5． Effects of Decontamination
5.1. Evaluation Pertaining to the Goals of the Basic Policy
The Basic Policy based on the Act on Special Measures Concerning the Handling ofEnvironmental Pollution by Radioactive Materials Discharged by the Nuclear Power Station
Accident Associated with the Tohoku District Off the Pacific Ocean Earthquake That
Occurred on 11 March (hereafter refer to "Act on Special Measures") sets the goals for themeasures for decontamination (Figure 5-1) and the Ministry of Environment (MOE)published the "Evaluation of the Goals of Basic Policy" in December 2013.
Basic Policy Based on the Act on Special Measures (excerpt)(2) The following goals are set for the region with an additional exposure dose of less than 20
mSv/y.
a. The additional exposure dose of 1mSv/y or less shall be targeted as the long-term goal.
b. By the end of August 2013, the annual additional exposure dose of the general public shallbe decreased by about 50% as compared with the value at the end of August 2011, by physicalattenuation of radioactive materials and other effects also being taken into account.
c. It is important to restore the environment for children’s life with peace of mind.
Decontamination of children's living environments such as schools and parks shall be
implemented with high priority, and by the end of August 2013, the annual additional
exposure dose of children shall be decreased by about 60% as compared with the value at theend of August 2011, considering physical attenuation of radioactive materials and othereffects.
Figure 5-1 Basic Policy based on the Act on Special Measures133 .

5.1.1. Facilities Subject to Evaluation
The evaluation was implemented covering about 33,000 facilities (about 12,000 facilities inSpecial Decontamination Areas; about 21,000 facilities in Intensive Contamination Survey
Areas) and at about 330,000 measurement points (about 100,000 points in Special
Decontamination Areas; about 230,000 points in Intensive Contamination Survey Areas),
where the decontamination work had been carried out by the end of August 2013.
SchoolSpecial Decontamination Area
Facility no.

Measurement points no.

Measurement points no.

Housing

Otherfacility

24

123

4,645

Intensive Contamination
Survey Area

2,229

1,980

12,513456

Special Decontamination Area

494

949

61,9801,785

Intensive Contamination
Survey Area

36,136
Road

Facility no.

Park, Square

41,286
Forest153

121,741

4,268

Farmland

Pasture
land

Total

Special Decontamination Area

1,792

2,319

3,204

111

12,371

Intensive Contamination
Survey Area

1,220

940

1,633

97

21,068Special Decontamination Area

18,274

9,541

10,764513

104,300

Intensive Contamination
Survey Area

8,496

2,678

10,404

2,919

227,928＊ Special Decontamination Area･･･Tamura City, Kawamata Town, Kawauchi Village, Naraha Town, Okuma Town,
Katsurao Village, Iitate Village ( However, the measurement result of the data more than 3.8 μSv/h have been excluded)

Figure 5-2 Numbers of facilities and measurement points to be evaluated concerning the
reduction of additional exposure dose134 .
133Source: Ministry of the Environment (MOE), Basic Policy Based on the Act on Special Measures

Concerning the Handling of Radioactive Pollution, December 2011
134Source: Ministry of the Environment (MOE), "Evaluation concerning the goals of basic policy," December

2435.1.2. Basic Approach of Evaluation Methods
The air dose rate at the end of August 2011 was estimated from the air dose rate measured
before decontamination and the air dose rate at the end of August 2013 was estimated fromthe air dose rate measured after decontamination. The evaluation for each classification offacilities was done by integrating the air dose reduction rate by decontamination and the
reduction rate by physical attenuation of radioactive materials and other effects.
It should be noted that the Basic Policy set its goal on the reduction of additional exposure
dose. However, the additional exposure dose cannot be directly measured. The evaluation was
done instead, on the assumption that the exposure dose was proportional to the air dose rate
(Figure 5-3).

Figure 5-3 Basic concept of evaluation methods.

5.1.3. Evaluation Methods and Results（1） Annual additional exposure dose of the general public
1）Evaluation methods
The average additional radiation exposure dose was calculated for each facility
classification* by estimating the air dose rate at the end of August 2011, using themeasured values on a day before decontamination.
The average additional radiation exposure dose was calculated for each facility
classification* by estimating the air dose rate at the end of August 2013, using themeasured values on a day after decontamination.
The additional annual exposure dose was estimated as the total of the dose rate
multiplied by a coefficient defined for each classified facility subject to life patterns.
* Concerning roads or forests, each unit divided by facility numbers in the investigation
was dealt with as one facility. Evaluation of additional annual exposure dose of children
was done in the same way.

2013 (Figure 5-3 to Figure 5-7 have the same source.)2442）Evaluation results
The goal of reducing the additional annual exposure dose was evaluated as having beenachieved, as seen in the overall reduction rate of about 64% over the two year period (Figure
5-4).

Additional exposure
dose (%)
Goal
SpecialDecontamination
Areas
Intensive
Contamination
Survey Areas
Overall

Contribution ofphysical attenuation
effect (%)

about 50
about 67

Contribution of
decontamination effect (%)
about 10
about 27

about 40

about 62

about 22

about 64
about 24
Figure 5-4 Evaluation results of reduction rate over 2 years(Annual exposure dose of the general public)（2） Annual additional exposure dose of children1）Evaluation methods
The average additional radiation exposure dose was calculated for each facility
classification* by estimating the air dose rate at the end of August 2011, using themeasured values on a day before decontamination.
The average additional radiation exposure dose was calculated for each facility
classification* by estimating the air dose rate at the end of August 2013, using themeasured values on a day after decontamination.
The additional annual exposure dose was estimated as the total of the dose rate
multiplied by a coefficient defined for each classified facility subject to life patterns.
2）Evaluation results
The goal of reducing the additional annual exposure dose was evaluated as having beenachieved, as can be seen in the overall reduction rate of about 65% over the two year period(Figure 5-5).

Goal
SpecialDecontamination
Areas
Intensive
Contamination
Survey Areas
Overall

Reduction of
additional exposure
dose (%)
about 60
about 66

Contribution ofphysical attenuation
effect (%)

Contribution of
decontamination effect(%)
about 20
about 26

about 40

about 64
about 65

about 24
about 25

Figure 5-5 Evaluation results of reduction rate over 2 years(Annual additional exposure dose of children)245

（3） Reduction rate of additional exposure dose for air dose rate range
Reduction rates of the additional exposure dose were evaluated for each air dose rate range
before decontamination. Higher reduction rates of the additional exposure dose tend to beachieved in areas of higher air dose rate before decontamination. Higher reduction rates ofchildren’s additional exposure dose are higher than those of the general public for all air dose
rate ranges.

0.99 or higher

Reduction of
additional
exposure dose (%)
about 73

0.80 to below 0.99

about 64

0.61 to below 0.80

about 63

0.42 to below 0.61

about 60

about 20

0.23 to below 0.42

about 55

about 15

Air dose rate
(μSv/h)Contribution ofphysical attenuation(%)

Contribution of
decontamination effect (%)
about 33
about 24

about 40

about 23

Figure 5-6 Reduction rate of additional exposure dose for each air dose range (the generalpublic).

0.99 or higher

Reduction of
additional
exposure dose (%)
about 74

0.80 to below 0.99

about 67

0.61 to below 0.80

about 67

0.42 to below 0.61

about 63

about 23

0.23 to below 0.42

about 58

about 18

Air dose rate
(μSv/h)Contribution ofphysical attenuation(%)

Contribution of
decontamination effect (%)
about 34
about 27

about 40

about 27

Figure 5-7 Reduction rate of additional exposure dose for each air dose rate range (children).

5.2. Overview on the Decontamination Effects
The “Decontamination effects (air dose rate) in the decontamination work implemented by
the National Government and local municipalities” (prepared by the MOE, Decontamination
Team, December 2013) reviewed the decontamination effects (air dose rate) in thedecontamination work to date, focusing on to what extent the air dose rate (at the height of 1m) could be reduced by decontamination, from the viewpoint of evaluating the exposure doseto the general public.

246

5.2.1. Data for Evaluation
The report reviewed about 250,000 data (two measured values before and after
decontamination per one measurement point) of the air dose rate (measured at the heights of
1 m and 50 cm; unit, μSv/h), roughly between March 2012 and October 2013 in thedecontamination work implemented in JFY 2012 onward (in 10 municipalities under the
National Government jurisdiction and in 90 municipalities in 8 prefectures under local
jurisdiction).
The evaluation was limited to the data collected at the time of evaluation. Decontamination
methods and decontamination target places include various types depending on the situations.
In residential areas, for example, the evaluation of air dose rate was based on the results fromvarious complex effects of gardens with soil, paved surfaces, roofs, walls, etc. The following
data were excluded from the evaluation.
The air dose rate data below 0.23μSv/h before decontamination.
Top 1% and bottom 1% of the reduction rate data (Outlier data, unsuitable for grasping
the overall trend).

Classification work

National Government

Land- use Classification

Air dose rate(1m)Air dose rate(0.5m)

Public facilities *2

approx. 12,000-

Residential area

approx. 54,000

Road

approx. 28,000-

Farm land

approx. 11,000-

Forestapprox. 10,000-

Sum

Local municipalities

approx.116,000-

Public facilities *2

approx. 36,000-

Residential area

approx. 37,000

-

Road

approx. 6,000-

Farm land

approx. 10,000-

approx. 3,000--

approx.40,000

approx.92,000

approx.40,000

approx.208,000

approx.40,000

ForestChildren’s living environment

*3

Sum
Total

Note: There is a case in which the total does not match due to rounding off the fractional.
＊1：Less than 0.23μSv/h of decontamination data before, data of upper reduction rate 1% and lower reduction rate
1% are excluded and calculated.
＊2：Public facilities include school, park or large facility.
＊3：Children’s living environment include elementary school, kindergarten and park.

Figure 5-8 Data for evaluation135 .

5.2.2. Summary of the Results
In terms of typical distribution ranges of air dose rate (the range here refers to rates
between the 25th percentile value and the 75th percentile value), the air dose rate before
decontamination was 0.36 to 0.93 μSv/h, and it was reduced to 0.25 to 0.57 μSv/h after
135Source: Ministry of the Environment (MOE), Decontamination Team, “Decontamination effects (air doserate) implemented by the National Government and local municipalities,” December 2013 (Figure 5-9 to
Figure 5-14 have the same source.)247

decontamination. As a whole, the air dose rate was reduced and at the same time, its
distribution range became narrower after decontamination. This indicates the
reduction rate of air dose rate by decontamination in the higher air dose rate areas islarger and the reduction rate in lower air dose rate areas is smaller.
The air dose rate was reduced by decontamination by about 30 to 50% on average in all
dose rate ranges (below 1μSv/h, 1 to 3.8μSv/h and above 3.8μSv/h, respectively, before
decontamination). This indicates the higher the dose rates before decontamination, thelarger the decontamination effects and the air dose rate reduction.
In the current review, the evaluation was done by air dose rates (μSv/h) from theviewpoint of evaluating exposure dose of the general public. Regarding the difference of
decontamination effects (reduction rates) depending on the target place and thedecontamination methods, the evaluation results by surface contamination densities(cpm) were made public in January 2013, in which the decontamination effect byremoving radiocesium from the decontamination targets had been confirmed.
The air dose rate reduction features varied subject to influences from the surroundingarea, depending on the characteristics of decontamination site, type of land-use andothers.
Concerning the relation between the type of land-use and decontamination effects, thedecontamination effects were relatively high in the residential areas and relatively low
in the forests. It should be noted that the data for forests do not directly indicate theeffects on the neighboring living environment such as residential areas because thedata for forests included a considerable number of data collected inside the forests.
(Note) The forests were decontaminated by removing accumulated leaf litter and woody
materials. The decontamination guidelines were revised based on the new knowledge
obtained for more effective decontamination, by, for example, adding the removed
accumulated organic materials to targets for the decontamination methods, and also byconsidering the migration of radiocesium over time.
Regarding the living environment for children such as schools, parks, etc., there weresome data measured at different heights. Therefore, the data were reviewed separately
in individual cases. As the result, the reduction rate was roughly 50% to 80%, tending
to be higher compared with that of the whole area (air dose rate at 1 m in height).

Air dose rate *1,2
(measurement
hight 1m)
Reduction rate of
air dose rate
(average) *2,3
ex) Reduction rateof surface
contamination
density *4

Before decontamination : 0.36 to 0.93μSv/h
After decontamination : 0.25 to 0.57μSv/h
Before decontamination
ｌess than 1μSv/h

Before decontamination
1~3.8μSv/h

Before decontamination
3.8μSv/h or more

43%

51%

32%

Asphalt pavement of parking lot: washing is aprox.50 to 70%
High-pressure washing is approx.30 to 70%
Soil ground: stripping of surface soil is approx..80 to 90%＊1.Band of value of 25 percentile and 75 percentile of air dose rate.
＊2.Data at measurement height 0.5m is not included in the data of living environment for children on school etc..
＊3.Average data of reduction rate of air dose rate at each decontamination classification before.
( reduction rate(%) =(1-air dose rate before decontamination/ air dose rate before decontamination)×100)＊4.Announcement “effect of decontamination method in the work by National Government and local municipalities" has been Press
released on 18.Jan.2013.

Figure 5-9 Decontamination effects in the decontamination work implemented by the
National Government and local municipalities (main results).

248

5.3. Decontamination Effects in Five Areas: Public Facilities, Residential Areas,
Roads, Farmland and Forests
The “Decontamination effects (air dose rate) in the decontamination work implemented by
the National Government and local municipalities” (prepared by the MOE, Decontamination
Team, December 2013) reviewed the decontamination effects also by land-use classification(five categories consisting of: public facilities and the like; residential areas; roads; farmland;
and forests) in addition to the review as a whole.

5.3.1. Public Facilities
The data of public facilities and the like included various data such as those of groundsurfaces of bare soil, asphalt paved surfaces, gravel, etc.
About 70% of the data were from the facilities with the air dose rate below 1 μSv/h
before decontamination and the average reduction rate for all public facilities was
about 34%.
In the areas with the air dose rate was below 1 μSv/h before decontamination, theaverage reduction rate was about 29% and the air dose rate after decontamination was
0.38μSv/h or less at half of the measurement points. The reduction rate was higher in
the areas with higher air dose rate before decontamination and the average air dose
rate at the points of 1 μSv/h before decontamination was about 0.6 μSv/h (a reduction
rate of about 40%).
In the areas with the air dose rate ranges of 1 to 3.8 μSv/h and 3.8 μSv/h or higher
before decontamination, the reduction rates were higher in the areas with higher air
dose rate as compared with those in the areas with the rate of less than 1 μSv/h, andthe average reduction rate in the areas with the rate of more than 3.8 μSv/h before
decontamination was about 53%.
Most of the data with high air dose rate were data obtained by decontamination of apublic facility as a single target. For this reason, the air dose rate of public facilities
after decontamination tended to be higher when compared with the air dose rate ofresidences which were decontaminated zone-wise including the surroundings. However,
the air dose rate of public facilities is expected to be reduced through decontaminationof their surroundings.

249

Figure 5-10 Air dose rate (at 1m) in the National Government work (public facilities).

5.3.2. Residential Areas
The number of data measured in residential areas was about 50,000, about half of thedata were from the work by the National Government, which included a wide variety ofdata such as bare soil, gardens, grass fields, gravel, concrete paved surfaces, etc.
About 70% of the data were from the zones with the air dose rate below 1 μSv/h before
decontamination and the average reduction rate for all residential areas was about
43%, which was relatively higher than for all decontamination work.
In the zones with the air dose rate below 1 μSv/h before decontamination, the average
reduction rate was about 40% and the air dose rate after decontamination was
0.33μSv/h or less at half of the measurement points. The reduction rate was higher inthe zones with higher air dose rate before decontamination and the average air dose
rate at the points of 1 μSv/h before decontamination was about 0.5 μSv/h after
decontamination (a reduction rate of about 50%).
In the zones with the air dose rate ranges of 1 to 3.8 μSv/h and 3.8 μSv/h or higher
before decontamination, the reduction rates were higher in the areas with higher air
dose rate as compared with those in the zones with the air dose rate of less than 1
μSv/h, and the average reduction rate in the zones with the air dose rate of more than
3.8 μSv/h before decontamination was about 57%.

250

Figure 5-11 Air dose rate (at 1 m) in the National Government work (residential areas).

5.3.3. Roads
The data for roads included those of paved roads, gravel and crushed stone roads, etc.
About 70% of the data were from the roads with the air dose rate below 1 μSv/h before
decontamination and the average reduction rate for all roads was about 33%.
On the roads with the air dose rate below 1 μSv/h before decontamination, the average
reduction rate was about 29% and the air dose rate after decontamination was
0.40μSv/h or less at half of the measurement points. The reduction rate was higher on
the roads with higher air dose rate before decontamination and the average air dose
rate at the points of 1 μSv/h before decontamination was about 0.6 μSv/h after
decontamination (a reduction rate of about 40%).
On roads with the air dose rate ranges of 1 to 3.8 μSv/h and 3.8 μSv/h or higher before
decontamination, the reduction rates were higher on roads with higher air dose rate ascompared with that on the roads with the air dose rate of less than 1 μSv/h, and theaverage reduction rate on the roads with the air dose rate of more than 3.8 μSv/h before
decontamination was about 53%.

251

Figure 5-12 Air dose rate (at 1m) in the National Government work (roads).

5.3.4. Farmland
The data on farmland included those on orchards and pasture land, but most of themwere data on plowed land (deep plowing, top soil scraping). Most of the data on
farmland with the air dose rates exceeding about 2μSv/h before decontamination wereobtained from the farmland where decontamination was done by topsoil scraping.
About 70% of the data were from farmland with the air dose rate below 1 μSv/h before
decontamination and the average reduction rate for all farmland was about 34%.
On farmland with the air dose rate below 1μSv/h before decontamination, the average
reduction rate was about 28% and the air dose rate after decontamination was
0.44μSv/h or less at half of the measurement points. The reduction rate was higher on
the farmland with the higher air dose rate before decontamination and the average air
dose rate at the points of 1 μSv/h before decontamination was about 0.6 μSv/h (areduction rate about 40%).
On farmland with the air dose rate ranges of 1 to 3.8 μSv/h and 3.8 μSv/h or higher
before decontamination, the reduction rates were higher on farmland with higher air
252dose rate as compared with those on farmland with the air dose rate of less than 1
μSv/h. On farmland with the air dose rate exceeding about 2 μSv/h before
decontamination, the air dose rate was reduced to about 1 μSv/h, regardless of the air
dose rate before decontamination, because the decontamination was mostly by topsoil
scraping.

Figure 5-13 Air dose rate (at 1m) in the National Government work (farmland).

5.3.5. Forests
Most data of forests were those obtained by removing organic matter such as fallen
leaves and woody materials.
About 60% of the data were from forests with the air dose rate of below 1 μSv/h before
decontamination, lower in proportion of the data than in other land-use categories. The
average reduction rate for all forests was about 22%, lower than for all
decontamination work.
For forests with the air dose rate below 1 μSv/h before decontamination, the average
reduction rate was about 18% and the air dose rate after decontamination was
0.57μSv/h or less at half of the measurement points. The reduction rate was higher forforests with the higher air dose rate before decontamination and the average air dose253

rate at the points of 1 μSv/h before decontamination was about 0.75 μSv/h (a reduction
rate of about 25%).
For forests with the air dose rate of 1 μSv/h or higher before decontamination, thereduction rate was slightly higher than that for the forests with the air dose rate of lessthan 1 μSv/h before decontamination, and the average reduction rate for the forests
with the air dose rate of 1 to 3.8 μSv/h before decontamination was about 27%.
It should be noted that the data for forests do not directly indicate the effects on theneighboring living environments such as residential areas because the data for forests
included a considerable number of data collected inside the forests.

Figure 5-14 Air dose rate (at 1m) in the National Government work (forest).

5.4. Effects at Each Target Decontamination Place
The “Effectiveness of decontamination methods in the decontamination work implemented
to date by the National Government and local municipalities” (prepared by the MOE,
Decontamination Team, January 2013) reviewed the results of decontamination work in theearly stage (mainly in JFY 2011) implemented by the National Government and local254municipalities mostly in the area with comparatively high dose areas in Fukushima
Prefecture, focusing on to what extent the radioactive materials could have been reduced bydecontamination work.

5.4.1. Outline
The data collected mainly in the neighboring areas of residential areas such asbuildings and structures, roads, etc. were reviewed, which had been obtained in thedecontamination work at the first stage. (Data one plowed land and forests were
excluded from the review because the numbers of data points were insufficient.)
The effectiveness of decontamination methods was evaluated in terms of reduction
rates of surface contamination densities because the review purpose was to evaluate
the effectiveness of each decontamination method.
The data to be reviewed were limited to those with surface contamination densities
before decontamination of higher than 2,000 cpm, in order to reduce data deviations
due to the influences from objects other than the target object.
ObjectNumber of Data
(2,000cpm or more)

Number of Data
(whole data)

Decontamination method for analysis

Rainwater gutter

343

772

High-pressure washing, Swabbing after removal of
sediments

Rainwater basin

85

214

High-pressure washing after removal of sediments

Side ditch

132

306

Removal of sediments, High-pressure washing after
removal of sediments

Roof

464

751

Wiping, Washing, High-pressure washingOuter wall

64

997

Wiping, Washing, High-pressure washing

Garden ground

446

628

Grass mowing, Stripping of top soil, Soil replacement,
Peeling off of lawn

Pavement surface of parking lots

601

781

Washing, High-pressure washing, Scraping off

Ground (soil)
271of additional exposure
343
Strippingof toppublic)
soil
Fig.5-6 Reduction rate
dose
(generalRoad (surface of asphalt pavement)

506

539

Total

2,912

5,331

Washing, Pressure washing, Scraping off

Figure 5-15 Target objects of decontamination, numbers of data and decontamination
methods136 .

136Source: Ministry of the Environment (MOE), Decontamination Team, “Effectiveness of decontamination

methods in the decontamination work implemented to date by the national government and local
municipalities", January 2013 (Figure 5-16 to Figure 5-29 have the same source.)255

5.4.2. Effectiveness of Decontamination Methods for Each Target Decontamination Place（1） Buildings and structures
1）Rainwater gutters and street drainsa.) Rainwater gutters
The reduction rate of surface contamination densities was around 60 to 80% by wiping
after sediment removal and around 40 to 80% by high-pressure water washing after
sediment removal. Higher reduction rate by wiping after sediment removal wasachieved than by high-pressure water cleaning.
Substantial amounts of radioactive materials were accumulated in the sediments inrainwater gutters. It should be noted that sediment removal is an effective approachfor decontamination.

Figure 5-16 Decontamination effect for a target decontamination place (rainwater gutters).

256b.) Rainwater cisterns
The reduction rate of surface contamination densities was around 60 to 90% by
high-pressure water washing after sediment removal.
The effect by sediment removal was considered large, too.
It should be noted in data interpretation that radioactive materials sunk into seams orcracks in high concentrations from rainfall in the early stage after the nuclear power
plant accident and lowered the reduction rate.
It is a point of careful attention in decontamination that soil and other objects in thesurrounding area might be contaminated in case the rainwater cisterns are damaged
and leaking.

Figure 5-17 Decontamination effect for a target decontamination place (rainwater cisterns).

257c.) Street drains
The reduction rate of surface contamination densities was around 70 to 90% bysediment removal and around 60 to 90% by high-pressure water washing after
sediment removal.
Substantial amounts of radioactive materials were accumulated in street drains. It is apoint of careful attention in decontamination that simple removal of sediments can beeffective enough and that the possibility should be considered for contamination of thesoil and other objects in the surrounding area in case the street drains are damaged
and leaking.

Figure 5-18 Decontamination effect for a target decontamination place (street drains).

2582）Roofs and other house structures
The reduction rate of surface contamination density on the roofs was around 0 to 20%(*) by wiping, around 20 to 60% by water washing, and 40 to 80% by high-pressure
water washing. (* The reduction rate was improved to 20 to 50% using a better way of
wiping in the decontamination of roofs of private houses implemented in the autumn of2012.)The reduction rate for rooftops was around 60 to 90% by high-pressure water washing.
The rooftop shapes are generally not very complicated and therefore the high-pressure
water washing is effective.
The reduction rate for verandas and similar structures was around 20 to 50% by
high-pressure water washing. But the available data were limited. If the high-pressure
water washing was done after the sediments were removed, the reduction rate reachedaround 60 to 90%.
Points of attention in data interpretation are:Data for roofs had deviations depending on their shapes or surface materials.
Data deviations occurred in high-pressure water washing, since contaminatedwastewater was left.
Low reduction rates were experienced in some cases of water washing and wipingof roofs even with high surface contamination densities before decontamination.
These cases were for cement tiles, unglazed clay tiles and painted steel plates. The
cause of the low reduction rate is considered to have come from the influence ofrust or the roof materials themselves.
Points of attention in decontamination are:Measures should be taken to prevent wastewater from spreading when
decontaminating using water.
If rust is present, it should be removed by wiping and other means before
high-pressure water washing, because its presence lowers the effect.
A possibility should be considered in high-pressure water washing of damaging thestructures, for instance, peeling off their surface materials.

259

Figure 5-19 Decontamination effect for a target decontamination place (roofs and others).

2603）Exterior wallsa.) Concrete walls
The reduction rates of surface contamination densities were around 10 to 30% by
wiping and around 20 to 80% by high-pressure water washing. However, the data of
wiping were limited.
Many data were available for low surface contamination densities (less than 2,000 cpm)
before decontamination. This is likely because the amount of radioactive materials
attached was small or the radioactive materials had been washed away to some extent
by rainfall.
It is a point of attention in data interpretation that contamination of exterior walls was
generally low, since rain, dust and other things were less likely to be attached on thewalls than on the roofs, rainwater gutters, etc.
Points of attention in decontamination are:
The need for decontamination should be assessed by comparing the backgroundradiation levels and the contaminated situation of the objects.
A possibility should be considered in high-pressure water washing of damaging thestructures, for instance, peeling off wall surface materials.

Figure 5-20 Decontamination effect for a target decontamination place (concrete).

261b.) Metal walls, windows, doors and shutters, etc.
Few data were available for metal walls, windows, doors and shutters, etc.
For metal walls, the reduction rate was around 40 to 70% by cleaning and around 40 to
90% by high-pressure water washing.
For windows, doors and shutters, the reduction rate was around 70 to 80% by wiping,around 20 to 70% by water washing, and around 50 to 90% by high-pressure water
washing.
Many data were available for low surface contamination densities (less than 2,000 cpm)
before decontamination. This is likely because the amount of radioactive materials
attached was small or radioactive materials had been washed away by rainfall.
It is a point of attention in data interpretation that the contamination of windows,
doors and shutters is generally low, since rain, dust and other things are less likely to
be attached on these surfaces than on the roofs, rainwater gutters, etc.
It is a point of attention for decontamination that the need should be assessed bycomparing the background radiation levels and the contaminated situation of theobjects.

Figure 5-21 Decontamination effect for a target decontamination place (metal walls, windows,
doors and shutters, etc.).

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c.) Tiles and sidings
The reduction rate of surface contamination densities was around 60 to 70% by
high-pressure water washing. But the data were limited.
The reduction rate by high-pressure water washing of tiles and sidings was higher thanthat of concrete walls.
Many data were available for low surface contamination densities (less than 2,000 cpm)
before decontamination. This is likely because the amount of radioactive materials
attached was small or the radioactive materials had been washed away by rainfall.
It is a point of attention in data interpretation that the contamination of tiles andsidings is generally low, since rain, dust and other things are less likely to be attachedon the tiles and sidings than on the roofs, rainwater gutters, etc.
It is a point of attention for decontamination that the need should be assessed bycomparing the background radiation levels and the contaminated situation of theobjects.

Figure 5-22 Decontamination effect for a target decontamination place (tiles and sidings).

2634）Ground surfaces such as gardensa.) Bare soil and grassland
The reduction rate of surface contamination densities was around 0 to 60% by grass
mowing, around 40 to 80% by topsoil scraping, and around 70 to 100% by soil
replacement.
Soil replacement was applied in cases where the surface contamination density was
relatively high before decontamination.
The points of attention in data interpretation are:Topsoil scraping of gardens may lower the certainties of decontamination work
because of the presence of vegetation or more unevenness than on other types ofground surfaces.
The effect of decontamination by grass mowing may possibly change because theattachment of radioactive materials to the grass changes with time and also as
grass grows uptake of radioactive materials may occur.
In some cases, the reduction rate becomes lower due to decrease of shielding effectsof beta rays by grass as a result of mowing.

Figure 5-23 Decontamination effect for a target decontamination place (bare soil, grassland)264b.) Lawns
The reduction rate of surface contamination densities was high; 70 to 90% by peelingoff of lawns and about 90% by soil replacement (coverage with crushed stones after
removal of lawns).
It is a point of attention in decontamination that it is necessary to consider “closemowing combined with topsoil removal(*),” for which a certain effect of dose reduction
has been confirmed, from the viewpoint of controlling the amount of removed soil
generated as well as regeneration of the lawns.
(*) Close mowing combined with topsoil removal: a method to remove the topsoil
including the root layer of dead lawns and other grasses depending on the situation ofradioactive materials.

Figure 5-24 Decontamination effect for a target decontamination place (lawns).

2655）Paved surfaces such as parking lotsa.) Asphalt paved surfaces
The reduction rate of surface contamination densities was around 50 to 70% bycleaning, around 30 to 70% by high-pressure water washing, and around 70 to 90% by
surface scraping.
In high-pressure water washing, the reduction rate had large deviations irrespective of
surface contamination densities before decontamination.
A point of attention in data interpretation is that the decontamination effects may havelarge deviations because of variations in decontamination conditions of high-pressure
water washing at each decontamination place (nozzle elevations above ground surface,work time per unit area, and other conditions) and the size of the area to be
decontaminated like parking lots or the different conditions of paved surfaces(permeability or drainage capability).
Points of attention in decontamination are:Measures should be taken to prevent wastewater from spreading when
decontaminating using water.
The possibility that radioactive materials may have deposited into cracks should
be considered.

Figure 5-25 Decontamination effect for a target decontamination place (asphalt paved
surfaces).

266b.) Concrete paved surfaces
The reduction rate of surface contamination densities was around 40 to 70% by
high-pressure water washing and around 60 to 90% by surface scraping.
The reduction rate varies depending on the work method of surface scraping.
A point of attention in data interpretation is that the decontamination effects may havelarge deviations because of variations in decontamination conditions of high-pressure
water washing at each decontamination place (nozzle elevations above ground surface,work time per unit area, and other conditions) and the size of the area to be
decontaminated like parking lots or the different conditions of paved surfaces(permeability or drainage capability).
Points of attention in decontamination are:
Relatively high reduction rates are obtained on the concrete surfaces because ofless unevenness, but contamination tends to be concentrated around moss-covered
spots.
Measures should be taken to prevent wastewater from spreading when
decontaminating using water.

Figure 5-26 Decontamination effect for a target decontamination place (concrete paved
surfaces).

267c.) Interlocking block surfaces
The reduction rate of surface contamination densities was around 50 to 80% by
high-pressure water washing and around 40 to 70% by scraping.
Points of attention in data interpretation are:
The reduction rate can be lowered in scraping if scraped chips and radioactive
materials are left in the gaps between the interlocking blocks.
The reduction rate by scraping (abrasive material blasting and concrete surface
planing) of interlocking blocks is lower than that by scraping of asphalt paved or
concrete paved surfaces. The scraped chips left in the gaps of interlocking are
likely one reason for this.

Figure 5-27 Decontamination effect for a target decontamination place (interlocking blocks).

2686）Ground surfaces and the like (soil)High reduction rates of around 80 to 90% were achieved by topsoil scraping.
Stable reduction rates seem to have been obtained, since the grounds have limited
unevenness.
It is a point of attention in decontamination that it is necessary to check the depth ofcontamination from the surface layer in advance and determine the optimum thicknessof scraping.

Figure 5-28 Decontamination effect for a target decontamination place (ground surfaces andthe like (soil)).

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（2） Roads (asphalt paved surfaces)
Most data are from decontamination by cleaning and the reduction rate was around 0
to 50%. Large deviations were seen in the reduction rate because most data wereobtained from decontamination by special cleaning vehicles that restore permeable
pavement.
The reduction rate by high-pressure water washing was around 10 to 50%. However,the data were limited.
The reduction rate by scraping was around 10 to 70% (* the reduction rate is currently
being improved by better collection of scraped chips.)
The reduction rates of the asphalt-paved roads by any decontamination methods ofcleaning, high-pressure water washing, or scraping were in many cases lower thanthose of asphalt-paved surfaces in parking lots of structures such as buildings.
Points of attention in data interpretation are:
The decontamination effect may have large deviations because of deviations indecontamination conditions of high-pressure water washing at eachdecontamination place (nozzle elevations above ground surface, work time length
per unit area and other conditions) and the size of the area to be decontaminatedlike parking lots or the different conditions of paved surfaces (permeability or
drainage capability).
The reduction rate tends to be low when vehicles to restore permeable pavements
are used with low water pressure and recirculated wastewater. Also, the cleaning
and wastewater collection performance are downgraded on the road surfaces
distorted or damaged by the earthquake and other reasons.
Measures should be taken to prevent wastewater from spreading, when decontaminating
using water.

Figure 5-29 Decontamination effect for a target decontamination place (asphalt paved
surfaces).

270