The Impact
Fukushima11032011
Radiological Effectsof the Nuclear Accidents
in Fukushima on 11 March 2011

Table of Contents
1

Introduction			 42 INES classification, determination of the volumes released		 6
2.1
Overview		6
2.2
INES classification of the event		 7
			
2.2.1
Systematic scheme of the INES scale		 7
			
2.2.2
Application of the INES scale to Fukushima Dai-ichi		 8
2.3
Release of radioactive substances into the atmosphere		 102.4Release of radioactive substances via water into the sea		 152.5Summary and assessment		 193 Ambient dose rates on the power plant site		 203.1Overview		20
3.2
Results and development of the ambient dose rate measurements		 203.3Summary and assessment		 254 Radiation exposure and working conditions for staff		 264.1Overview		26
4.2
Dose limits for staff exposed to radiation in the course of their work in Japan		 274.3Dosimetric monitoring of plant staff		 28
			
4.3.1
Status prior to the events of 11 March 2011		 28
			
4.3.2
Changes to dosimetric monitoring subsequent				to the accident		 28				4.3.2.1
Measures in the Fukushima Dai-ichi nuclear power plant		 28				4.3.2.2
Measures in “J Village”		 30				4.3.2.3
Radiation protection equipment and planning of work		 304.4Status of radiation exposure		 30
			
4.4.1
Army and police units		 30
			
4.4.2
Fire brigades		 31
			
4.4.3
Plant staff and external workforce		 31
			
4.4.4
Violation of dose limits and potential causes		 33
			
4.4.5
Exceptional radiation exposures		 344.5Dose reduction measures		 35
			
4.5.1
Measures to monitor and reduce radiation doses		 35
			
4.5.2
Measures in the Main Anti-Earthquake Building		 374.6Summary and assessment		 385 Exposure of the population in the surrounding area to radiation 		 405.1Overview		40
5.2
Deposits of radioactive substances on the ground		 41
			
5.2.1
Weather situation		 41
			
5.2.2
Ambient dose rate due to activity deposits
				on the ground		 42
			
5.2.3
Measurements of soil activity:				
volatile nuclides, I-131, Cs-134 and Cs-137		 47
			
5.2.4
Measurements of soil activity: other nuclides (Sr, Pu, U)		 505.3Contamination of food		 525.4Contamination of drinking water		 56

2|3

5.5
5.6
			
			
5.7
			
			
5.8

Contamination of seawater and the seabed		Measures to reduce radiation exposure		
5.6.1
Evacuation of the population in the surrounding area		
5.6.2
Decontamination measures		
Estimation of doses for the population in the surrounding area		
5.7.1
Dose in the acute phase		
5.7.2
Estimation of the long-term dose		
Summary and assessment		

58
61
61
63
63
63
64
65

6 Effects on the population in Switzerland(Contribution by the Federal Office of Public Health (FOPH))		
66
6.1
Overview		66
6.2
Measurements of airborne radioactivity		 67
			
6.2.1
High-volume samplers (HVS, air filters)		 67
			
6.2.2
Gaseous I-131		 68
			
6.2.3
High-altitude in-flight filter measurements (HFF) 		 696.3Food and environmental samples from Switzerland		 706.4Summary and assessment		 707 Comparison of events at Fukushima with those at Chernobyl(with contributions from the Gesellschaft
für Anlagen- und Reaktorsicherheit mbH, GRS)		
7.1
Accident progression and release		
7.2
Radiological situation on the plant site		
7.3
Radiological situation in the surrounding area		
7.4
Radiation exposure for the operational staff and the population		
7.5
Estimation of long-term exposures		
7.6
Summary and assessment		

72
72
74
76
78
79
83

8 List of Table les and figures		84

9 List of Table les and figures		86

10 References			89

1 | Introduction

1

Introduction

The Tohoku-Chihou-Taiheiyou-Oki earthquake off the Japanese coast at 2.46 p.m.
(local time) on 11 March 2011 was the most
severe earthquake in the history of Japan
since records began to be kept. The resultant tsunami flooded extensive tracts of thenorth-eastern coast and reached the Fukushima Dai-ichi (Fukushima I) nuclear plants
at 3.27 p.m. with a first wave, and at 3.35
p.m. with a second wave. The earthquake
and the subsequent tsunami damaged the
Fukushima Dai-ichi plants to such an extent
that, on 12 April 2011, the Japanese authorities classified it as a “major accident” according to level 7 of the International Nuclear
and Radiological Event Scale (INES).

Nach dem Unfall vonFukushima-Dai-ichi
plant die japanische
Regierung die nukleare
Aufsicht aus dem METI
auszugliedern und neu
unter der Führung desUmweltministeriums zu
bündeln

The Tokyo Electric Power Company (TEPCO)
operated six boiling water reactors (BWR) at
the Fukushima Dai-ichi site, with a total net
power output of 4,547 megawatts (electric)(MWel), a common spent fuel pool and a
dry cask storage facility. Together with theneighbouring Fukushima Dai-ni (FukushimaII) site at a distance of 12 km, where four
more power plant units with 1’100 MWel eachwere available, this complex constituted theworld‘s largest nuclear power plant site. At
the time of the earthquake, units 1 to 3 werein power operation at Fukushima Dai-ichi.
Units 4 to 6 had been shut down for several
months due to inspection work. The fuelassemblies from the reactor pressure vessel(RPV) of unit 4 were in place in the unit‘s
own spent fuel pool in the reactor building.
The four units of the Dai-ni power plant werein power operation at the time of the earthquake.
In addition to Fukushima I and Fukushima II,
additional nuclear power plants (Onagawa
1-3, Tokai and Higashidori) were affected by
the earthquake and tsunami, albeit not withserious consequences.

From 2.30 p.m. on 12 March 2011 onwards,
there were significant releases of radioactive
substances into the environment at the Fukushima Dai-ichi site. These releases had – andto some extent are still having – enormous
consequences for the population in the more
immediate vicinity. There was a threat thatradiation from the drifting radioactive cloud,the absorption of radioactive substances byinhalation and deposits of radioactive substances on the ground would contaminate
the population in the surrounding area withgreatly increased radiation doses. In order toprevent this, residents had to be evacuatedon a large scale. The accident also impacted
the living conditions of people resident in thearea due to the penetration of activity into
the drinking water, the sea and into plants
and animals, leading to contamination of thefood chain.
On 12 March 2011, in response to the eventsin Japan, the Swiss Federal Nuclear Safety
Inspectorate (ENSI) mobilised its emergency
response organisation, which monitored
the event continuously and issued ongoingassessments of the situation in the stricken
nuclear plants. After the situation had beenstablilised, the ENSI emergency responseorganisation was returned to routine readiness on 24 March 2011. An analysis teamwas then assigned to continue monitoring
developments in Japan and to undertake acomprehensive analysis of the accident at
Fukushima Dai-ichi. The detailed progressionof the accident /47/, an in-depth analysis of
the accident giving special consideration tohuman and organisational factors /48/, andthe knowledge gained from these studies(Lessons Learned) /49/ were each publishedby ENSI as separate reports.

4|5

The present Report describes the state ofknowledge regarding the radiological effectsof the accident at Fukushima Dai-ichi on the
population in the surrounding area and thestaff at the power plant site up to October 2011.
Section 2 begins with an explanation of thecorrelation between the accident on the
Fukushima Dai-ichi nuclear power plant site
and its assessment according to international
criteria. This section goes on to describe andassess the discharge of radioactive material
from the reactors in units 1 to 3. The presentation also includes the average ongoingrelease rates and the treatment of contaminated water present at the plant.
Section 3 presents the dose rates on the
nuclear power plant site caused by deposits and distribution of the fission products
after the venting procedures and hydrogen
explosions. These rates provide the basis forradiation exposure for the assigned staff as
described in section 4, and they determined
the working conditions for such staff. Thissection also outlines the difficulties withdosimetric monitoring encountered by theplant operator after the accident, and thecountermeasures that were initiated. The status of radiation exposure for employees andother operational staff as currently known to
ENSI, and the difficulties in coping with anaccident of such proportions, are explainedwith the help of selected examples.
Section 5 describes the radiation exposurefor the population due to the release of radioactive substances in the area surrounding
the nuclear power plant. In the first phase
after the accident, the main contribution to
the dose was supplied by external irradiation from the drifting radioactive cloud andthe absorption of radioactive substances
via the respiratory tract. In the subsequent
ground-level phase, radioactive substances

deposited on the ground resulted in a further
long-term contribution to the dose due toexternal irradiation. Radioactive substancesthat were either directly or indirectly transferred onto and into forage crops andvegeTable les represented another importantsource for the dose, via the consumption offood (ingestion). Moreover, radioactive substances reached the human food chain fromlakes, rivers and the sea, via fish and seafood.
Discharges of radioactive substances into
surface water (rivers and lakes) contaminated drinking water reservoirs and contributed
to the increased radiation exposure via thedrinking water supply. This section also sets
out the measures implemented by the Japanese government to reduce radiation doses
for the population.
Section 6 of this report describes the effectsof the accident on Switzerland. The precautionary measures taken by the Federal Officeof Public Health (FOPH) as a consequenceof the accident and its impact on the Swiss
population are outlined. The main measurement results and conclusions for Switzerland
are also documented.
Section 7 contains a comparison of theevents in Fukushima with those at Chernobyl,
examining the various aspects and comparing the effects on the population and theenvironment, insofar as this is possible withthe data available at present.
Section 6 of this report originates from theFederal Office of Public Health (FOPH). The
Gesellschaft für Anlagen- und Reaktorsicherheit mbH (GRS) contributed key passages tosection 7.

2 | INES classification2	INES classification, determination of the volumes released
2.1 Overview
This section explains the classification of theaccident at the Fukushima Dai-ichi nuclear
power plant site in accordance with thecriteria of the International Atomic Energy
Agency (IAEA).
The International Nuclear and Radiological
Event Scale (INES scale) was developed in1990 following the accident at Chernobyl,
in order to classify and assess events innuclear plants. The scale extends from level

Level

Brief
designation

1 – “anomaly” – to level 7, which represents a“major accident”. Events at levels 1 to 3 aredesignated as “incidents”; events classified
at higher levels are regarded as “accidents”.
Events with little or no importance in termsof safety are assigned to level 0.
In order to classify an event, reference ismade to an extensive catalogue of criteria
which is published in an IAEA manual (cf. /2/).

Aspects
Radiological effects outside theplantRadiological effects inside theplant

Impairment of safety precautions

7

Major
Accident

Most serious releases:
effects on health and environment
in an extensive surrounding area

-

-

6

Serious
Accident

Substantial release:full deployment of disasterprotection measures

-

-

5

Accident
with Wider
Consequences

Limited release:
deployment of individual disasterprotection measures

Severe damage to the reactor
core / radiological barriers-

4

Accident
with Local
Consequences

Minor release:radiation exposure for the
population about the same as
natural exposure to radiation

Limited damage to reactor core
/ radiological barriers Radiation
exposure for staff leading
to death-3

Serious
Incident

Very minor release:radiation exposure for the
population equal to a fractionof natural radiation exposure

Severe contamination
Acute damage to health of staff

2

Incident-

Substantial contamination
Inadmissibly high radiation
exposure for staff

Incident Limited failureof in-depth defence precautions

1

Anomaly--

Divergence from permissible
ranges for safe plant operation

0

-

-

-

No or very minor safetysignificance“Near accident”
Extensive failure of indepth defence precautions

Table 2-1 Assessment aspects for the INES classification according
to the international scale
3 | Source: Federal Office for Radiation Protection (BfS) http://www.bfs.de/de/kerntechnik/ereignisse/ines.html

6|7Classification of the Fukushima accident at
the highest INES level is based on estimatesof the released radioactive substances.
Release of the nuclides Iodine-131 andCesuim-137 (which are critical for classification purposes) increased continuously after
the accident and finally exceeded the value
above which an accident is classified at level
7 on the INES scale.
In addition to the INES classification of theevent, the following section provides a moredetailed explanation of the release paths
for radioactive substances from the reactor
buildings into the environment, and the extent of the releases is quantified. As well as
the discharge of gaseous radionuclides andthose in particle form into the atmosphere,leakages in the primary containments also
resulted in radioactively contaminated water
being fed into the adjacent sea.

INES (cf. Figure 2-1). The significance of theindividual levels is indicated by a number anda brief description.
The levels are characterised by various
aspects, as shown in Table 2-1.

7
Major Accident

Accidents

6
Serious Accident
5
Accident with Wider
4
Accident with Local
Consequences
Incidents
3
Serious Incident

The actual progression of the accident ispresented in detail in a separate ENSI publication (cf. /47/).

2
Incident

1
Anomaly

2.2 	INES classificationof the event
2.2.1	Systematic schemeof the INES scale
The international assessment scale fornuclear events (International Nuclear andRadiological Event Scale, INES) comprises
levels 1 to 7 for events of major safety significance and level 0 for events with minor orno safety significance. It is therefore possible
to classify events at eight levels according to0
Event with little or no safetysignificanceFigure 2-1 The international assessment scale
for nuclear events - INES2

2 | Source: Bundesamt für Strahlenschutz (BfS) http://www.bfs.de/de/kerntechnik/ereignisse/ines.html
														
		2 | INES classification

2.2.2 Application of the INES scale		 to Fukushima Dai-ichi
At 4:36 p.m. on 11 March 2011, the Japanese
Nuclear and Industrial Safety Agency (NISA)
provisionally classified the event at the
Fukushima Dai-ichi site as INES 3. The reason
for this was the failure of the supply pumps,
entailing the loss of the emergency andresidual heat removal systems of units 1 and
2 following the failure of the AC power
supply (cf. /1/). The INES classification wasmade in consideration of the aspect mentioned in Table le 2-1, “Impairment of safety
precautions” based on the criterion: “Nearaccident, extensive failure of in-depth
defence precautions”.
On 12 March 2011, venting of the primarycontainment in unit 1 was carried out and ahydrogen explosion occurred in the reactor
building. Based on the measurement resultsfrom monitoring of the surrounding area,
NISA announced the emission of radioactive
iodine, cesium and other substances into thesurrounding area. At this point in time, NISA
calculated the released activity as 0.1% of thecore inventory, and it increased the provisional classification of the event to INES 4
for unit 1 (cf. /1/).

On 18 March 2011, once it had to be assumed
that there was severe core damage in units
1-3, NISA increased the classification of theevent for each of units 1-3 to INES 5; thequantity released was now said to be several
per cent of the core inventory (cf. /1/).
Classification as INES 5 was made on thebasis of the aspect of “Radiological effects
inside the plant” mentioned in Table 2-1, andit was now assumed that the criterion ofsevere core damage and/or severe damage
to the radiological barriers was met.
NISA carried out calculations on the quantity
released into the atmosphere (cf. /5/). The
results obtained, compared with the NSC(Nuclear Safety Commission) values, areshown in Table 2-2 below.
On the basis of cooperation between the
Nuclear Safety Commission (NSC) and theJapan Atomic Energy Agency (JAEA), thequantities of radionuclides I-131 and Cs-137
released into the atmosphere at the Fukushima Dai-ichi site were determined independently in the period from 11 March 2011
until 5 April 2011. The amounts released
during the aforementioned period arequantified as 1.5E+17 Bq for I-131 and 1.2E+16
Bq for Cs-137 in the NSC publication dated
12 April 2011 /4/.

Assumed quantity released from Fukushima Dai-ichi [Bq]
NuclideNISA data

NSC data(Reference value) Quantity
released at Chernobyl unit 4
[Bq]

I-131

1.3E+17

1.5E+17

1.8E+18

Cs-137

6.1E+15

1.2E+16

8.5E+16

Cs-137 converted into
I-131 equivalent

2.4E+17

4.8E+17

3.4E+18

Total I-131 equivalent

3.7E+17

6.3E+17

5.2E+18

Table 2-2 Comparison of determined quantities released for the INES classification 4

4 | Source: /5/
5 | The conversion of the Cs-137 values into an I-131 equivalent was carried out by NISA, taking account of INES User's Manual 10.

8|9

Figure 2-2 below shows the accumulated
releases over the aforementioned period as
calculated by NSC (publication dated 12 April2011), in graphic form (cf. /4/).

Figure 2-2 Cumulative release of I-131 and Cs-137 according to NSC calculationsin the period from 11 March 2011 to 5 April 2011 6

On 12 April 2011, NISA made the classification
for the entire Fukushima Dai-ichi site. Thiswas undertaken on the basis of the aspectof “Radiological effects outside the plant”,
according to the criterion of “Major releaseof radioactive material with widespread
health and environmental effects” in level
INES 7. The classification was justified by thecalculated quantities of Iodine equivalentreleased, i.e. 3.7E+17 Bq (NISA) and 6.3E+17
Bq (NSC and JAEA) (cf. /1/). According to
the INES Manual (cf. /2/), an event must beclassified as INES 7 if the release of radioactive substances into the atmosphere isradiologically equivalent to a release of several 10’000 TBq (1E+16 Bq) of Iodine-131. The
calculated releases are described in greater
detail in sections 2.3 and 2.4 below.

6 | Source: NSC http://www.nsc.go.jp/NSCenglish/geje/2011%200412%20press.pdf							
		2 | INES classification

2.3 	Release of radioactive
substances into theatmosphere
According to knowledge at present, almost
the entire release of radioactive material
from the reactors in units 1 to 3 at Fukushima
Dai-ichi was due to two processes. On the
one hand, unfiltered venting operations of
the primary containment caused the releaseof large quantities of radioactive substances
via the air. On the other, hydrogen explosions
caused further releases, finally leading to theloss of safety barriers to retain activity.
In detail, the releases were based on the following processes. The loss of the integrity of
the fuel assemblies, up to meltdown of thenuclear fuel and subsequent partial transfer
into the bottom head dome area of the reactor pressure vessel (RPV), and the partial
loss of the integrity of the RPV, were due tothe fact that the rector cores were at times
not covered with coolant.

Due to the failure of the core cooling andthe resultant need to reduce pressure in the
RPV via the pressure relief valves, primarily
airborne fission products were transferred
via the condensation chambers (designed in
the shape of a torus in Mark I containments)
into the primary containments. Due to theongoing influx of energy into the primarycontainments with no removal of heat to theoutside, the pressure and quantity of the activity inventory in them rose in each case. As
the incident proceeded, emergency measures (containment venting operations) led tohigh discharges of activity into the surrounding area. It is also suspected that leaks occurred on the lid seal of the primary containment and on wall leadthroughs, due to theincrease of heat and pressure in the primarycontainment as mentioned above. Thispartial loss of primary containment integrity
caused the transport of radionuclides andhydrogen from the primary containment into
the reactor building. The subsequent H2 explosions destroyed the reactor buildings andreleased larger quantities of radionuclides.
From then on, the reactor buildings (whichwere now open) led to a continuous anddiminishing release of radioactive substances(cf. Figure 2-4). Due to the subsequent supply of additional coolant with emergency
equipment and also because of internal leakages (e.g. on the Torus, the containment lid
or the containment itself) and leaks in buildings, radioactive substances were released
into the surrounding area via water.

10 | 11

Inspection of the spent fuel pools in units 2,
3 and 4, including associated nuclide measurements, have so far provided no grounds
for assuming major damage to the fuel assemblies (FA) stored there. It is concluded
from this that the main releases took place
via the containment venting operations orleakages. No statements are yet available
regarding the spent fuel pools belonging tounits 1, 5 and 6. However, it may be assumed
that no releases took place from units 5 and6, which were less seriously affected by thetsunami and whose reactor buildings remained intact (cf. /11/). Both the fuel assembly wet storage facility and the storage containers in the dry storage facility remained
intact and did not contribute to the releaseof activity into the surrounding area. The
dry storage facility, which is located near theturbine hall of unit 5, was damaged by thetsunami (cf. Figure 2-3). As it was not possible to determine any releases of activity bymeans of measurements /3/, it is assumed
that the containers remained intact.

Figure 2-3 Situation in the dry storage facility
at the Fukushima Dai-ichi nuclear power plant 7

Analyses by NISA in May 2011 indicatedrelease of the core inventory for the Fukushima Dai-ichi site, depending on the reactor
unit, of approx. 0.4 – 7% for Iodine-nuclides,
approx. 0.4 – 3% for Tellurium nuclides, approx. 0.3 – 6% for the Cesium nuclides andalmost the entire inventory of noble gases.

7 | Source: Tepco http://www.tepco.co.jp/en/news/110311/images/110909_69.jpg

2 | INES classification

These values are therefore higher than thefirst estimates made for the purpose of the
INES classification. The releases of fission
products into the surrounding area at thestart of the events are listed for the individual units in Table 2-3 /1/.
However, the calculated release proportions
depend on assumptions, e.g. regarding operating conditions, amounts of water fed into
the RPV and regarding possible leakages.
The calculated releases may vary within certain bandwidths according to the influencing
variables on which they are based. Information about operating data was not fully knownat the time the calculations were undertaken,
so the behaviour of the plants cannot be
described with the necessary accuracy.

12 | 13

NuclideHalf-life 9Quantity released [Bq]
Unit 1

Unit 2

Unit 3

Total for units 1-3

Xe-1335.25 d

3.4E+18

3.5E+18

4.4E+18

1.1E+19

Cs-1342.06 a7.1E+14

1.6E+16

8.2E+14

1.8E+16

Cs-13730.17 a5.9E+14

1.4E+16

7.1E+14

1.5E+16

Sr-89

50.5 d8.2E+13

6.8E+141.2E+15

2.0E+15

Sr-90

28.64 a6.1E+124.8E+138.5E+13

1.4E+14

Ba-14012.75 d1.3E+14

1.1E+15

1.9E+15

3.2E+15

Te-127m

109.0 d2.5E+147.7E+14

6.9E+13

1.1E+15

Te-129m

33.6 d

7.2E+142.4E+15

2.1E+143.3E+15

Te-131m

30.0 h

9.5E+13

5.4E+10

1.8E+129.7E+13

Te-13276.3 h

7.4E+144.2E+11

1.4E+13

7.6E+14

Ru-10339.35 d2.5E+91.8E+93.2E+97.5E+9Ru-106373.6 d7.4E+85.1E+88.9E+82.1E+9Zr-95

64.0 d

4.6E+11

1.6E+132.2E+11

1.7E+13

Ce-14132.5 d

4.6E+11

1.7E+132.2E+11

1.8E+13

Ce-144284.8 d3.1E+11

1.1E+13

1.4E+11

1.1E+13

Np-2392.355 d3.7E+127.1E+13

1.4E+127.6E+13

Pu-23887.74 a5.8E+81.8E+10

2.5E+81.9E+10

Pu-2392.411E+4 a

8.6E+7

3.1E+94.0E+7

3.2E+9Pu-2406‘563 a8.8E+73.0E+94.0E+7

3.2E+9Pu241

14.35 a3.5E+10

1.2E+12

1.6E+10

1.2E+12

Y-91

58.5 d3.1E+112.7E+124.4E+11

3.4E+12

Pr-143

13.57 d3.6E+11

3.2E+125.2E+11

4.1E+12

Nd-14710.98 d1.5E+11

1.3E+122.2E+11

1.6E+12

Cm-242

162.94 d

1.1E+107.7E+10

1.4E+101.0E+11I-131

8.02 d1.2E+16

1.4E+17

7.0E+15

1.6E+17

I-132

2.3 h

4.5E+149.6E+11

1.8E+13

4.7E+14I-133

20.8 h

6.5E+14

1.4E+122.6E+13

6.8E+14I-135

6.61 h6.1E+14

1.3E+122.4E+13

6.3E+14

Sb-127

3.85 d1.7E+15

4.2E+15

4.5E+14

6.4E+15

Sb-1294.4 h

1.6E+148.9E+103.0E+12

1.6E+14Mo-99

66.0 h8.1E+7

1.0E+4

6.7E+68.8E+7

Table 2-3 Provisional calculation to estimate the airborne release of radioactive substances in the early phase of
the accident (taking account of operating data until 16 May 2011) 8

8 | Source: /1/
9 | Half lives as per /45/

2 | INES classification

The Ministry of Economy, Trade and Industry(METI) publishes progress reports at regularintervals (cf. /6/), with estimates of the average release rate. As shown in Figure 2-4, theaverage release rate decreased by several
orders of magnitude, i.e. from approx. 8E+14
Bq/h on 15 March to approx. 1E+8 Bq/h in
the period from 3 to 13 October 2011. Theseestimates are based on individual air concentration measurements. In the meantime,
precipitation collectors were installed to allow more accurate values.

On 24 August 2011, the NSC announced
that the JAEA had carried out new calculations taking account of further radiologicalmeasurements in the surrounding area andadditional factors at the start of the accident.
Taking account of these new conditions, thequantity of radioactivity released between
11 March and 5 April 2011 is calculated as
1.3E+17 Bq for I-131 and 1.1E+16 Bq for Cs-137.
The total emission of iodine and aerosols
would therefore be approx. 10% less than thevalue published in April (cf. Table 2-2). There
were no significant releases at the Fukushima
Dai-ni, Tokai and Onagawa sites.

Figure 2-4 2-4 Release rates for units 1-3 at Fukushima Dai-ichi 1010 | Source: METI http://www.meti.go.jp/english/earthquake/nuclear/roadmap/pdf/111017_nps_1pdf1

14 | 15

2.4 	Release of radioactive
substances via water
into the sea
Activity was transported into the primarycontainments due to the RPV depressurising operations and through the three RPVs
which developed leaks due to core meltdown. At least in part, water was able toescape from the primary containments due
to leakages. This water accumulated in thelower levels of the reactor buildings. Especially in unit 2, where it is suspected that theTorus is leaking, a large quantity of radioactive water escaped. Another presumed causeof the penetration of activity is the outflow
of the mixture of hydrogen, water vapour
and nitrogen from the primary containments
into the reactor buildings (cf. section 2.3).

After the detonations, and with the reactor
buildings open, the spent fuel pools were initially supplied by fire extinguishing cannons
and later with concrete pumps. This made it
possible to flush radionuclides into the lower
levels of the reactor buildings, and rain also
caused washouts of the debris distributed
over the pool levels by the detonations. Fromthe lower levels of the reactor buildings, thecontaminated water flowed into the turbinehalls via connecting ducts/channels. The turbine halls, in turn, are connected to the pumphouses for the water intakes via cable ducts
and concrete shafts (cf. Figure 2-5). The contaminated water reached the sea en route to
the water intakes. At the start of September
2011, approx. 90’000 m3 of contaminatedwater was present in units 1 to 4.

Figure 2-5 Path by which contaminated water spread into unit 2 11

1 1 | Source: ICAPP/TEPCO https://www.sfen.fr/ICAPP-11											2 | INES classification

The analysis results for nuclide concentrations in the accumulated water in the turbinehalls at the end of March 2011 are shown in
Table 2-4 (cf. /1/). The analysis of the waterin the turbine hall of unit 2 showed activity
content levels of 1.3E+10 Bq/l for I-131 and3.0E+9 Bq/l for Cs-137 (cf. /7/). The values
exceed those measured in units 1 or 3 by afactor of about 10. The suspected cause is
the leaking Torus. The accumulated volume
of water by the end of March 2011 was estimated at 25’000 m3 for unit 2.

A dose rate of >1 Sv/h was measured in thecable shaft near the water intake of unit 2 on
2 April 2011; this was caused by the highly
contaminated water with activity values for
I-131 of 6.9E+9 Bq/l and for Cs-137 of 2.0E+9
Bq/l. According to NISA's estimates, approx.
520 m3 of this water, which originated fromthe turbine hall of unit 2, flowed into the sea
via connecting ducts/channels and cable
shafts as a result of leakages in the concrete.
It was possible to halt this outflow on
6 April 2011.

16 | 17

Unit

Unit 1

Unit 2

Unit 3

Unit 4

Sampling location

Basement,
turbine hallBasement,
turbine hallBasement,
turbine hallBasement,
turbine hallDate

26.03.2011

27.03.2011

24.03.2011(22.04.2011)24.03.2011(21.04.2011)

Mo-99(66.0 h)

< NWG 12

< NWG

< NWG
(< NWG)

1.0E+3(< NWG)

Tc-99m
(6.0 h)

< NWG

< NWG

2.0E+6(< NWG)

6.5E+2(< NWG)

Te-129m(33.6 d)

< NWG

< NWG

< NWG
(< NWG)

1.3E+4(< NWG)

I-131(8.02 d)1.5E+81.3E+10

1.2E+9(6.6E+8)

3.6E+5(4.3E+6)I-132(2.30 h)

< NWG

< NWG

< NWG
(< NWG)

1.3E+4(< NWG)

Te-132(76.3 h)

< NWG

< NWG

< NWG
(< NWG)

1.4E+4(< NWG)

Cs-134(2.06 a)1.2E+83.1E+81.8E+8(1.5E+9)

3.1E+4(7.8E+6)

Cs-136(13.16 d)

1.1E+7

3.2E+82.3E+7(4.4E+7)

3.7E+3(2.4E+5)

Cs-137(30.17 a)

1.3E+83.0E+91.8E+8(1.6E+9)

3.2E+4(8.1E+6)

Ba-140(12.75 d)< NWG

6.8E+85.2E+7(9.6E+7)< NWG(6.0E+5)

La-140(40‘272 h)< NWG

3.4E+89.1E+6(9.3E+7)

4.1E+2(4.8E+5)

Nuclide(T1/2)
Activity[Bq/l]

Table . 2-4 Nuclide concentrations in contaminated water in the turbine halls 13

12 | LOD = limit of detection
13 | Source: /1/

2 | INES classification

In the course of the emergency measures,the decision was taken to discharge approx.
9’070 m3 of weakly contaminated water fromthe central waste treatment plant into thesea because the storage capacities were exhausted. In order to create additional storage
capacities, weakly active water in unit 2 was
pumped from the condenser in the turbinehall into the condensate storage tank andinto the Torus compensating reservoir. From
19 April 2011 onwards, part of the highly active wastewater from the turbine hall and theadjacent shafts and ducts/channels of unit 2
could then be pumped into the central waste
treatment plant and the condenser. Thanks
to the falling water level, the risk of leakages into the sea or the groundwater was
reduced.
Another leak was discovered on the channelof unit 3 on 10 May 2011. It was possible toseal this by 11 May 2011. The outflow calculations produced a volume of approx. 250 m3
with an activity content of 2.0E+13 Bq.

Furthermore, approx. 1’320 m3 of low active
water was pumped into the sea from theconcrete shafts of units 5 and 6 between
4 and 9 April 2011. The total activity of thisliquid alone that was discharged into theenvironment was about 1.5E+11 Bq. By way ofcomparison, the approved annual amount ofdischarged activity for Fukushima Dai-ichi is
2.2E+11 Bq (cf. /1/).
The total quantity of activity released into
the sea as per /1/ is approx. 4.7E+15 Bq.
Since mid-June 2011, the radioactively contaminated water has been cleaned with thehelp of specially installed decontamination
plants, and has been re-used to cool the reactors (more or less in line with the recirculation principle).

18 | 192.5 	Summary andassessment
After the loss of all safety barriers provided
to retain the radioactive substances (fuelmatrix, fuel rod cladding, reactor pressure
vessel (RPV) with primary circuit, containment with concrete shield and reactor buildings), fission products were released into
the environment on a significant scale fromreactors 1 to 3.
The releases took place in the course of various accident progressions in units 1 to 3, andin several phases. For these reasons, the classifications as per INES had to be re-assessedas the progression of the event continued,
with adaptations to current developments.
The Japanese authorities undertook theassessments required for this purpose by
applying evaluated computing codes which
are in widespread international use (e.g.
MELCOR). These require the input of certain
boundary conditions such as fuel burnup,
retention in the building, etc.

Likewise, the exact quantities of radioactive
substances discharged into the sea are notknown. The available figures are based onrough estimates by TEPCO, the operatingcompany, because the precise outflow periods and leaked volumes (especially at thestart of the accident) cannot be traced. The
aim of the deliberate introduction of radioactively contaminated water into the ocean
was to mitigate the consequences of theaccident and was necessary in the specificsituation.
Since the beginning of April 2011, work has
been under way to stem the radioactive releases which still continue to a lesser extent.
The destruction and contamination of theplant site caused by the hydrogen explosions
are a considerable impediment to this work.
Moreover, the simultaneous timing of theaccidents in units 1 to 3 poses an enormous
challenge in terms of staff and work outlay,
as well as interactions between the units.
According to the operating company's current
rehabilitation plan, it will take approximately
three more years to stem the releases completely and to decontaminate the plant site.

3 | Ambient dose rates

3	Ambient dose rates
on the power plant site
3.1 Overview
This section documents the ambient dose
rates (ADR) measured during and after
the accident on the site of the Fukushima
Dai-ichi nuclear power plant.
Due to the earthquake and the tsunami,
there were partial failures of the stationary
ADR measuring probes. With the help ofauxiliary provisions and mobile measuring
instruments, it was nevertheless possible tomaintain measuring operations. In the courseof dealing with the accident, measuring
operations were expanded and the stationary probes were returned to operation.
At the start of the accident, the ambient
dose rates were severely affected by theradioactive releases during the containment
venting operations and the hydrogen
explosions. Between 11 March 2011 and 27
March 2011, the progression of the accident
led to significantly accentuated dose rate
peaks. As measures were taken to cope withthe accident, the ambient dose rate thendropped constantly from 27 March 2011
onwards, and it is now dominated by theradioactive deposits on the site and thebuilding structures. Pieces of debris or plantcomponents with particularly high dose
rates – known as Hot Spots – are present inlarge numbers in the plants and on the site,making working conditions for the operational staff even more difficult.
zusätzlich.

3.2 Results and development of the ambient dose
rate measurements
Extensive values measured by the operators are available for the plant site. Figure 3-1
shows the permanently installed monitoring
posts (measurement points) used to register the ambient dose rate (ADR) in blue. In
some cases, the function of these monitoring
posts was impaired by the earthquake and/or the tsunami. Damage was inflicted on the
power supply, the data lines and the computing units in the main building. Partially, theprobes were then supplied from mobile batteries and the measured data were evaluatedwith the help of portable computers.
Due to new ADR measuring points (temporary monitoring posts) installed during thepost-accident phase (shown in red), thescope of data changed. Complete data series
are not available for all the monitoring posts
because of the problems with the power
supply.
At the start of the accident, the measured
ADR values originated from the releases during venting from the primary containmentsof the reactors and from the releases due tothe H2 explosions. Based on the chronology,
key events can be assigned to the individual
dose rate peaks during the progression of
the accident. These are indicated in Figure
3-2, which originates from the Gesellschaft für
Anlagen- und Reaktorsicherheit mbH (GRS).

20 | 21

Figure 3-1 Locations of ADR monitoring posts on
the Fukushima Dai-ichi plant site 14

Measured dose rates at selected monitoring posts
Fukushima Dai-ichi – data from TEPCO, the operator
Monitoring post MP 1
Explosion and fire in unit 4 in
the area of the spent fuel pool,approx. 06:00–11:16

Monitoring post MP 2
Further
explosion,unit 2,
approx. 10:00

Monitoring post MP 3
Monitoring post MP 4

Dose rate in μSv/h

Monitoring post MP 5
Repeat venting,unit 2,
approx. 20:35

Venting, unit 2?
approx. 13:50

Monitoring post MP 8
Monitoring post main gate

Releases fromunits 2 and 3

Monitoring post west gate
Monitoring post main building,north side
Monitoring post main building,south side
Monitoring post seismicallyprotected building

Monitoring post
main building,north side

Venting, unit 3,
approx. 09:20

Development of smoke, unit
3 (15:55) and unit 2 (18:22)

Explosion, unit
1, 15:36
Monitoring post
west gate

Monitoring post
main gate

Monitoring post
seismically protectedbuilding

Monitoring post
main building,south side

Time of measurement (local time at the Japanese plant)

Figure 3-2 Overview of ADR values in the period from 12 to 31 March 2011 15

14 | Source: TEPCO http://www.tepco.co.jp/en/nu/fukushima-np/f1/index-e.html
15 | Source: GRS http://fukushima.grs.de/kommunikation-medien/japan-statusmeldung-stand-31-03-2011-1400																							3 | Ambient dose rates

The H2 explosions scattered radioactive debris
over extensive areas of the site. In addition,
there are numerous Hot Spots (see Figure3-4) which cannot be easily removed. Moreover, the radioactive substances deposited
due to precipitation and other effects leadto increased dose rates on the plant site. The
short half life of the iodine nuclides in particular has a favourable effect on the long-term
dose rate. Remote-controlled machines arebeing used to remove contaminated rubble
and debris in order to reduce the ambient
dose rate. On the other hand, new sourcesof radiation are created again by the installation of auxiliary equipment to control andreduce the consequences of the accident(e.g. water treatment plants, hoses to pumpcontaminated water). There are also ongoingreleases from the reactors (cf. section 2.2).
The following charts show the ADR values
measured by TEPCO with mobile probes(cf. /1/). As measurements were taken atrela­tively few points on 23 March 2011 −mainly in the area directly surrounding thereactor units (cf. Figure 3-3) – it later became
possible to take measurements in most of
the areas surrounding the power plant units
after the debris had been removed (cf. Figure
3-4).

Figure 3-3 ADR values on the Fukushima Dai-ichi site on 23 March 2011 16

16 | Source: TEPCO http://www.tepco.co.jp/en/nu/fukushima-np/f1/images/f1-sv-20110323-e.pdf														
			22 | 23

The reduction in the ADR values in wide
areas around the units is clearly recognisable.
However, Hot Spots with very high dose
rates are repeatedly discovered during theremoval of the debris (U1/2 SGTS ­>­10’000 mSv/h) (cf. Figure 3-4).

Figure 3-4 ADR values on the Fukushima Dai-ichi site on 1 August 2011 17

17 | Source: TEPCO http://www.tepco.co.jp/en/nu/fukushima-np/f1/images/f1-sv-20110802-e.pdf																				
			3 | Ambient dose rates

On 21 May 2011, for example, a dose rate of
1’000 mSv/h was measured in debris near
unit 1 (cf. Figure 3-5).

On 1 August 2011, measurements were taken
at these points with the use of a telescopic
detector (cf. Figure 3-7). According to
TEPCO, the surface dose rate at the point
where the pipes are integrated into the vent
stack was >10 Sv/h (cf. /8/). The operator
states that this is the highest dose rate yetmeasured outside the reactor buildings.
The pipes connect the Standby Gas Treatment System (SGTS), also known as theEmergency Gas Treatment System, to thestack.

Figure 3-5 Radioactive debris near unit 1 18

On 31 July 2011, TEPCO discovered by useof a gamma camera high gamma levels at
the bottom of the vent stack shared by units
1 and 2 (cf. Figure 3-6).

Figure 3-7 Base of stack between units 1 and 2,
measurement with a telescopic detector 20

Figure 3-6 Base of stack, units 1 and 2,
photographed with a gamma camera 19

18 | Source: TEPCO http://www.tepco.co.jp/en/news/110311/images/110521_7.jpg
19 | Source: TEPCO http://www.tepco.co.jp/en/news/110311/images/110802_2.jpg
20 | Source: TEPCO http://www.tepco.co.jp/en/nu/fukushima-np/images/handouts_110803_01-e.pdf

24 | 25

According to TEPCO, an ambient dose rate
>5000 mSv/h was measured on 2 August
2011 on level 2 of the connecting building forthe turbine hall (Turbine Building) of unit 1,
near the entrance to the so called train room
for the emergency gas treatment system(cf. Figure 3-8).
This is the highest ambient dose rate yetmeasured inside the reactor building. According to /9/, it was detected on pipes thatwere used to vent unit 1 on 12 March 2011.

3.3	Summary andassessment
There was a major increase in the ambient
dose rates inside the reactor units and on
the plant site due to the partial lack of water
coverage for the reactor cores and the massive releases of radioactive substances fromthe reactors. Especially at the start of theaccident, the workers were confronted withdose rates that no longer permitted workinside the plant, according to the radiation
protection rules. Due to the high dose rates,
the staff had to leave individual plant areasand (at times) the entire unit on several occasions.
The venting operations for the primarycontainments and the hydrogen explosions
caused widespread distribution of radioactive substances and debris over the plantsite. Dose rates, sometimes in the range ofseveral Sv/h, presented enormous obstacles
to dealing with the accident and made itnecessary to set up restricted zones.

Figure 3-8 ADR values [mSv/h] inside the connecting building for theturbine hall of unit 1 21

Even today, the dose rates still impose severe
constraints on the clearance work. In someplaces, the debris can still only be removed
remotely.
The ambient dose rate on the plant site has
been decreasing steadily since the end of
March 2011. This is due to the radioactive
decay of the short-lived fission products inparticular, the reduced release of radioactive
substances from the reactors and the ongoing clearance of debris.

21 | Source: TEPCO http://www.tepco.co.jp/en/nu/fukushima-np/images/handouts_110803_01-e.pdf														
			4 | Radiation exposure and working conditions

4	Radiation exposure andworking conditions for staff
4.1 Overview
This chapter presents the radiation exposure
which the staff at the Fukushima Dai-ichi
nuclear power plant was exposed to fromthe accident on 11 March 2011 till the beginning of September 2011. All the data listed
here is publicly accessible via the Internet.
The earthquake and the tsunami waves(flooding) destroyed not only the structuresof the buildings and of the technical systemsof the Fukushima Dai-ichi nuclear power
plant, but also a large part of the infrastructure for the dosimetry system. The power
plant operator and the staff no longer had
enough functioning dosimeters at theirdisposal directly after the tsunami. For thisreason, it was impossible to carry out any
automatic dosimetry of the staff with Active
Personnel Dosimeters (APDs), as normal
prior to the earthquake, until about midApril. Instead, alternative methods wereused, such as the calculation of accumulated
individual doses by estimating the timespent at the location of action and theambient dose rate there. Only the leader of
each operational group could be equippedwith an electronic dosimeter. The radiationdose determined with this dosimeter was
assumed as the individual dose for eachmember of the group. The accumulated
doses were read after the assignments, andwere entered manually in Excel tables.

Difficulties arose with determining the in­ter­nal radiation exposure using whole bodymonitors due to the increased backgroundradiation at the Fukushima Dai-ichi site.
The number of persons to be examined was
too great, and there was a shortage of wholebody monitors.
For the reasons just stated, uncertainty prevails regarding the radiation doses that wereactually accumulated. Extensive information
about the accumulated individual doses due
to external and internal radiation exposure isavailable on the Internet, but cannot always
be interpreted. There seems to be a lack ofconclusive data relating to collective doses.
Based on the dose limits stipulated in Japan,
the personal dosimetry prior to the accident
is compared to that during the response to
the accident, and consideration is also given
to protective measures and equipment, andto the exceptional working conditions. Oneof the key points in this chapter is the radiation exposure of people working in the plant
during and after the accident, together with
reported violations of dose limits. The chapter is completed by information on measures
to reduce the doses during work on theplant.

26 | 27

4.2 	Dose limits for persons
occupationally exposed
to radiation in Japan
In Japan, the legally stipulated dose limit for
occupationally exposed persons is 50 mSv
per year during normal conditions. A maximum of 100 mSv may be accumulated during a five-year period. For women, a maximum limit of 5 mSv during a 3-month period
is specified (cf. /39/).
For occupationally exposed persons andwho have to carry out emergency work, theeffective dose limit is 100 mSv per year. The
limit for the dose equivalent for the eye lens
is 300 mSv and for the skin 1 Sv per year.
The above mentioned limits are based on
the ICRP 1990 Recommendations, Pub. 60(cf. /35/) and were specified by the Radiation Review Council of the Ministry of Education, Culture, Sport, Science and Technology(MEXT).
In case of a nuclear accident, higher dose
limits may be specified if this is necessary
in order to deal with incidents. In areas
where measures are undertaken to manage
a nuclear accident, the effective annual dosecan be raised from 100 mSv to 250 mSv
from the declaration of the emergency until
it is lifted. The emergency was declared on
14 March 2011 and the increase was decided

by the Ministry of Health, Labour and Welfare (MHLW) on the next day (cf. /36/). The
increase of the limit to 250 mSv was justified on the basis of ICRP 1990 (cf. /35/). The
recommendation advises a maximum doseof 500 mSv for persons who participate
voluntarily in emergency operations with theaim of preventing worse effects.
The President of the MHLW and the Ministerof Education, Culture, Sports, Science andTechnology (MEXT) discussed the adjustment of the dose limits in advance with
the Radiation Review Council at MEXT andreceived feedback that such an increase wasappropriate.
MHLW has published additional documents
for the administrative regulation of radiation exposure for staff who were involved inemergency work at the start and who thencarried out different work which entailed
exposure to radiation.

4 | Radiation exposure and working conditions

4.3 	Dosimetric monitoringof plant staff

4.3.2 Changes to dosimetric monitoring subsequent to the accident

4.3.1 	Status prior to the events of 11
March 2011

4.3.2.1 Measures in the Fukushima
Dai-ichi nuclear power plant

Prior to the accident, TEPCO implemented
radiation protection measures with the aimof minimising radiation exposure for occupationally exposed persons. At the Fukushima
Dai-ichi nuclear power plant, a dosimetry
system was in operation to measure radiation exposure during work in the controlled
zone; this guaranteed that each person was
equipped with an electronic dosimeter (Active Personnel Dosimeter, APD). This system
ensures automatic personal allocation of
the individual doses and computer-assisted
evaluation of the doses.

When the tsunami waves reached the Fukushima Dai-ichi nuclear power plant and theside of the buildings facing the sea in which
the entrances to the controlled zones are located, the dosimetry monitoring system, thereading stations and numerous APDs were
flooded and therefore became unusable.
According to a report from the Kyodo news
agency dated 1 April 2011, 5’000 dosimeters
were available to the staff at the Fukushima
Dai-ichi nuclear power plant before the accident on 11 March 2011. Only 320 devices werestill capable of functioning after the tsunami.

In addition, the radiation dose of each person was measured as they entered and left
the controlled zone. Radiation doses werealso recorded individually when donning
protective equipment and on reading the
APD immediately before entering a controlled zone.

It was no longer possible to equip eachindividual with an APD directly after theaccident. TEPCO therefore decided thatinstead, each leader of an operational group
had to wear a dosimeter. The radiation dose
registered by this dosimeter was assumed as
the individual dose for each member of thegroup. After TEPCO was asked by NISA toundertake every necessary effort in order toindividually record and monitor the radiation exposure for the staff, TEPCO procured
enough dosimeters (from 1 April 2011 onwards) so that every person could again be
equipped with a personal dosimeter.

TEPCO regularly carried out measurements
to monitor incorporation by the staff, withthe help of whole body monitors. These
measurements were taken when a person
first entered a controlled zone and every
three months thereafter.

28 | 29

Due to the rising level of radiation and contamination on the power plant site, the staff
were ordered to remain in an earthquakeresistant building (Main Anti-Earthquake
Building) on the plant site when not engaged
in operations. The work assignments were
to be prepared, the APDs were to be distributed and the accumulated radiation doses
were also to be recorded in this building.
At the outset, staff dosimetry and the recording of radiation doses had to be carriedout by hand. The results of the radiationdose measurements had to be typed into
Excel tables manually so that they could be
stored in a database.
APD’s were not worn in the Main Anti-Earthquake Building. For this reason, the externalradiation exposure there was determinedon the basis of the time spent in the radiation field and the ambient dose rate (ADR);
likewise, suitable protective equipment (suchas protective masks) was not worn there,
although the air contamination in this building exceeded the limits (cf. /37/). This led toincorporations and to violation of the threemonth limit for two female workers.
On 14 April 2011, it was possible to commission a new dosimetry system which was
almost identical to the previous system(automatic recording of names and radiation doses). Work on the restoration of theregular dose monitoring system was thenvirtually completed.

As the whole body monitors could not be
used in the Fukushima Dai-ichi nuclear power plant due to the increased backgroundradiation, mobile whole body monitors weremade available. In addition, the operational
staff was taken to other plants for radiation protection checks and incorporation
measurements. Due to the large number of
persons to be monitored, TEPCO decided tomeasure individuals with high external radiation doses and those involved in emergency
work during March as a priority.
Later the Japanese government in its no. 12of the Lessons Learned (cf. /11/) called formeasures to improve the radiation protection system in case of an accident,. Amongother things, there is a recommendation forcooperation by operators subject to instructions from NISA, with the aim of establishingcontinuous personal dosimetry even in caseof accidents. In addition, rules were defined
to guide the radiation protection staff regarding the relevant tasks to cope with the
emergency. These measures aim to ensure
maintenance of radiation protection in caseof emergencies. In order to attain this goal,
training of staff in accomplishing radiation
protection tasks during emergencies should
be encouraged.

4 | Radiation exposure and working conditions

4.3.2.2 Measures in “J Village”
From 17 March 2011 onwards, the “J Village”,
a TEPCO sports facility about 20 km southof the Fukushima Dai-ichi nuclear power
plant, was also used to make preparations
for operational assignments in the nuclear
power plant. Among other activities, protective suits were donned here and decontamination tests were carried out.
A dosimetry system was established in “J
Village” for personnel of the Fukushima Daiichi nuclear power plant who were exposed
to radiation in the course of their work andwho were unable to enter the earthquake-resistant building in order to obtain their APDs
there. The dosimeters used in “J Village”
were of different designs; they were madeavailable at short notice by several organisations. By the daily return to “J Village”,
the accumulated radiation doses had to becollected and registered manually. Since thestart of June 2011, TEPCO has operated abarcode system for individual identification.
In August 2011, TEPCO transferred the wholebody monitors from Fukushima Dai-ichi
and Fukushima Dai-ni to “J Village”. A newwhole body monitor for “J Village” was also
procured.

4.3.2.3 Radiation protection
equipment and planningof work
It was difficult to prevent the penetration ofradioactive substances into the “Main AntiEarthquake Building” because the entrance
door was not designed to be airtight andthe H2 explosions in units 1 and 3 had caused
damage to the door. Moreover, no special
protective equipment was installed in orderto mitigate the consequences of a nuclear

accident. Persons present in this building
therefore incorporated radioactive substances. As a countermeasure, a separate ventilation plant with active carbon filters was
finally set up in the entrance zone in orderto reduce airborne activity in the building.
TEPCO considered that no additional measures were necessary.
For work in areas with high dose rates, work
plans with appropriate radiation protection
measures were drawn up. The staff was also
informed about the radiological situation.

4.4	Status of radiation
exposure
Assignments at the location of the accident
and in its immediate vicinity caused andstill causes a significant radiation exposure
for all operational staff. The staff consists ofexternal and internal members. In addition to
the plant's own staff, third-party personnel
from external companies and people from
deployment organisations (army, police, firebrigade, etc.) were operational.

4.4.1		 Army and police units
The deployment personnel (Self-Defense
Forces of Japan) working within the 30 km
zone around the Fukushima Dai-ichi nuclear
power plant assessed their radiation exposure prior to deployment on the basis of thelatest ADR values at the operational locationand the planned time of the operation. The
protective equipment was selected accordingly. The deployment personnel also used
dosimeters to register their accumulated
radiation exposure. The limit for the accumulated individual dose is 50 mSv per year, i.e.
the same as for persons exposed to radiation
during the course of their work.

30 | 31

If an individual dose of 30 mSv is attained
during the deployment, the deployment is interrupted so that a buffer is available in order
to withdraw from the operational location.
For female deployment personnel, on-site
deployment is interrupted in a similar manner at 3 mSv (the limit for female deployment personnel is <5 mSv per quarter).
The maximum individual dose is specified as
250 mSv for emergencies and life-saving operations. Women are not allowed to take partin assignments of this sort. According to theavailable information (cf. /1/), no deployment
personnel exceeded the aforementioned
dose limits.

dose limits are specified by the fire brigade
command centre, taking account of the data
mentioned above and with minimisation ofradiation doses in mind.

4.4.3		Plant staff and external
workforce
By 23 May 2011, about 7’800 persons wereinvolved in the emergency work at the
Fukushima Dai-ichi nuclear power plant.
Until then, the average individual dose due
to external radiation exposure was approx.
7.7 mSv. 30 persons had accumulated
individual doses of more than 100 mSv(cf. Figure 4-1).

As of 22 March 2011, 19’703 US air force personnel and marines were deployed in Japan
as part of Operation Tomodachi to provide
humanitarian aid and to manage the disaster(cf. /38/). No precise information is currently
known regarding the number of US military
personnel deployed at Dai-ichi, the provencontamination of individuals, the surface
contamination measured in the plants andthe accumulated radiation doses for the persons involved.

4.4.2		 Fire brigades
The maximum individual doses for membersof the fire brigade are specified in the firebrigade manual (“Operation Measure Manualof the Fire and Disaster Management Agency”). This manual defines the upper limit forlive-saving operations as 100 mSv, with alarm
limits of 30 to 50 mSv. A maximum of
100 mSv may be accumulated during a fiveyear period, with a maximum annual dose of
50 mSv.

Figure 4-1 Distribution of accumulated radiation doses, 11 March until
approx. 23 May 2011 22

In case of an operation within the 20 km
radius around the Fukushima Dai-ichi nuclear power plant, the operation-specific22 | Source /1/																							4 | Radiation exposure and working conditions

External and internal radiation exposurestaken into account, 3’715 persons had
accumulated an average individual dose of
22.4 mSv, according to a report by theJapanese government /1/. In April 2011,
3’463 persons had accumulated an average
individual dose of 3.9 mSv and in May 2011,
2’721 persons had accumulated an individual
dose of 3.1 mSv on average (cf. Figure 4-2).

Number of persons

Average individual dose [mSv]

Number of persons and average individual doses March to May 2011

March

April

Number of persons
average individual doses

May

Figure 4-2 Number of persons and average individual doses,
March to May 2011

According to the follow-up report by theJapanese government /11/, about 9’900
persons working at the Fukushima Dai-ichi
nuclear power plant had been examined forexternal and internal radiation exposure by
10 August 2011. 103 persons (84 from TEPCO's own staff and 19 third-party staff) haveaccumulated individual doses of more than
100 mSv. If the external radiation doses forthe period from March to July 2011 and theinternal radiation doses for the period fromMarch to May 2011 are totalled, the result isan average dose of 10.4 mSv. The maximum
individual dose is approx. 672 mSv.
According to information from JAIF (cf. /42/),the dose values of 10 August 2011 were
updated by TEPCO. As of 30 September
2011, therefore, out of about 14’800 persons
who had been examined up to then, 99 had
accumulated an individual dose of more than
100 mSv (100-150 mSv: 77 persons (as of 10
August 2011: 81); 150-200 mSv: 14 persons;200-250 mSv: 2 persons; >250 mSv: 6 persons). The observed differences (decrease
from 103 to 99 persons with a dose of morethan 100 mSv) are plausible given the measurement accuracy of personal dosimetry.

32 | 33

4.4.4 	Violation of dose limits andpotential causes
TEPCO employees have accumulated radiation doses above the limit of 250 mSv. At
the time of the H2 explosions in units 1 and3, they were mostly carrying out work inthe main control rooms (MCR). Because thedoors were destroyed, contaminated air wasable to reach the main control rooms and,because work was undertaken without protective masks in some cases, led to incorporations.
The following factors may have played key
parts for the incorporations of six persons(three operators and three persons from themaintenance staff):•

The accident occurred unexpectedly andquickly, so there was little time to adapt
to the necessary radiation protection
measures.

•

The persons in the control room occasionally removed their masks in order to
eat and drink.

•In the case of two persons wearing
glasses, it is possible that the masks did
not always seal tightly.

•

Two persons “lifted” their masks for ashort time so that they could work better.

•

Four persons were working near the
emergency door of the control room,
where airborne activity was very high.

On 24 March 2011, two persons sustained
heavy contamination on their feet while laying cables in the turbine hall of unit 3, wherecontaminated water was present at this time.
The footwear worn during this work was too
low, so the skin on their feet was contaminated by the water. As a consequence, there
was a risk of so called “Beta-Burns”. TEPCO
immediately implemented decontamination
measures, and the affected persons weretransported to the Fukushima Medical University Hospital where NISA also carried out
checks. A follow-up examination on 11 April
2011 did not establish any acute effects on
health. The resultant radiation exposure on
the feet of the affected individuals amounted
to an equivalent dose for the skin of 2 to 3 Sv.
After an evaluation of the radiation doses,
TEPCO confirmed on 27 April 2011 that theradiation dose for one female was over 5
mSv (the limit for occupationally exposed
females in order to protect unborn life) for aperiod of three months (January – March).
On 22 April 2011, it was confirmed that one
female had accumulated an effective dose of
17.6 mSv. Of this, an internal radiation doseof 13.6 mSv was caused by inhalation as she
removed her protective clothing. On 1 May
2011, it was determined that a second female
had an effective dose of 7.5 mSv. Medical
examinations of these two women showedthat no health risks were present for unborn
life (cf. /41/).

4 | Radiation exposure and working conditions

4.4.5		Exceptional radiation
exposures
Dose rates of up to 700 mSv/h were measured at some places in the reactor buildingof unit 1 at Fukushima Dai-ichi where repair
work had to be carried out. With such adose rate, the staff may only work on site forabout 20 minutes. Staff who measured thedose rates accumulated an individual dose of
up to 11 mSv in about 30 minutes.
After the explosion on 15 March 2011, staff
entered the reactor building of unit 2 for the
first time on 18 May 2011. Four persons inprotective clothing, including breathing protection (compressed air cylinders) had thetask of investigating the radiological situation and collecting other relevant data. They
accumulated radiation doses of between 3
and 4 mSv per person.
On 19 May 2011, staff entered the reactor
building of unit 3 for the first time after the
explosion of 14 March 2011. Two persons,wearing protective equipment and breathing
protection (compressed air cylinders) stayedin the building for about ten minutes in orderto take radiation protection measurements.
They measured ambient dose rates of up to
170 mSv/h. These two persons accumulated
individual doses of between 2 and 3 mSv
while taking these measurements.
In the thyroid glands of two persons who
were working in the control rooms of units
3 and 4, but also at other locations, 9’760
Bq and 7’699 Bq of iodine-131 (respectively)
were measured.

These values are about 10 times as high as
those for other persons who were on operational assignments during the accident.
In addition, the two persons accumulated
external radiation doses of 74 and 89 mSv
respectively. It must be assumed that theexternal and internal radiation doses led tomore than 250 mSv per person. Both theaffected individuals had no previous healthproblems. No results from biological dosimetry (blood counts to detect chromosomechanges) are available.
One person forgot to place the filter on thefull protection mask for about two hours
while working on the nuclear power plantsite in the open air. The external radiation exposure was 0.5 mSv. TEPCO is investigating
whether this could be due to deficient safetymeasures.
TEPCO is unable to indicate the current
whereabouts of 198 persons who worked in
the Fukushima nuclear power plant following the accident of 11 March. MHLW asked
TEPCO to locate these persons and to examine them for radiation exposure. In a report,
TEPCO stated that the 198 persons could not
be found, but at the same time confirmedthat they were entered in the lists of namesof the nuclear power plant for March andApril 2011.
TEPCO reports that two persons wereunintentionally sprayed with heavily contaminated water from the water treatment
system which is used to purify water that
accumulates in the reactor buildings. One
person accumulated 0.2 mSv and was decontaminated. The second person, who was
wearing a raincoat, accumulated 0.1 mSv.
TEPCO states that neither of the two persons
incorporated any radioactive substances dueto this incident.

34 | 35

4.5 	Dose reduction
measures4.5.1	Measures to monitor andreduce radiation doses
In their respective supervisory reports,
MHLW and NISA (the supervisory authorities) issued several instructions and requests
to TEPCO for the purpose of reducing theradiation exposure of persons on the power
plant site. The following countermeasures
were ordered on 6 June 2011 in order to prevent violations of the limits during activities
to deal with the accident:•

If the whole body measurement showsthat a person's internal radiation exposure exceeds 100 mSv, further work in
the plant is prohibited for the work colleagues of the individual who was examined until the results from whole bodymeasurements are also available.

• ach person with an individual doseE
above 170 mSv may only undertake workin the Main Anti-Earthquake Building.

It was also determined that several persons
had not been correctly reported as having
been exposed to radiation in the course of
their work. NISA warned TEPCO on accountof this error, and requested a review of theprocedure for radiation protection monitoring at the Fukushima Dai-ichi nuclear power
plant. On the basis of the results, the operator's company had to initiate appropriate
countermeasures to exclude the possibilityof a repetition.

A report had to be submitted to NISA on thismatter. After reviewing the report, NISA issued the following instructions to TEPCO on
25 May 2011:•

Periodic reports must be submitted
regarding the procedure for internal andexternal dose monitoring for the assigned
staff, and the implementation of temporary medical checks, as specified in /40/.

•

 pecial emergency work must be notiS
fied in advance to the “Labor Standards
Inspection Office” so that monitoring ofradiation exposure can be supervised.

•A database must be set up in which theradiation doses for persons who took partin emergency work can be tracked overa lengthy period. Onward tracking mustalso be possible in cases where persons
who carried out emergency work change
their job. It must also be possible to track
the state of health of these persons overthe long term.

At both nuclear power plants, Fukushima
Dai-ichi and Dai-ni, the radiation doses due
to work on dealing with the emergency wereadded to those arising from normal activities. The dose limit was set at 250 mSv (seesection 4.2). This also applies to staff who
were not previously registered and employedin the nuclear power plants but who are now
assigned to emergency work.

4 | Radiation exposure and working conditions

Persons designated as not occupationally
exposed persons were working in the Main
Anti-Earthquake Building, so a procedure toclassify them as occupationally exposed had
to be developed subsequently. The persons
to be so designated were entered in lists. In
the course of the process, these persons
were recognised and officially registered,and from then on were monitored forexternal and internal radiation exposure.
Checks with a whole body monitor are still
specified if these persons no longer undertake any work as persons exposed to radiation in the course of their work.

TEPCO has implemented the following
improvements in recent months:

The persons working in the Main Anti-Earthquake Building included four female employees designated as not occupationally exposed persons. Two of these women
accumulated about 3.4 mSv. In Japan, thelimit for not occupationally exposed personin the course of their work is 1 mSv per year.
ENSI assumes that these persons were
subsequently classified as “occupationally
exposed”. This reclassification would thenmean that there were no further violations of
the limit.
Staff is informed about their individual
radiation exposure each month. If a guidancevalue (see below) is exceeded, the following
measures are implemented:•

If 100 mSv is exceeded: external radiation exposure > whole body measurement to determine incorporation;•If 150 mSv is exceeded: external radiation exposure > review of further work;•If 200 mSv is exceeded: external andinternal radiation exposure > no further
work may be undertaken in the radiation
field.

•

 osimetry system: new organisation andD
more staff to monitor radiation doses;•Individual identification system,
barcodes;• hole body measurements, more wholeWbody monitors with better access;• se of robots in areas with high doseU
rates;•

 raining of radiation protection staff,
Ttraining for 4’000 persons is planned.

Active carbon filters have been installed in
the ventilation systems of main control
rooms. In addition, special areas have been
identified where material and equipment
must be checked for contamination.
Because dose limits were exceeded for two
female employees (see above), all women
have been prohibited from working in the
Fukushima Dai-ichi nuclear power plant since
23 March 2011 until further notice.
Temporary sleeping accommodation has
been provided for about 1’600 persons. Thishas been used by staff since the end of June.
The installation of several waiting rooms andrest rooms with air conditioning was completed between April 2011 and June 2011.
Work was suspended on account of the heat
between 2:00 o’clock p.m. and 5:00 o’clock
p.m. in July and August 2011.
Doctors are available to the staff round theclock.

36 | 37

4.5.2	Measures in the Main AntiEarthquake Building

Conditions in the Main Anti-Earthquake
Building are being continuously improved byadditional measures:

The ambient dose rate on the site of the
Fukushima Dai-ichi and Dai-ni nuclear power
plants increased due to the release of radioactive substances. As a consequence of theambient dose rates measured on the Dai-ichi
nuclear power plant site, the entire operational site was classified as a controlled zone.
At the Fukushima Dai-ichi nuclear power
plant, the staff must wear Tyveks (synthetic
paper overalls) and gloves as protection
against contamination. This should also
prevent radioactive substances from being
spread into the Main Anti-Earthquake Building. Protective masks must be worn as soon
as airborne activity exceeds the reporting
thresholds. Depending on the weather conditions and the contamination level, additional
protective equipment must be worn.

•

Installation of active carbon filters;•

Installation of lead shielding;• etting up a temporary buffer zoneS
to prevent the spread of contamination(security entrance with lock);•Removal of carpet which is difficult
to decontaminate;•Installation of floors and surfaces that canbe decontaminated.

The Main Anti-Earthquake Building was initially regarded as a non-contaminated zone.
This is why no activity measurements weredone inside the building before 24 March
2011. On 3 April 2011, the contaminationlevels for air contamination exceeded thestatutory limit (1E+3 Bq/m3, average value
over three months), so the building could nolonger be regarded as outside the controlled
zone. Since then, radiation protection checks
and the wearing of protective equipment
have been stipulated. Air extraction systems
have been installed in the Main Anti-Earthquake Building and in the sanitary facilities
and rest areas. Cleaning work is undertaken
on a continuous basis.

This work is planned on the basis of detailed advance investigations (e.g. regarding the radiological situation). The staff is
kept constantly informed regarding safetyissues. Radiation exposure is kept as low as
possible by closing off areas with increased
dose rates. Additional instruction on radiation protection has been provided for thestaff. Since the accident, the ambient dose
rate (ADR) values on the site and in theMain Anti-Earthquake Building have fallen
to about one tenth of the maximum values.
So far, no damage to the health of staff has
been identified due to the incorporation ofradioactive substances.

4.6 	Summary andassessment
The reports by governmental authorities
and by the operator indicate that personal
dosimetry did not function as usual in thefirst hours and days of the accident. Morethan two thirds of the necessary personal
dosimeters were missing. Shortcomings are
particularly evident regarding dosimetry forincorporations. It is striking that the triage
monitors (hands-/feet-clothing) and wholebody monitors were unable to supply reliablemeasurements on account of the high background radiation at the accident location.
Given the severity of the accident, however,
the radiation exposure for the plant's own
staff and third-party personnel proves to bemoderate. There have been no deaths fromradiation and no cases of persons with a radiation syndrome. In this context, it would beinteresting to note the results of biologicaldosimetry (blood counts for chromosomechanges) for persons with a dose of morethan 100 mSv. After the dose limit was set
at 250 mSv due to the accident, as is usual
both internationally and in Switzerland, six
persons with limit violations were identified.
This total does not include the two women
for whom the applicable limit (for them)of 5 mSv in three months was exceeded.

Since the accident, radiological working
conditions in the premises of the plant andon the Fukushima Dai-ichi power plant site
differ greatly from the status quo. The measures that were initiated also show that evenin the event of such a serious accident, there
are still numerous possibilities for reducing
doses and for the effective prevention of incorporation and skin contamination, provided that the protective equipment is utilised
consistently. In case of an accident involving
release of activity, the outlay of staff, materials and equipment for radiation protection
is many times higher than during normal
operation. This suggests the conclusion that
more reserves for accidents than was previously assumed must be kept in readiness inthese areas.
Experience gained at Fukushima yields many
indications that could also be relevant for
the improvement of radiation protection in
Switzerland. ENSI has already presented corresponding checkpoints for personal dosimetry and operational radiation protection (cf.
/49/). The practical training of persons withradiation protection tasks will have to give
more consideration than so far to behaviourin the case of extensive and very high air andsurface contamination.

38 | 39

Fukushima
37° 25‘ 26.57“ N, 141° 1‘ 56.87“ E11.03.2011

5 | Radiation exposure

5	Radiation exposure of the population in the surrounding area
5.1 Overview

Radioactivity that is either deposited directly
on forage crops and vegetables or which
penetrates the soil and reaches the plants
there via their roots (cf. section 5.3) represents another significant dose source
through the consumption of food (ingestion).

Radioactive substances that are released
to the environment in the case of an accident such as the one at Fukushima Daiichi contribute to radiation exposure forthe population in the surrounding area via
various pathways (cf. Figure 5-1). In the firstphase after an accident (known as the cloudphase), it is mostly the external irradiationfrom the radioactive cloud passing-by andthe incorporation of radioactive substances
via the respiratory tract (inhalation) thatmake the main contributions to the dose
(cf. sections 5.6 and 5.7). In the subsequent
ground phase, radioactive substances
deposited on the ground result in a further
long-term contribution to the dose by meansof external irradiation (cf. section 5.2). The
radioactive decay of the substances andtheir penetration into lower soil levels (whichcauses shielding of the radiation) causes thisdose to decrease continuously over time.

Propagation(air path)

Shieldingfactor

Discharges

Fluid discharges into surface water (rivers,
lakes) may contaminate the drinking water
reservoirs and consequently cause exposure
to radiation via the drinking water supply (cf.
section 5.4). In addition, radioactivity fromlakes, rivers and the sea reaches the humanfood chain via fish and seafood (cf. section
5.3 and section 5.5, respectively).

Air

Inhalation

Respiration

Deposit

Dispersal

Soil

Gamma radiation
shielded in soil

mixing

Leaf

Shielding factor

Dilution(water path)

Immersion

Groundradiation

Vegetables,
fruit,
cereals

Roots

dwell

Grass/forage
crops
Water
Bodies ofwater
Groundwater
Sea

Milk,
meat

Consumption

Ingestion

Transfer

Drinking
water, fish
Transfer

Dose

Figure 5-1 Schematic view of the main dose paths that contribute to radiation
exposure in the area surrounding a nuclear plant 23

23 | Source /10/ with the addition of the sea and groundwater paths																						40 | 415.2	Deposits of radioactive substances on the
ground
5.2.1 Weather situation
The main discharges from Fukushima Daiichi from 15 March 2011 onwards were largely
the consequence of the explosion in unit 2,
as Figure 3-2 illustrates. On the evening of
15 March, there were prevailing winds from asouth-easterly direction at an altitude of 100
m above the power plant site; and during
the night from 15 to 16 March 2011, repeatedprecipitation (rain or snowfall) was recorded
downwind (cf. Figure 5-2, top). As a result,
there were substantial deposits of radioactive iodine and cesium isotopes (Cs-134 andCs-137) in aerosol form in a north-westerly
direction, at distances of up to about 50 – 60km from the site (cf. Figure 5-2, bottom). By
comparison, there were significantly smaller
deposits of radioactive substances to thenorth, in the south-western quadrants and inparticular along the coast.
In the course of 16 March 2011, the windveered westerly again so the radioactive
discharges from the site were conveyed overthe Pacific Ocean.
In addition to the usual routine programme,various official and private bodies launched
an extended environmental measurement
programme in the area surrounding thenuclear plant after the release of radioactive substances in order to determine theambient dose rate (ADR) and the locallydeposited activity on the ground and in thesoil causing the ADR. This programme wascoordinated by MEXT and included regular
ADR measurements at various points inside

Figure 5-2 Figure 5-2 Weather situation on theevening of 15 March 2011 in the area surrounding
the Fukushima Dai-ichi nuclear power plant 24

and outside the prohibited zone around theplant. In addition, extensive aeroradiometricmeasuring flights were carried out in collaboration with the U.S. Department of Energy(DOE) (cf. section 5.2.2). Furthermore, theconcentrations of activity in the soil and theirprogression over time were determined bydirect sampling and nuclide-specific evaluations (cf. sections 5.2.3 and 5.2.4).

24 | Source: Japan Meteorological Agency (JMA) http://www.jma.go.jp/jma/en/menu.html
																							5 | Radiation exposure

5.2.2 	Ambient dose rate due
to activity deposits on the
groundThe ADR values measured in the area surrounding the Fukushima Dai-ichi nuclear
power plant were mainly caused by theIodine isotope I-131 at the outset. This largely
decayed in the meantime due to its relatively
short half life of 8.02 days, therefore since
the end of April 2011, it are primarily the two
Cesium isotopes Cs-134 (half life of 2.06
years) and Cs-137 (half life of 30.17 years
which give rise to the ADR.
Very soon after the accident, MEXT collaborated with the U.S. DOE to carry out

measuring flights to provide cartography forthe ambient dose rates. A map indicating theresults for 29 April 2011, i.e. about one and ahalf months after the accident, is shown in
Figure 5-3. This figure also contains maximum values for the activity concentration of
Cs-137 in the soil and the seawater for several
selected points.
The map clearly shows the trail of deposits
resulting from the radioactive discharges,
which mostly originated from reactor unit 2
on 15 March 2011. In the area shaded in red,
the ambient dose rate (caused primarily by
Cs-134 and Cs-137 at this time) was over
19 μSv per hour or approx. 200 times the
background radiation. A person continuously
present in the open air in this zone would

Figure 5-3 Ambient dose rates in the area surrounding Fukushima Dai-ichi on 29 April
2011, selected activity concentrations in soil and seawater 25
25 | Source: JAIF http://www.jaif.or.jp/english/news_images/pdf/ENGNEWS01_1316677149P.pdf

																							42 | 43

accumulate a dose of well over 100 mSv due
to external irradiation in the course of a year.
In the yellow area, this annual dose would
still be about 20-50 mSv. The red, orange
and yellow zones extend to the north-west
for about 40-50 km, i.e. significantly further
than the 20 km radius from which the population was evacuated as a first step immediately after the accident. The area in question
was subsequently evacuated for this reason(cf. section 5.6) in order to comply with thelimit for the yearly dose. Conversely, there
are some areas within the 20 km radius(especially along the coast to the north andsouth of the site) where the external radiation during one year would lead to doses ofless than 5 mSv.
The aeroradiometric measurements wereextended and refined until the end of July
2011 (cf. Figure 5-4). As was to be expected,
the ADR fell marginally as time went on, as
can be seen from the slightly smaller size ofthe areas with specified contamination. Thiscan be explained by the penetration of radioactivity into the soil, leading to a somewhat
higher shielding of external ionising radiation. On the other hand, the decrease due toradioactive decay is hardly significant (T1/2 of
Cs- 137: 30.17 a). At distances of more than
75 km from the power plant site, only isolated instances of increased ADR values can bemeasured as compared to the background(in Switzerland: typically about 0.1 μSv/h).
Figure 5-4 Ambient dose rate in the area surrounding Fukushima Daiichi, extended and refined measurement for July 2011 26

26 | Source: MEXT http://radioactivity.mext.go.jp/en/1270/2011/07/1270_0727.pdf																							5 | Radiation exposure

Figure 5-5 Defined monitoring posts for regular determination of the ambient dose rate outside the 20 km
prohibited zone (data in μSv/h) 27

As well as the aeroradiometric measurements − which allow a comprehensive
overview of the ADR in the surrounding area
, and hence the deposited radioactivity −measurements coordinated by MEXT weretaken at a large number of monitoring posts
inside and outside the 20 km prohibitedzone from about 17 March 2011 onwards. Figure 5-5 provides an overview of the monitoring posts outside the prohibited zone. The
values measured on 13 September 2011 areentered in the chart by way of example.

27 | Source: MEXT http://radioactivity.mext.go.jp/en/monitoring_around_FukushimaNPP_monitoring_out_of_20km/2011/09/13511/index.html

																							44 | 45

The progression of the ADR between 17
March 2011 and the start of September 2011is shown in Figure 5-6 for all the monitoring
posts; Figure 5-7 shows the progression for
the five monitoring posts with the highest
ambient dose rates values after the accident.

The measurement results at the monitoring
posts on the ground correlate very well withthe aeroradiometric measurements presented above, within the expected range ofaccuracy.

Figure 5-6 Progression of the ambient dose rate at the defined monitoring posts outside the 20 km prohibited zone around Fukushima 28
Dose progression at certain selected points between 20 and 30 km

Dose rate [μSv/h]In the first phase, the ADR was dominatedby radiation from iodine-131. From mid-April
2011 onwards, however, this iodine, which has
a short half life of 8.02 days, had decayed
to such an extent that the measured ADR
was now caused almost entirely by Cs-134
and Cs-137. As time went on, the ADR only
decreased slightly; this decrease was primarily due to the penetration of these nuclides
into the soil and the resultant shielding. The
model calculation for monitoring post 32
shows the ADR progression that would havebeen expected taking account of radioactive
decay only. It is apparent that the radionuclides must already have penetrated the soilvery quickly in the first phase. However, thesubstantial daily fluctuations suggest thatthe measurements were not always taken atexactly the same measuring point or underidentical measuring conditions (measuring
instruments, etc.).

Monitoring post 32 (31 km NW)
Monitoring post 79 (29 km WNW)Monitoring post 81 (30 km NW)
Monitoring post 83 (24 km NW)
Model calculation (point 32)

Date

Figure 5-7 Progression at monitoring posts with the highest ambient dose rates
directly after the accident

Figure 5-8 shows the ADR progression inlarger eastern Japanese cities (including Tokyo). Several peaks due to I-131 deposits canbe seen clearly; these occurred to the southof the site when the wind turned in this direction in the initial phase of the accident.

28 | Source: MEXT http://radioactivity.mext.go.jp/en/monitoring_around_FukushimaNPP_monitoring_out_of_20km/2011/09/12475/index.html
																							5 | Radiation exposure

One of the effects of these iodine deposits
was that in Tokyo, for example, the I-131 limit
for infants in drinking water was briefly exceeded (cf. section 5.4). During the course ofApril, the ADR values normalised again due
to the radioactive decay of the I-131. They
have now returned to a range of 0.1 μSv/h,as (for example) is typical for the Mittelland
region of Switzerland.

Figure 5-8 Progression of ambient dose rates in major cities in eastern Japan between 15 March and the start of September 29

29 	| Source: JAIF http://www.jaif.or.jp/english/news_images/pdf/ENGNEWS01_1316677149P.pdf
																										46 | 47

5.2.3 Measurements of soil activity:
volatile nuclides, I-131, Cs-134
and Cs-1377
Shortly after the accident, direct measurements of activity concentrations in the soil
were taken in the surrounding area, and thedose rate values determined by means ofaeroradiometry were also converted into
activity concentrations in the surface layerof the soil. The result of this conversion isshown in Figure 5-9.
The trail of deposits in a north-westerly
direction is again clearly visible. In the red
shaded area, the calculated surface contamination values were over 3 MBq/m2. In thearea shaded grey-green, the deposited
activity concentrations of the two Cs-isotopes were still 30-60 kBq/m2, a value that
was also measurable in some areas in thesouth of the canton of Ticino after thereactor accident at Chernobyl in 1986.
Directly after it was deposited on the
ground, I-131 was the nuclide for which thehighest soil contamination was measured on
account of its high volatility and the large
concentration in the reactor. At this time, thedeposits of Iodine on the ground exceeded
those of the two Cs-isotopes by factors of 3
to 20 each (cf. by way of example, the “Soil”
rows in Table 5-1). The fluctuating Cs/I
conditions on the ground and the significantly divergent conditions on the surfacesof plants can be explained by the different
washout and penetration behaviours of
Iodine and Cesium. Due to the comparatively
short half life of I-131, the two Cs isotopes
dominated soil contamination from about
April onwards.
Figure 5-9 Cs-134 and Cs-137 activity (Bq/m2) deposited on the
ground, derived from the aeroradiometric measurements 30

30 	| Source: MEXT http://radioactivity.mext.go.jp/en/1270/2011/07/1270_0727.pdf																												5 | Radiation exposure

Maximum measurement values for Cs-137
activity concentrations as measured atvarious points in the soil are shown in Figure5-3. The highest value was 227’000 Bq/kg,
although a direct comparison with theaeroradiometric measurements stated in Bq/
m2 is very difficult in this case as the depth
down to which sampling was carried out is
unknown.
From the end of May 2011 onwards, theJapanese Ministry of Agriculture, Forestry
and Fisheries (MAFF) launched a campaign
entailing gamma-spectroscopic investigationof the activity concentrations of radiocesiumin soil used for agricultural purposes at a
total of 580 points in the prefecture of
Fukushima and the five neighbouring
prefectures (Miyagi, Tochigi, Gunma, Ibaraki
and Chiba). The results of these measurements are grouped together in Figure 5-10.

As the depth to which the soil was sampled
is defined in this case, a direct comparison
with the aeroradiometric measurements
presented above is possible. The results
determined with the two measurement
methods correspond very well within themeasurement accuracy that can be expected. In the case of cesium, an average transfer
factor of 0.05 from soil into the plant isassumed. This means that from a value of
10’000 Bq/kg upwards (red and orange dotsin the figure), it must be expected that plant
products grown in this soil will exceed theJapanese average limit for Cesium in food of
500 Bq/kg (cf. section 5.3).

48 | 49

Figure 5-10 Activity concentrations of radiocesium in soil used for agricultural purposes in thearea of the plants' roots 31

31 | Source /11/																					5 | Radiation exposure

5.2.4		Measurements of soil activity:
other nuclides (Sr, Pu, U)
In addition to Iodine and Cesium, comparable quantities of other nuclides with long
half lives are formed in a reactor during
operation (cf. Table 2-3), but they are
significantly less volatile by comparison. In
this context, of special interest are pure beta
emitters such as Sr-89 and Sr-90 or alphaemitters such as Plutonium or Uranium,
which can lead to significant radiation
exposure if absorbed into the human body
via the respiratory tract or through food;however, measurement of these emittersusually involves relatively high outlay.
Following the accident, there was particular
discussion of a potentially increased releaseof Plutonium (which nevertheless has very
low volatility) because so-called mixed oxide(MOX) fuel assemblies were used in thereactor of unit 3 at Fukushima Dai-ichi. In
these fuel assemblies, a small proportion of
the fissile Uranium is replaced by Plutonium,
resulting in a higher Plutonium share than in
the case of pure Uranium fuel assemblies.
Immediately after radioactive substanceswere deposited, the Japanese authorities
took soil samples at various points which
they analysed for Iodine, Cesium and Strontium. Figure 5-11 provides an overview of thesampled locations; sampling locations 1 to 3
are situated centrally in the main direction of
the dispersal plume.

Figure 5-11 Sampling points where activity conditions for further nuclides were investigated immediately
after deposits occurred 32

32 | Source: MEXT http://radioactivity.mext.go.jp/en/1260/2011/03/1305074_0412.pdf														50 | 51

SampleSampling
location

Activity per nuclide [Bq/kg](moist soil, plants unprocessed)

Date
I-131

Cs-134

Cs-137

Sr-89

Sr-90

Soil

Namie Town

17.03.201130‘000

2‘300

2‘300

13

3.3

Soil

Namie Town

16.03.2011

100‘000

20‘00019‘000

81

9.4

Soil

Iitate Village

16.03.2011

160’000

52’00051’000260

32PlantsOotamaVillage19.03.2011

43’00089’00090’00061

5.9

PlantsMotomiyaCity

19.03.2011

21’00057’00057’00028

3.7

PlantsOno Town

19.03.2011

22’00012’00012’00012

1.8

PlantsNishigou
Village19.03.2011

12’00025’00025’00015

3.8

Table . 5-1 Measurement results for activity concentrations in the soil for radioactive iodine, cesium andstrontium about one week after the occurrence of the accident 33

As shown in Table 5-1, the measured Sr-89
concentrations in the soil are in all cases lessby a factor of at least 100 than the values
measured at the same point for Cs-134 or
Cs-137, and the Sr-90 concentrations are lessby a factor of at least 1’000. The Cs/Sr ratio
for plants is even greater. This makes it
possible to state that the radiation exposurein the area surrounding Fukushima, ascompared to those for the two Cs isotopes,
are of subordinate importance, even taking
into account the less favourable transfer
factors and dose factors for Strontium.

The concentration of the measured Plutonium there was about 1 – 2 Bq/kg, but,nevertheless, this is of a magnitude that can(for example) be detected in Switzerland asa consequence of atomic weapons tests bynuclear powers.

In the immediate area surrounding thenuclear power plant, the operating company
TEPCO detected traces of Plutonium in thesoil in the case of two samples. In both cases,
the isotope ratio suggested that this may
have originated from one of the damaged
reactors.

33 | Source: MEXT http://radioactivity.mext.go.jp/en/1260/2011/03/1305074_0412.pdf																					5 | Radiation exposure

In the wider area surrounding the nuclear
power plant, the Plutonium concentration
was below the detection limit, even in themain deposit trail. The Uranium measured at
the same locations shows a natural isotope
ratio between U-235 and U-238 (cf. Table
5-2). If the measured Uranium originatedfrom a reactor, a shift in the ratio in favour of
U-235 would be expected due to the enrichment of the fuel.
The radiological effects of Plutonium andUranium are therefore of minor significanceas compared to Cs-134 and Cs-137. Other
nuclides were proven to be present in thesurrounding area, but they are of considerably less radiological importance than the
nuclides already mentioned.

Sampling
location

Date

ADR[μSv/hActivity per nuclide[Bq/kg]Pu-238

Pu-239&240

Activity ratio
U-235/U-23836

Near Kodeya,
Kuzuo Village

23.03.2011

43.5

< 0.1
(< LOD) 35< 0.1(< LOD)

7.31E-3

East of the
Hirusone Tunnel,
Namie Town

23.03.2011

46.5

< 0.1
(< LOD)< 0.1(< LOD)

7.26E-3

Akougi, Namie
Town

22.03.2011

50.1

< 0.1
(< LOD)< 0.1(< LOD)

7.23E-3

5.3 Contamination of foodIn an operation coordinated by the MHLW
after the accident, more than 15’000 samplesof food were taken throughout Japan up to
September; their Iodine and Cesium content
was determined and compared with the following limits that apply to food in Japan:•

For Iodine (primarily I-131) in milk and milk
products as well as drinking water: 300
Bq/kg for adults and 100 Bq/kg for infants; in vegetables and fish: 2’000 Bq/kg;•

For Cesium (Cs-134 and 137) in milk andmilk products as well as drinking water:
200 Bq/kg; in vegetables, fish, meat, eggs
and all other food: 500 Bq/kg;•

For Uranium in drinking water, milk andbaby food: 20 Bq/kg, for all other food:
100 Bq/kg;•

For transuranium elements in drinking
water, milk and baby food 1 Bq/kg, for allother food: 10 Bq/kg.

The applicable activity limits for food according to MHLW are listed in detail in the following Table 5-3.

Table 5-2 Measurement results for activity concentrations in the soilfor Plutonium and Uranium about two weeks after the accidentcesium[LOD = Limit Of Detection] 34

34 | Source: MEXT http://radioactivity.mext.go.jp/en/1250/2011/04/1305381_0401.pdf
35 | According to MEXT, the values measured for the plutonium isotopes are below the detection limits.
36 | 	The abundance in the natural occurring element of U-235 and U-238 are 0.7204% and 99.2742% respectively (cf. /45/),and the natural U-235/U-238 ratio is approx. 7.26E-3.

52 | 53

NuclidesProvisional limit for radioactive substances infoods according to the “Food Sanitation Act”
[Bq/kg]Drinking water300
Milk and dairy productsRadioactive
IodineVegetables (except root and tuber
vegetables)

2‘000

Fishery products
Drinking water200
Milk and dairy productsRadioactive
CesiumVegetables
Cereals

500

Meat, eggs, fish, etc.
Baby food
Drinking water

20

Milk and dairy products
Uranium
Vegetables
Cereals

100

Meat, eggs, fish, etc.
Alpha emitters,
Plutonium andtransuranium
elements (total
concentration of
Pu-238, Pu-239,
Pu-240, Pu-242,
Am-241, Cm-242,
Cm-243, Cm-244)

In Switzerland, the limits for radioactivity
in foods are stipulated in significantly moredetail in the Ordinance on Foreign Substances and Constituents in Food (FIV) /12/.
The present Swiss concept differs somewhat
from the Japanese procedure in that the limit
is preceded by a lower tolerance value as
from which a product is regarded as “diminished in value”. For the radionuclides mentioned above, the limits are comparable interms of magnitude.

Baby food
Drinking water

1

Milk and dairy products
Vegetables
Cereals
Meat, eggs, fish, etc.

10

By way of example, Table 5-4 shows an
excerpt from the data published by MHLW
for the prefectures of Fukushima and Ibaraki. For various food groups, the numberof measured samples is compared with thenumber of samples determined to haveviolated the limit in the seven months between the accident (March 2011) and midOctober 2011.
In Fukushima, approx. 10’500 samples were
examined. The limit was exceeded for about
4.5% of them. In the neighbouring prefectures, the percentage of food samples thatexceeded the limits were 3% (Tochigi), 2%(Ibaraki, Chiba and Miyagi) and less than 1%(Gunma).

Table . 5-3 Activity limits for food in Japan 37

The highest activity value measured was fora sample of spinach taken at Ibaraki on 20
March 2011, with a measured I-131-concentration of significantly more than 50’000 Bq/
kg and Cs-134/137 activity of approx. 2’000
Bq/kg. Consumption of one kilogram of suchcontaminated spinach would lead to an effective dose of 1 mSv for an adult.

37 | Source: MHLW http://www.mhlw.go.jp/english/topics/2011eq/dl/food-110405.pdf														5 | Radiation exposure

In March 2011, maximum concentrations ofabout 5’000 Bq/kg for Iodine-131 and approx. 400 Bq/kg for Cs-134/137 were determined in milk and milk products. Theseamounts of activity are also more or lessequivalent to a dose of 1 mSv if an infant
were to drink one litre of this milk.
In a seawater fish (sand lance) from the prefecture of Fukushima, I-131 and Cs-134/137 wereproven in a concentration of approx. 12’000
Bq/kg in each case as late as mid-April 2011 .
Origin(prefecture)

Food group

Numberof samples tested

Samples thatexceeded thelimit

Examples of affectedfood samples (number)

Vegetables

5‘215

260

Bamboo shoots (55),spinach (39), shiitake
cultivated outdoors (40),broccoli (21), ume (11),rapeseed (6), cabbage(6), etc.

Fish andseafood

1‘379

109

Ayu (21), common skate(14), greenling (10), sandlance (6), deep-sea cod(5), etc.

Milk and milk
products

448

18

Unprocessed milk (18)Meat and eggs

1‘907

61

Beef (56), pork (3), Asiatic black bear (2)Cereals1‘502

1Wheat (1)Others30

2

Tea (1), rape (1)Total

10‘481451

Vegetables

735

43

Spinach (29), parsley (7),shiitake cultivated outdoors (4), etc.

Fish andseafood

473

6

Sand lance (5), deep-sea
cod (1)

Milk and milk
products

90

5

Unprocessed milk (5)Meat and eggs

2‘582

4

Pork (4)

Cereals

469--

Others83

13

Tea (13)

Total

4‘432

71

Fukushima

IbarakiTable 5-4 Examined food samples and number of limit violations ascertained, using the prefectures of Fukushima and Ibaraki as examples 38

38 | Source: MHLW http://www.mhlw.go.jp/english/topics/2011eq/dl/17Oct2011_Sum_up.pdf

54 | 55

Due to the short half life, violations of the Iodine limits in food occurred only until about
the end of April 2011. Thereafter, the limit
violations were all attributable to high Cs-134
or Cs-137 concentrations. Broken down by
product groups, the highest Cs concentrations (Cs- 134 + Cs-137) in foods were as
follows:••

Vegetables: 34’000 Bq/kg (spinach, endof March), 13’000 Bq/kg (mushrooms,
start of April), 3’000 Bq/kg (tea, midMay), 4’600 Bq/kg (mushrooms, midAugust), 1’300 Bq/kg (tea, mid-August),
2’400 Bq/kg (citrus fruit, end of August)Milk, milk products: 400 Bq/kg (midMarch)•Fish, seafood: <15’000 Bq/kg (sand lance,
April), approx. 1’000 Bq/kg (various,
May), approx. 4’500 Bq/kg (ayu, June),approx. 1’800 Bq/kg (ayu, August)•Meat: up to approx. 4’500 Bq/kg (beef,from July onwards)

The highest concentrations of Cs activity
were found for vegetables (leaf vegetables)
immediately after the discharge of radioactivity into the environment, in a period of
about two months (direct deposits on theleaves). The aforementioned value of 34’000
Bq/kg in spinach would be equivalent to aneffective dose for an adult of about 0.5 mSv
if one kilogram were to be consumed. In thefollowing phase, the activity concentration inplants was dominated by absorption throughthe roots – the values therefore decreased
significantly as compared to the period directly after the discharge.
Processed and stored plants such as tea
constitute a special case. Tea leaves are dried
after they are harvested, which entails anadditional increase in concentration in respectof the activity present per unit of mass. They arethen stored for a very long time before consumption. Especially for long-lived nuclides suchas Cs-137, this means that the leaves harvested
in the first phase after the accident with activity directly deposited on the leaf can remain incommercial circulation and can therefore reachconsumers for quite a long time.
The transfer of radionuclides from forage crops
into milk takes place relatively quickly, and freshmilk also goes into commercial circulation soonafter production. Consequently, the maximum
activity in fresh milk correlates very well withthe maximum activity in and on forage crops.
The situation is different for meat (beef). In thiscase, the rearing and storage period for themeat prior to sale and consumption is rather
long. This explains (similarly to the situation withtea leaves) why the maximum activity concentration occurs after a delay of several months inrelation to the maximum activity in the forage
plant; this statement applies very generally tostored products.
The concentration of activity in fish and seafood
correlates with the concentration in the water oflakes and the sea and – to a lesser extent – withthe concentration in sediments. In this case too,however, the growth period for fish and seafood,and the resultant delay in catching and processing, leads to a time shift between the maximum
concentration in the water and in the fish or
seafood.
On the basis of the measurements that were
made, MHLW ordered food bans where necessary in order to minimise the dose for the population due to the consumption of contaminatedfood.

5 | Radiation exposure

5.4 Contaminationof drinking water
Depending on the wind conditions, there
were brief violations of the I-131-limit indrinking water for adults or infants in thedays following the accident, due to depositsof radioactive substances in surface waterin the catchment area of the drinking watersupply. Figure 5-12 illustrates this using theexamples of two waterworks in the villageof Iitate (violation of drinking water limit for
adults of 300 Bq/kg) and Tokyo (violation of
the guidance value for infants of 100 Bq/kg).

The authorities subsequently urged the population to avoid drinking water taken fromsurface water sources for a short time. Dueto the radioactive decay of iodine-131 andthe diminishing discharges and/or deposits,
the limits were respected again everywherefrom the end of March 2011 onwards.

Figure 5-12 Violation of the I-131 activity limit indrinking water after the accident, using the examples of two waterworks in Iitate (prefecture of
Fukushima) and Tokyo 39

39 | Source: MHLW /13/

56 | 57

Figure 5-13 and Figure 5-14 show the progression of activity in drinking water in various provinces for I-131 and Cs- 134/137: fromabout mid-April 2011 onwards, the values returned to the level of those measured before
the accident, they were therefore significantly below the limits again.

Figure 5-13 Activity concentration for I-131 in the drinking water systemsof various prefectures in northern Japan 40

Figure 5-14 Activity concentration for Cs-134/137 in the drinking water systemsof various prefectures in northern Japan 41
40 | Source: MHLW /13/
41 | Source: MHLW /13/														5 | Radiation exposure

5.5 Contaminationof seawater andthe seabed
At the start of April 2011, major amounts ofseverely contaminated water escaped into
the sea through an underground shaft anda leak (cf. section 2.4). This discharge wasmanifested in an increase in the concentration of activity in the seawater at the monitoring posts around the reactors affected by
the accident (cf. Figure 5-15 and Figure 5-16)

Figure 5-15 Activity concentrations for I-131, Cs-134 and Cs-137 in the seawater around the Fukushima Daiichi nuclear power plant on 5 May 2011 42

42 | Source: MEXT http://radioactivity.mext.go.jp/en/1340/2011/05/1305678_0505.pdf

58 | 59

and also – albeit after a delay – by higher
activity concentrations in fish and seafood(cf. section 5.3). Depending on the ocean
currents, the Japanese limits (90 Bq/l for Cs)
were almost reached or even exceeded by asmuch as a factor of 4 at some points (taking account of the total of Cs-134 and Cs-137
activity).

Once major discharges into the sea weresuccessfully halted, the activity values decreased again. Almost without exception,
they were again below the detection limit
from May 2011 onwards.

Figure 5-16 Activity concentration of I-131, Cs-134 and Cs-137 in the seawater around the Fukushima Dai-ichi
nuclear power plant on 7 May 2011 43

43 | Source: MEXT http://radioactivity.mext.go.jp/en/1340/2011/05/1305678_0505.pdf														5 | Radiation exposure

Waterborne discharges in surface water andin the sea can be deposited on the seabedin a similar manner to the way airborne
discharges are deposited on the soil. At theend of July 2011, JAEA took measurementson the coast around Fukushima Dai-ichi (andDai-ni). The results are grouped together inFigure 5-17. Significantly increased activity
concentrations were ascertained at several
points, especially to the south and east of
the power plant site. These may also represent a source of higher radioactivity concentrations in fish and seafood in the longer
term. However, the effects here should besignificantly less than in the case of a direct
increase in activity in the seawater.

The samples from the monitoring posts withthe highest Cs values were subsequently
examined for possible deposits of Sr-89 andSr-90, but the measured values were below
the detection limits in these cases (cf. Figure5-18).

Figure 5-18 Sr deposits on the seabed andin the sediment surrounding the Fukushima
Dai-ichi nuclear power plant 45

Figure 5-17 Cs deposits on the seabed andin the sediment around the Fukushima Dai-ichi
nuclear power plant 44

44 | Source: MEXT http://radioactivity.mext.go.jp/en/monitoring_around_FukushimaNPP_sea_marine_soil/2011/08/1350_081310.pdf
45 | Source: MEXT http://radioactivity.mext.go.jp/en/monitoring_around_FukushimaNPP_sea_marine_soil/2011/09/1350_091610.pdf

60 | 61

5.6 	Measures to reduceradiation exposure•On 22 April 2011, due to measurementsin the surrounding area outside the 20
km zone around the Dai-ichi power plant,a special evacuation zone was set up(the “Deliberate Evacuation Area”). The
20 km zone itself was declared to be a
“Restricted Area”. A further zone between
20 and 30 km was defined for any subsequent evacuation that might be necessary(“Evacuation- Prepared Area in Case of
Emergency”); this zone would have to be
evacuated in case of a further deterioration of the situation.

•In June 2011, individual locations for potential evacuation were identified in otheradjacent areas (“Specific Spots Recommended for Evacuation”).

5.6.1	Evacuation of the population in
the surrounding area
Evacuation around the Fukushima Dai-ichi
power plant site was carried out in the following stages (cf. /1/, /11/ and /14/):
•

•

•

•

On 11 March 2011 at 8:50 p.m., the government triggered the preliminary warning
for the 2 km zone around the Dai-ichi
power plant to be evacuated due to thesituation in unit 1.
On 11 March 2011 at 9:23 p.m., the government ordered people to evacuate the 3 km
zone and to remain in their houses in the
3 to 10 km zone due to the aggravation of
the situation.
On 12 March 2011 at 05:44 a.m., the government ordered the evacuation of the 10 km
zone around the power plant.
On 12 March 2011 at 6:25 p.m., as a consequence of the hydrogen explosion inunit 1 and the increase in the ADR on the
power plant site, evacuation of the 20 km
zone around the power plant was ordered.

• n 15 March 2011 at 11:00 a.m., peopleO
were ordered to stay in their houses in the
20 to 30 km zone. At 23:30 hours, completion of the evacuation of the 20 km
zone was reported.

• n 25 March 2011, the government adO
vised the population to evacuate the 20
to 30 km zone around the power plant on
a voluntary basis.

The evacuation around the Fukushima Dai-ni
power plant site was carried out in the following stages:•

On 12 March 2011 at 07:45 a.m., the government ordered people to evacuate the 3 km
zone and to stay in their houses in the
3 to 10 km zone around the Dai-ni power
plant.

•

On 12 March 2011 at 5:39 p.m., evacuationof the 10 km zone was ordered.

•On 21 April 2011, the evacuation zone was
reduced to 8 km. As a precaution, thepopulation was initially evacuated withina radius of 20 km around Fukushima Daiichi (cf. Figure 5-19).

5 | Radiation exposure

At individual places in additional adjacentareas, the authorities recommended compliance with special precautionary measuresor departure from the location in question
where a yearly dose of over 20 mSv would
be accumulated (“Specific Spots Recommended for Evacuation”), (cf. Figure 5-20).

Figure 5-19 Evacuation zones around
Fukushima Dai-ichi 46

The authorities subsequently decided to extend the evacuation zone for specified areas(“Deliberate Evacuation Areas”) beyond the
20 km radius in cases where the population
would accumulate a dose of more than 20
mSv by March 2012. The affected municipalities are located to the north-west up to a
distance of approx. 40 km from the Fukushima Dai-ichi nuclear power plant. The 20 km
zone around the Fukushima Dai-ichi power
plant that had already been evacuated wasconverted into a prohibited zone (“Restricted Area”). Residents were recommended toleave the other contaminated areas between
20 and 30 km (“Evacuation-Prepared Areas
in Case of Emergency”).

Figure 5-20 Figure 5-20 Evacuation areas
outside the 20 km zone 47

On 30 September 2011, the stipulation regarding “Evacuation-Prepared Areas in Caseof Emergency” (orange zone in Figure 5-19)
was lifted again by the Nuclear Emergency
Response Headquarters.

46 | Source: METI http://www.meti.go.jp/english/earthquake/nuclear/roadmap/pdf/evacuation_map_a.pdf
47 | Source: METI http://www.meti.go.jp/english/earthquake/nuclear/roadmap/pdf/evacuation_map_b.pdf

62 | 63

5.6.2 Decontamination measures
On 26 August 2011, the Japanese parliament
passed a new law on “Special measures for
dealing with contamination of the environment by radioactive substances released asa consequence of the Tohoku earthquake”.
The Japanese Nuclear Emergency Response
Headquarters also declared that the decontamination of radioactively contaminatedareas was an urgent requirement. The objective of the planned decontamination is to
reduce radiation exposure in highly contaminated areas (current dose >20 mSv per year)
to less than 20 mSv per year. In the other areas, the value should be less than 1 mSv per
year. Top priority in this context is assigned
to the decontamination of kindergartens,
school premises and other locations wherechildren are present on a daily basis.
Various measures were initiated in order toachieve the defined goals. In the towns ofDate and Minamisoma, pilot projects havebeen running since the end of August 2011
with the aim of demonstrating how residential areas can be decontaminated. In Fukushima and the neighbouring prefectures, information events were staged at municipality
level on the following topics, among others:“Basis of decontamination work”, “Special
measures for dealing with radioactive contamination”, “Precautionary measures to be
paid attention when decontamination workis carried out by residents” and “The procedure for dealing with waste produced duringdecontamination”.
One particular challenge is also posed by
the decontamination of large areas of land
and forest used for agricultural purposes.
Since May 2011, various feasibility studies
on this aspect have been in progress. Suitable decontamination methods have also
been developed. On 30 September 2011, theNuclear Emergency Response Headquarters
officially published various methods which it
consider as suitable for the decontaminationof land and forest areas used for agricultural
purposes. It should be noted in this context
that virtually no international experience of
decontamination work over large areas isavailable. Other open questions include what
is to be done with the radioactive materials
produced during decontamination, and how
or where they can ultimately be stored.

5.7 	Estimation of doses
for the population in thesurrounding area
5.7.1 Dose in the acute phase
At the outset, a substantial percentage of theradioactive substances were carried out overthe Pacific by the prevailing westerly winds.
As major releases of radioactive substances
only began to be carried simultaneously
over land areas from approx. 8:00 p.m. on
14 March 2011 onwards, prompt evacuationof the population (about 70’000 to 80’000
people) was possible within a radius of 20
kilometres. The evacuation was subsequently
extended individually to more heavily contaminated areas outside of this zone.
About 78’200 people were living in the 20
kilometre zone and another 62’400 people
lived in the zone between 20 and 30 kilometres from the plant (cf. /1/).
Iodine mainly accumulates in the thyroid
gland, and children are particularly sensitive.
An intake of non-radioactive iodine cancause the thyroid gland to become saturated, so that radioactive iodine no longer
accumulates there. Single intakes of nonradioactive iodine were recommended for5 | Radiation exposure

specific groups of individuals; however, theauthorities warned the public against the uncontrolled use of such preparations. Schools
were subject to particularly intensive monitoring.
By the end of May 2011, no signs of impairments to health were ascertained in 195’345
people who were examined. No increased
iodine radiation doses were found in the thyroid glands of any of the 1’080 children who
were examined (cf. /16/). Likewise, no absorption by humans of radioactive strontium
was determined up to that time (cf. /15/).

5.7.2	Estimation of the long-term
dose
The French Institut de Radioprotection etde Sûreté Nucléaire (IRSN) calculated the
expected doses due to external irradiationfor one year (cf. Table 5-5) and for 10 and 70
years (cf. Table 5-6) on the basis of deposits
measured on the ground (cf. Figure 5-9 and
Figure 5-10). The number of persons affec­
ted, which is also stated, refers to the area
outside the 20 km prohibited zone that was
originally evacuated. On the basis of thesecalculations, all other persons with a forecast
dose of more than 20 mSv for the first year
were evacuated in addition (cf. Figure 5-20).

Deposits of Cs-134 + Cs-137 (according to MEXT)>300 kBq/m2>600 kBq/m2>1 MBq/m2>3 MBq/m2

6 – 30 MBq/
m2

Dose due to external irradiation in the first year
(16.6 mSv/MBq/m2)>5 mSv>10 mSv>16 mSv>50 mSv

100 – 500
mSv

Number of persons affected(excluding the prohibited zone)292‘000

43‘00021‘100

3‘100

2‘200

Table . 5-5 Expected external radiation exposure in relation to soil
contamination for a period of one year spent in the location 48

Deposits of Cs-134 + Cs-137 (according to MEXT)>300 kBq/m2>600 kBq/m2>1 MBq/m2>3 MBq/m2

6 – 30 MBq/
m2

Dose due to external irradiation in the first 10 years(70 mSv/MBq/m2)>19 mSv>38 mSv>63 mSv>190 mSv

380 – 1‘900mSv

Lifetime dose due to external irradiation (70 years)(160 mSv/MBq/m2)>41 mSv>82 mSv>136 mSv>408 mSv

816 – 4‘080
mSv

Number of persons affected(excluding the prohibited zone)292‘000

43‘00021‘100

3‘100

2‘200

Table 5-6 Expected external radiation exposure in relation to soil
contamination for periods of 10 and 70 years spent at the location 49

48 | Source: /22/
49 | Source: /22/

64 | 65

This conforms to the recommendations of
the International Commission on Radiological Protection, ICRP-103 (cf. /17/) and ICRP109 (cf. /18/). In the absence of additional
measures (e.g. decontamination, shielding,restriction of time spent in the open air, etc.)
this would mean that those persons who
were not evacuated would accumulate amaximum lifetime dose of about 100 mSv
due to external irradiation. This does nottake into account any additional contributions to the dose from direct radiation fromthe cloud at the start of the accident or fromthe consumption of any contaminated food.
Thanks to the promptly implemented evacuation, the personal measurements that weretaken and the measures that were initiatedfor food (monitoring of food contamination
and ban on selling it where appropriate),
it can nevertheless be assumed that thesecontributions to the dose are likely to be oflittle significance.

5.8 Summary
and assessment
From 12 March 2011 onwards, releases ofradioactive substances occurred as a consequence of the accident at the Fukushima
Dai-ichi nuclear power plant. In the firstphase (until 15 March 2011), rare gases weredischarged mainly during venting of the
primary containments of various units, anddue to the explosion in the reactor buildingof unit 1. As the winds were blowing from theland towards the sea during this acute phaseand as the Japanese authorities had initiatedevacuation measures at an early stage, thedoses for the population due to the direct
radiation from the cloud were of minor
relevance.

From 15 March 2011 onwards large quantities
of radioactive iodine and radioactive cesium have been release to the environment
in particular due to the hydrogen explosionin unit 2. As the prevailing winds were fromthe south-east during this day and there washeavy rainfall, the area to the north-west of
the power plant was heavily contaminatedby deposited radioactive substances up
to a distance of about 50 km. In the affected area, this led in some cases to highly
increased ambient dose rates from direct
radiation, and also to the contamination offoodstuffs produced in these area. Even atpresent time (November 2011), the ambient
dose rates outside of the areas evacuatedby the Japanese authorities are still highenough in places to result in an externalradiation exposure of 20 mSv in the first year
after the event, or of 100 mSv for the lifetime, if a person would stay constantly outdoors. However, the additional dose by the
consumption of food (ingestion) is of minor
importance for the Japanese population.
Besides the airborne discharge of radioactive substances, leakages in a cable duct led
to a significant discharge of radioactivity
into the sea at the start of April 2011. The
concentration of the activity in the waterin thesurroundings of the plant normalised
again by the end of April 2011. Nevertheless,isolated samples are even now being foundin Japan in fishery products where the limit
for Cs-137 is exceeded. In the meantime, theJapanese government has published a plansetting out the options for decontamination measures in order to continue reducing
radiation exposure for the population.

6 | Effects

6	Effects on the populationin Switzerland(Contribution by the Federal Office of Public Health (FOPH))

6.1 Overview
The accident at the Fukushima Dai-ichi
nuclear power plant caused by the extreme
earthquake on 11 March 2011 and the associated tsunami led to the release of large
amounts of radioactivity in the following
days. Air masses with radioactivity from thisreactor accident even reached Switzerland
at the end of March 2011, albeit in muchdiluted form.
Radioactivity in the environment and in foodis monitored in Switzerland by the Federal
Office of Public Health (FOPH). This takes
place in collaboration with the cantonal laboratories and other specialised laboratories atfederal and cantonal level. After the reactor
accident at Fukushima Dai-ichi in March 2011,
the ongoing sampling plan was expandedwith the addition of extra air filter, grass,vegetables and milk samples. This section
documents the main measurement results
and conclusions.
The radionuclide concentrations measured in
Switzerland were below the detection limitsof the automatic alarm measurement networks (NADAM, MADUK and RADAIR), andIodine-131, particulate
High Volume Sampler BAG, 2011

Jan

Feb

Mar

Apr

May

Cesium-134
High Volume Sampler BAG, 2011

Güttingen TG

Güttingen TG

Geneva GE

Geneva GE

Klingnau AG

Klingnau AG

Oberschrot FR

Oberschrot FR

Monte Ceneri TI

Monte Ceneri TI

Jun

Jul

Jan

Feb

Mar

Apr

May

Jun

they were 1’000 to 10’000 times lower thanthe concentrations measured in Switzerland
after Chernobyl.
Primarily, it was possible to determine increased concentrations of Iodine-131 in the
air close to ground level with the help ofsensitive measuring equipment. Other radioisotopes originating from Fukushima suchas Cesium-134 and Cesium-137 were also detected in lower concentrations. I-131 occurredin particulate form and also in gaseous form,in concentrations that were up to five times
higher. The maximum total concentrationof I-131 (particulate and gaseous) measured
close to ground level in Switzerland wasabout 2’000 μBq/m3. Traces of I-131 carried in
the air also reached rainwater, grass and outdoor vegetables (a few Bq per kilogram offresh/wet weight). Of the milk samples from
Switzerland that were measured, only one
single sample sho­wed the slightest tracesof I-131 (0.1 Bq/kg). The radioactivity from
Fukushima that was detected in Switzerland
was harmless to the health of the population.
Since mid-April 2011, the concentrations of all
isotopes from Fukushima in the air in Switzerland have declined (cf. Figure 6-1).
High-volume samplers (HVS) were used totake aerosol samples at five different locations, followed by gamma-spectroscopic
analysis in the laboratory. In March and April
2011, the emissions from Fukushima led tosignificantly increased measurement values,
although these were harmless to the healthof the population in Switzerland at all times.

Jul

Figure 6-1 Progression of I-131 (left, particulate) and Cs-134 concentrations (right)
in Switzerland from the start of January until the end of July 2011 50
50 | Source: BAG

																							66 | 676.2	Measurements ofairborne radioactivity

Iodine-131, particulate
Maximum average daily valuein Germany after Chernobyl
Immission limit
in Switzerland

6.2.1	High-volume samplers(HVS, air filters)
Samples for high-sensitivity measurement ofradioactivity in atmospheric dust are taken atfive locations in Switzerland using high-volume samplers, as they are known. With thehelp of a powerful pump, atmospheric dust
(aerosols) is collected on a filter for a periodof one week. The filter is then analysed bymeans of gamma-spectroscopy for various
radioactive nuclides in the FOPH laboratory
in Bern. For all five stations, it was possible
to provide clear proof of radioactivity thatwas released during the reactor accidents
at Fukushima and dispersed over extensive
areas (cf. Figure 6-1). In particular, there wereincreased concentrations of I-131 (maximum
concentration: 450 μBq/m3) and, to a lesser
extent, Cesium isotopes (Cs-137 and Cs-134).
The maximum concentrations of Cs-134 wereabout 10 times lower than those of I-131. The
ratio of Cs-137 to Cs-134 was almost 1. Shortlived isotopes such as Tellurium-132 (Te-132),
I-132 and Cs-136 were also detected in somesamples.
Figure 6-2 compares the progression overtime of the I-131 concentrations in Geneva
with the values from a measuring station in
Japan (Takasaki, Gunma province), a stationin the US (west coast, Sacramento, California) and the Schauinsland station near
Freiburg in Germany immediately following
the accidents at Fukushima (Source: www.
bfs.de). The upper dotted red line shows the
maximum average daily value that occurredin Germany after the accident at Chernobyl

51 | Source: FOPH with reference to www.bfs.deJapan
USA (west coast)
Germany
Switzerland

Detection limit (LOD) for HVS, Geneva
March

April

May

Figure 6-2 Development of the concentration of particulate
iodine-131 in the atmosphere 51

in 1986. The Swiss immission limit (maximum
concentration over a lengthy period) is also
shown.
The European measuring stations registered
increased radioactivity from about 22 March2011 onwards. The highest values (up to
6’000 μBq/m3 for particulate I-131) occurred
between 28 March and 6 April 2011, predominantly in the northern part of Europe.
Towards the end of May 2011, the concentrations in Europe returned to values seenprior to the accident, i.e. generally below thedetection limit.

6 | Effects

6.2.2 Gaseous I-131
In Switzerland, gaseous I-131 is measured byfour detectors (NaI) which automaticallytrigger alarms in case of increased values(RADAIR iodine). These detectors arelocated in the cantons of Geneva, Fribourg,
Aargau and Ticino. The quantities of gaseousI-131 that occurred in Switzerland after theaccidents in Japan were too small to beregistered directly by the Iodine alarmsystem. On the other hand, some cartridges
containing silver/nitrate granulate, whichbind gaseous Iodine, were subsequently
measured in the laboratory – a process thatallows a lower detection limit. For the period
from 31 March until 7 April 2011, activity
levels for gaseous I-131 of between 1’000 and
1’800 μBq/m3 were determined at three
RADAIR Iodine locations. The concentrationsof gaseous I-131 were therefore four to six
times higher than those of particulate I-131,
a result which corresponds well to measurements in other European countries.

68 | 69

6.2.3	High-altitude in-flight filter
measurements (HFF)The fact that lower values were measured
on the ground in Switzerland is probably
explained by the weather situation (southerlywind).

High-altitude air samples were collectedfrom two air filters installed on Tiger- F5 jetsof the Swiss Air Force.

The spectrum shown in Figure 6-3 originatesfrom an aerosol sample that was collected
on 30 March 2011 by a Tiger-F5 at an altitudeof 7’900 m.

The results of these HFF measurements areshown in Table 6-1. At the end of March 2011,high-altitude air showed similar I-131 activity(with up to 1’900 μBq/m3) as air near groundlevel in northern Europe.

Date

Specific activity per nuclide[µBq/m3]

Altitude[m]Be-7

Cs-137

Cs-134

I-131

Co-60

23.03.2011

6’100

5’000±750

<17

<15

140±30<1624.03.2011

7’000

4’200±640

<16

<13

<20

<23

25.03.2011

8’070

5’500±830

<20

<19

230±40<30

25.03.2011

5’030

6’900±900

<11

<9

40±12

<11

30.03.2011

5’200

2’000±330

25±12

<8

280±40<830.03.2011

7’900

10’500±1’500

170±40170±301’900±260<1408.04.2011

12’65031’800±4’000

30±16

<10

21±4

<13

Table 6-1 Results from high-altitude in-flight filter (HFF) measurements 52

Pulses (logarithmic)

High-altitude in-flight filter, 30.3.2011,
7900 mEnergy (keV)

Figure 6-3 Gamma spectrum of an air filter from Switzerland withradioisotopes from the reactor accident at Fukushima 53
52 | Source: FOPH http://www.bag.admin.ch/themen/strahlung/00045/02372/11747/index.html?lang=de
53 | Source: FOPH

6 | Effects

6.3	Food andenvironmental samples
from Switzerland
Air contamination also led to small depositsof radionuclides on the ground. Measurements of radioactivity on grass samples from
Switzerland showed values of the order ofseveral Bq/m2. The maximum I-131 activity
levels in the grass were a few Bq/kg of fresh(wet) weight. The highest values occurred athigh altitudes where the quantities of precipitation are proportionately larger. As expected, similar activity levels to those in grasswere also found in unwashed leaf vegetables.
An approximate factor of 1/3 applies to thetransfer of I-131 from grass into milk; i.e. ata constant value of 3 Bq/kg of fresh weightin grass, up to 1 Bq/kg must be expectedin milk. Of the milk samples measured after
Fukushima, however, only one single sample
contained the slightest traces of I-131 (0.1 Bq/kg). Many cows had not yet been fed withfresh grass at the beginning of April. The
limit for Iodine-131 in food from Japan is 300
Bq/kg in liquid foods (milk) and 2’000 Bq/
kg in all other foods. While I-131 was also
detected in rainwater, drinking water was notaffected by any radioactive contamination,
as expected. Other radioisotopes that definitely originated from Japan included Cs-134,
of which minimal traces were detected insome grass samples. Three milk samples andthree of lettuce taken in the Lausanne region
at the start of April were also examined forradioactive Strontium (Sr-90). No increased
values were determined. An overview of themeasurements of food and environmental
samples taken in Switzerland from midMarch to the end of May is shown in Table 6-2.

MediumNumberof samples

I-131
Maximum

I-131
MedianAir (HVS)

44456 µBq/m3

48 µBq/m3

Rain

12

1.4 Bq/l

0.2 Bq/l

Vegetables

29

1.2 Bq/kg< 0.5 Bq/kg

Grass

22

4.6 Bq/kg

0.7 Bq/kg

Milk

61

0.1 Bq/kg< 0.2 Bq/kg

Drinking water22< 0.1 Bq/l

In-situ3< LOD

Table . 6-2 Overview of environmental and foodsamples measured following the reactor accidents
at Fukushima (15 March to 30 April 2011) 54

6.4	Summary andassessment
Although it was also possible to detect
traces of the radioactivity released at Fukushima Dai-ichi in Switzerland with the helpof high-sensitivity processes, there was no
danger to the health of the Swiss population
at any time.
Contributions to the dose from direct radiation and inhalation were so small as to be
negligible.
The radioactivity from Fukushima ingested
with food would only have amounted to
0.5 μSv, even if 25 kg of the most heavily
contaminated vegetables (leaf vegetables)
were consumed. This corresponds to one
ten-thousandth of the annual radiation contamination for the population in Switzerland,
which is about 5 mSv.

54 | Source: FOPH																							70 | 71

Fukushima
37° 25‘ 26.57“ N, 141° 1‘ 56.87“ E11.03.2011

7 | Comparison of events7	Comparison of events
at Fukushima with thoseat Chernobyl(with contributions from the Gesellschaft für Anlagen- undReaktorsicherheit mbH, GRS)

7.1 	Accident progression
and release
Chernobyl: In the night from 25 to 26 April
1986, there was an explosion in reactor no. 4of the Chernobyl nuclear power plant after
overcriticality had been reached. This wascaused by an uncontrolled power excursion
in the reactor core, due among other factors
to the physical characteristics of the reactor
which was of type RBMK (Russian: Reaktor
Bolshoi Moschtschnosti Kanalny = English:
high-power channel-type reactor).
The damage to the reactor building was considerably more serious as compared to thatcaused by the explosions at Fukushima Daiichi. For example, the explosion destroyedlarge parts of the reactor building of unit 4,
the turbine hall and the intermediate connecting building. The walls of the reactor hall
were partially destroyed and the roof wasentirely destroyed. The upper horizontal coreplate of the reactor vessel weighing approx.
3’000 t was raised and has since stood at anangle of 15° to the perpendicular. The southeastern quadrant of the lower core plate andthe emergency cooling system in the northeastern part of the reactor building were entirely destroyed. The reactor shaft, in which
the reactor was located, is virtually empty. A
large part of the nuclear fuel was hurled into
the reactor hall or is present in the form ofsolidified lava beneath the original positionof the reactor.
The explosion of the reactor and the fire in
the reactor core that lasted for several days
afterwards led to a substantial release of radioactive material into the environment andto the ejection of debris containing fuel fromthe reactor core into the area surrounding
the power plant.

During this intensive release, which continued for about ten days, there were constantchanges in weather conditions in the immediate and more distant areas surrounding
the site. The radioactive substances releasedby the explosion and the fire were initiallywhirled up to an altitude of as much as 1’200m and were then transported in a northwesterly direction across Belarus as far as
Finland and into the central and northern
regions of Sweden. On the next day, the windveered west. The path of the radioactively
contaminated air masses passed over Poland,
the Czech Republic and Austria to southern
Germany, where they arrived between 30
April and 1 May 1986. On the following day,the wind changed to blow towards Greece
and Turkey, and then back again towards
Scandinavia.
Fukushima Dai-ichi: By contrast, the progression of the ambient dose rate at the Fukushima Dai-ichi site features several separate
releases in the period from 11 to about 27
March 2011 (cf. Figure 3-2). During thisperiod, the wind was mainly blowing fromwesterly directions, so a large part of thereleases were blown onto the open Pacific
Ocean. On 15 March 2011, however, there wasa situation with an airflow from south-easterly directions combined with precipitation,
so larger quantities of radioactive substanceswere deposited in a band running north-west
from the site on that day (cf. section 5.2).
Chernobyl: The quantity of radioactive substances released up to 6 May 1986 – disregarding the noble gases (most of which haveshort half-lives) and the Tritium – was estimated in 1986 as 1.8E+18 Bq, with an uncertainty of ± 50%. Also in 1986, the proportionof nuclear fuel located outside the reactor
after the accident was determined as 3.5 ±
0.5% of the nuclear fuel mass (190 t). Both72 | 73

estimates have been confirmed by more
recent studies. Almost all of the noble gases
Krypton and Xenon and the Tritium contained in the core escaped. Major uncertainty
continues to prevail regarding the estimateof the released percentages of highly volatile
Cesium and Iodine isotopes. A more recent
assessment results in a value of 33 ± 10% of
the core inventory for the Cesuim-137 release. This corresponds to activity of approx.
2.9E+17 Bq, cf. Table 7-1.
Even greater uncertainty attaches to the determination of the release of Iodine isotopes,
which can occur as aerosols as well as in
the gaseous state. The relative constancy of
the ratio of Iodine-131 and Cesium-137 in thefallout in most European countries makes it
possible to set a lower limit on the releaseof Iodine. A released percentage of at least
50% of the Iodine-131 core inventory should
be taken as the most accurate estimate. Taking account of radioactive decay, this corresponds to a release of activity amounting
to approx. 3.1E+18 Bq. Strontium-90, with areleased percentage of 4% of the total inventory, is representative of the group of noteasily volatilised radionuclides. A quota of
3% is assessed for the release of alpha-emitting actinides (which are mostly long-lived),
i.e. in particular for Plutonium.
The released percentages in Table 7-1 correspond to the values stated in UNSCEAR
2000 (cf. /19/).

Radionuclide

Half life[days]

Core inventory[Bq]

Estimated proportion released
[%]

Kr-85

3‘930

3.3E+16

100

Xe-133

5.27

7.3E+18

100

I-131

8.05

3.1E+1850

Te-132

3.25

3.2E+18

15

Cs-134750

1.9E+17

33

Cs-13711‘0002.9E+1733

Ru-106368

2.0E+18

3

Sr-89

53

2.3E+18

4

Sr-90

10‘2002.0E+17

4

Pu-23831‘5001.0E+15

3

Pu-2398‘900‘000

8.5E+143

Pu-2402‘400‘000

1.2E+15

3

Pu-2414‘800

1.7E+173

Cm-242164

2.6E+16

3

Table . 7-1 Percentages of the main radionuclides released in the accident at Chernobyl, as known in 1996 55

Fukushima Dai-ichi: In order to determine
the total airborne release of radioactive substances at the site, NISA published two estimates on 12 April 2011 /5/. These were madeby NISA and the NSC. According to them,the estimated release release of 1.3E+17 Bq
of Iodine-131 and 6.1E+15 Bq of Cesium-137
corresponded to about 10% of the quantityof radioactive substances (Iodine equivalent)
released due to the accident at Chernobyl.
At the start of June 2011, the Japanese government published a report addressed to the
IAEA which updated and gave more precise
definitions of the estimates for the airborne
release of radioactive substances /1/. The
result of the calculations, covering a wide
spectrum of nuclides, is shown in Table 2-3.

55 | Source: /20/																							7 | Comparison of events

As compared to the accident at Chernobyl,
it is apparent that the releases at Fukushima are dominated by Iodine and Cesium
isotopes. In particular, the percentages of
not easily volatilised radionuclides such as
Strontium (cf. /31/) and/or of long-lived
alpha-emitting actinides such as Plutonium(cf. /32/) are estimated as lower by several
orders of magnitude.

7.2 	Radiological situationon the plant site
Chernobyl: Following the explosion in unit
4, the most urgent priority was to isolate thedestroyed reactor from the surrounding environment in order to prevent a further discharge of highly radioactive substances. For
this purpose, a concrete and steel structure,
known as the “site enclosure” or “sarcophagus”, was erected around the destroyed
reactor in the period from May to October
1986. No time was left for detailed planning
due to the urgency of the matter.
Fukushima Dai-ichi: Enclosures are to be
erected over the reactor buildings of units 1,
3 and 4 so as to prevent further activity frombeing discharged. The structure in this caseis made of steel, covered with reinforced
watertight plastic film (cf. Figure 7-1). The
construction work on unit 1 at the Fukushima
Dai-ichi plant began on 10 August 2011.
According to TEPCO, the operating company, work on the enclosure was successfully completed on 28 October 2011. TEPCO
goes on to state that a start can be made onbuilding the enclosures for units 3 and 4 insummer 2012 at the earliest, after the debris
has been cleared away.

Figure 7-1 Enclosure for unit 1, view from the north 56

Chernobyl: Of the 190 t of spent nuclear
fuel located in unit 4 of the nuclear power
plant at the time of the explosion, about
96% is still stored inside the sarcophagus,
and about 0.5 to 1% is scattered on the site
at distances of up to approx. 500 m fromthe sarcophagus, mainly in the form of finely
dispersed particles but also as pieces ofdebris from the active zone. Another quota
of about 1.5% is located in the form of finely
dispersed particles in a zone with a radius of
80 km, although most of it is in the 30 km
zone around the power plant. The remaining component of about 1.5% was carried
by atmospheric propagation beyond thisdistance of 80 km (and in some cases muchfurther away) in the form of finely dispersed
particles. The total mass of radioactive dustin the sarcophagus is estimated at 1 t, withan activity of 4.3E+15 Bq. The lower rooms of
the sarcophagus contain approx. 3’000 m3 ofcontaminated extinguishing water and rainwater that has penetrated from outside.
Fukushima Dai-ichi: By means of the provisional feed for a few hours and/or days after
the occurrence of the event, the reactors
and spent fuel pools were initially supplied
exclusively with non-contaminated waterfrom outside (initially seawater and later

56 | Source: TEPCO http://www.tepco.co.jp/en/news/110311/images/110917_02.jpg

74 | 75

fresh water). As a result of this, several hundred cubic metres of highly contaminatedwater were created each day, especially inthe reactor pressure vessel (RPV). Moreover, large quantities of contaminated water
accumulated in the buildings' lower storeys,and in trenches and shafts outside the buildings. Due to leaks in the area of the coolingwater intakes, highly contaminated water
entered the Pacific on several occasions. According to JAIF, up to approx. 100’000 m3 ofcontaminated water with activity of 720’000
TBq was present on the plant site.

Turbine hall

Unit 4, Chernobyl
nuclear power plant

Intermediate connecting
building

Chernobyl: Figure 7-2 shows the ADR at
the Chernobyl site ten years afterwards.
The ADR for gamma radiation in the area
immediately surrounding the sarcophagus,
the degasifier wing and the turbine halls ofunit 4 at a height of 1 m above ground levelis about 0.3 to 0.5 mSv/h. The dose rate at
distances of up to approx. 150 m from theaforementioned buildings is about 0.1 to 0.2
mSv/h. There are about 10 waste tombs forradioactive substances (dumps) with dimensions of up to about 10 x 10m on the site,
mainly on the west wall of the sarcophagus.
It is suspected that at least three of these

Waste infills
Provisional dumps (waste tombs)

Cartogram for the ambient dose rate of Cesuim 137 at a height of one meter
above ground level

waste tombs contain highly active waste
and possibly pieces of debris from the active
zone. The waste tombs were dug during thedecontamination work and when the sarcophagus was being built. The Cesuim-137
concentrations on the nuclear power plantsite are approximately between 1’000 and >10’000 kBq/m2
Fukushima Dai-ichi: The ADR at the “Mainbuilding, south side” monitoring post on theplant site is currently about 0.3 mSv/h. In
the immediate vicinity and inside units 1 to 4,
significantly higher ADR values are measured
in some cases. The main deposits detectedin soil samples to date are of Iodine-131,
Cesuim-137 and Cesuim-134. Due to its shorthalf life of 8.02 days, Iodine-131 no longer
contributes to the ambient dose rate, as isalso the case on the Chernobyl site.
Chernobyl: In 1986, a medical committee
decided on the criteria for evacuation measures in the current 30 km zone around theChernobyl nuclear power plant. In the firstweeks of the evacuation, the main objective
was to protect residents (and especially children and pregnant women) living in the area
immediately surrounding the nuclear power
plant against ionising radiation.
At Chernobyl, the decision criterion applied
for evacuation was the measured ambient
dose rate. Areas where an additional radiation dose of more than 5 mSv/a /20/ could
be expected for members of the population
were to be evacuated first. The first evacuation at short notice on 27 April involved
116’000 persons. This was followed on 2 and3 May 1986 by a second phase of evacuation from the 10 km zone around the stricken
reactor, involving about 10’000 persons.

Figure 7-2 Ambient dose rate at Chernobyl unit 4,
1 m above ground level 57

57 | Source: /20/																							7 | Comparison of events

The 30 km zone around the reactor was also
evacuated from 4 and 5 May 1986 onwards.
According to a United Nations report, a totalof almost 400’000 people (150’000 in Belarus, 150’000 in the Ukraine and 75’000 in
the Russian Federation) relocated either on a
mandatory basis or of their own accord.
Fukushima Dai-ichi: An evacuation of the
population within a 3 km radius around unit
1 was effected on the evening of 11 March
2011. Prior to the cloud phase, the evacuation
zone was extended several times within one
day until it finally covered a radius of 20 km.
On 15 March 2011, the population around this
20 km evacuation zone was recommended
to stay inside buildings, within a radius of
up to 30 km. On 10 April 2011, it was decided
to extend the 20 km evacuation zone so
as to include areas where an annual radiation
exposure of more than 20 mSv could
be expected. A total of approx. 153’000
residents were affected by the evacuation
measures /22/.

7.3 	Radiological situationin the surrounding area
Chernobyl: Outside of the prohibited zone,
areas in Russia, Belarus and the Ukraine with
Cesuim-137 activity levels in the top layer ofsoil of > 37 kBq/m2 are defined as contaminated and are subject to radiological monitoring, as it is called. According to official
information from Belarus, the areas affected
10 years after the event were 46’500 km2 in
Belarus /23/, 57’000 km2 in Russia /24/ and41’800 km2 (including the prohibited zone) in
the Ukraine /25/.
Fukushima Dai-ichi: By comparison, areas inJapan with a Cesuim-137 activity level in the
top layer of soil of > 30 kBq/m2 are limited

to a few thousand km2 (cf. Figure 5-19). This
results in substantially lower radiation exposure for the population (cf. Table 7-3) and,with suitable decontamination measures,
soon makes it possible for many residents toreturn to their home towns or villages.
Chernobyl: Because the locations of thepower plants at Chernobyl and Fukushima
are very different, the impacts on the adjacent bodies of water also differ greatly. The
Chernobyl nuclear power plant is situatedin the interior of the country, on the river
Prypyat. The cooling water was taken fromthe cooling pond located in the south-east of
the site (cf. Figure 7-4). This is a significant
feature in terms of ecology. With a lengthof 11.4 km, a width of 2 km and an average
depth of 6 to 20 m, its water capacity is approx. 149 million m3. It was heavily contaminated by the accident. Radioactive particles
and “Hot Particles” were introduced into thecooling pond by the radioactive cloud; in addition, approx. 5’000 m3 of heavily contaminated water was pumped into the coolingpond. The total intake is estimated at approx.
2’200 TBq. Measurements indicate that thecontamination nowadays consists mainly ofCesuim-137 and Strontium-90, about 90% of
which is bound in the sediment. Each year,
between 3.6 and 14 GBq of Strontium-90
flow into the river Prypyat from the coolingpond /27/.
Fukushima Dai-ichi: The power plant is located directly on the coast of the Pacific Ocean.
Due to the emergency measures that were
implemented to cool the reactors, part of
the approximately 100’000 tonnes of highly
contaminated water was able to escapeuncontrolled into the Pacific (cf. section 2.3).
The concentrations of radioactive Iodine andCesuim isotopes in the seawater rose sharply
after this.

76 | 77

Minsk

Mahiliou

Belarus
Babruisk

Russia

Homel

Masyr
30 km

Tschernihiw
Chernobyl

Prohibited zone
> 1480 kBq/m2
Continuous monitoring zone
555 - 1480 kBq/m2

Kiew

Periodic monitoring zone
185 - 555 kBq/m2

Schytomyr

Unknown zone
37 - 185 kBq/m2

Ukraine
040 km

30 km radiusFigure 7-3 Cesium-137 contamination in Ukraine, Belarus and Russia after the reactor
accident at Chernobyl 58

Figure 7-4 Cooling pond at the Chernobyl nuclear power plant withsediments drawn in 59

58 | Source: University of Texas at Austin, http://www.lib.utexas.edu/maps/commonwealth/chornobyl_radiation96.jpg
59 | Source: /21/																							7 | Comparison of events

According to estimates by TEPCO, approx.
11’000 tonnes of water with total activity of
approx. 5E+15 Bq escaped into the Pacific in
the period between 1 April and 11 May 2011,
either in a controlled manner by pumping, orin an uncontrolled manner due to leakages(cf. section 2.4). The concentrations of Cesuim-137 measured at the monitoring posts
along the coast are shown in Figure 7-5 below. Until about 8 April 2011, a sharp increasein the concentrations of radioactive Iodine
and Cesuim isotopes can be observed. Since
then, the contamination of the seawater withradioactive substances has gradually diminished, and for those monitoring posts not
located in the area immediately surrounding
the plant, is below the detection limit.

Contamination of seawater with Cesuim-137
Data from TEPCO, the operator
MP (1): 330 m south
MP (2): 30 m northMP (3): 10 m south
MP (4): 16 m south
Limit for Cs-137

Time of measurement

Fig. 7-5 Fukushima Dai-ichi: contamination of seawater with
Cesuim-137 60

60 | Source: /28/

7.4 	Radiation exposurefor the operational staff
and the population
Chernobyl: At Chernobyl, the reactor'soperational staff, fire brigade personnel andmembers of the army such as helicopter
pilots were deployed to fight the fire directly
and to cover the open reactor core. Some of
the individuals in this group received very
high radiation doses. About 300 persons
were taken to hospital, 134 persons showed
symptoms of acute radiation sickness withweakness, vomiting and dizziness, as well
as skin burns. Despite intensive medical
efforts, sometimes involving bone marrowtransplants at specialised clinics in Moscow
and Kiev with the help of American doctors,
28 persons died of radiation sickness and of
their sustained burn injuries within the first
four months after the accident. The bodydoses were as much as 16 Gy (in this case, 1
Gy corresponds to an effective dose of 1 Sv).
By 1998, another 11 persons had died due toreceived doses of between 1.3 and 5.2 Gy /19/.
Fukushima Dai-ichi: In the case of the reactor accident at Fukushima, on the other
hand, no deaths occurred due to radiation
sickness. The report by the Japanese government /1/ indicates that up to 23 May,
approx. 7’800 persons entered the plant site
at Fukushima to carry out work there. On
average, these persons received an effective dose of 7.7 mSv, including 30 employees
who received doses above 100 mSv. The
limit for male power plant staff in emergency
situations was increased from 100 to 250
mSv per year (effective dose) on 15 March
2011. According to information from theoperator /29/, six persons received a doseof more than 250 mSv (external and internal
exposure) in March.

78 | 79

On 24 March 2011, the feet and legs of twoworkers came into contact with contaminated water, and they received local skin dosesof 2 to 3 Sv.

equivalent of 100 mSv for a one-year-old
infant) was not exceeded in any of the 1’080
children aged from 0 to 15 years who were
examined /1/.

Chernobyl: Members of the army and civilians from many parts of the Soviet Union
were deployed to carry out the decontamination and clearance work in the region of
the accident-stricken Chernobyl reactor.
The size of this group – known in general as“liquidators” – is difficult to determine, butaccording to Soviet sources they numbered
600’000 persons. According to the UN Scientific Committee on the Effects of Atomic
Radiation (UNSCEAR 2000), there has so far
been no noticeable increase in the generaland cancer-related death rates, or in the rateof leukaemia cases. Comparable data on
these aspects from Fukushima are not available as yet.

7.5 	Estimation of long-term
exposures

The radiation exposure for the population
due to the reactor accident at Chernobyl isessentially attributable to short-lived Iodine131 and long-lived Cesuim-137. Up to now, it
has not been possible to prove an increasein mortality among the population in thecontaminated areas as a consequence ofincreased exposure to radiation after the accident at Chernobyl. According to the WHO,
however, a significant radiation-induced
increase in carcinomas of the thyroid glandhas been observed among children /30/.
Fukushima Dai-ichi: No noticeable doses
have yet been proven among the populationin Fukushima. 195’345 persons had been examined by 31 May in the prefecture of Fukushima. During the investigation of thyroid
gland doses in Iwaki City, Kawamata Town
and Iitate, the screening level of 0.2 mSv/h(corresponding to a thyroid gland dose

Table 7-2 below shows the doses for the
population due to external radiation exposure resulting from soil contamination for the
first year after the events at Chernobyl. Internal exposures due to inhalation and ingestion are not included in the data (except for
Switzerland). Likewise, no account is taken of
additional contributions to the dose due to
direct cloud radiation at the start of the accident (Fukushima) or due to the consumptionof possibly contaminated food.
In contrast to the situation at Chernobyl,
residents within a radius of 20 km or 30 km
were mostly evacuated in good time before
the cloud phase in Japan.

Location

Average effective dose
(external) per resident(mSv/year)

Number ofresidents
affected

Comments

Fukushima

5-20

approx.
340’000

Outside of the evacuated zone
as far as approx. 70 km to thenorth-west

1-14

approx. 75
millionOutside of the evacuated zone,
30 – 1’000 km

120

approx.
135’000

Inside the evacuated zone, 0-30km from 26 April to 5 May 1986

ca. 0.11

7.8 million(as of 2000)

Averaged over the whole of
Switzerland + approx. 0.15 mSv
internal dose

Chernobyl

Switzerland
following
Chernobyl

Table . 7-2 Doses for the population due to external radiation exposurefor the first year of presence in relation to soil contamination 61

61 | Source: /43/, /46/																							7 | Comparison of events

Chernobyl: Figure 7-6 provides an overview
of the propagation of the radioactive cloudfrom Chernobyl in relation to the progression over time. In most of Switzerland, Cs-137
contamination in the soil of <3 kBq/m2 could
be proven (e.g. in the Mittelland region: 1.8
kBq/m2), with up to 50 kBq/m2 in southern
Ticino.

Figure 7-6 Directions of propagation and time
progressions for the radioactive cloud from
Chernobyl 62

Fukushima Dai-ichi: Figure 7-7 provides an
overview of deposits of Cs-134/137 around
Fukushima Dai-ichi and of the expected
doses in the first year after the events ofMarch 2011. The evacuation zones are shownin Figure 5-19 and Figure 5-20

62 | Source: /20/

80 | 81

Cumulate deposits of Cesium (Cs-134 and Cs-137) anddoses estimated by MEXT (5 mSv, 10 mSv, 20 mSv)
5 mSv

20 mSv

30 km

20 km
10 mSv

Fukushima Dai-ichi

Fukushima Dai-ni

Effective doses due to external
irradiation (mSv/year)
Population

20
10

200 000 - 350 000

5Deposits of Cs-134/Cs-137 (kBq/m2)

50 000 - 100 000

6 000 á 30 000

20 000 - 50 000

3 000 á 6 000
10 000 - 20 000

1 000 á 3 000

0 - 10 000

600 á 1 000
300 á 600

0

5

10

20

30

40 km

Figure 7-7 Soil contamination (Cs-137 + 134) caused by the Fukushima accident
and expected effective doses due to external irradiation in the first year 63

63 | Source: /22/																							7 | Comparison of events

The following Table provides an overview ofthe estimated long-term doses for the population due to the external action of radiation.
The dose values for Switzerland and Germany are based solely on the deposits following
Chernobyl; as described in section 6.4, thecontribution from Fukushima is extremely
small and is disregarded in the estimate.

Location

Average effective dose
(external) per resident(mSv/year)

Number of residents
affected

Comments

Fukushima

approx. 100 in 10 years
approx. 160 in 70 years

approx. 340’000

Outside of the evacuated zone as far as approx. 70 km
to the north-west

Chernobyl

approx. 190 in 50 years

approx. 75 million

Outside of the evacuated zone, 30 – 1’000 km

Switzerland, estimated according
to /44/ and /46/

approx. 0.6 in 50 years
approx. 2.2 in 50 years

7.8 million(as of 2000)

In southern Ticino due to rain

Germany /44/

approx. 0.6 in 50 years
approx. 2.2 in 50 years

Table . 7-3 Cumulative average effective doses due to external radiation
exposure for periods of 10, 50 and 70 years spent at the location

North of the Danube;
south of the Danube;
due to rain, 30.04

82 | 83

7.6 	Summary
and assessment
Based on the available information, a comparison of the ecological and radiologicalconsequences of the two reactor accidents
at Chernobyl and Fukushima shows that theone at Chernobyl should definitely be assessed as more serious. The explosion andfire inside the reactor at Chernobyl caused
the release of about five to ten times moreradioactive substances, which were carriedin the air for substantially longer distances
than in Fukushima where a large part of therelease was directed away from inhabitedareas and towards the Pacific Ocean. The
impact on health of the radiation on the sitearound the reactor in connection with theimplementation of emergency measures was
also more drastic at Chernobyl. At Fukushima, however, the work to bring the plant
into a permanently stable condition and toestablish a closed cooling circuit has not
yet been completed, nor is all the relevant
information available for Fukushima in order
to arrive at a comprehensive assessment of
the long-term consequences. According to
the data available so far, the effective radiation doses due to the accident in Fukushima
will be substantially lower for a (worldwide)
population group that is smaller by several
orders of magnitude. Moreover, it can alreadybe stated that in Japan itself, the impactof the accident on the population and thesurrounding area is considerably less thanat Chernobyl. However, a conclusive assessment must be made at a later point in time.

In all these considerations, it should not be
forgotten that the Tohoku-Chihou-TaiheiyouOki earthquake was not only the cause of
the reactor accident at Fukushima, but that
it was also responsible for approx. 24’000
dead and missing persons, as well as enormous damage to the economy and theinfrastructure with, among other consequences, 792’000 buildings damaged or
destroyed (cf. /11/).

8 | List of abbreviations

8 List of abbreviations

APD

Active Personnel Dosimeter

FOPH

Federal Office of Public HealthFA

Fuel assembly

BfS(German) Federal Office for Radiation Protection

BMU(German) Federal Ministry for the Environment,
Nature Conservation and Nuclear Safety

DOE

U.S. Department of Energy

EDI

Federal Department of Home Affairs

ENSI

Swiss Federal Nuclear Safety Inspectorate

FIV

Ordinance on Foreign Substances and Constituents in Food

GRS

Gesellschaft für Anlagen- und Reaktorsicherheit mbH[Plant and Reactor Safety Company Ltd]

HFF

High-altitude in-flight filter

HVS

High volume sampler

IAEA

International Atomic Energy Agency

ICAPP

International Congress on Advances in Nuclear Power Plants

ICRP

International Commission on Radiological Protection

INES

International Nuclear and Radiological Event Scale

IRSN

Institut de Radioprotection et de Sûreté Nucléaire
[Institute of Radiation Protection and Nuclear Safety]

JAEA

Japan Atomic Energy Agency

JAIF

Japan Atomic Industrial Forum, Inc.

JMAJapan Meteorological Agency

NPP

Nuclear power plant

MADUK

Automatic network for monitoring the dose rate in
the neighbourhood of nuclear power plants

MAFF

Ministry of Agriculture, Forestry and Fisheries

METI

Ministry of Economy, Trade and Industry

MEXT

Ministry of Education, Culture, Sports, Science and Technology

MHLW

Ministry of Health, Labour and Welfare

MOX

Mixed oxide

NADAM

Automatic network for monitoring the ambient dose rate andfor giving the corresponding alarm

NISA

Nuclear and Industrial Safety Agency

NPP

Nuclear Power Plant

NPS

Nuclear Power Station

84 | 85

NSC

Nuclear Safety Commission

LOD

Limit of detection

ADR

Ambient dose rate

RADAIR

Réseau Automatique de Détection dans l'Air d'Immissions Radioactives[Automatic In-Air Detection Network for Radioactive Immissions]

RBMK

Reaktor Bolshoi Moschtschnosti Kanalny[High-power channel-type reactor]

RPV

Reactor pressure vessel

SGTS

Standby Gas Treatment System

SSSDB

Sarcophagus Safety Status Database

BWR

Boiling water reactor

T1/2

Half life

TEPCO

Tokyo Electric Power Company

UN

United Nations Organisation

UNSCEAR

United Nations Scientific Committee on the Effects of Atomic Radiation

USA, US

United States of America

WHO

World Health Organisation

9 | List of tables and figures

9 	List of tables and figures
TablesPage

Table 2-1

Assessment aspects for the INES classification according to the international scale

6

Table 2-2

Comparison of determined quantities released for the INES classification

8

Table 2-3

Provisional calculation to estimate the airborne release of radioactive substancesin the early phase of the accident (taking account of operating data until 16 May 2011)13

Table 2-4

Nuclide concentrations in contaminated water in the turbine halls

17

Table 5-1

Measurement results for activity concentrations in the soil for radioactive Iodine,
Cesuim and Strontium about one week after the occurrence of the accident

51

Table 5-2

Measurement results for activity concentrations in the soil for Plutonium and Uranium
about two weeks after the occurrence of the accident

52

Table 5-3

Activity limits for food in Japan

53

Table 5-4

Examined food samples and number of limit violations ascertained, using the prefecturesof Fukushima and Ibaraki as examples

54

Table 5-5

Expected external radiation exposure in relation to soil contamination for a periodof one year spent at the location

64

Table 5-6

Expected external radiation exposure in relation to soil contamination for periodsof 10 and 70 years spent at the location

64

Table 6-1

Results from high-altitude in-flight filter (HFF) measurements

69

Table 6-2

Overview of environmental and food samples measured following the reactor accidents
at Fukushima (15 March to 30 April 2011)70

Table 7-1

Percentages of the main radionuclides released in the accident at Chernobyl, as known in 1996

73

Table 7-2

Doses for the population due to external radiation exposure for the first year of presence
in relation to soil contamination

79

Table 7-3

Cumulative average effective doses due to external radiation exposure for periodsof 10, 50 and 70 years spent at the location

82

FiguresPage

Figure 2-1

The international assessment scale for nuclear events – INES

Figure 2-2

Cumulative release of I-131 and Cs-137 according to NSC calculations in the period
from 11 March 2011 to 5 April 2011

6
9

Figure 2-3

Situation in the dry storage facility at the Fukushima Dai-ichi nuclear power plant

11

Figure 2-4

Release rates for units 1-3 at Fukushima Dai-ichi

14

Figure 2-5

Path by which contaminated water spread into unit 2

15

Figure 3-1

Locations of ADR monitoring posts on the Fukushima Dai-ichi plant site

21

Figure 3-2

Overview of ADR values in the period from 12 to 31 March 201121

Figure 3-3

ADR values on the Fukushima Dai-ichi site on 23 March 201122

Figure 3-4

ADR values on the Fukushima Dai-ichi site on 1 August 201123

Figure 3-5

Radioactive debris near unit 1

24

Figure 3-6

Base of stack, units 1 and 2, photographed with a gamma camera

24

Figure 3-7

Base of stack between units 1 and 2, measurement with a telescopic detector

24

Figure 3-8

Dose rate inside the connecting building for the turbine hall of unit 1

25

Figure 4-1

Distribution of accumulated radiation doses, 11 March until approx. 23 May 201131

Figure 4-2

Number of persons and average individual doses, March to May 201132

86 | 87

FiguresPage

Figure 5-1

Schematic view of the main dose paths that contribute to radiation exposure in the areasurrounding a nuclear plant

40

Figure 5-2

Weather situation on the evening of 15 March 2011 in the area surrounding
the Fukushima Dai-ichi nuclear power plant

41

Figure 5-3

Ambient dose rates in the area surrounding Fukushima Dai-ichi on 29 April 2011,selected activity concentrations in soil and seawater

42

Figure 5-4

Ambient dose rate in the area surrounding Fukushima Dai-ichi, extended and refinedmeasurement for July 201143

Figure 5-5

Defined monitoring posts for regular determination of the ambient dose rate outside
the 20 km prohibited zone (data in μSv/h)

44

Figure 5-6

Progression of the ambient dose rate at the defined monitoring posts outside
the 20 km prohibited zone around Fukushima

45

Figure 5-7

Progression at monitoring posts with the highest ambient dose rates directly after the accident

45

Figure 5-8

Progression of ambient dose rates in major cities in eastern Japan between 15 Marchand the start of September

46

Figure 5-9

Cs-134 and Cs-137 activity (Bq/m2) deposited on the ground, derived fromthe aeroradiometric measurements

47

Figure 5-10

Activity concentrations of radiocesium in soil used for agricultural purposesin the area of the plants' roots

49

Figure 5-11

Sampling points where activity conditions for further nuclides were investigated
immediately after deposits occurred

50

Figure 5-12

Violation of the I-131 activity limit in drinking water after the accident, using the examplesof two waterworks in Iitate (prefecture of Fukushima) and Tokyo

56

Figure 5-13

Activity concentration for I-131 in the drinking water systems of various prefectures in northern Japan

57

Figure 5-14

Activity concentration for Cs-134/137 in the drinking water systems of various prefecturesin northern Japan

57

Figure 5-15

Activity concentrations for I-131, Cs-134 and Cs-137 in the seawater aroundthe Fukushima Dai-ichi nuclear power plant on 5 May 2011

58

Figure 5-16

Activity concentration of I-131, Cs-134 and Cs-137 in the seawater aroundthe Fukushima Dai-ichi nuclear power plant on 7 May 201159

Figure 5-17

Cs deposits on the seabed and in the sediment around the Fukushima Dai-ichi nuclear power plant

60

Figure 5-18

Sr deposits on the seabed and in the sediment surrounding the Fukushima Dai-ichi
nuclear power plant

60

Figure 5-19

Evacuation zones around Fukushima Dai-ichi

62

Figure 5-20

Evacuation areas outside the 20 km zone

62

Figure 6-1

Progression of I-131 (left, particulate) and Cs-134 concentrations (right) in Switzerlandfrom the start of January until the end of July 201166

Figure 6-2

Development of the concentration of particulate Iodine-131 in the atmosphere

67

Figure 6-3

Gamma spectrum of an air filter from Switzerland with radioisotopes from the reactor
accident at Fukushima

69

Figure 7-1

Enclosure for unit 1, view from the north74

Figure 7-2

Ambient dose rate at Chernobyl unit 4, 1 m above ground level

75

Figure 7-3

Cesium-137 contamination in Ukraine, Belarus and Russia after the reactor accident at Chernobyl

77

Figure 7-4

Cooling pond at the Chernobyl nuclear power plant with sediments drawn in77

Figure 7-5

Fukushima Dai-ichi: contamination of seawater with Cesuim-137

78

Figure 7-6

Directions of propagation and time progressions for the radioactive cloud from Chernobyl

80

Figure 7-7

Soil contamination (Cs-137 + 134) caused by the Fukushima accident and expected effective doses
due to external irradiation in the first year

81Fukushima
37° 25‘ 26.57“ N, 141° 1‘ 56.87“ E11.03.2011

88 | 89

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34	Pretzsch, G. (GRS), Evaluation of the Radionuclide Release of the Chernobyl Accident (Orrest Calculation), Workshop on
Dose Reconstruction GSF/CEC/IAEA/
GAST, Bad Honnef, Jun 6-9, 1994
35 International Commission on RadiologicalProtection (ICRP) 1991. 1990 Recommen
dations of the International Commission
on Radiological Protection. ICRP Publication 60. Ann. ICRP 21 (1-3), superseded
ICRP Publication 103

10 | Referenzen

36	Ministry of Health, Labour and Welfare(MHLW), The damage situation of andmeasures taken for the Great East Japan
Earthquake (80th announcement),
2011-06-21 http://www.mhlw.go.jp/
english/topics/2011eq/dl/110628_02.pdf
37 Tokyo Electric Power Corporation(TEPCO), Press Release (May 25,2011),
Receipt of Instruction from NISA regar
ding report on investigation of cause anddevelopment of preventive measures
regarding exposure exceeding dose limit
to radiation dose engaged person at 		
Fukushima Dai-ichi Nuclear Power 		Station, 2011-05-25 http://www.tepco.
co.jp/en/press/corp-com/release/11052511-e.html

41 Tokyo Electric Power Corporation(TEPCO), Report on investigations ofcause and development of preventive
measures regarding exposure exceedingdose limits to radiation dose engaged
person at Fukushima Dai-ichi Nuclear
Power Station, 2011-05-02 http://www.
tepco.co.jp/en/press/corp-com/		
release/11050211-e.html
42 Japan Atomic Industrial Forum,
Inc. (JAIF), Status of countermeasures forrestoring from the accident at Fukushima
Dai-ichi Unit 1 through 4. as of October
7th, 2011 http://www.jaif.or.jp/english/
news_images/pdf/ENGNEWS01_1317958363P.pdf

38	Feickert, Chanlett-Avery - Congressional
Research Service, Japan 2011 Earthquake:
U.S. Department of Defense (DOD)
Response, 2011-03-22 http://fpc.state.gov/
documents/organization/159781.pdf

43 Gesellschaft für Anlagen- und Reaktorsicherheit (GRS), Neuere Erkenntnisse
zum Unfall im Kernkraftwerk Chernobyl,	Teil 2 Radiologische Effects in der
Bundesrepublik Deutschland und im 		
europäischen Ausland, GRS-S-40(Februar 1987)

39	Ministry of Labour, Ordinance on Prevention of Ionizing Radiation Hazards,
Ordinance No. 41 of September 30, 1972;
Latest Amendments: Ministry of Health,Labour and Welfare Ordinance No. 172 ofJuly 16, 2001 http://www.jniosh.go.jp/
icpro/jicosh-old/english/law/IonizingRadiationHazards/index.html

44 Deutsches Atomforum e.V.,
Der Reaktorunfall in Chernobyl,
April 2011 http://www.kernenergie.de/kernenergie/documentpool/			Service/025reaktorunfall_tscherno		
byl2011.pdf

40 Nuclear Emergency Response Headquarters, Roadmap for Immediate Actions
for the Assistance of Nuclear Sufferers,
May 17, 2011 http://www.meti.go.jp/		
english/earthquake/nuclear/roadmap/
pdf/110517roadmap_assistance.pdf

45 J. Magill, G. Pfennig, J. Galy,
European Commission – Joint ResearchCentre – Institute for Transuranium 		Elements, Forschungszentrum Karlsruhe,
Karlsruher Nuklidkarte, 7. Auflage 2006
46 Bundesamt für Gesundheit (BAG),
20 Jahre seit dem Reaktorunfall von 			Chernobyl, Die Effects auf die Schweiz,
April 2006

92 | 93

47 Eidgenössisches Nuklearsicherheitsinspektorat ENSI, Ablauf Fukushima 		
11032011, Ereignisabläufe Fukushima 		Dai-ichi und Dai-ni infolge des TohokuChihou-Taiheiyou-Oki Erdbebens vom
11.03.2011, August 2011
http://static.ensi.ch/1314627152/ensi_ab
lauf_260811_web.pdf
48 Eidgenössisches Nuklearsicherheitsinspektorat ENSI, Analyse Fukushima
11032011, Vertiefende Analyse des Unfalls
in Fukushima am 11. März 2011 unter 		besonderer Berücksichtigung der 		
menschlichen und organisatorischen 		
Faktoren, August 2011 http://static.ensi.
ch/1314626452/ensi_analyse_290811_
web.pdf
49	Eidgenössisches Nuklearsicherheitsinspektorat ENSI, Lessons Fukushima
11032011, Lessons Learned und Prüfpunkte aus den kerntechnischen Unfällen
in Fukushima, Oktober 2011
http://static.ensi.ch/1320054384/fukushi
ma_lessons-learned.pdf

Issued by
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CH-5200 Brugg
Phone +41 (0)56 460 84 00
Fax+41 (0)56 460 84 99
info@ensi.ch
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Published 16.12.2011