Fujita Technical Research
ReportNo.49 2013

Development of construction material databasefor low-activation sheilding

Ken-ichi Kimura

Abstract
After huge quantities of radioactive plume were dispersed over almost half of Japan, radioactive
cesium has been detected across a large percentage of Japanese land. That causes some effects
to the raw material for construction work and this influence will continue to expand because of137Cs. Due to this situation, the development of a radioactive database for construction materials

after March 11th 2011 has been started to compare with a database from before the accident inFukushima. In this paper, some natural radioactivities in fly ash were reported to understandthe baseline level of radioactivity. Secondly, radioactive cesium in combustion ashes and slags,
which were taken from all over the Japan after the accident, were measured to investigate thelevels of contamination. Based on the measurements obtained, the trial investigation of theinfluence of the use of the construction materials with radioactive cesium on the shielding pod
was conducted using a Monte Carlo calculation. The calculated dose rates from the shielding
concrete itself with radioactive cesium were greater than those from concrete shielding pods
containing contaminated soils in one case. These results confirmed the necessity of thedevelopment of radioactive database for the construction materials.

§1. Introduction
materials [1] across from a range of locations
Concrete is one of the main materials usedover different periods of time. The collection offor constructing building, infrastructure, andthese materials comprised 2000-3000 kinds offacilities, which are a major portion of humanaggregates including crushed natural stones,

public activities. In addition, these materials

by–products, and burning slags, approximately

are typically used in reactor and accelerator

1000 cement samples including various types offacilities for shielding.

PortlandFor

thedesignof

radiation

cements,aluminacements,andshielding,clinkers which varied in the production year,

detailed data for the material elements are

and 1000-2000 kinds of additive including fly

required, and thus it is very important toashes, limestone powders, and combustion

establish a construction material database forashes. Among these materials, approximately

radiation shielding. A lot of effort has been500 samples were analyzed for major and rare

made to collect a variety of construction

elements, including some radioactive nuclides.
On the other hand, it is also important todevelop

Keywords : database, construction material, clearancearadioactive

databasefortheconstruction materials for shielding especiallylevel, Monte Carlo, radioactive cesium

gamma-ray－67－shielding.

And

that

database

Fujita Technical Research Report No.49

should include naturally occurring radioactive

Understanding the radioactivity level of thematerials (NORM) and radioactive nuclides

coal–fired ash is important for their use inproduced by the accident in Fukushima.

concrete materials.

In this paper, some natural radioactivities inMore than 60 fly ashes were gathered fromfly ashes were reported to understand the level

all over the Japan. 20–30kg samples of fly ashof radioactivity for NORM. Radioactive cesium

were carefully taken from each plants site, andin combustion ashes and slags, which weresent to us. These fly ashes were sampled in two

taken from all over Japan after the accident,

ways – over a wide area at a single point inwere also measured to investigate the levels oftime, and at a single location over an extended

contamination. Based on these results, the trialperiod. Two plants were chosen for theinvestigation on the influence of the use of theinvestigation of changes over an extended

construction materials with radioactive cesium

period of more than 10 years. Samples fromon the shielding pod was conducted using aanother 19 plants collected in a single year

Monte Carlo calculation.

(2010).

regionality.

§2.
Radioactivity in raw materials forradiation shielding –typical example-wereexaminedtounderstandEstimation of activities for fly ash samples
were conducted by gamma ray measurement
withanHPGe

detector.

Thenuclides

measured

were214Pb,

the coal fired fly ashes and radioactive cesium

nuclides),228Ac,

212Pb,

for the furnace slags and coal fired fly ashes

nuclides), and 40K, which are known as typicalwere estimated to recognize baseline levels.

nuclidesIn this section, the quantities of NORM forforNORM

214Bi

(238U

series

208Tl(232Thseries(naturallyoccurring

radioactive materials). 30–50g of each fly ash
was packed into a U-8 cylindrical plastic case,

2.1 Radioactivity in fly ash
Coal fired fly ash is one of the major additive

and were sealed by waterproof gel in order tomaterials for concrete. An advantage of the use

ensure air-tightness and keep the radioactiveof fly ash in the concrete is to reduce the initial

equilibrium for nuclides of 232Th series and 238U

stress of thermal heat by cement hydration

series for more than one month.

reaction because of its small particle size. This
property is particularly useful in thick concretesuch as that used for radiation shielding.
On the other hand, some of the coal ashes
areknown

asartificiallyconcentrated

materials of NORM. The level of activity is
obviously higher than coal itself and could bearound same level as Clearance Level (CL)[2].

Figure 1 Activities of Th-232 &U-238series nuclides
for 2010 gathered fly ashes.

－68－

Development of construction material database for low-activation sheilding

Table 1 Number of samples for measurement.

analysed are less than 1.0 Bq/g [3].
2.2

Estimation of contaminated construction

materials
Tremendous quantities of radioactivity weredispersed from Fukushima Daiichi nuclear
power plant. That caused some effects to theraw material for construction work and thisFigure 2 Activities of Th-232 &U-238series and K-40 for2010 gathered fly ashes and Plant B.

influence will increase in long term. Beside theaccident

Figure 1 shows the levels of radioactivity for
238U

series and232Th

facilities,Therefore,shown in horizontal axis). These figures

shouldbealsotakenaccount.

estimationofthelevelofimportant.

series are higher than the others, respectively.

41 samples (15 for furnace slags and 26 for

These tendencies are similar in other samples.

coal-fired fly ashes) were gathered after the212Pb and 214Pb are defined as the representive
238U

otherradioactivity for construction raw materials isindicate 214Pb in 238U series and 212Pb in 232Th

series andFukushima,experiments, or other accidents from nuclear

coal-fired power plants in Japan (named A to S

232Th

thecontamination sources, such as nuclear weapon

series for fly ashes

gathered in 2010 physical year from 19

nuclide forinaccident in Fukushima and 49 samples,

seriesincluding eight fly ash samples from therespectively in latter section for the estimation

sample storage in addition to the above, wereof the activity in fly ash, therefore.

analysed using an HP Ge detector. Samples of

The upper side of the Figure 2 shows thefly ash were only taken for two plants locatedlevels of activities in summation of 212Pb, 214Pb

in Tohoku area, because there were no reports

and 40K, for gathered from 19 coal-fired powerof radioactive cesium for samples prior to 2010.

plants in 2010 with each sample number at

15 furnace slags were gathered from all overhorizontal axis, which are distributed in a

the Japan including Tohoku area, which wererange of 0.7 Bq/g. The lower side in the figure 2

produced before and after the accident. Table 1

describes another variety of data gathered forsummarizes the quantity and conditions of themore than ten years in one particular site.

samples analysed.

These figures indicate that 40K is the largest

In 2 of the 15 furnace slag samples, 134Cs andcontribution in total activities in most cases,

137Cs were detected as 0.987 and 1.20 Bq/g forand 232Th series and 238U series tend to behave

first slag (S1) and 0.183 and 0.287 Bq/g forsimilarly. The range of activity is from 0.4 tosecond slag (S2), compared with detection

1.1 Bq/g, and all but one of the 60 samples－69－Fujita Technical Research Report No.49

φ

Table2 Size of shielding pods.

Ordinary Middle
Concrete pod

Size

th’hφ’

concrete§3. Investigation of the influence on the effectof contaminated construction materials to useradiation shielddensityconcrete

For the proper containment of contaminatedt200150

soils in Fukushima, concrete shielding pods

φ700600

could be one idea. We therefore considered theh800

700effect of radioactive materials in the shielding

φ’300

h’400

Containmen

concrete used in construction of the shielding
pods.

Unit：mm

3.1 Monte Carlo simulation for the investigation

Figure 3 Calculation geometry.

The MCNP4C2 code [5] was employed forMonte Carlo simulation of photon in thisOrdinary concrete
shield with 0.2m

work using MCNPLIB02 photo library [6]Without shieldwith “Radiation dose conversion coefficientsfor radiation shielding calculations: 2010” [7].

With shield
Middle densityconcrete shieldwith 0.15m

The geometry of the simulation is shown in
Figure 3 and Table 2, with a cylindricalvolumeFrom contamination
with clearance levelin shield concrete

sourceandcylindricalconcreteshielding pod. Isotropic photon sources were
uniformly placed in the region of the soil
blocks in the case where the contaminatedsoil was contained in the concrete shielding

Figure 4 Calculated dose rates for the effect of contamination.

pod.

To

estimatetheinfluenceofcontaminated material use in the concrete,
the photon sources were set only inside of thelimits for 134Cs and 137Cs of 0.027 Bq/g andshielding

0.030Bq/g respectively. These values wereconcrete

uniformlywithsingle

element (cesium or potassium) to evaluate thelarger than the level of clearance level for 134Cs

dose rate caused by that element. Cylindricaland 137Cs (0.1 Bq/g [2]). Radioactive cesium wassurface tallies were set along the line thatnot detected among samples produced before

lengthened

March 2011. The ratio of 134Cs and 137Cs isperpendicularlyfrom

thecylindrical lateral central part as estimators.

different in samples S1 and S2. The ratio ofDose rates were calculated at distances of 0.1

134Cs and 137Cs for S2 (0.64) is about the same

to 0.7 m from surface of the soil block for theas that for the contaminated soil samples foundcase of soil block only (without shield), at

in a separate study [4]. In the above analyses,

distances of 0.2 to 0.7 m for ordinary concreteno radioactive cesium was found in samples

shield with 0.2 m thickness, and 0.15 to 0.7 m

before or after Fukushima that originated infor middle density concrete shielding with 0.15

nuclear weapon experiments.

m thickness. The validity of this simulation
withthiscomparison

geometrywithanother study [4].
－70－wasconfirmed

experimental

databyfrom

Development of construction material database for low-activation sheilding

Table 3 Calculated dose rates at 0.3m from the cylindrical containment side with various photon sources.

* Max value in the reference [8]thickness, middle density concrete pod with
3.2 Investigation result

0.15 m thickness, and without shield. The
photon source was set in four different

Figure 4 shows the result of the calculation formaterialsa soil block only versus two types of concrete

contaminated slags described section 2.2)

pods – ordinary concrete with 2.13 g/cm3

uniformly with radioactive cesium or(marked red in the figure) and middle density

Activities for radioactive cesium were set at theconcrete with 3.09 g/cm3 (marked blue in thelevel of measured data in the experiment forfigure). Solid lines were attenuation curves of“soils”, clearance level for “concrete”, anddose rate for the experimental soil block (22.4

measured data in this work for “aggregate”.

kg with a volume of 18.1l, 6.86E5 Bq of 134Cs,

Activity of 40K was set to the maximum valueand 1.07E6 Bq of[4]. Dashed lines

in the concrete reported in the reference [8].

indicated the influence on the dose rates that

This table indicates that the influences of thethe contaminated cesium radionuclide gave,radioactive materials are 10% to 200 % in thewith empty containment (no contaminated soil

ratio to the containment (contaminated soils).

137Cs)(soils,concrete,andtwo40K.

block inside). The activities of radioactive§4. Conclusion

cesium nuclides in the shielding concrete wereset equal to the clearance level (0.039 Bq/g for
134Cs,

and 0.061Bq/g for 137Cs with the sameratioof134Cs

contaminated soils

and137Csfor

As radioactive nuclides were widely spread all

existingover[4]). This figure indicates

theJapan,rawmaterialfor

theconstruction has certain influence. In order tothat the levels of dose rates become smaller indevelop1/10 degree in the order of those for Bare

construction materials, a radioactive survey of(without shield), those for contaminated soil

construction materials was conducted.

with concrete shield, and those for shielding

Firstly natural radioactivities in fly ashes

concrete themselves with radioactive cesium ofwere measured for more than 60 samples onclearance level.

twoTable 3 shows the calculated dose rates byradioactive cesium nuclides were measured for

MCNP4C2

49 samples gathered from all over the Japan,

with

same

library,

conversion

thebases

radioactive(areaanddatabaseperiod).

for

Secondly

factors, and geometry as described section 3.1,

and two of these exceeded clearance level.

at 0.3 m from the cylindrical lateral central

Basedpart for three shielding conditions, such as

investigation was conducted to estimate theordinary concrete pod with 0.2 m shielding

effect for the use of the materials containing－71－onthemeasured

data,

atrialFujita Technical Research Report No.49

radioactive cesium and radioactive potassium.

Nuclear Facilities, Promotion program for

The calculated dose rates from the shielding
concrete with radioactive cesium exceed thosescientific research to establish a soundmaterial-cycle society, Tokyo, Japan, February

from the radioactive material in shielding

21-23, (2011) pp168-172.
[4] K.Kimura, Y. Suzuki, T. Takata, Y. Fujikura, H.

concrete in some cases. These results indicatedtothenecessity

radioactiveofKubota, Y. Lee, S. Pareek, and Y. Araki, A

construction

development of optimized radiation shieldingof

thedevelopment

databaseforthedesign method for contaminated soil inmaterials.

Fukushima, Proc. Int. Conf. on Radiation

Shielding (ICRS-12), Nara, Japan, Sept.3-7,

Acknowledgements(2012 )(to be published).

The works described in section 2.2 wereconducted by the fund of Japan Coal Energy[5] X-5 Monte Carlo Team, MCNP-A General

Center (JCOAL). The authors wish to thankMonte Carlo N-Particle Transport Code,JCOAL.

Version 5, LA-UR-03-1987 (2003)[6] Atomic Energy Society of Japan, Radiation doseconversion coefficients for radiation shielding
References

calculations: 2010, Atomic Energy Society of[1] K. Kimura, A. Hasegawa, K. Hayashi, M.

Japan, (2010), ISBN 978-4-89047-336-6..

Uematsu,T. Ogata, T. Tanosaki, R. Yoshino, M.

[7] G. Hughes, Information on the photo library

Sato, M. Saito and M. Kinno, Development ofMCNPLIB02, LANL X-6: HGH-93-77, 1993

low-activation design method for reduction ofradioactive waste below Clearance Level, Proc.

of Int. conf. on nuclear Engineering(ICONE16),
Florida, USA, May 11-15, (2008) 48484.
[2]International

AtomicEnergyAgency,Application of the concepts of exclusion,
exemption and clearance, Safety standards

Ken-ichiKimuraseries No. RS-G-1.7, (2004).
[3] K.Kimura, and T.Tanosaki, A fundamental
Study on Radioactivity in Fly Ash for the－72－

Short comment
R&D forlow-activation concrete has long history.
Obviously the phase was changed after
3.11. At that situation, maintenance ofconstruction material database forlow-activation shielding is very important.
So, I try to proceed to upgrade of thedatabase and make every effort to apply
this material every possible market
related radiation field.