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Module13External gamma dose assessment from
building materials according to IAEA SSG-32
DTU-COST-RILEM DOCTORAL COURSE, TECHNICAL UNIVERSITY OF DENMARK, LYNGBY, DENMARK, 17/08/2016
“The project leading to this application has received funding from the European Union’s Horizon 2020research and innovation programme under the Marie Sklodowska-Curie grant agreement No 701932”
By-BM Project H2020-MSCA-IF-2015 Research Fellow
Geopolymer Team, School of Natural and Built Environment
Queen’s University Belfast (QUB)
Dr Zoltan Sas
Electromagnetic radiation from
the core
No chare, no mass
High penetration (energy
dependant)
Not decay just a follwing effect
Discrete energy of the energy
nievaus
Usually, it the gamma radiation is
generated right after the decays
Gamma radiation
Gamma spectra of NORM sample
Red mud sample from Ajka
Photoeffect
Total enertgy of
the photon
imparted to theelectron
Compton scattering 100 keV < Eg < 2MeV
The photon imparts energy but
not the total!
Energy of the scattered photon is
lower after scattering and the
direction also changes
The difference is the kinetic
energy of the Compton electron
Pair production Eg > 1.02 MeV
The photon iteracts with
electromagnetic field of the atom
The total energy is imarted
Gamma radiation is the main source of
external indoor exposure on residents
Introduction of dose assessement method
This module of the training course about dose assessments
provides examples relating to massive concrete structures (e.g.
apartment blocks) and for a smaller, simpler type of structure
such as those widely found in the rural areas of developing
countries
A calcualtion is based on of the approach of Markkanen
presented for calculating dose due to external gamma radiation
from BMs
The results are given in tabular form as specific dose rates
This allows the most typical dose assessments to be made without
computer calculations
Introduction of dose assessement method
The method is based on calculating the dose rate for a
rectangular building constructed of BM of uniform density
and containing radionuclides of uniform activity
concentration.
The calculation covers situations in which the radionuclides
are distributed in two layers of separate BMs with different
densities and activity concentrations;
e.g.: concrete walls covered with a thin layer of another
material such as tiles
Introduction of dose assessement method
The reference level of 1 mSv/a used for BMs is defined as due to the ‘excess
exposure’ caused by these materials above the exposure due to normal
background levels of radiation
The effects of doors and windows will lower the dose
rate by only a minor amount and so for simplicity
doors and windows are not considered in the
calculation
In many cases, BMs themselves provide significant
shielding against gamma radiation from the soil in the
terrestrial background
In the case of massive concrete structures, the
shielding is almost complete
Introduction of dose assessement method
The basic approach in determining the ‘excess exposure’ is as follows:
The total exposure due to the BM and the
background levels is calculated, after allowance for
the shielding provided by the BM against gamma
radiation in the terrestrial background
The exposure to gamma radiation in the terrestrial
background is then subtracted
The result for comparison with the reference level is
referred to as the ‘excess exposure’
Introduction of dose assessement method
The world population weighted average dose
rate of 60 nGy/h is assumed for gamma radiation
in the terrestrial background (reported in
UNSCEAR2000 Annex B)
The possible shielding effect of BMs for cosmic
radiation is considered to be small, and therefore
exposure to cosmic radiation is not considered in
the assessments
The gamma dose rate is calculated in the middle
of the standard sized room shown in Figure
Longer sidewall
Introduction of dose assessement method
The total dose rate indoors is calculated by
summing the separately calculated dose
rates due to walls, floor and ceiling given in
Table VI–1 of IAEA SSG-32
A conversion factor of 0.7 Sv/Gy is used for
converting the absorbed dose in air to an
effective dose [UNSCEAR1993] (for adults)
Introduction of dose assessement method
Risica et al. have carried out a sensitivity analysis concerning the effects of
changes in the parameters for the room on the dose in the room and found
the following results:
The variation in the dose rate in air in relation to the position in the room was found
to be limited to approximately 10% at a distance of up to 1 m from the walls.
The maximum variation in the dose rate obtained was 6% from the calculation for a
room with a volume of 60 m3
The absorbed dose rate in air was calculated as a
function of room dimensions for a fixed height of 2.8
m and various widths and lengths of the room
ranging from 2 m to 10 m were used, in both
rectangular and square shapes.
Introduction of dose assessement method
The absorbed dose rate in air in the room was calculated
as a function of the wall, floor and ceiling thickness
It was found that up to a thickness of 0.4 m, increasing
the thickness increases the radiation dose rate, whereas
when the thickness is greater than 0.4 m, self-absorption
in the material makes the effect of a further increase in
thickness negligible
It can therefore be concluded that the variation in the dose rate in the model
room is not significantly affected for room sizes ranging from 12 m2 to 100 m2
for a fixed room height of 2.8 m, or for variations in the wall thickness
First steps
Data collection: Ra-226; Th-232; K-40
(Bq/kg), Density (kg/m3), Thickness (m)
Calculate Mass per unit Area (M/A) of
wall, ceiling or floor material (kg/m2)
Select the closest value from the 1st
column TABLE VI–1.
Multiple the dose conversion factor
with activity concentrations
Summarize them in function of the
number of the walls, covers, etc
To get effective dose use 0.7 Sv/Gy
dose conversion factor
To get annual excess multiple the dose
rate considering the occupancy
factor
Ra-226 Th-232 K-40
W1 - - - - - - - -
W2 - - - - - - - -
Floor - - - - - - - -
Ceiling - - - - - - - -
Tile_W1 - - - - - - -
Tile_W2 - - - - - - -
Tile_Floor - - - - - - -
Tile_Celiling - - - - - - -
Roundup
with Tile
Roundup
without
Tile
Activity concentration Density
(kg/m3)
Thickness
(m)
M/A
(kg/m2)
Exposure to gamma radiation in a concrete room with tiles on
the walls
First steps
Data collection: Ra-226; Th-232; K-40
(Bq/kg), Density (kg/m3), Thickness (m)
Calculate Mass per unit Area (M/A) of
wall, ceiling or floor material (kg/m2)
Select the closest value from the 1st
column TABLE VI–1.
Multiple the dose conversion factor
with activity concentrations
Summarize them in function of the
number of the walls, covers, etc
To get effective dose use 0.7 Sv/Gy
dose conversion factor
To get annual excess multiple the
dose rate considering the occupancy
factor
Ra-226 Th-232 K-40 Ra-226 Th-232 K-40
w1
Longer sidewall:
12.0×2.8 m
0 0 0 0 95 110 8
25 9 10 0.73 87 100 7.3
50 18 21 1.5 80 94 6.7
100 35 40 2.8 65 77 5.6
150 50 56 3.9 52 62 4.6
200 61 70 4.9 40 50 3.8
300 79 91 6.4 24 31 2.5
500 96 110 8.1 8 12 1
-
0 0 0 0 32 37 2.7
25 2.7 3.1 0.22 30 35 2.5
50 5.5 6.2 0.44 28 32 2.3
100 11 12 0.85 22 27 2
150 15 18 1.2 19 23 1.7
200 20 22 1.6 16 19 1.4
300 26 30 2.1 10 13 1
500 33 38 2.7 3.7 5.4 0.45
0 0 0 0 350 420 30
25 46 52 3.7 310 370 27
50 90 100 7.1 270 330 24
100 160 190 13 200 250 18150 220 250 18 150 180 14200 260 300 21 110 140 11300 310 360 26 56 78 6.3500 350 420 30 15 27 2.2
Floor or Ceiling:
12.0×7.0 m
Wall, ceiling or floor material
(top layer)
0.2 m thick concrete behind the
wall, ceiling or floor material
(pGy/h per Bq/kg) (pGy/h per Bq/kg)
(pGy/h per Bq/kg) (pGy/h per Bq/kg)
w2
Smaller sidewal:
7.0×2.8 m
Wall, ceiling or floor material
(top layer)
0.2 m thick concrete behind the
wall, ceiling or floor material
(pGy/h per Bq/kg) (pGy/h per Bq/kg)
Mass per unit
area of wall,
ceiling or floor
material (kg/m2)
Radionuclide
Wall, ceiling or floor material
(top layer)
0.2 m thick concrete behind the
wall, ceiling or floor material
First steps
Data collection: Ra-226; Th-232; K-40
(Bq/kg), Density (kg/m3), Thickness (m)
Calculate Mass per unit Area (M/A) of
wall, ceiling or floor material (kg/m2)
Select the closest value from the 1st
column TABLE VI–1.
Multiple the dose conversion factor
with activity concentrations
Summarize them in function of the
number of the walls, covers, etc
To get effective dose use 0.7 Sv/Gy
dose conversion factor
To get annual excess multiple the dose
rate considering the occupancy
factor
w1 0 0 0 0 0 0 0
w2 0 0 0 0 0 0 0
Floor 0 0 0 0 0 0 0
Ceiling 0 0 0 0 0 0 0
w1_Tile 0 0 0 0
w2_Tile 0 0 0 0
F_Tile 0 0 0 0
C_Tile 0 0 0 0
100
80
60 0.00
0 00.00 0.00 0.00
0.00 0.00 0.00
0.00 0.00
Adult Children Infant
0
Σ D_rate
(nGy/h)-BG
Excess
E_D_rate
(nSv/h)
Occupancy
(%)
Annual effective excess dose mSv/y
Ra-226 Th-232 K-40 Dose rate
(µGy/h)
Σ D_rate
(nGy/h)(pGy/h per Bq/kg)
Calculation examples
Check Annex VI of IAEA SSG-32 on page 75
Work in pairs with the help of excel on the basis of the guide
P1 Example 1: Exposure to gamma radiation in a concrete room where the
concentrations of Ra-226 and Th-232 are slightly above average
P2 Example 4: Exposure to gamma radiation in a room where lightweight walls
are made of materials with an elevated concentration of Ra-226
P3 Example 5: Exposure to gamma radiation in a room where the concrete walls
are made of material with an elevated concentration of Ra-226
After finish discuss the results
Calculation
Check By-BM calculator on bybmproject.com
Calculation examples
Check Annex VI of IAEA SSG-32 on page 75
Work in pairs with the help of excel on the basis of the guide
P1 Example 1: Exposure to gamma radiation in a concrete room where the concentrations of Ra-226 and Th-232 are slightly above average
P2 Example 4: Exposure to gamma radiation in a room where lightweight wallsare made of materials with an elevated concentration of Ra-226
P3 Example 5: Exposure to gamma radiation in a room where the concrete walls are made of material with an elevated concentration of Ra-226
Discuss the results
Solve Example 3: Work together
Every participant should search litrature about Ra-226; Th-232, K-40 activityconcentration in BMs
Make you own calculation
Use the prepared excel sheet in case of your future publication
Comparison of RP-112 and IAEA SSG-32
on the example of By-BM Database
By-BM database
This study is based on the continuously growing database of
the By-BM (H2020-MSCA-IF-2015) project.
The aim of this project to characterize the mechanical and
radiological parameters of constituents and prepared By-BM
geopolymers made from industrial by-products.
This project is strongly connected to, and provides information
to the NORM (naturally occurring radioactive material)
database of COST TU 1301 NORM4Building Action.
By-BM database unified selection criteria
Only individually reported sample information about the Ra-226, Th-232 and
K-40 were obtained by gamma spectrometry was used
Average results of certain materials were used only if the investigated
material originated from same site, e.g. quarries, mines, reservoirs.
In the case of commercial building materials the brand and the type of the
samples had to be clearly mentioned in the reference to fulfil selection
criteria.
In several cases the U-238 activity concentration values were published. In
that cases the reported data was imported into the database only if the
results were obtained from the Rn-222 progenies (Bi-214, Pb-214) to avoid the
disequilibrium in the decay chain
By-BM database unified selection criteria Generally, to limit gamma exposure originated from building materials the widely used
I-index – defined in RP112 – is applied. The I-index can be calculated by the followingequation:
Where CRa-226, CTh-232, CK-40 are the Ra-226, Th-232 and K-40 activity concentrations inBq/kg.
The calculation method the I-index based on the model of Markkanen with fixedparameters of concrete building (density and thickness of the walls are 2350 kg/m3, 20cm, respectively)
MARKKANEN, M., Radiation Dose Assessments for Materials with Elevated Natural Radioactivity, Publication STUK-B-STO 32, Finnish Centre for Radiation and NuclearSafety, Helsinki (1995).
The I-index value of 1.0 can be used as a conservative screening tool for identifyingmaterials that during their use would cause doses exceeding the reference level (1mSv/y excess in addition to outdoor exposure) in the case of bulk amount inbuilt.
In the European Union to control the gamma exposure originated from buildingmaterials the I-index is recommended for the member states to screen them.
kgBq
C
kgBq
C
kgBq
CI KThRa
/3000/200/300
40232226
By-BM database unified selection criteria
The Council Directive allows the dilution and mixing of construction materials (I-
index<1.0), which makes possible the mixing of NORM by-products with low activity
level raw materials.
In the case of the calculation of dose needs to take into account other factors such
as density, thickness of the material as well as factors relating to the type of building
and the intended use of the material (bulk or superficial) to get precise dose
estimation of residents. The density and the thickness of modelled concrete room are
a constant parameters.
In the case of the International Atomic Energy Agency (IAEA) released No. SSG-32
(Specific Safety Guide) the simplified calculation method is based on the same
model of Markkanen but the thickness and the density of the building material are
taken into consideration during the calculation.
By-BM database
By-BM database contains
individual data about Ra-226, Th-
232, K-40 activity concentration of
30 different materials (23 building
materials, 7 by-products
Altogether 431 by-products and
1095 building materials and raw
materials were collected from 48
countries.
The worldwide distribution and
the number of data are illustrated
on Figure
By-BM database Material
name
Number
of
samples
Density Material
type Material
name
Number
of
samples
Density Material
type
kg/m3 BM/BP kg/m3 BM/BP
Aggregate 9 1900 BM Serizzo 5 2650 BM
Basalt 3 3000 BM Sienites 5 2700 BM
Brick 243 1900 BM Silstone 1 2350 BM
Cement 87 1500 BM Slate 1 2650 BM
Ceramics 94 2400 BM Tile,
asbestos 4 1750 BM
Concrete 63 2350 BM Travertine 9 2300 BM
Gas
concrete 37 700 BM Tuff 10 2100 BM
Granite 297 2600 BM Volcanic 7 1800 BM
Gypsum 66 865 BM Bottom ash 59 700 BP
Limestone 16 2600 BM Fly ash 145 720 BP
Marbles 72 2550 BM Manganese
clay 44 2800 BP
Pumice 3 650 BM Phosphogyp
sum 45 1500 BP
Rock 29 2300 BM Red mud 92 1600 BP
Sand 19 1500 BM Steel slag 41 2600 BP
Sandstone 14 2323 BM Residue of
TiO2 5 4300 BP
Results
In case of the building materials the natural isotope content
varied widely (Ra-226: <DL-27851 Bq/kg; Th-232: <DL-906
Bq/kg, K-40: <DL-17922 Bq/kg), more so than the by-products
(Ra-226: 7-3152 Bq/kg; Th-232: <DL-1350 Bq/kg, K-40: <DL-3001
Bq/kg).
But the mean value of Ra-226, Th-232 and K-40 content of
reported by-products were 2.52, 2.35 and 0.39 times higher in
case of the by-products than the building materials,
respectively.
This is the reason why the radionuclide content cannot be
ignored since the by-products can cause increased
radiological risk.
Density considertion on calculated dose rate
Overestimation without density
consideration of absorbed dose
Absorbed dose rates of BMs calculated
with different methods in the function
of I-indexes
Results
In this study the absorbed gamma dose rate of a model
room with 20 cm thickness with various density were
calculated applied with dose conversion factors of RP-112
without density consideration and the IAEA No. SSG-32.
The data about Ra-226, Th-232 and K-40 activity
concentration of the building materials were collected from
worldwide scientific reported sources.
The I-indexes of the building materials were also calculated
and compared with the absorbed gamma dose rates of the 2different calculation methods.
Conclusion
The absorbed gamma dose rates results were compared and
clearly proved that without density consideration the calculated
dose rate significantly higher in the case of low density buildingmaterials
Under 1000 kg/m3 even 60-70% higher dose rate can be estimated.
This is the reason why with density consideration the calculated I-
indexes belong to lower dose rate which clearly proves the
overestimation of I-index in connection with generated dose rate
It means the I-index provides a conservative and superficial
approximation.
In the case of building materials with low density e.g. commonly
used perforated bricks, which can make significant overestimation
and unnecessary restriction in the case of certain low density
building materials
“The project leading to this application has received funding from the European Union’s Horizon 2020
research and innovation programme under the Marie Sklodowska-Curie grant agreement No 701932”
