risks to persons exposed in Japan at the time of the Fukushima accident and in its aftermath depend on
the level of the radiation doses received.
Exposure to the radioactive releases caused by the accident largely depended on where the persons were located,their way of life (activity, food, travel, etc.) and compliance with the protective actions implemented by theauthorities, most notably emergency or delayed evacuation, or the taking of stable iodine tablets.
The doses actually received by different categories of person remain very difficult to estimate, even one year after
the accident, because they depend on the number and quality of the radioactivity measurements available (in theenvironment or on individuals) and the information collected concerning the conditions of exposure.

Work iscurrently underway under the auspices of UNSCEAR (United Nations Scientific Committee on the Effects of Atomic
Radiation) in order to assess, in particular, the dosimetric and health consequences in Japan. IRSN participates
actively in this work.
Thus, at its annual session in May 2011, the United Nations Scientific Committee on the Effects of Atomic Radiation
decided to start writing an initial report on the accident at the Fukushima Dai-ichi power plant and its consequenceson the health of persons exposed to the radioactive fallout.
In order to accomplish this task, UNSCEAR called upon all governments to nominate experts, who would be appointed
to write this report on a voluntary basis. A total of nearly 60 experts, from Europe, Japan, Canada, the USA, Brazil,
Korea, Russia, Belarus, Ukraine, and Australia, were appointed. There are nine experts from France: five from IRSN
and four from the CEA.
The experts have been divided into four working groups:-

The first group, led by an American delegate, is responsible for collecting measurement data and checking
its quality. IRSN is represented by an expert in charge of one of the three sub-groups of this working group,-

The second group, led by a German delegate, is responsible for evaluating the atmospheric and marine
dispersion of the radioactive discharge. IRSN is represented by one expert in this working group,-

The third group, led by an Australian delegate, is responsible for assessing doses and risks to the populationand non-human species. IRSN is represented by two experts in this working group,-

The fourth group, led by a French delegate from IRSN, is responsible for assessing doses and health effects
to workers.

Moreover, a coordination group consisting of the Chairman of UNSCEAR, the Chairman of the Japanese delegation to
UNSCEAR, the leaders of the four working groups, and the Scientific Secretary of UNSCEAR and his colleagues,
ensures the smooth progress of the report drafting process.
A first interim report will be presented at the 59th annual session of UNSCEAR in May 2012, and the final report,
whose publication is expected at the end of 2013, will be presented at the 60th annual session of UNSCEAR in May
2013.
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This UNSCEAR report will also benefit from contributions by the main international organizations, most notably theWorld Health Organization and the World Meteorological Organization.
To assess the dosimetric impact and health risks affecting persons exposed in Japan, IRSN collected information or
performed evaluations for three categories of the population in Japan:-

Workers (including outside workers) present on the site during the accident and in the phase of restoring
control over the facilities on the site, which is still ongoing,-

The Japanese population residing in the areas most exposed to accidental releases and radioactive
deposition,-

French nationals returning from Japan and checked by IRSN.

8.1. GENERAL CONCEPTS
Overall, the risks expected after a nuclear accident of this magnitude essentially consist of an increased probabilityof the occurrence of certain types of cancer in the most exposed segments of the population, particularly thyroid
cancer in small children. The two indicators used in this report to assess these risks are the effective dose and theequivalent dose to the thyroid.
The effective dose accounts for the doses delivered to each organ of the human body exposed to ionizing radiation,
the nature of that radiation, and the inherent sensitivity of each of the organs to this radiation. It is expressed in aunit called the sievert (Sv) or divisions thereof: millisievert (mSv, thousandths of a sievert), microsievert (µSv,
millionth of a sievert), or nanosievert (nSv, billionth of a sievert). The equivalent dose to the thyroid is the dosedelivered specifically to the thyroid, particularly by the radioactive iodines.
The assessment of the dose received by an individual following incorporation of a radioactive substance involves acomplex approach. It requires knowledge of how the activity in that substance will evolve in the organism, and acalculation of the dose received by the various tissues and organs. The determination of incorporated activity
depends on retention measurement (whole-body and pulmonary in particular), of the radionuclides and their urinary
and/or fecal excretion (radiotoxicological analysis).
Whole-body countings (i.e. in vivo measurements) involve determining the activity of the radionuclides incorporated
in the organism by detecting the x-rays and gamma rays they emit outside the organism. This technique requires nobiological sampling, and it can identify the radionuclide(s) concerned according to the energy of their emissions,quantify the activity at a given instant, and use it to estimate the initial intake.
The radiotoxicological analysis of excreta (i.e. in vitro bioassays) consists of determining the activity of theradionuclides eliminated in urine or in feces following the intake of radioactive substances. These tests are lessdemanding than whole-body countings (WBCs) with regard to the nature of the radiation that can be detected. They
allow all types of radioactive emission to be measured, but nonetheless require the implementation of more
extensive logistics. In fact, given the sample volumes required and in order to take fluctuations in daily excretion
into account, they require 24-hour resting times for the urine, and this can rise to three days for feces. The samples
must then be taken to a radiotoxicological testing laboratory and processed according to the nature of theradionuclides to be measured.
When a nuclear accident occurs, the main radionuclides likely to be detected in the exposed persons are the isotopesof cesium and iodine. These can equally well be detected by whole-body counting and by urine bioassays.

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8.2. EXPOSURE OF WORKERS AND OTHER PARTICIPANTS ON THE
FUKUSHIMA DAI-ICHI SITE
The only information currently available concerning doses received by the workers involved in the operations carriedout at the Fukushima Dai-ichi power plant are those provided by the TEPCO company, which has been publishing amonthly report since April 2011. This information concerns employees of TEPCO and its subcontractors only. No
precise information concerning the other categories of worker exposed (firemen, police officers, municipal
employees, civilian security personnel) has yet been obtained, even though at least some of those workers haveundergone dosimetric monitoring.
The last report published on February 29th 2012 concerned 3,340 TEPCO employees and 16,775 employees ofcompanies subcontracted by TEPCO. The mean dose received by those workers between March 11th and 31st January
2012 was 24.72 mSv for TEPCO employees, and 9.35 mSv for subcontractor employees. Note that a comparison withthe data supplied by TEPCO on January 31st 2012 indicates an unexplained discrepancy of 66 workers. If theinformation given in the report dated January 31st 2012 is compared to the information in the report dated February
29th 2012, the February 2012 month-end report should have mentioned 3,405 TEPCO employees and 16,776
employees of subcontractor companies.
Table 8-I – Summary dated February 29th 2012 of doses recorded by TEPCO for its own workers and thoseof its subcontractor companies
Cumulative dose

TEPCO

Contractors

Total> 250 mSv

6

0

6

200 – 250 mSv

1

2

3

150 – 200 mSv

22

2

24

100 – 150 mSv

117

17

134

50 – 100 mSv

409

347

756

20 – 50 mSv

646

2,078

2,724

10 – 20 mSv

494

2,667

3,161

< 10 mSv

1,645

11,662

13,307

Total

3,340

16,775

20,115

Maximum (mSv)

678.80238.42678.80Mean (mSv)

24.72

9.35

11.90

As at February 29th 2012, six workers, all employed by TEPCO, had received a dose exceeding 250 mSv. According to
TEPCO, 85% of the dose received by those six workers was caused by inhaling iodine 131 due to not wearing suitable
protective masks. The maximum recorded dose was 678.80 mSv.
Note that very little precise information is available concerning the methods used to evaluate the doses received by
the workers, in particular for those who were not wearing dosemeters in the days immediately following theaccident. Requests for additional information were recently sent to the Japanese authorities by the United Nations
Scientific Committee on the Effects of Atomic Radiation.
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8.3. EXPOSURE OF THE JAPANESE POPULATION
8.3.1. THE VARIOUS POPULATION EXPOSURE PATHWAYS FOR RADIOACTIVE
SUBSTANCES RELEASED INTO THE ENVIRONMENT
The radioactive releases into the atmosphere as a result of the accident had the most immediate and significant
impact in terms of local population exposure. Although there were also substantial direct releases into the sea, these
could only have had an indirect impact through possible consumption of contaminated fish and seafood products(algae, coastal fish, shellfish, etc.).
The exposure pathways, the rate at which doses were accumulated (dose kinetics) and, ultimately, themagnitude of the doses received largely depend on the timeline of the accident and of course on a person’s
location.
At the time when the releases were dispersed in the air, in the form of a radioactive plume, the population may
have been exposed via two main pathways (Figure 8-1):-

external exposure by radiation emitted by gamma-emitting radionuclides dispersed in the atmosphere (inthe form of gas or fine particles in suspension, called “aerosols”), including those present above groundlevel;-

internal exposure by inhalation of radioactive gas or aerosols present in the ambient air at ground level.
The radionuclides inhaled cross the pulmonary barrier into the bloodstream relatively easily and thendistribute throughout the body. Some radionuclides tend to concentrate in specific organs, e.g. radioactive
iodine in the thyroid. The radionuclides incorporated irradiate surrounding tissues and organs and continue
to do so for as long as they remain in the body, even after the person concerned is no longer exposed tocontaminated air. The residence time in the body depends on the radioactive half-life of the radionuclide
and how fast it is eliminated by natural bodily functions.

External irradiation due to the plumeInternal contamination by inhalation of radioactive
substances

Figure 8-1 - Main exposure pathways to contaminated air caused by accidental radioactive release.

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For a given person and radionuclide, the higher the radionuclide concentration in the air andthe longer the air is contaminated, the larger the dose. Consequently, a similar dose may bereceived after brief exposure to a high concentration or prolonged exposure to a lower
concentration.

When the person exposed is inside a permanent building with the doors and windows closed, internal exposure
by inhalation may be temporarily delayed and reduced (the time taken for the radionuclides in the outside air topenetrate into the rooms). Furthermore, the gamma radiation emitted by the radionuclides present outside thebuilding is attenuated by the construction materials (the effectiveness of attenuation depends on the type used andthe size of the building), which can help to lower the doses received, typically by about 30%.

Figure 8-2 - Protection provided by a building against radioactive contamination of the outside air: theconstruction materials attenuate the gamma radiation and delay the penetration of radioactive particles
into the building.

Emergency evacuation of areas likely to be exposed to the plume prevents population exposure if evacuation canbe carried out before any releases start. This is the most effective protective measure in the event of a high level ofambient air contamination or prolonged radioactive releases (longer than about ten hours), but is difficult toimplement and is not without risk (emergency protective measures during the accident cf. 7.1.1).
Taking stable iodine tablets reduces the dose to the thyroid from exposure to radioactive iodine, especially iodine131. This treatment, which is particularly appropriate for children and pregnant women, must be administered justbefore the radioactive releases occur or shortly after initial exposure; for maximum effectiveness, the recipients
must also take shelter.
The Japanese authorities are reported to have issued instructions to take stable iodine on March 16, 2011 during
evacuation of the area within a 20 km radius of the damaged power plant. No evacuated residents seem to havetaken any tablets, since the evacuation was apparently over by the time the instructions were made public.
According to the SPEEDI information system45 set up by the Japanese authorities, no dose rate higher than the limit
of detection of 0.2 μSv/h (equivalent to a thyroid dose of 100 mSv for a 1-year-old child) was measured during ascreening program carried out on 1,149 children between March 26 and 30, 2011.

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Radioactive aerosols and gases gradually sink to ground level. The radioactive deposits thus formed will contribute to
the exposure of people located in the contaminated areas, via the following main pathways:-

external exposure from the gamma-emitting radionuclides deposited. The intensity of exposure mainly
depends on the extent of the radioactive deposition, the topology of the areas contaminated, and individual
lifestyle (time spent outdoors);-

internal exposure from ingestion of contaminated foodstuffs harvested in these areas. As with internal
exposure by inhalation, the radionuclides incorporated cross the digestive barrier and remain in the tissues
and organs for a varying amount of time, leading to exposure of the body to ionizing radiation;-internal exposure from inadvertent ingestion of radioactive particles. This exposure pathway, which isusually of secondary importance, exists when someone touches a surface that has unstable deposits(radionuclides not fixed on the surface) or loose contaminated materials (soil) then puts their hand to theirmouth. Young children are at particular risk unless precautions are taken.

Contamination by foodstuffs
Contamination by unintentional
ingestion of labile deposits

External irradiation by deposition

Figure 8-3 - Main exposure pathways to radioactive deposits in a post-accident situation
On a secondary level, there is a risk of exposure by inhalation of suspended radioactive particles from deposits,
particularly in windy conditions or as a result of human actions (vehicles passing by, for example). The corresponding
doses are usually low compared with those due to other exposure pathways. Nevertheless, this risk must be taken
into consideration for people carrying out dirty work in heavily contaminated areas.
As we shall see in the next section, the doses due to exposure to the radioactive plume may be high in the vicinity ofthe damaged nuclear plant and may be received over a short period, ranging from a few hours to several days, as was
the case in the Fukushima accident. The doses due to deposition are received more gradually but may become
significant over time. Taking into account the presence of radionuclides with a short radioactive half-life in thedeposits and phenomena specific to contamination of the food chain (see Chapter 6), the doses likely to be received
from external exposure to deposition or from ingestion of contaminated foodstuffs may be particularly significant
during the first month following formation of the deposits. This is why, even though protecting the public fromexposure to the radioactive plume must always be a priority in the most affected areas, initial preventive
measures in relation to radioactive deposits must be implemented as soon as possible, especially in areas thatare further away, where these deposits may have a significant short-term impact on food chain contamination.
It is important to stress that in the case of the Fukushima accident, radioactive deposition started to become
significant in Japan from March 15-16, 2011, whereas significant radioactive releases continued until March 25 (seeChapter 6). This means that during the release phase (from March 12-25), the public could have received a dose fromboth the plume and the radioactive deposits. After March 25, in the absence of new significant releases into the

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the contaminated areas, resulting in a gradual increase in the doses received.

8.3.2. ESTIMATE OF THE DOSES LIKELY TO HAVE BEEN RECEIVED BY THE LOCALPOPULATION DURING THE ATMOSPHERIC RELEASE PHASE
Within the context of work carried out in 2011 to evaluate atmospheric releases and simulate their dispersion overJapan (see Chapter 6), IRSN assessed the doses potentially received by a 1-year-old child assumed to haveremained in the same location from March 12 (when the releases began) until midnight on March 25 (when thephase of significant releases ended), without any protection (i.e. outdoors). This exposure scenario is obviously
not realistic but makes it possible to conservatively identify what are likely to have been the most exposed areas,
i.e. those where emergency protection issues needed to be given priority attention. This conservative approach is
one that IRSN commonly adopts in the event of an emergency to predict the potential dosimetric impact of an
accident in progress, in order to recommend reasonably cautious protective measures to the authorities at a time ofheightened uncertainty. The “1-year-old child” category is used because young children are most vulnerable toexposure to radioactive releases, especially iodine (in terms of thyroid doses received).
To assess these doses, IRSN considered the three main exposure pathways during this release phase:-external exposure to gamma radiation emitted by the radioactive plume;-internal exposure by inhalation of radionuclides present in the air;-external exposure to gamma radiation emitted by the radioactive deposits on the ground, which aregradually formed according to the trajectories of the radioactive plume and the rain.

The dose likely to have been received by ingestion of contaminated foodstuffs is not taken into account here, as it is
not a determining factor in the emergency protection strategy (sheltering or evacuation, administration of stableiodine). Moreover, in the case of the Fukushima accident, IRSN does not have sufficient data to make a reliable
estimate of this dose.
The maps in Figure 8-4 and Figure 8-5 represent, respectively, the cumulative effective dose and equivalent dose to
the thyroid at the end of the release phase (midnight on March 25, 2011), based on the assumptions described above
and calculated on a local scale (using model pX) and on a regional scale (using model ldX).
As expected, the doses likely to have been received were highest at local level. Whatever the scale, these estimatesshow that the marine environment suffered the greatest impact from the atmospheric releases. This obviously refers
to virtual doses, because there are no full-time human inhabitants of that environment (especially not a 1-year-old
child). Moreover, in the absence of any direct environmental measurements at the time of the releases, dose
estimation is particularly inaccurate in this sector.
On land, the highest doses during the release phase could have been received in the coastal areas, to the north andespecially to the south of the Fukushima Dai-ichi power plant. According to this simulation, effective doses above
10 mSv could have been received, assuming the people concerned continuously remained outdoors, up to 40 km to
the south; the effective doses calculated exceed 50 mSv(46) inside a 20 km radius, corresponding to the emergency
evacuation zone on March 12. Concerning the equivalent doses to the thyroid, theoretical values above 50 mSv47
could have been received as far as 60 km to the south of the power plant, in Iwaki. These correspond to a releasefrom Reactor 2 on March 15 between midnight and 5 am, when the wind was blowing towards the south.

46

An effective dose of 50 mSv corresponds to the intervention level in France for emergency evacuation of populations exposed toan accidental atmospheric release.
47

A 50 mSv equivalent dose to the thyroid corresponds to the intervention level in France for the administration of
stable iodine tablets in the event of exposure to an accidental release of radioactive iodine. In Japan, theintervention level is 100 mSv, in compliance with IAEA recommendations.
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Regional scale (idX)

Local scale (pX)

Effective dose likely to have been received by a 1-year-old child who remained without
protection (outdoors) from March 12 to midnight March 25, 2011

Figure 8-4– Maps of the effective doses potentially received by an unprotected 1-year-old child during therelease phase of the Fukushima accident. The doses on the regional scale map are only representative
more than 100 km from the release point, taking into account the ldX modeling conditions. Within ashorter distance (area inside red circle), the doses on the local scale map, which was obtained using model
pX, are representative.
Local scale (pX)

Regional scale (idX)

Equivalent dose to the thyroid likely to have been received by a 1-year-old child who
remained without protection (outdoors) from March 12 to midnight March 25, 2011

Figure 8-5– Maps of the equivalent doses to the thyroid likely to have been received by an unprotected 1year-old child during the release phase of the Fukushima accident. The doses on the regional scale map
are only representative more than 100 km from the release point, taking into account the ldX modelingconditions. Within a shorter distance (area inside red circle), the doses on the local scale map, which was
obtained using model pX, are representative.

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It should be emphasized that there is some uncertainty concerning the position of the radioactive plume in thesouthern sector because of the imprecise nature of the data and the modeling of meteorological conditions on a local
scale, particularly for the release event occurring on March 15 and 16, 2011 (cf. 6.1.2.2). The plume heading south
might therefore have passed more over the marine environment.
Further away, the doses received during the release phase, in the absence of protection, would have beensignificantly lower:-

below 10 mSv for the effective dose more than 40 km to the south, and of the order of 0.1 mSv in the Tokyo
metropolitan area;-

below 50 mSv for the thyroid dose more than 40 km to the south, and of the order of 1 mSv in the Tokyo
metropolitan area.

It should be noted that the doses determined from the individual measurement results for French citizens living
within a 60 km radius of the Fukushima Dai-ichi power plant at the time of the releases (see 8.4) seem significantly
lower than the conservative ones derived from the model.
It is interesting to note that the areas most affected by radioactive deposition, located to the north-west of the
Fukushima power plant, are not the areas where the doses due to exposure to the plume were highest. This canbe explained by the strong influence of rainfall or snowfall, which caused these deposits during the night of March
15-16, whereas in the areas most exposed to the plume, the deposits consisted mainly of dry deposits in a lesser
quantity.
On the local scale, for equal levels of dose potentially received, there is a large disparity from one location toanother concerning the contribution of the various exposure pathways and the dose kinetics during the release
phase from March 12 to 25, 2011 (Figure 8-6).

South and south-west of
Fukushima Dai-ichi

North-west of Fukushima
Dai-ichiwet deposits
dry deposits
wetdeposits
dry deposits

plume

plume
inhalation

inhalation

total
plume
dry deposits
wet deposits
inhalation
Dose (mSv)

Dose (mSv)

total
plume
dry deposits
wet deposits
inhalation

Figure 8-6 - Contribution of the exposure pathways and dose kinetics (effective dose, without protection)
during the release phase (March 12-25, 2011) in two different locations (Kawauchi and Iitate, shown in
Figure 8-4) within 40 km of Fukushima Dai-ichi (cumulative doses calculated using model pX).

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The example of Kawauchi is representative of the exposure situation during the release phase in the areas situated tothe south-west and south, and on the coast north of the damaged power plant (Minamisoma):-the effective doses received between March 12 and 25 were due primarily (70-80%, depending on thelocation) to internal exposure by inhalation of radioactive substances and secondly (15-20%) to external
exposure to dry deposits;-these doses were received over brief periods (in stages), mainly around March 15-16 (except in the north,where first exposure occurred on March 12 and 13) then around March 22-23;-

after the release phase, exposure continued at a more moderate level.

The example of Iitate is characteristic of the exposure situation during the release phase in the areas situated to thenorth-west, heading towards the town of Fukushima:-

the effective doses received between March 12 and 25 were due primarily (about 85%) to external exposure
to wet deposits and secondly (about 12%) to internal exposure by inhalation of radioactive substances;-these doses were received gradually from March 15, 2011 onwards;-

after March 25, exposure persisted because of significant deposition.

Whereas the effective dose levels were of the same order of magnitude in the two examples mentioned (a few mSv
received in 14 days), these significant differences in dose kinetics and respective contributions of the exposure
pathways to the dose received are the result of differences in the intensity of rainfall at the time of the releases,
which was concentrated in the north-west during the night of March 15-16, leading to high levels of radioactive
deposits (see 6.2). In these areas, external exposure to radioactive deposits quickly became the main exposure
pathway, and persisted well beyond the release phase.
These differences in contribution of exposure pathways and dose kinetics can be analyzed retrospectively in terms of
population protection strategy:-

in areas where internal exposure by inhalation of airborne radionuclides accounted for the largest
contribution, with rapid dose kinetics, emergency protective measures such as sheltering, evacuation oradministration of stable iodine were most appropriate (cf. 8.3.1);-

in areas where external exposure due to radiation from radioactive deposits accounted for the largest
contribution, with slower but long-lasting dose kinetics, protective measures considered in a post-accident
situation were most appropriate, in particular short-term withdrawal (albeit less urgent than emergency
evacuation in the event of exposure to the plume) for people living in areas with the highest levels ofradioactive deposition.

8.3.3. ESTIMATE OF THE DOSES LIKELY TO HAVE BEEN RECEIVED BY THE LOCALPOPULATION FROM EXTERNAL EXPOSURE TO RADIOACTIVE DEPOSITSOn April 8, 2011, IRSN made an initial estimate of the doses likely to have been received by people living in thecontaminated areas in Japan as a result of external exposure to gamma radiation emitted by radioactive deposits; it
did so by interpreting aerial dose rate measurements obtained by the American DoE/NNSA and published on its
website on April 7, 2011. On that date, IRSN had no measurement data concerning the isotopic composition of theradioactive deposits, and the forecasts of doses potentially received during the first year following the accident used
the isotopic composition of the source term estimated by IRSN at the time (see 6.1) and the analysis of the decay
profiles of the dose rate measured at various points in the areas affected. In late April 2011, MEXT published newmaps showing dose rates and caesium-134 and caesium-137 deposits, as well as a map of estimated doses due toexternal exposure to deposits during the first year (see map in Figure 8-7). MEXT then updated this dose forecast
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published at the end of April 2011. As expected, the highest dose levels concerned the areas that had received thelargest deposits, formed between March 15 and 16, 2011 over an area covering several tens of kilometers north-westof the Fukushima Dai-ichi power plant, during heavy rainfall and snowfall at the time of the atmospheric dispersion
of a release from Reactor 2.

Cumulative doses from external exposure to radioactive
deposits, during the first year following the start of the
Fukushima accident(IRSN retranscription of MEXT estimates obtained
from a dose rate map compiled on April 24, 2011)

LegendMEXT estimated doses

Figure 8-7 – Map of predicted cumulative doses during the first year after the accident (from March 11,2011 to March 11, 2012), received from external exposure to radioactive deposits (based on the MEXT
map compiled on April 24, 2011).

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The estimate of the doses likely to have been received from external exposure to radioactive deposits over a given
period (one month, three months, a year, etc. after the start of the accident) takes into account several factors:-

the rate of decrease of the ambient dose rate resulting from the radioactive deposits, which depends on thetheir initial isotopic composition. In its first assessment, IRSN had overestimated the barium-140/lanthanum140 ratio in the deposits, which meant that it underestimated the dose potentially received after a year by afactor of 2.5 compared with the MEXT estimates. The latter take into account measurements of radionuclide
activity in the deposits, which revealed that the deposits initially contained short-lived radionuclides(iodine-131 and tellurium-132/iodine-132) and then, once these had disappeared due to radioactive decay,
mainly caesium-134 and caesium-137 (cf. Chapter 6);-

the assumptions about the time spent outdoors and about the shielding factor (SF) of buildings (dose rate
lower indoors than outdoors; see 8.3.1). The values used by IRSN (12 hours a day spent outdoors and SF =0.3) were different from those used by MEXT (8 hours a day spent outdoors and SF = 0.4), but combining
these two parameters ultimately produces an equivalent result (a dose reduction by a factor of 0.65 for
IRSN, and 0.6 for MEXT).

These estimates are indicative and do not consider the variability of factors taken into account, related mainly
to the local heterogeneity of the radioactive deposits (presence of “hot spots”; see Chapter 6) or to people’s
lifestyle (time spent outdoors, shielding provided by various types of buildings, movements, etc.). For example,
spending only four hours a day outdoors in the contaminated areas can reduce the dose received by about 20% (oreven more, depending on the shielding effect of the buildings) compared to the value estimated by MEXT.
By comparing the dose map published by MEXT with the map of cumulative deposits of caesium-134 and caesium-137,
it is possible to derive a conversion factor relating the cumulative dose from external exposure to deposits over the
first year to the surface activity of caesium-134 and caesium-137: 16.6 mSv per MBq/m2 of 134+137Cs. Moreover, using
the demographic data concerning the Fukushima prefecture provided by the Statistics Bureau, Ministry of Internal
Affairs and Communications, Japan (http://www.stat.go.jp/), IRSN deduced that, outside the emergency
evacuation zone 20 km around the Fukushima Dai-ichi power plant, close to 70,000 people living in areas with
134+137

Cs deposition exceeding 600,000 Bq/m2 were likely to receive a dose greater than 10 mSv in the first year

due to external exposure to the deposits. If the most contaminated areas (annual dose exceeding 20 mSv) had notbeen evacuated, as the Japanese authorities decided to do on April 22, 2011, this dose could even have been higher
than 50 mSv for approximately 5,300 people. Inside the 20 km exclusion zone, even higher doses, in excess of 200
mSv, could have been reached, according to the maps published by MEXT. These estimates confirm that it would
have been unthinkable to allow the return of the people urgently evacuated from this zone at the time of theaccident.
As in the release phase, the dose kinetics due to radioactive deposition were not constant over time. Immediately
after formation, during the night of March 15-16, 2011, the surface deposits were composed primarily of short-lived
radionuclides (131I, 132Te/132I); after a month, due to rapid decay of these radionuclides, the total activity of theresidual surface deposits represented just 15% of the initial activity, and the ambient dose rate measured in thesame areas over the same period had decreased accordingly (see 6.2.3.4). The maps in Figure 8-8 therefore
represent the cumulative doses for the first month (from March 15 to April 15, 2011) of external exposure to thedeposits, and the cumulative doses for the subsequent 12 months (from April 15, 2011 to April 15, 2012). IRSN
obtained these by interpreting the iso-dose rate map for April 24, 2011, as published by MEXT, assuming an isotopic
composition of the deposits, deduced from the source term estimated by IRSN. The doses were calculated for a
person assumed to spend half of his time outdoors (12 hrs/day) and the other half in a building with a shielding factorof 0.3.

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The estimates made show that the doses potentially received during the first month from external exposure to
the deposits represent approximately one-third of the cumulative doses over the subsequent 12 months. These
results confirm the importance of taking action to protect the population as promptly as possible, by removing
people from the most contaminated areas because they could be exposed to significant doses in the initial months
following the formation of deposits. As an illustration, the area (excluding the 20 km exclusion zone) where a dose
exceeding 10 mSv could have been received between March 15 and April 15, 2011 is represented on the map in Figure
8-9, deduced from the left-hand map in Figure 8-8; in this area, the doses could have been higher than 25 mSv,
without counting doses due to exposure to the radioactive plume between March 12 and 25 (cf. 8.3.2) or doses due topossible consumption of contaminated foodstuffs (cf. 8.3.4). This area includes part of the municipalities of
Minamisoma (south-west), Iitate, Namie, and Katsurao (east).

External dose estimate during first month(March 15, 2011 to April 15, 2011)

LegendDoses month 1 (mSv)

Isolines based on dose rate measurements obtained by
MEXT between March 16 and April 24.

External dose estimate during months 2-13
(April 15, 2011 to April 15, 2012)

LegendDoses months 2-13 (mSv)

Isolines based on dose rate measurements obtained by
MEXT between March 16 and April 24.

Figure 8-8 – Maps representing the doses from external exposure to radioactive deposits likely to havebeen received by the end of the first month (left-hand map) and during months 2-13 following theformation of the deposits in the Fukushima prefecture (IRSN estimate deduced from the MEXT iso-dose
rate map for April 24, 2011).

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LegendDoses month 1 (mSv)

Figure 8-9 – Area (in yellow) where the doses from external exposure to radioactive deposits are likely tohave been higher than 10 mSv at the end of the first month following the formation of the deposits in the
Fukushima prefecture (based on the left-hand map in Figure 8-8). The circular area shaded redcorresponds to the 20 km zone urgently evacuated at the time of the accident.
Likewise, the area (excluding the 20 km exclusion zone) where a dose exceeding 10 mSv could have been received
between April 15, 2011 and April 15, 2012 is represented on the map in Figure 8-9, deduced from the left-hand map
in Figure 8-8. This area is larger than the previous one and corresponds approximately to the planned displacementzone set up on April 22 by the Japanese authorities (except for a small sector in the municipality of Date), which
includes the municipalities of Iitate, Namie, and Katsurao as a whole (in addition to the parts of the latter two
municipalities that had already been urgently evacuated on March 12) as well as part of the municipalities of
Minamisoma and Kawamata (district of Yamagiya). In the most contaminated parts of this zone, the doses that could
have been received during this period if evacuation had not taken place are estimated at more than 75 mSv, inaddition to the doses already received during the first month following the formation of deposits or via otherexposure pathways (inhalation, ingestion of contaminated foodstuffs, inadvertent ingestion).

LegendDoses months 2-13 (mSv)

Figure 8-10 – Area (in green) where the doses from external exposure to radioactive deposits are
estimated to be higher than 10 mSv between April 15, 2011 and April 15, 2012 in the Fukushima
prefecture (based on the left-hand map in Figure 8-8). The circular area shaded red corresponds to the 20
km zone urgently evacuated at the time of the accident.

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As before, these dose estimates are indicative and do not take into account any specific radiologicalcharacteristics that might lead, locally, to dose levels being significantly adjusted up or down.

8.3.4. RISKS ASSOCIATED WITH INTERNAL EXPOSURE FROM INGESTION OF
CONTAMINATED FOODSTUFFSIRSN does not yet have sufficient data to make a reliable estimate of the doses received in Japan from ingestion ofcontaminated foodstuffs, especially during the weeks following the accident, for people living in the areas thatreceived the highest levels of deposits on the ground. Estimating these doses does in fact depend not only on thelevel of contamination of foodstuffs produced in these areas, which is partly known from published measurements(see 6.3), but also on having information about the food intake of the people concerned and their degree ofcompliance with the restrictions imposed by the Japanese authorities.
In order to determine the level of risk to which part of the Japanese population could have been exposed, without
giving an opinion on the actual risk in Japan, IRSN calculated the doses received in a scenario involving ingestion offoodstuffs contaminated at levels observed in certain areas of Japan. Immediately after dispersion of the radioactive
releases, two foodstuff categories were particularly sensitive to the radioactive fallout and therefore posed asignificant risk to consumers in Japan:-

leafy vegetables, such as spinach, which were found to be contaminated with several tens of thousand
Bq/kg of iodine-131, caesium-134 and caesium-137, a hundred kilometers from the Fukushima Dai-ichi
power plant. Theoretically much higher contamination levels, over a million Bq/kg, could have beenreached in the most contaminated areas outside the 20 km exclusion zone but there is no evidence of thisfrom the measurements carried out in Japan, perhaps because the accident happened at the end of thewinter, before any crops were ready for harvesting in these areas;-

cow’s milk, which was found to be contaminated with several thousand Bq/l of iodine-131 and several
hundred Bq/l of caesium-134 and caesium-137 for about a week, especially in Iitate and Kawamata.
Theoretically much higher contamination levels, in the region of 100,000 Bq/l for each of these three
radionuclides, could have been reached in the most contaminated areas of Iitate during the same period (cf.
6.3.2.2), but once again there is no evidence of this from the measurements carried out in Japan, probably
because the accident happened at the end of the winter, when the livestock were being fed fodder that had
been harvested the previous year and was therefore only relatively lightly contaminated (except possibly if
it had been kept in the open air).

Calculations were performed based on the measurement data available for milk and some vegetables (Tables 8-II and
8-III), assuming that these had been consumed by children aged between 1 and 5. It should be noted that the bulk of
the milk and vegetables for which radioactivity levels are shown in the tables below were not sold on the market.

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Table 8-II – Iodine and cesium concentrations measured in milk sampled (but not sold on the market) at theend of March 2011 in the prefectures of Fukushima and Ibaraki

Prefecture

Fukushima

Fukushima

Fukushima

Ibaraki

Ibaraki

Fukushima

Fukushima

Ibaraki

Fukushima

Fukushima

Fukushima

Ibaraki

Fukushima

Fukushima

IbarakiSampling

Measurement

date

date

03/20/11

03/20/11

5,300

9

11

03/19/11

03/20/11

5,200

210

210

03/22/11

03/23/11

2,600

24

30

03/22/11

1,700

64

03/22/11

1,700

15

03/17/11

03/19/11

1,510

ND

ND

Kunimi-machi

03/19/11

03/19/11

1,400

13

23

Kawachi-

03/19/11 –machi

03/21/11

03/22/11

1,300

03/20/11

03/20/11

1,200

9.5

8.7

03/16/11

03/18/11

1,190

ND

18.4

Iitate-mura

03/22/11

03/23/11

1,000

25

28

Kawachi-

03/19/11 –machi

03/21/11

03/22/11

1,000

Iwaki-shi

03/19/11

03/19/11

980

ND

6.6

03/18/11

03/19/11

932

ND

ND

03/22/11

900

SectorKawamatamachi
Iitate-mura
Kawamatamachi
Kawachi-

03/19/11 –machi

03/21/11

Mito-shi

Kawamatamachi

Kawamatamachi
Kawamatamachi

Kawamatamachi

03/19/11 –03/21/11

Kawachi-

03/19/11 –machi

03/21/11

I-131 (Bq/l) Cs-134 (Bq/l)

Cs-137(Bq/l)

54

38

68

ND: not determined

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Table 8-III – Iodine and cesium concentrations measured in vegetables sampled (but not sold on themarket) at the end of March 2011 in the prefectures of Fukushima and Ibaraki
Sampling

Measurement

I-131

Cs-134

Cs-137date

date(Bq/kg)(Bq/kg)(Bq/kg)Spinach03/18/11

03/20/11

54,100

1,931

Hitachi-shi

Spinach03/18/11

03/20/11

25,200

1,105

Kitaibaraki-shi

Spinach03/18/11

03/20/11

24,000690

Shinobuhuyuna

03/21/11

03/22/11

22,00014,000Spinach03/18/11

03/20/11

19,2001,040

Spinach03/21/11

03/22/11

19,00020,000Spinach03/18/11

03/20/11

17,800908

Prefecture

SectorVegetable

Ibaraki

Hitachi-shi

Ibaraki
Ibaraki

Fukushima

Ibaraki

Fukushima

IbarakiKawamatamachi
Hitachioomiyashi
Tamura-shi
Hitachioomiyashi

Fukushima

Iitate-mura

Broccoli

03/21/11

03/22/11

17,0007,000

IbarakiNaka-shiSpinach03/18/11

03/20/11

16,100911

Fukushima

Hirata-mura

Spinach03/21/11

03/22/11

16,0001,000

IbarakiTakahagi-shi

Spinach03/18/11

03/19/11

15,020524

Fukushima

Motomiya-shi

Kukitachina

03/21/11

03/22/11

15,00041,00014,00020,000

6,900

1,100

41,000In the absence of any sufficiently detailed information about these children’s diets, it was assumed that theirconsumption of milk and vegetables was similar to that of young children in France, on average. The calculations
then show that, for a given level of contamination of these foodstuffs, a 1-year-old child receives the highest doses.
The average effective dose calculated for a 1-year-old child who has consumed the contaminated milk shown in
Table 8-II is 0.07 mSv, mainly due to iodine-131. The maximum value obtained for the most contaminated milk is
0.22 mSv/day. The average effective dose for the vegetables is 0.14 mSv, with a maximum of 0.35 mSv. Using thesame assumptions, the equivalent doses to the thyroid would be 1.5 and 4.5 mSv/d respectively for milk, and 2.6 and6.9 mSv/d for the leafy vegetables in Table 8-III. However, it cannot be ruled out that concentrations 10 to 100 times
higher than the average values were reached in the most contaminated areas. The associated doses would then haveto be multiplied accordingly, i.e. committed effective doses possibly exceeding about 10 mSv per day.

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It should be noted that these dose estimates do not take account of the other radionuclides likely to be present. The
simulation shows that the estimated doses might be increased by about 10-30% if all the radionuclides present in thereleases were to be taken into consideration.
The following comments can be made concerning these estimates: the calculations were carried out for daily foodconsumption at the end of March, i.e. when food contamination was highest. They cannot be extrapolated beyond
this period. In fact, given the rapid decrease in the concentrations found in these foodstuffs between March 20 and
April 20 (by a factor of 100 to 1,000) due to the combined effect of radioactive decay (for iodine) and dilution of theinitial level of leaf deposition as a result of biomass growth (for both iodine and cesium), the daily committed doses
from the end of March onwards would have been much lower. Furthermore, the calculations do not take into accountany loss of activity between sampling and consumption of the foodstuff, particularly because of the way in which it
was prepared. Lastly, the food contamination checks and consumption bans implemented by the Japanese authorities
most likely contributed to reducing the doses actually received.
Ingestion of soil
The dose due to inadvertent ingestion of contaminated soil can be estimated from the specific activity data given in
Table 6-III. Assuming that a 1-year-old child ingested 0.1 g48 of soil on March 31, 2011, the effective dose received is0.002 mSv. Assuming the date of ingestion was March 15, when deposition was thought to be at its highest level,
gives a dose of 0.007 mSv. The equivalent dose to the thyroid is 0.03 mSv and 0.13 mSv respectively for ingestion on
March 31 and March 15, 2011.

8.4. RESULTS OF CHECKS CARRIED OUT BY IRSN ON FRENCH NATIONALS
Within 48 hours of the accident, IRSN began receiving enquiries from occupational health physicians responsible formonitoring French employees returning from Japan, aircrew members, and journalists who went to Japan to cover
the events, and also from French expatriates in Japan planning to return to France either temporarily or
permanently. All of these people contacted IRSN to find out whether or not they had been contaminated byradioactive elements during their stay in Japan.
In response to the concerns of these French nationals, IRSN offered to perform whole-body countings at its Le Vésinet
site near Paris to detect the presence of any radioelements that might have been incorporated and to quantify theiractivity. The data obtained could then be used to calculate the internal dose received by the individual concerned.
Each person underwent an in vivo γ-ray spectrometry including 2 measurements: a whole-body counting (duration: 20
minutes) and a thyroid counting (duration: 15 minutes).
By the end of 2011, IRSN had carried out 280 in vivo γ-ray spectrometries on 268 people: 95 journalists, 62 company
employees working in Japan, 36 aircrew members and 75 private individuals (Figure 8-11). The number of in vivo γray spectrometries is higher than the number of people measured, as some were measured several times, either
because they went to Japan a few times or because they were employees who were checked before their departureand upon their return.

48

This quantity of soil is regarded as a guideline for dose assessment. For information, it is the value recommended in the Guide
méthodologique – Gestion des sites potentiellement pollués par des substances radioactive (Methodological guide for managementof industrial sites potentially contaminated by radioactive substances), French Ministry of Ecology, Sustainable Development,
Transport and Housing – IRSN – ASN, December 2011.
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28%

36%

13%
23%

Journalists

Company employees

Aircrew members

Private individuals

Figure 8-11 – Breakdown of people undergoing in vivo γ-ray spectrometries between March 14, 2011 andDecember 19, 2011

Table 8-IV shows that of the 84 in vivo γ-ray spectrometries revealing the presence of radioactivity in the person
measured (i.e. 30% positive results), none concerns Air France aircrew members. The airline actually very quickly
decided to ground its aircraft and personnel in Seoul, with Tokyo’s Narita Airport temporarily serving as a stopover todisembark and embark passengers. Following this decision by Air France, the physician responsible for monitoring
aircrew limited his requests for in vivo γ-ray spectrometries to those employees who were in a particularlyheightened state of anxiety.

Figure 8-IV – Breakdown of in vivo γ-ray spectrometries performed and positive in vivo γ-ray
spectrometries obtained between March 14, 2011 and December 19, 2011, by category of people
measured
No. of people measured

No. of in vivo γ-ray
spectrometries
performed

Journalists

95

99

Company employees

6270

Flight personnel

36

36

Private individuals

75

75

Total

268

280

No. of positive in vivo γray spectrometries62(62.6%)
4(5.7%)
0
(0%)
18
(24%)
84
(30%)

Figure 8-12 indicates that 77% of the in vivo γ-ray spectrometries on journalists were performed during the first three
weeks following the accident. As regards private individuals (expatriates and students), the measurements were
essentially concentrated in two waves, with one-third carried out during the first two weeks and two-thirds during
the July-September 2011 vacation period. As for company employees, the timing of the measurements correspondedwith their business trips to Japan.

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Nombre d'examens
No. exams
30
25
20
15
10
5
1s
tw
e
d ek
we
ek
3r
d
w
4t eekhw
5t eek
h
we
e
6t
h k
w
7t eekhw
8t eekhweek
9th
10 weekthw
11 eek
th
we
ek
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ne
Ju
ly
A
ug
us
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t
pt
em
be
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to
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ve
m
b
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ec er
em
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r

0
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e
ainain e in e n e n e e e
in n esemsemsemaemaimaimers se se aemaimain ain eain e in e i n te1è2èm èmeème ms se sem em ma Ju ille oû t r e e
3 4 5è eèmeème mes se
Ju A emb tobrmbr e bre
6 7 8è ème me mt
c e
9 10è 1è em
1
Se p O Nov Déce

Employees
Salariés

Privateindividuals
Particuliers

Journalists
Journalistes
Privateindividuals
Particuliers
Salariés
Employees

Journalists
Journalistes

Figure 8-12 – Trends in the number of in vivo γ-ray spectrometries performed on journalists, private
individuals and company employees between March 11, 2011 and December 19, 2011

The effective dose and the equivalent dose to the thyroid were calculated for each person who tested positive forthe presence of radioactive elements. Iodine-131 was the isotope most frequently detected, though iodine-132 andtellurium-132, and much more rarely caesium-137, were detected in a few people.
Figure 8-13 and Figure 8-14 respectively show the distribution of effective doses and equivalent doses to the thyroid
calculated for people who tested positive in their in vivo γ-ray spectrometry.

Nombred'examens
No. exams
60

50

40

30

20
10
0

ntif
10
sécaga
0
020
0,0
ne n
v
i
e
,03
t
<0,
5-<
40
m
a
0
a
0
g
- <0
150, 0
5
0
0,
,
2
NEex
0
0
5-<
0,

0,0

3

45
0,0

0
,05
06 0
-<0
0 70
0
< 0,
0
<0,
,08
550
5
,09
,
6
-<0
0
0
5
,
7
-<0
0
0
5
,
8
0
0,0

Employees
Salariés

Privateindividuals
Particuliers

Journalists
Journalistes
Privateindividuals
Particuliers
Employees
Salariés

Journalists
Journalistes

Figure 8-13 – Distribution of the effective doses received by the different categories of people measured(in mSv)

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60
No. exams
Nombre d'examens

50

40
30
20
10
0
anf
eégsac ti
v
i
n
t
egean

am
ExN

0,1

5
0,1
0-<

0
5-<
0,2

,30

0
0-<
0,4

,45

0
0,6
5
5-<
0,7
0
0,5
0-<
0,9
0,7
5-<
0,8

Employees
Salariés

PrivateindivsParticuliers

1
0-<
1,1

,15

Journalists
Journalistes
Privateindividuals
Particuliers
Employees
Salariés

0
1,3
5-<
1,2

Journalists
Journalistes

Figure 8-14 – Distribution of the equivalent doses to the thyroid received by the different categories ofpeople measured (in mSv)
For the most exposed person, the effective dose is less than 0.1 mSv, and the equivalent dose to the thyroid lessthan 1.4 mSv. For the purposes of comparison, the regulatory dose limit for the public is an effective dose of 1
mSv/year (compared with the calculated maximum dose of 0.1 mSv for the French nationals measured) and theequivalent dose to the thyroid that triggers the process of administering stable iodine is 50 mSv (compared with thecalculated maximum dose of 1.4 mSv for the French nationals measured). At these levels of exposure, the Frenchnationals measured have no cause for concern in terms of health effects.
Figure 8-15 shows the geographical distribution of private individuals staying in Japan, in the cities of Sendai, Iwaki,
Koriyama, or Fukushima, during the most significant release events, i.e. between March 15 and 16, or in Tokyo(March 15 and 16 and between the afternoon of March 20 and March 23), who had a positive result in the in vivo γ-ray
spectrometry performed upon their return to France.
Sendaï
Sendai
1616personnes
people7 examens
positifs
7 positive scans
Doses
Thyroïde
: 0,01-0,18
Thyroiddoses: 0.01-0.18
mSvmSv
Fukushima
Sendai Ville
2 16personnes
people2 examens
positifs
7 positive scans
Doses
Thyroïde
0,02-0,05
mSv
Thyroiddoses: :0.01-0.18
mSv
Koriyama
Koriyama
4 personnes
4 people
4 examens
positifs
4 positive scans
Doses
Thyroïde
0,03-0,25
mSv
Thyroiddoses: :0.03-0.25
mSv
Iwaki
Koriyama
1 personne
4 people1 4examen
positive positif
scans: 1,38 mSv
Dose Thyroïde
Thyroiddoses: 0.03-0.25
mSv
Tokyo
Koriyama
104 personnes
people4 4examens
positifs
positive scans
Doses
Thyroïde
: 0,01-0,07
Thyroiddoses: 0.03-0.25
mSvmSv

Figure 8-15 – Geographical distribution of private individuals staying in Sendai, Fukushima, Koriyama, or
Iwaki during the releases on March 15-16 or in Tokyo (releases on March 15-16 and March 20-23, 2011),
whose in vivo γ-ray spectrometry produced a positive result

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Figure 8-16 shows the geographical distribution of journalists present in Tokyo, Soma, or Sendai during the mostsignificant release event, i.e. between March 15 and 16, who had a positive result in the in vivo γ-ray spectrometry
performed a few days later upon their return to France.

SendaiSendaï
0.01 mSv < Thyroid doses < 0.13 mSv(9 people)
0,01 mSv < DoseThyroïde < 0,13 mSv(9 personnes)

Soma
Soma
0.20 mSv < Thyroid doses < 0.53 mSv
0,20 mSv < Dose(3 Thyroïde
people) < 0,53 mSv(3 personnes)Tokyo
andetsurroundingTokyo
ses environsarea
0.02 mSv < Thyroid doses < 0.08 mSv
0,02 mSv < Dose
(20Thyroïde
people) < 0,08 mSv(20 personnes)

0.13 mSv < Thyroid doses < 0.36 mSv
0,13 mSv < Dose Thyroïde < 0,36 mSv(9 people)(9 personnes)

Figure 8-16 – Geographical distribution of journalists present in Sendai, Soma, or Tokyo during thereleases on March 15-16, whose in vivo γ-ray spectrometry produced a positive result

These results show that the contamination of people at the time of the releases and in the days that followed
essentially depended on their behavior (especially the time they spent outdoors) and their precise location while
they were in the contaminated areas, the influence of local weather conditions being the dominant factor. These
results cannot be generalized to everyone staying in a given city, but do give an indication of the possible dose range
to which people may have been exposed on those dates and in those locations.

8.5. HEALTH EFFECTS
WORKERSAND

MEDICAL

MONITORINGOFEXPOSED

8.5.1. HEALTH EFFECTS
According to the information provided by the Japanese authorities, no health effect attributable to exposure toionizing radiation has been observed to date in the workers involved in operations conducted at the Fukushima
nuclear power plant. However, according to statements made by physicians at the National Institute of Radiological
Sciences (NIRS), in view of the nature of the operations remaining to be carried out, the appearance in the coming
months of effects on workers’ health directly related to radiation exposure cannot be ruled out.

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To date, the deaths of six workers have been recorded. Apparently, none of these deaths could be attributed to
exposure to ionizing radiation. According to the Japanese authorities:-

two workers died on March 11, 2011 as a direct result of the tsunami and the earthquake,-

two workers died of heart failure, one on May 14, 2011 and the other on January 9, 2012,-

one worker died of acute leukaemia in August 2011,-

one worker died of septic shock on October 6, 2011.

Moreover, hyperthermia (increased body temperature) has been observed in 43 workers, probably due to insufficientcooling of their work clothing.

8.5.2. MEDICAL MONITORING
A database to contain all the information concerning the monitoring of workers’ health is currently being set up.
Every worker, including those no longer involved in the operations underway at Fukushima Dai-ichi, will receive abasic medical check-up including tests of their eyesight, hearing, lungs, cardiovascular system, and digestive system,
as well as biological tests and an evaluation of the person’s psychological and psychiatric condition.
In addition, workers who have received a dose exceeding 50 mSv will receive special monitoring aimed at detecting
the formation of cataracts, and those whose dose exceeds 100 mSv will undergo additional tests to monitor the onsetof thyroid disorders and certain types of cancer (lung, stomach, and colon).
Based on the observations recorded, the medical monitoring could be reviewed in three years’ time.

8.6. EPIDEMIOLOGICAL MONITORING OF EXPOSED POPULATIONS IN
JAPAN
8.6.1. PRINCIPLE OF THE STUDIES CONDUCTED
In late June 2011, the Japanese health authorities devised and set up epidemiological studies to evaluate the healthof individuals exposed to the radioactive releases and to monitor changes in their state of health over time.
Depending on the group concerned, these studies are based on a questionnaire, to be supplemented in certain casesby medical examinations. The results of these epidemiological studies will provide information concerning the baserate of occurrence of certain pathologies in the Japanese population (cancer, leukaemia, psychological disorders,
thyroid problems, liver or kidney disease, diabetes, etc.) and allow an evaluation of any health effects on the
population due to exposure to radioactive fallout. The planned duration of these studies is 30 years, and they are
conducted under the leadership of Fukushima Medical University in collaboration with other Japanese medical
centers.
These studies consist of the following tasks:-

Conducting a basic survey of all persons present in the Fukushima prefecture during the release phase. The
aims of this survey are to estimate the external dose received by the individuals exposed, to gather
information concerning the administration of stable iodine tablets and the consumption of food products anddrinking water, and to identify those people for whom long-term medical monitoring might be necessary.
This survey is to be carried out on 2,057,053 people.

-

Thyroid screening of all children under the age of 18 who were present in the Fukushima prefecture during
the release phase. The main aim of this study is to reveal any increase in the occurrence of thyroid cancer,
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approximately 360,000 children born before March 1, 2012.
-

Monitoring any genetic or congenital abnormalities that might appear in children born of women who
declared their pregnancy between August 1, 2010 and July 31, 2011. This study will include approximately
20,000 women and will supplement an earlier study launched in 2010 in a dozen regions of Japan by theJapanese Ministry of the Environment, concerning approximately 100,000 pregnant women. The aim of thelatter study (JECS: Japan Environment and Children’s Study) is to evaluate the consequences of exposure tochemical and physical environmental toxins in children born of those mothers. From the time it was
implemented, the JECS study included places near the Fukushima Dai-ichi nuclear power plant (Fukushima,
Minami Souma, Namie). In August 2011, the Japanese authorities decided to include in this study a group of
6,900 women from some of the towns and cities most exposed to radioactive fallout (Kawamata, Koori,
Date, Kunimi). All the children born of mothers recruited into the JECS study will be monitored until the ageof 12.

-

Special medical check-ups for people who were evacuated from the areas most exposed to radioactive
fallout. This study will concern approximately 210,000 people and will provide information concerning
lifestyle (smoking, alcohol consumption), psychological condition based on a questionnaire, the basic rate ofoccurrence of pathologies such as cancer, leukaemia, diabetes, or liver and kidney disorders, and any
radiological examinations carried out that could affect the external dose received (particularly CT scans).
Moreover, special additional monitoring over a ten-year period of psychological disorders in approximately
30,000 people from the prefectures of Fukushima, Iwate, and Miyagi will be implemented by the Japanese
Ministry of Health.

8.6.2. PROGRESS AND INITIAL RESULTS
Dosimetric questionnaire
Since late June 2011, 29,097 questionnaires have been sent to people who were in the towns of Namie, Iitate, andKawamata at the time of the radioactive releases. As at January 20, 2012, the response rate was 50.2%. The lowest
response rate concerned people aged between 21 and 30 (36.5% of questionnaires filled in), and the highest was frompeople in the 61-70 age group (63.1% of questionnaires filled in).
0-10
0-10ans
yrs

21-30ans
yrs
21-30
41-50ans
yrs
41-50
61-70ans
yrs
61-70
81ans
yrs
>>81
0

1000

2000

Questionnaires
completed
Questionnaires complétés

3000

4000

5000

Questionnaires
sent
Questionnaires envoyés

Figure 8-17 – Summary (as at January 20, 2012) of responses to questionnaires sent to people who were in
Namie, Iitate, or Kawamata at the time of the releases

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Based on the completed questionnaires, the external doses received were calculated, using special softwaredeveloped by the NIRS, for 1,589 people from Namie, Iitate, or Kawamata: for 62.1% of them, the external dose
calculated was below 1 mSv, and the maximum dose calculated was 14.5 mSv for one person.
1200
1000

987

800
600
400
200

366
129
37

17

22

8

3

2

3

1

2

0

0

1

01
m
1- Sv
2
m
2- Sv
3
m
3- Sv
4
m
4- Sv
5
m
5- Sv
6
m
6- Sv
7
m
7- Sv
8
m
8- Sv
9
m
9- Sv
10
10 mS
-1
v
1
11 mS
-1 v
2
12 mS
-1 v
3
13 mS
-1 v
4
14 mS
-1 v
5
m
Sv

0

Figure 8-18 – Initial results of the calculations of external doses received by people who were in the
Fukushima prefecture at the time of the releases

From the end of August 2011, questionnaires were sent out more widely, to all 2,057,053 people who were in the
Fukushima prefecture at the time of the radioactive releases. As at January 20, 2012, the overall response rate was
20.8%.

Iwaki 20.3%

Namie, Iitate,
Kawamata

Soso 18.6%

50.2%

Aistu 35.3%
North 23.5%

Minami 12.6%
Center 18.6%
Aitsu 14.1%

South 16.0%

Figure 8-19 – Summary (as at January 20, 2012) of responses to questionnaires sent to people who were in
the Fukushima prefecture at the time of the releases

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Evaluation of thyroid disorders in children exposed to the radioactive releases
Between October and December 2011, 19,715 children who were in Namie, Iitate, or Kawamata at the time of theradioactive releases were invited for thyroid screening: 4,908 children were tested at Fukushima Medical University,and 14,807 at other medical centers in the Fukushima prefecture.

16000
14000
12000
10000
8000
6000
4000
2000
0
Fukushima University

Other medical centers

Screens planned

Screens done

Figure 8-20 – Progress of thyroid screening of children at all of the medical centers involved

As at December 31, 2011, 14,442 children had undergone initial thyroid screening, consisting essentially of an
ultrasound examination of the thyroid, possibly supplemented by biological and histological tests if any pathologicalabnormality was detected. Of the children screened, 23.7% were aged from 0 to 5 years, 27.3% from 6 to 10 years,
29.6% from 11 to 15 years, and 19.4% were older than 16.

6000
5000
4000
3000
2000
1000
0
0-5 ans

6-10 ans

11-15 ans

> 16 ans

Figure 8-21 – Breakdown by age group of children who had undergone thyroid screening at Fukushima
Medical University as at December 31, 2011

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Of the 3,765 children screened by Fukushima Medical University, the thyroid ultrasound produced normal results for
69.6%. At least one fluid-filled cyst considered as subnormal (diameter less than 20 mm) was detected in 28.8% of thechildren, while 1.5% had at least one nodule, again considered as subnormal (diameter less than 5 mm). At least one
nodule with a diameter greater than 5 mm was found in 0.7% of the children screened, but without any additional
tests being necessary in the opinion of the physicians. Finally, no fluid-filled cyst larger than 20 mm in diameter was
found.

Pas de kyste liquidien> 20 mm détecté

Kyste liquidien < 20 mm
28,8 %

Nodule > 5 mm
0,7 %Aucune anomalie détectée69,6 %

Nodule < 5 mm
1,5 %Figure 8-22 – Observations made on 3,765 children who have had a thyroid ultrasoundBetween January and March 2012, 27,467 children who were in Date, Tamura, Hirono, Naraha, Tomioka, Kawauchi,
Okuma, Futaba, or Katsurao at the time of the radioactive releases were invited for thyroid screening. The remainderof the children involved in the study will receive invitations sequentially between April 2012 and March 2014.
Starting in April 2014, follow-up thyroid screening will be performed on the 360,000 children concerned at a rate ofonce every two years until age 20, and then every five years above the age of 20.
No information is currently available concerning the progress of the studies planned for pregnant women andevacuees.

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9. VERY LONG-RANGE IMPACT
Although located a long way from the site of the accident, France and its overseas departments, regions andcollectivities in the northern hemisphere were nonetheless affected by masses of slightly contaminated air. Verylong-range calculations were used to predict the arrival dates of these contaminated air masses and the expectedlevels of activity. IRSN implemented an enhanced radioactivity monitoring plan in March 2011 covering the whole ofFrance and its overseas territories. This involved stepping up vigilance with IRSN’s traditional monitoring equipment,
combined with deployment of additional resources to monitor ambient radioactivity and undertake environmental
sampling.

9.1. IMPACT IN FRANCE AND IN FRENCH OVERSEAS DEPARTMENTS,
REGIONS AND COLLECTIVITIESThe Institute has published a report49, which is available on its website, providing a scientific analysis of the resultsof these enhanced monitoring efforts. The report collates and interprets more than 5,700 measurement results
obtained by IRSN on some 1,400 samples and approximately 3,000 results submitted by nuclear operators.
The key points to note are as follows:-in France, the various measurement results relating to air, rainwater and land-based products revealed thatno traces of radionuclides attributable to the Fukushima accident were detected prior to March 24, 2011.
Monitoring detected trace levels of the main radionuclides released into the atmosphere during the accident(iodine-131, cesium-134 and cesium-137, and smaller quantities of tellurium-132) and enabled changes to be
tracked until May 2011. For example, the maximum iodine-131 levels detected were of the order of a few
millibecquerels per cubic meter of air, approximately 10 becquerels per kilogram of plant matter, and a few
becquerels per liter in rainwater or milk. At no time did these concentrations pose any environmental or
health risk;-

the various observations revealed that all French regions were affected to the same extent, albeit withsome geographic and chronological fluctuations due to the movements of the air masses. These levels are
consistent with the forecasts based on modeling by IRSN in association with the French meteorologicalinstitute, Météo-France. These concentrations were between 500 and more than 1,000 times lower thanthose measured in France in early May 1986, following the Chernobyl accident.

-

the maximum exposures by inhalation and by ingestion of iodine-131 were calculated, based on significant
iodine measurements obtained over the period. The maximum dose by inhalation was 2 microsieverts (µSv)
for 1-year-old infants, and 0.03 µSv for adults. The doses by ingestion were 43 µSv and 0.17 µSv
respectively. These estimated doses are very low and confirm that at no time did the concentrations ofradionuclides of artificial origin (iodine-131, cesium-134, and cesium-137) measured in the various
compartments of the environment in France and its overseas departments, regions and collectivities pose anenvironmental or health risk.

49

Report: Analyse de l’impact de l’accident de Fukushima en France (métropole et DROM-COM) à partir des résultats de lasurveillance renforcée de la radioactivité dans l’environnement (Analysis of the impact of the Fukushima accident in France and in
French overseas departments, regions and collectivities, based on the results of enhanced environmental radioactivity monitoring)
http://www.irsn.fr/FR/expertise/rapports_expertise/Documents/environnement/IRSN_Analyse-impact-FukushimaFrance_012012.PDF (in French with an English abstract)
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It should be noted that six months after the accident, the ambient level of cesium-137 (less than 0.4 µBq/m3), theonly artificial radionuclide still measurable, was only double the pre-accident background level.

9.2. ATMOSPHERIC CONTAMINATION IN EUROPE
Simulations were carried out on a global scale (Figure 9-1) using Météo France data and show that the plume beganpassing over the North American continent on March 16. French overseas territories (St Pierre and Miquelon) andnorthern Scandinavia were affected from March 19 onwards, the West Indies from March 22, and other European
countries from March 23.

a)

b)

c)

Figure 9-1 - Dispersion of the plume on a global scale on three separate dates: 03/16 (a), 03/19 (b), and03/22 (c)In Europe, the measurements obtained by the national airborne radionuclide monitoring networks were analyzed50
and compared with the predictions made by IRSN’s calculation code LdX.

50

O. Masson et al. (2011) Environ. Sci. Technol., 45, pp. 7670-7677
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9.2.1. SCOPE OF THE ANALYSIS
As indicated in Chapter 6, radioactive emissions into the atmosphere began on March 12. Isotopes of xenon, chiefly
Xe-133 (133Xe; T1/2 = 5.2 days), were the main contributors to the source term (approximately 6.1018 becquerels).
Only five sampling stations in Europe had the capability of quantifying airborne levels of 133Xe. Most of these areoperated under the auspices of the comprehensive nuclear-test ban treaty organization (CTBTO) and the results were
not available outside this organization. Of the various radionuclides released in large quantities and of major
importance for assessing the long-range health impact, iodine-131 (131I; T1/2 = 8.0 days), cesium-134 (134Cs; T1/2 = 2.1
years), and cesium-137 (137Cs; T1/2 = 30.1 years) were easily detected. Other short-lived radionuclides, such as
tellurium-132 (132Te; T1/2 = 3.2 days) and iodine-132 (132I; T1/2 = 2.3 hours), were also measured in trace amounts. All
were carried across the Pacific towards the North American continent and reached Europe, despite dispersion anddeposition occurring along the route of the contaminated air masses.
Most European countries have developed airborne radionuclide monitoring programs since the 1950s. More than 150
sampling points are distributed throughout Europe and operate continuously as part of the networks set up to detect
trace levels of airborne radionuclides. These stations are equipped with high-volume air samplers for specificradionuclides and some also have adsorbers for collecting gaseous iodine. The sampling periods were reduced toprovide an overview of the daily variations in 131I, particularly in its particulate form and – to a lesser extent – in its
gaseous form. Most of the data was passed on by the participating laboratories to the “Ring of Five (Ro5)” network,
which is an informal group set up in 1983 with the aim of ensuring rapid data exchange in the event of any increasein the concentration of artificial radionuclides likely to be found in trace amounts in the atmosphere (typicallybetween 1 and 10 micro-becquerels per cubic meter of air). In addition to “measurement laboratories”, otherpartners were involved, including national meteorological services, university staff and International Atomic Energy
Agency (IAEA) personnel.

9.2.2. AIR MONITORING STATIONSThe sampling stations located in Europe are equipped with various types of aerosol collectors that operate atdifferent flow rates. In every case, the particulate fraction is collected on filters, made from fiber glass or
polypropylene fiber. Traps, usually filled with activated carbon, were also used to sample gaseous radioiodine. After
sampling, the activity levels were measured by gamma spectrometry (usually on high-purity germanium detectors).
During the period studied (from March 20 to April 13), isotopes of cesium and iodine were detected above theirdetection thresholds. A correction for summation effects was made to the determination of 134Cs in order to obtainthe true 134Cs/137Cs ratio. In the aftermath of the Chernobyl disaster, it was found that there was considerable
variation in this ratio, probably because this correction had not commonly been made. The midpoint of the sampling
period was chosen as the reference time for all the stations. For short-lived 131I, a correction for decay was made inaccordance with this reference. For the purposes of quality control, the level of 7Be of natural origin was used asinternal standard. The range in natural variation of the specific activity of 7Be is well known for each station, making
it possible to validate the sampling and measurement procedures.

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9.2.3. RESULTS AND DISCUSSION
After the initial releases on March 12, contaminated air masses arrived on the North American continent on March
1751. As regards Europe, 131I was first detected between March 19 and 20 in Iceland, between March 19 and 21 innorthern Scandinavia, and between March 23 and 24 for most other European countries. Rising levels were generally
recorded over the next 10 to 12 days, up to March 28 or 30, for western and central Europe, and up to April 3 for
Belarus (Figure 9-2). A second peak of a similar amplitude was also observed between April 3 and 5. The falling
values in between these peaks coincided with the occurrence of an event marked by precipitation over most ofEurope and may also be explained by the air masses being scavenged in transit, dry deposition, the decrease in theatmospheric source term, and the half-life of 131I. Throughout the measurement period, the peak values ranged fromless than 1 mBq/m3 up to 6 mBq/m3 for the particulate fraction of 131I, and up to 11 mBq/m3 for the gaseous fraction.
These values are three to four orders of magnitude lower than the activity levels recorded in western Europe after
the Chernobyl accident, in April 1986. On a European scale, the average values for 132Te and 132I were 0.032 and0.043 mBq/m3 respectively, with a maximum of 0.12 mBq/m3. For a given location, the 132Te and 132I levels wereapproximately in equilibrium. After the second week in April, they were no longer quantifiable above detection
thresholds.
7

Orsay, FR
Cadarache, FR
Beo Moussala, BG
Chilton, UK
Sacavem, PT
Thessaloniki, GR
Barcelona, ES
Dublin, IE
Linz, ATMonaco, MC
Geneva, CH
Cluj Napoca, RO
Cagliari, IT
Firenze, IT
Milano, IT
Piacenza, IT
Bratislava, SK
Mol, BE

7
6

Particulate

6

Particulate 131I (mBq m-3)

5

5
4
3
2
1

4

0

20/Mar 22/Mar 24/Mar 26/Mar 28/Mar 30/Mar 1/Apr

3/Apr

5/Apr

7/Apr

9/Apr 11/Apr 13/A

131

-3

I (mBq m )7

Particulate131I (mBq m-3)

6

5

3
2
1
0

4

20/Mar 22/Mar 24/Mar 26/Mar 28/Mar 30/Mar 1/Apr

3/Apr

5/Apr

7/Apr

9/Apr 11/Apr 1 /Apr 13/Apr

3

2

1

0
20/Mar 22/Mar 24/Mar 26/Mar 28/Mar 30/Mar 1/Apr

3/Apr

5/Apr

7/Apr

9/Apr

Schauinsland, DE
Vienna, AT
Luxembourg, LU
Bilthoven, NL
Umeå, SE
Rovaniemi, FI
Ylöjärvi, FI
Spitsbergen, NO
Budapest, HU
Caceres, ES

11/Apr 13/Apr

Helsinki, FI
Oslo, NO
Svanhovd, NO
Stockholm, SE
Krakow, PL
Braunschweig, DE
Postdam, DE
Offenbach, DE
Reykjavik, IS
Prague, CZ
Octeville, FR
Caceres, ES
Minsk, BY
Mstislavl, BY
Braslaü, BY
Vilnius, LT

Figure 9-2 – Time series of activity levels of airborne particulate 131I (mBq.m-3) in northern and central
Europe (bottom graph), and in western and southern Europe (middle and top graphs), due to releases
caused by the accident at the Fukushima nuclear power plant (O. Masson et al, 2011, Environ. Sci.
Technol., 45, pp. 7670-7677)

51

Diaz Leon, J.; Jaffe, D.A.; Kaspar, J.; Knecht, A.; Miller, M.L.; Robertson, R.G.H.; Schubert, A.G.; Arrival time and magnitude ofairborne fission products from the Fukushima, Japan, reactor incident as measured in Seattle, WA, USA. J. Environ.
Radioact. Article in press.
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During the last couple of weeks of March, weather conditions in Europe led to the formation of a “corridor”, within
which higher activity levels were recorded (Figure 9-3). This corridor lay along a north-west/south-east axis,
stretching from Scandinavia through eastern Germany, Poland, the Czech Republic and Belarus. Activity peaks forparticulate 131I, of about 6 mBq/m3, were thus recorded in Krakow (Poland), Braslaw and Mstislaw (northern Belarus),
and also in Brunswick (northeastern Germany). Countries in western and southern Europe (Ireland, the UK, Belgium,
Switzerland, France, Italy, Portugal, and Greece) measured peak levels typically less than 1.5 mBq/m3. The arrival
dates of the contaminated air masses and the corridor of higher values were in fact predicted by the simulations
carried out using the Eulerian LdX dispersion model developed by IRSN and integrated into the Polyphemus modelingplatform. Figure 9-4 shows the simulations for 137Cs, arbitrarily calculated at 12:00 UTC so as to simplify day-to-day
comparisons. The contamination footprint is broadly similar for 131I, since the ratio of 131I to 137Cs levels remained
relatively constant. The model took into account the fact that the air masses were gradually depleted by deposition.
Dry deposition of 137Cs was modeled using a simple diagram, at a constant deposition rate (Vd = 2.10-3 cm/s). With
regard to wet deposition, the parameters used in this study were of the form Λ=aP0b; with a=5.10-5 h/mm/s, b=1 andrain intensity (p0) in mm/h. This model used the meteorological data obtained from Météo-France's Arpège model,
with a resolution of 0.5°.
Many uncertainties persist regarding the assessment of the source term, the weather conditions encountered by the
air masses in transit, the parametrization of the efficiency of scavenging, and the long-distance atmosphericdispersion between Japan and Europe. The comparison between the values measured and the simulation cannot
therefore be used to calculate absolute values, but does demonstrate the ability of simulations to identify thoseregions where levels were higher, and also hot spots. For example, the relatively high value measured over the
Iberian peninsula, on March 29, was actually predicted by the LdX model.

Particulate 131I
(mBq m-3)

Figure 9-3 - Daily activity levels of particulate 131I measured between March 22 and April 7, 2011 (O.
Masson et al, 2011, Environ. Sci. Technol., 45, pp. 7670-7677)

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Figure 9-4 – Simulations of airborne activity levels of 137Cs in Europe between March 22 and April 7, 2011
(O. Masson et al, 2011, Environ. Sci. Technol., 45, pp. 7670-7677)

Characterizing airborne iodine levels is complex, as this element co-exists in two forms, particulate and gaseous,requiring different types of samplers. At the time of the Chernobyl accident, relatively few measurements of thegaseous 131I fraction were conducted. Subsequently, many sampling sites were equipped with activated carbon
samplers to collect gaseous iodine, which means that it is now possible to obtain more detailed information about
this fraction and also about the gaseous/particulate ratio, in terms of both spatial distribution and variation overtime. Based on around 210 pairs of values acquired up to April 12, the average gaseous/total 131I ratio obtained is
77.2% ± 13.6% (Figure 9-5). This is identical to the average ratio found after the Chernobyl accident52. The greater
variability of this ratio can be explained by higher measuring uncertainties for the low levels of total iodine. Thisratio also varies over time, since the particulate fraction is particularly sensitive to wet deposition. For example, thegaseous/total ratio on a given site varied between 0.79 and 0.90, and even up to 0.96 over a few days. Anothersource of uncertainty may stem from the adsorption properties of the adsorbent used for the gaseous fraction and, inparticular, its collection efficiency in moist conditions. Apart from the capture characteristics, overall uncertainties
probably reflect different aerosol washout/scavenging conditions as well as effects related to the chemical reactivityof the two fractions, while in transit. Consequently, the predicted estimate of the gaseous iodine concentration
based on values for the particulate fraction must be treated with caution.

52

Cambray, R.S.; Cawse, P.A.; Garland, J.A.; Gibson, J.A.B.; Johnson, P., Lewis, G.N.J.; Newton, D.; Salmon, L.; Wade, B.O.
Observations on radioactivity from the Chernobyl accident. Nuclear Energy. 1987, 26, issue 2, 77-101.
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100

70
60

Gaseous

131

131

80

I / Total

I (%)

90

50
40
30
20
Mean value

10Standard Deviation

0
0

2

4

6

8

10

12

14

Total 131I (mBq m-3)
Figure 9-5 - Gaseous 131I / total 131I ratio in the atmosphere in Europe after the accident at the Fukushima
nuclear power plant (O. Masson et al, 2011, Environ. Sci. Technol., 45, pp. 7670-7677)

As a first approximation, it can be assumed that there is a gradual transfer of gaseous iodine into the particulate
form, as if gaseous 131I were acting as a reservoir for the latter. According to the measurements conducted on thesite of the Fukushima Dai-ichi power plant between March 22 and April 4, the average particulate 131I / gaseous 131I
ratio was 0.46 ± 0.17, i.e. a gaseous 131I / total 131I ratio of 71% ± 11%. This is identical to the value observed inEurope (Figure 9-5), indicating that 131I remained mainly in its gaseous form in transit. Consequently, the transfer ofgaseous iodine into its particulate form, if it occurs, is not sufficient within the space of two weeks tocounterbalance the decrease associated with the deposition of particulate 131I, mainly by rain. In fact, the gasparticle conversion time for 131I is typically two to three weeks53. In this respect, it can be seen that the temporalvariation in the gaseous 131I / total 131I ratio shows a slight upward trend over time on average (Figure 9-6). This
probably corresponds to a faster decrease in the particulate form.
As was the case after the Chernobyl accident, 134Cs and 137Cs were detected. While tracking the air masses originatingfrom Fukushima as they passed over Europe, these isotopes were usually detected three or four days after 131I, theirconcentrations having exceeded the metrological decision threshold at a later point in time. In Europe, 134Cs had notbeen measured in the atmosphere since the mid-1990s due to its relatively short half-life (2.06 years). Conversely,
137

Cs was still measurable in trace amounts before the Fukushima accident: less than 1 μBq/m3 in central Europe andless than 0.3 μBq/m3 in northern and southern Europe taken as a whole. Its persistence in the atmosphere can be
explained partly by its longer half-life (30.1 years) and partly by the fact that soil particles containing traces of old
deposits (originating from Chernobyl fallout and/or global fallout from atmospheric nuclear testing) are regularly
resuspended. Another source is the emission of ash during biomass fires. Unlike iodine, which is mainly in gaseous
form, cesium isotopes bond rapidly with aerosols and are therefore easily scavenged by rain. The temporal andspatial averages of cesium values recorded from March 20 to April 12 in Europe were 0.076 and 0.072 mBq/m3 for137

Cs and 134Cs respectively, with a first activity peak of 0.75 mBq/m3 in Lodz (Poland) between March 28 and 30, anda second peak of 1.0 mBq/m3 in Vilnius (Lithuania) between April 3 and 4. Compared with the situation in theaftermath of the Chernobyl accident, the 137Cs airborne activity levels in Europe after the Fukushima accident were53

Uematsu, M.; Merrill, J.T.; Patterson, T.L.; Duce, R.A.; Prospero, J.M. Aerosol residence times and iodine gas/particle conversion
over the North Pacific as determined from Chernobyl radioactivity. Geochem. Journal, 1988, 22, 157-163.
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at least 10,000 to 100,000 times lower. Irrespective of the radionuclide considered, activity levels remained low
enough not to pose any public health risk in Europe.

10090

I / Total

70
60

Gaseous

131

I (%)

80

40

Helsinki, FI
Oslo, NO
Svanhovd; NO
Krakow, PL
Vienna, AT
Prague, CZ
Cadarache, FR

131

50

30
20
10
0

20/Mar 22/Mar 24/Mar 26/Mar 28/Mar 30/Mar 1/Apr

3/Apr

5/Apr

7/Apr

9/Apr 11/Apr 13/Apr 15/Apr

Date

Figure 9-6 – Temporal variation in the gaseous 131I / total 131I ratio in Europe after the accident at the
Fukushima nuclear power plant (O. Masson et al, Environ. Sci. Technol., 45, pp. 7670-7677)
The 134Cs/137Cs ratio in the Chernobyl fallout in 1986 was between 0.5 and 0.654, but remained close to 1 in
the Fukushima fallout (Figure 9-6). This ratio was relatively constant over time during the first three weeks ofthe study period. Figure 9-8a shows the relationship between 131I (particulate fraction or total fraction) andthe values for 137Cs. It is known that dry deposition of the gaseous fraction of 131I was substantial andsignificantly higher than that of cesium55. The value range of the 137Cs/131I ratio found in this study is
consistent with the deposition values observed in the United Kingdom56 after the Chernobyl disaster. The
variations had been attributed to the amount of rainfall in different places.

54

De Cort, M. et al. Atlas of cesium deposition on Europe after the Chernobyl accident (Office for Official Publications of theEuropean Communities, ECSC-EEC-EAEC, Brussels-Luxemburg, 1998.
55
Tschiersch, J.; Shinonaga, T.; Heuberger, H. Dry deposition of gaseous radioiodine and particulate radiocesium onto leafy
vegetables. Sci. Total Environ. 2009, 407, 5685-5693.
56
Clark, M.J.; Smith, F.B. Wet and dry deposition of Chernobyl releases. Nature. 1988, 332, 245-249.
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180

Max
rd
3
quartile
Mean
Medianst
1quartile

160
140

100
80

134

Cs /

137

Cs (%)

120

60
40
20
0

22/Mar 24/Mar

26/Mar28/Mar30/Mar 1/Apr

3/Apr

5/Apr

7/Apr

9/Apr

11/Apr

Date

Figure 9-7 – Temporal variation in the 134Cs/137Cs ratio in Europe after the accident at the Fukushima
nuclear power plant (O. Masson et al, 2011, Environ. Sci. Technol., 45, pp. 7670-7677)

Between March 19 and April, the measurements carried out near the nuclear power plant by the operator show thatthe 137Cs/particulate 131I ratio increased from 0.35 to 11%. This means that the radioactive plume contained moreiodine at the start of the accident, which is consistent with the fact that iodine is more volatile than cesium. In
Europe, from the time when 137Cs began to be detected (March 22 onwards), this average overall ratio varied little
Europe-wide (between 4.6% and 6.5%) up to March 27 but then increased due to the arrival of more concentrated air
masses (Figure 9-9b). This may indicate adsorption of gaseous 131I on non-contaminated aerosols situated on the edgeof the contaminated air masses. This interpretation may corroborate the significantly lower 137Cs/131I ratio observedat the Jungfraujoch alpine station (Switzerland, 3,450 m), i.e. at an altitude approximately corresponding to theupper limit of the planetary boundary layer57.
To check whether any parameters other than the radioactive decay of 131I might explain the increase in this ratiowith time, the average values were corrected for radioactive decay of iodine-131 (triangles in Figure 9-9b) andextrapolated back to March 11, corresponding to the emergency shutdown initiated when the earthquake was
detected. It can be clearly demonstrated that the radioactive decay of 131I is primarily responsible for the increase inthis ratio. Consequently, it can be assumed, as a first approximation, that the scavenging coefficient for cesium isalso applicable for particulate 131I and that the transfer of particulate iodine from the gaseous fraction, if it occurs, isof negligible importance in view of the long distance travelled in the atmosphere from Fukushima.

57

Colluad, Coen M.; Weingartner, E.; Furger M.; Nyeki S.; Prévôt A.S.H.; Steinbacher M.; Baltensperger U.; Planetary boundary
influence at the Jungfraujoch analyzed by aerosol cycles and synoptic weather types. Atmos. Chem. and Phys. Discuss. 2011, 11,985-1024.
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10

40

14

14

Total I-131

62

R = 0,6814

4

4

131

without decay correction

Particulate

y = 5,5537x + 0,1627

6

Cs / particulate

8

131

8

Max
3rd quartile
Mean
Median
1st quartile
Min

30
25

7,5

5

20
15

2,5

10

137

10

Total 131I (mBq m-3)

10

I (%)

12

-3

I (mBq m )12

Without I-131 decay correction
I-131 decay corrected

5

2

2
0

0

0

0
0

0,1

0,2

0,3

0,4

0,5

0,6

137

Cs (mBq m )

0,7

0,8

0,9

1

-3

-5

22/Mar 24/Mar 26/Mar 28/Mar 30/Mar 1/Apr

Figure 9-8 a - Particulate 131I and total 131I, as afunction of the 137Cs levels measured in Europe

03/Apr 05/Apr 07/Apr 09/Apr 11/Apr

Date

-10

Cs / particulate 131I decay corrected (%)

35

137

Particulate I-131-2,5

Figure 9-9 b – Temporal variation in the average
137

Cs/131I ratio in Europe after the Fukushima

after the Fukushima accident (O. Masson et al,accident (O. Masson et al, Environ. Sci. Technol.,Environ. Sci. Technol., 45, pp. 7670-7677)

45, pp. 7670-7677)

The highest concentrations of 131I measured in Europe based on samples taken at ground level persisted for about 10
days. The average concentrations in the higher activity corridor were approximately 1 mBq/m3 for particulate 131I and
4 mBq/m3 for the two fractions. There is little data available on the vertical distribution of 131I in the troposphere;
nevertheless, the activity levels seem to be fairly homogeneous in the vertical plane in Europe. In fact, samples
taken at the Jungfraujoch alpine station (3,450 m) showed 131I activity levels of up to 0.9 mBq/m3, while highaltitude samples collected by aircraft on March 30 over Switzerland (at up to 8,000 m) indicated a level of
2.3 mBq/m3, and a few mBq/m3 over northern Germany (at up to 10,000 m). It is therefore reasonable to assume
that 131I was well mixed from ground level right up to the upper part of the troposphere. Assuming a representative
average concentration of 10 days (i.e. 240 hours), that the air masses moved at an average speed of 50 km/h, andthat the corridor with the highest concentrations was 3,000 km wide with a mixing height of 5.5 km, a volume ofabout 3,000 X (240 X 50) X 5.5 km3 is obtained. If an average iodine-131 concentration of 4 mBq/m3 is used, it can be
estimated that approximately 1015 Bq of 131I passed over Europe, i.e. less than 1% of the amount released into theatmosphere at the Fukushima nuclear power plant.

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10. CONCLUSION
The accident at the Fukushima Dai-ichi nuclear power plant has revealed the vulnerabilities of some nuclear
facilities, even in a highly developed country with advanced technical skills such as Japan.
Awareness of the need for continuous progress in enhancing nuclear safety around the world has led to numerous
initiatives at the national and international levels. These initiatives are part of multiple objectives, which include
assessing the vulnerability of nuclear power plants in light of lessons learned from the accident, assessing the healthand environmental consequences of the accident, eventual improvements in preparing and conducting response
efforts in case of an emergency as well as safety standards, and the constant need to improve knowledge throughresearch efforts.

10.1. AT THE INTERNATIONAL LEVEL

United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR)

At its annual session in May 2011, UNSCEAR began writing an initial report on the accident at the Fukushima Dai-ichi
nuclear power plant and its consequences on the health of persons exposed to radioactive fallout.
In order to accomplish the task, UNSCEAR called upon all governments to nominate experts, who would be
responsible for writing the report on a voluntary basis. A total of nearly 60 experts from Europe, Japan, Canada, theUSA, Brazil, Korea, Russia, Belarus, Ukraine, and Australia were appointed. There are nine experts from France: fivefrom IRSN and four from the French Alternative Energies and Atomic Energy Commission (CEA).
The experts have been divided into four working groups:-

the first group, led by an American delegate, is responsible for collecting measurement data and checking
its quality. IRSN is represented by an expert in charge of one of the three sub-groups in this working group;-

the second group, led by a German delegate, is responsible for evaluating atmospheric and marine
dispersion of radioactive releases. IRSN is represented by one expert in this working group;-

the third group, led by an Australian delegate, is responsible for evaluating doses received by the populationand the consequences on the persons exposed and on non-human species. IRSN is represented by two
experts in this working group;-

the fourth group, led by a French delegate from IRSN, is responsible for evaluating doses received byworkers and the consequences on their health.

In addition, a coordination group consisting of the Chairman of UNSCEAR, the Chairman of the Japanese delegation to
UNSCEAR, the leaders of the four working groups, and the Scientific Secretary of UNSCEAR and his colleagues,
ensures the smooth progress of the report drafting process.
A first interim report will be presented at the 59th annual session of UNSCEAR in May 2012, and the final report,
whose publication is expected in late 2013, will be presented at the 60th annual session of UNSCEAR in May 2013.
The UNSCEAR report will also benefit from contributions by major international organizations, including the World
Health Organization and the World Meteorological Organization.

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International Atomic Energy Agency (IAEA)
The general public and many governments have expressed a strong desire to increase the role and powers of the IAEA
in the area of nuclear safety, including•

more rigorous application of the IAEA’s safety standards for the design and operation of nuclear reactors, aswell as the organization of inspection bodies;•

expanding the possibilities for IAEA to verify application, especially with expert assessments;•

strengthening the role of the IAEA in the area of information management in the event of a nuclear
accident.

The IAEA’s General Conference in September 19-23, 2011 adopted an extensive plan of actions, which includes thefollowing twelve measures:•assess safety vulnerabilities of nuclear power plants in light of lessons from the recent accident;•

step up reviews by IAEA experts to maximize benefits for its member States;•

step up preparedness and organization for emergency operations;•step up effectiveness of national inspection organizations;•step up effectiveness of operator organizations in the area of nuclear safety;•

examine and step up the IAEA’s safety standards and improve application;•

improve effectiveness of the international legal framework;•

facilitate implementation of infrastructure required by member States for starting a nuclear power program;•step up and maintain skill creation;•

ensure continuous protection of people and the environment from ionizing radiation after a nuclear
emergency;•

increase transparency and effectiveness of communications and improve the sharing of information;•

use research and development efficiently.

This plan proposes means for action and levers to create international dynamics and pressure that will result inprogress in safety, since incentives in this area are often more effective than legal obligations.
The IAEA’s Ministerial Conference following the accident, held on June 20-24, 2011, as well as the General
Conference in September 2011, also stressed the need to develop coordination among technical safety organizations(TSOs)58, particularly through the TSO Forum (TSOF). This upholds the conclusions at the International Conference on
Challenges Faced by Technical and Scientific Support Organizations in Enhancing Nuclear Safety and Security held inTokyo, Japan in October 2010, which concluded that “The IAEA should foster the establishment of a forum dedicatedto nuclear safety infrastructure development issues related to scientific and technical support.”
The objective of the TSOF, whose terms of reference were defined in July 2011, is to encourage open dialogue andsharing of scientific and technical information among TSOs worldwide, as well as the harmonization of practices. It
also aims to consolidate worldwide assessment and research ability and make it more available. Involvement of IRSN
and the European organization ETSON59 as members of TSOF will be stepped up.

A technical safety organization (TSO) is a technical and scientific organization that carries out
independent assessments and analyses of nuclear facility safety and radiological risks. Its activities
comply with best practices in the field of risk assessment and meet internationally accepted andapplicable scientific baselines and standards.
59
The members of the European Technical Safety Organisations Network (ETSON) agree to abide by a charter ofprinciples for action and values intended to ensure the highest level of expertise and foster the development of researchin nuclear safety and top-down harmonisation of their respective pratices, including a shared training platform for their
newly recruited staff members.
58

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Nuclear Energy Agency (NEA) of the Organisation for Economic Co-operation and Development (OECD)
For its part, the NEA led a discussion during the forum held on June 8, 2011 to advance its work in the fields ofnuclear facility safety and emergency response management. This primarily concerns three of its committees:•

Committee on Nuclear Regulatory Activities (CNRA);•

Committee on the Safety of Nuclear Installations (CSNI);•

Committee on Radiation Protection and Public Health (CRPPH).

Each of the committees has mobilized its working groups in recent months to make decisions on changes to be madeto established work programs. Closer coordination should be established between CNRA and CSNI, as well as with
CRPPH.
CSNI’s planned work program covers the following topics:•

external and internal hazards;•

accident management (sharing operating experience feedback on management of the Fukushima accident);•

severe accidents;•

improving robustness of nuclear reactors;•

emergency management.

In parallel, CNRA has created the CNRA Task Group on the Impacts of the Fukushima Dai-ichi Accident and identified
the following actions to be taken up by its working groups:•

WGRNR (regulation of new reactors): impact on site selection;•

WGOE (operating experience): increased sharing of international operating experience feedback on hazards;•

WGIP (inspection practices) inspections involving severe accidents and related equipment;•

WGPC (public communication): international aspects;•

Task Group on Long Term Operation: impact on extending service life of existing reactors.

World Association of Nuclear Operators (WANO)
WANO fosters mutual support, information exchange and good practices among nuclear operators to improve theperformance and safety level of nuclear power plants.
Beginning in March 2011, WANO released an initial document on immediate verifications to be performed byoperators in light of the Fukushima Dai-ichi accident. It issued another document on cooling of spent fuel pools in
July 2011.
During the NEA forum, WANO committed to applying the lessons of the Fukushima Dai-ichi accident and strengthening
its peer-review programs. WANO's changes to programs and organization are based on five measures:•

extend its field of activities to accident prevention and mitigation;•

develop an integrated strategy to respond to events, detailing the responsibilities of the installation•

take a series of measures aimed at improving its credibility and the quality of its products and services;involved, WANO's regional centers and the London office if another severe event occurs;•

become more visible to the public and recognized as the organization that represents nuclear operators
worldwide. Closer coordination with IAEA and regulatory agencies is planned to favor interaction andencourage members to publish the results of peer assessments;•

make efforts to improve internal consistency.

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World Health Organization (WHO)Following the Fukushima Dai-ichi accident, WHO requested that an expert from IRSN provide support to the technicalteam of the radiation protection program set up in its department of public health and the environment in order toimprove its response to the nuclear emergency at the Fukushima Dai-ichi nuclear power plant. IRSN provided support
to the WHO in implementing a dose assessment methodology and defining a work plan for assessing the healthconsequences for people exposed to radioactive releases from Fukushima Dai-ichi.

European initiatives
On March 25, 2011, the European Council sought to submit nuclear power plants in Europe to additional safetyassessments. ASN and IRSN made significant contributions to defining specifications of these analyses on the French
and European levels in a manner that is consistent in terms of content and scheduling. According to the specifications
prepared and proposed by WENRA60 on May 7, 2011, these stress tests consist of:•a targeted reassessment of behavior and safety margins of nuclear power plants in the event of extreme
natural events that jeopardize safety functions and lead to a severe accident: (a) assessment of responses
from nuclear power plants and (b) verification of prevention and mitigation measures;•

defense-in-depth tests: (a) analysis of loss of lines of defense in succession, (b) deterministic approach and(c) identification of weak points, cliff-edge effects, etc.;•

a report on initiating events: (a) earthquake, (b) flooding and (c) other extreme natural events;•

an assessment of a significant loss of safety functions: (a) loss of electrical supply and (b) loss of ultimate
heat sink;•a report on protection and management resources: (a) loss of core cooling function, (b) loss of cooling
function in the spent fuel pool and (c) loss of containment integrity.

Reports from various countries were submitted in late 2011 to European bodies. Peer reviews by experts from various
European countries have been organized. Conclusions from European stress tests will be submitted in June 2012.
In addition to the stress tests, the European Commission has encouraged several initiatives in response to theaccident at the Fukishima Dai-ichi nuclear power plant, including setting up a working group within the European
Nuclear Energy Forum (ENEF), with significant participation by industry members of Foratom/Eniss who plan toharmonize European standards at the top level. As part of the Sustainable Nuclear Energy Technology Platform, allstakeholders defining research programs on nuclear fission have also produced a document describing theconsequences of the accident in this area.

60

Western European Nuclear Regulator's Association
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10.2. AT THE NATIONAL LEVEL
Complementary safety assessments
Eight months after the Fukushima accident, complementary safety assessment have helped define an approach forsupplementing existing safety measures to improve facility robustness. This approach consists of implementing a“hardened safety core” to ensure the availability of equipment that plays an essential role in controlling safetyfunctions and emergency management.
It will be supplemented by targeted changes to certain baselines, without waiting for ten-year reviews(determination of contingencies for earthquake and flooding, protection from fire, combinations of hazards to betaken into account, etc.).
Beyond this initial step, IRSN has identified the need for a long-term effort on three main fronts:-

analysis and stabilization of the safety reference base, so that it includes the notion of “hardened safetycore” (the hardened core includes a set of structures, systems and components whose availability, in all
scenarios considered, will ensure the three basic safety functions: control of the nuclear reaction, removalof heat produced by the reaction and confinement of radioactive materials); the principles have been
defined, but must be applied both in terms of consequences for modifications to installations and its roleand the change it brings to the general safety demonstration for installations. In addition, emergency
management measures must be re-examined;-

analysis of proposals by industrial firms to modify equipment and/or operating and emergency proceduresand general operating rules for installations that result from implementing the “hardened core” concept;-

finally, in parallel, further expert analysis of the Fukushima accident.

Call for a research project on nuclear safety and radiation protection
After IRSN and other research organizations underlined the importance of such a project in the first months after the
Fukushima disaster, the French president announced at a press conference on June 27, 2011 his decision to releasesignificant additional resources to step up research in this field where France is acknowledged as a leader. He used
the research budget from the Investment for the Future that is part of a major national loan (which includes €22billion for research and higher education out of a total of €35 billion) coordinated by the Commissariat Général aux
Investissements d’avenir (CGI), which has asked the French National Research Agency (ANR) to organize a call for
research projects on nuclear safety and radiation protection ensuing directly from an initial study of the Fukushima
accident. The initial analysis was part of a presentation on the points of view of IRSN and CEA during the July 20,
2011 meeting of the Atomic Energy Committee. The analysis contributed to defining the scientific framework for thecall for projects. Assembling these details, and those from other stakeholders, CGI defined a budget (€50 million), a
deadline (April 26, 2012) and topics for research focusing on the following:1.

draw lessons from conditions leading up to major nuclear accidents, especially the one that occurred in
Fukushima on March 11, 2011, and take into account initial conclusions from ASN’s supplemental safetyassessments;

2.
3.

study methods of operators and public authorities for managing all major nuclear accidents to date;study the impact of these accidents in terms of releases and radioactive materials, impact on health and theenvironment and conditions for recovering contaminated regions;4.

application of these lessons on current and future French installations to increase operation safety,
resistance and the effectiveness of emergency mechanisms in the event of extreme events.

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IRSN stresses that in addition to improvements through regulations, inspections, changes in safety baselines, it is
crucial that the lessons of Fukushima give rise to an intensive effort of questioning and knowledge creation, whichmust be encouraged in France—as illustrated by this call for projects—but also more generally through international
cooperation.

10.3. NEED TO CHANGE RESEARCH PRIORITIESThe operation of nuclear power plants worldwide has been marked by three major accidents that affected nuclear
facilities at Three Mile Island in the United States in 1979, Chernobyl in the Ukraine in 1986 and recently Fukushima
Dai-ichi in Japan. Only the latter two accidents resulted in significant releases of radionuclides into the environment.
The accident at the Fukushima nuclear power plant was caused by an earthquake of very large magnitude thatgenerated high intensity mechanical stresses and a tsunami of exceptional size. These two external natural hazards,
with a causal connection, separately exceeded the limits considered in the design basis of the installation, and their
combination was also not considered. Together, the result was loss of core cooling in several boiling water reactors
resulting in partial core meltdown. Loss of cooling also affected fuel in the site’s spent fuel pools, raising fears overcriticality risks and meltdown in the spent fuel pool that had not been considered until present. The accident
resulted in significant releases of radioactivity into the environment at low altitude, which were however limited bymaintaining a certain level of protection offered by the reactor containments. The low-altitude releases
contaminated a zone over a moderate distance. According to IRSN’s current knowledge, relative confinement offission products likely limited worker exposure to levels that were lower than those of the Chernobyl accident. For
the general population, regional contamination was similar to that of Chernobyl, but over a smaller surface area.
For the sequence of the accident at the installation, operating experience feedback shows the need to increase
research on accident prevention. First, characterization of natural hazards (earthquakes and risks of flooding
whether or not caused by the earthquake) resulting in the accident must be improved and consideration of thesehazards in probabilistic safety assessments must be done more systematically in order to identify weak points inthese installations confronting these hazards. Probabilistic studies developed after the TMI accident and theirapplication for postulated accident studies on the basis of internal failures led EDF in France to implement, as part ofsafety reviews, countermeasures (procedures and/or equipment) that supplemented those issued from thedeterministic approach of the initial design. IRSN considers that the development of a comparable approach including
external hazards is necessary.
It is also important to improve identification of weak points of installations that could result from aging or operating
mode from the standpoint of human and organizational factors.
Operating experience feedback also demonstrates that the phenomenology of severe accidents is now relatively wellknown. This result must be credited to past ambitious research programs coordinated by IRSN, particularly the
Phebus Fission Products program (conducted at a CEA research facility). Significant uncertainties still remain,
however, concerning certain phenomena relating to the sequence of core meltdown accidents and still more relating
to pool dewatering. Research priorities concern in-depth analysis of the accident sequence and research targeted at
the most obvious gaps: thermohydraulic and thermomechanical behavior of fuel assemblies in loss of coolingconditions, effectiveness of emergency cooling makeup since partial meltdown of core elements affects
geometry, criticality risks, production of hydrogen while overheated fuel is cooling and related explosion risks,transient behavior of core meltdown debris in the vessel bottom head and reduction of radioactive releases.
This leads to the conclusion that beyond short-term measures to verify or, if appropriate, restore the safety margin
at sites, it is necessary to pursue major research programs like those in the past to continue to improve the resilienceof power reactors to phenomena that can lead to significant radioactive releases into the environment. In thisregard, IRSN considers that it must pursue experimental in-reactor research programs on issues related to reactivity
excursion and loss of cooling, as well as research on improving the resistance of confinement barriers (especially the
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years that such programs, conducted as a general rule as part of international cooperation to which the industry
contributes, are a key factor in progress both in knowledge and risk evaluation, and improving technology.
A third concern from the accident experience feedback involves environmental aspects and those related toemergency management and intervention. In this regard, IRSN wishes to stress that, if was able to provide relevant
information earlier to decision-makers, and also to make it available to the public in a manner that was quick,intelligible and yet still accurate, this is because it had the scientific knowledge and tools from past research in
the area of severe accidents, experience within its emergency response center from nuclear accident exercises
held nationally over many years, and finally the results of its strategic commitment for several years of an
approach characterized by openness to society and transparency.
Nevertheless, there are some discrepancies between the regional contamination predictions made by IRSN and the insitu measurements, suggesting that these predictive models need improvement. This is why IRSN deems it necessary,in light of the operating experience feedback, to increase certain research and development work in the area ofradionuclide transfer (in the atmosphere or as a liquid) and the impact of this transfer to various environments,
improve the installation section of emergency management tools and re-examine the regional radiological monitoring
system. The effectiveness of the emergency plan, and in particular the choice of decision to make for optimal
protection of the population as well as rapid collection of reliable data are essential, especially for densely
populated areas. The goal of this work is not to develop academic knowledge in these fields, but to develop
knowledge that is strictly necessary for developing operational tools for emergency management to supplement the
panoply of forecasting resources that IRSN uses for its technical support to public authorities responsible formanaging a nuclear emergency.
Finally, for aspects related to the radiation protection of the population near nuclear sites, the Fukushima accident
confirms the plausibility of accident scenarios that include significant releases, particularly over the long term. This
accident, unlike Chernobyl, can become a reference model of a severe accident with releases following partial
confinement failure. Taking into account operating experience feedback for the Fukushima accident thus also
appears essential from a perspective of changing policies concerning radiation protection of populations. Researchneeds in this area relate to-development of techniques for rapid and robust large-scale assessment of individual doses in a concerned
population;-

stepping up research on the effects of low doses received over time that affect the relevance of measures toprotect the public. This research would require developing appropriate experimental platforms.

ooOoo

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