ABSTRACT
The investigation of gamma radiation shielding and liquid permeability properties of kaolin, granite and their composites for radioactive waste management is an environmental engineering strategy for radioactive risk management. In this research, gamma radiation shielding properties and liquid permeability coefficients of compacted baked and unbaked granite powder treated with 0%, 10%, 20%, 30%, 40%, 50% 60%, 70%, 80%, 90%, 100%, of kaolin powder were investigated for possible deployment in radioactive waste management. A 3 x 3 inches Thallium Activated Sodium Iodide NaI(Ti) detector was used to measure the linear attenuation coefficients of all samples at commonly used gamma radiation energies of 661.6 keV, 1173.2 keV and 1332.5 keV. The elemental compositions of all samples were analyzed using Particle Induced X-ray Emission Spectroscopy (PIXE). The experimentally measured values for radiation attenuation coefficients were in good agreement with the theoretical results base on relative deviation values less than 6%. The study concludes that, unbaked samples were more efficient than baked samples in gamma radiation shielding and that all unbaked samples were good for radioactive waste management with optimum result obtained from compacted granite treated with 50% of micro scale kaolin powder with linear attenuation coefficient (LAC) 0.1700cm-1, 0.1469 cm-1, 0.1416 cm-1 and radiation protection efficiency (RPE) of 38.88%, 34.59% and 33.64% for gamma radiation energies levels of 661.6 keV, 1173.2 keV, and 1332.5 keV respectively and liquid permeability coefficient of 6.53 x 10-11 m/s. Comparing results obtained in this study with other results from available literature, granite and kaolin composites performed better than most materials and therefore should be deployed as a valid alternative to other radiation shielding materials used in liquid radioactive waste management.
TABLE
OF CONTENTS
CONTENTS Page
Title Page i
Certification ii
Declaration iii
Dedication iv
Acknowledgement v
Table of contents vi
List of tables ix
List of figures xi
List
of plates xiv
Abstract xvii
CHAPTER
1 1
I.0
Introduction
1
1.1
Background to the research
1
1.2
Theoretical background 4
1.3 Statement of the problem
7
1.4
Aim and objectives of the study
8
1.5
Justification
9
1.6
Scope of study 9
CHAPTER
2
2.0
Literature review 11
2.1 Review of related works 11
2.2. Physics of gamma
radiation 18
2.2.1 Gamma
radiation dose units 19
2.2.2
Interaction of gamma radiation with
matter 19
2.2.3 Biological effects of gamma radiation 22
2.3. Attenuation coefficients 22
2.3.1 Linear attenuation coefficient 23
2.3.2 Total linear attenuation coefficient (µ) 24
2.3.4 Mass attenuation coefficient (µ/p) 25
2.4. Liquid permeability 26
2.4.1 Factors affecting liquid permeability 30
2.5. Kaolin and clay 32
2.5.1 Types of clay 33
2.5.2 Locations of kaolin in Nigeria 34
2.6. Granite 34
2.7.
Sodium iodide NaI(Ti) detector 36
2.7.1 NaI(Ti) Detector mechanism 38
2.7.2 The NaI(Ti) detector efficiency 39
2.8 PIXE 40
2.8.1. WinXCOM 41
2.8.2 Advantage of WinXCOM over XCOM 42
2.8.3 Working principal of WinXCOM 42
CHAPTER 3 43
3.0
Materials and methods 42
3.1
Materials 42
3.2
Sample preparation 44
3.3
Calibration of
the NAI(TI) detector
48
3.4
Experimental set-up and procedure 49
3.5 Determination of LAC, MAC,
HVL, TVL and MFP 53
3.6 Elemental composition analysis 55
3.7 Simulation 56
3.8 Relative deviation between experimental and theoretical
values (RD) 57
3.9 Liquid permeability coefficient test (K) 57
3.10 Safety precautions 59
CHAPTER 4 62
4.0 Results and discussion 62
4.1 Results 62
4.1.1 Gamma
radiation shielding results 62
4.1.2
Computed results from gamma shielding test 64
4.1.3
Linear attenuation coefficient(lac) of samples for different energies 70
4.1.4 Element analysis results 72
4.1.5 Theoretical (WinXCOM) results for total linear
attenuation coefficient 76
4.1.6 Experimental
and Theoretical MAC and their relative deviations 77
4.1.7 Results of
gamma radiation Protection Efficiency 78
4.1.8 Liquid permeability test
results 82
4.1.9 Summary of important
results in this study 83
4.1.10 Summary results compared with
results from literature 85
4.2. Discussion of results 108
4.2.1 Gamma
radiation shielding results 108
4.2.2 Computed results from gamma shielding test 108
4.2.3 Linear attenuation coefficient(lac)
of samples for different energies 110
4.2.4 Element analysis results 110
4.2.5 Theoretical (WinXCOM) results for total linear
attenuation coefficient 111
4.2.6 Experimental and theoretical mac and their relative deviations 111
4.2.7 Results of
gamma radiation protection efficiency 112
4.2.8 Liquid permeability
test results 113
4.2.9 Summary of important
results in this study 114
4.2.10: Summary results compared with
results from literature 116
CHAPTER 5 117
5.0 Conclusion and recommendation 117
5.1
Conclusion 117
5.2 recommendation 120
References 121
LIST
OF TABLES
2.1 Gamma ray sources used for calibration 18
2.2 Location of kaolin in Nigeria 33
2.3
Specifications of NAI(TI) scintillation detector 36
3.1 Sample codes and percentage mixture by
weight 45
3.2 Sample codes and
percentage mixture by weight 45
3.3. The
present activity and half-life and emission probabilities of the radioactive
materials used to obtain energies. 48
4.1
Counts for unbaked granite
composites 62
4.2 Counts
for unbaked kaolin composites 62
4.3 Counts for unbaked kaolin composites 63
4.4 Counts
for unbaked kaolin composites 63
4.5 Result of unbaked samples for gamma energy
661.7kev from 137Cs 64
4.6 Result of unbaked samples for gamma energy 661.7kev
from 137Cs 64
4.7
Result of unbaked samples for gamma energy 1173kev from 60Co 65
4.8 Result of
unbaked samples for gamma energy 1173kev
from 60Co 65
4.9 Result
of unbaked samples
for gamma energy 1332kev from 60Co 66
4.10 Result
of unbaked samples
for gamma energy 1332kev
from 60Co 66
4.11 Result of
baked samples for gamma energy 661.7kev from 137Cs 67
4.12 Result
of baked
samples for gamma energy 661.7kev
from 137Cs 67
4.13 Result
of baked
samples for gamma energy 1173kev
from 60Co 68
4.14 Result
of baked
samples for gamma energy 1173kev
from 60Co 68
4.15 Result of
baked samples for gamma energy 1332kev
from 60Co 69
4.16 Result of
baked samples for gamma energy 1332kev from 60Co 69
4.17 Experimental linear
attenuation coefficient(LAC) granite composite with error in measurement
70
4.18 Experimental linear
attenuation coefficient(LAC) kaolin
composite with error in
measurement 71
4.19: Element
analysis result for unbaked granite composites
72
4.20: Element
analysis result for unbaked kaolin composites 73
4.21: Element
analysis result for baked granite composites
74
4.22: Element
analysis result for baked kaolin composites 75
4.23 & 4.24
Theoretical (WinXCOM) results for total linear attenuation coefficient
(LAC) unbaked samples 76
4.25 & 4.26
Theoretical (WinXCOM) results for total linear attenuation coefficient
(LAC) baked samples 76
4.27 The relative deviations (RD) between
theexperimental and theoretical (WinXCOM) results of unbaked granite composites 77
4.28 The
relative deviations (RD) between the experimental and theoretical (WinXCOM)
results of unbaked kaolin composites 77
4.29 The
relative deviations (RD) between the experimental and theoretical (WinXCOM)
results of baked granite composites 78
4.30 The
relative deviations (RD) between the experimental and theoretical (WinXCOM)
results of baked kaolin composites 78
4.31 The gamma
radiation protection efficiency %(Exp.) of unbaked granite composites 79
4.32 The
gamma radiation protection efficiency
%(Exp.) of unbaked kaolin composites 79
4.33 The
gamma radiation protection efficiency %(Exp.) of baked samples granite
composites 80
4.34 The
gamma radiation protection efficiency %(Exp.) of baked kaolin composites 80
4.35 Liquid
permeability test measuring parameters 81
4.36 Liquid
permeability test for granite composites 82
4.37 Liquid permeability
test for kaolin composites 82
4.38 Summary
results of unbaked granite composites 82
4.39 Summary results of unbaked kaolin
composites 84
4.40 Summary results of baked granite
composites 84
4.41 Summary results of baked kaolin composites 84
4.42
Gamma radiation attenuation and liquid permeability coefficient for some materials / composites. 86
LIST OF FIGURES
2.1. The
simple permeability test apparatus 28
2.2 Liquid permeability and hydraulic
conductivity for aquifer and confining barriers 30
2.3. Summary of granite components 35
3.1 Fig. 3.1: Samples for liquid permeability
text and elemental analysis exhibition after preparation 46
3.2 Samples for Gamma
Attenuation Test on Display after Preparation. 46
3.3.
Narrow beam transmission geometry 49
3.4
Experimental setup for measuring radiation shielding of a sample 50
3.5
Gamma ray spectrum obtained from 137Cs source. 51
3.6
Gamma ray spectrum obtained from 60Co source 51
4.1 Variation of linear attenuation
coefficient against % mixture for unbaked granite composites (column- graph) 85
4.2:
Variation of mass attenuation coefficient against % mixture for unbaked
granite composites (Line- graph) 85
4.3: Variation of linear attenuation coefficient
against % mixture for unbaked kaolin composites (column- graph) 86
4.4: Variation of linear attenuation coefficient
against % mixture for unbaked kaolin composites (line- graph) 86
4.5:
Variation of linear attenuation coefficient against % mixture for baked
granite composites (column- graph) 87
4.6: Variation of linear attenuation
coefficient against % mixture for baked granite composites (line- graph) 87
4.7: Variation of linear attenuation coefficient
against % mixture for baked kaolin composites (column- graph)
88
4.8: Variation of linear attenuation coefficient
against % mixture for baked kaolin composites (line- graph) 88
4.9:
Variation of mass attenuation coefficient with incident energy for different
samples of unbaked granite composites 89
4.10: Variation of
mass attenuation coefficient with incident energy for different samples of
baked kaolin composites. 89
4.11: Variation of
mass attenuation coefficient with incident energy for different samples of
baked granite composites 90
4.12: Variation of
mass attenuation coefficient with incident energy for different samples of
baked kaolin composites. 90
4.13: Variation of % kaolin in granite against liquid
permeability granite composites 91
4.14: Variation of density against liquid permeability for
granite composites 91
4.15: Variation of % mixture against liquid permeability
for kaolin composite 92
4.16: Variation of density against liquid
permeability for kaolin composites 92
4.17. Graphical representation of major, micro &
trace elements in unbaked granite & its composites 93
4.18: Graphical representation of
major, micro & trace elements in unbaked Kaolinand its composites 93
4.19: Graphical representation of
major, micro & trace elements in baked granite and its composites 94
4.20: Graphical representation of
major, micro & trace elements in baked kaolin & its composites 94
4.21: Simple linear regression
analysis correlating mac experimental to theoretical (WinXCOM) results for
661.6kev photon energy on unbaked granite composites 95
4.22: Simple linear regression
analysis correlating mac experimental to theoretical (WinXCOM) results for 1173.2kev photon energy on unbaked granite
composites 95
4.23: Simple linear regression
analysis correlating mac experimental to theoretical (WinXCOM) results for 1332.3kev photon energy on unbaked granite
composites 96
4.24: Simple linear regression
analysis correlating mac experimental to theoretical (WinXCOM) results for
661.6kev photon energy on unbaked kaolin composites 96
4.25: Simple linear regression
analysis correlating mac experimental to theoretical (WinXCOM) results for
661.6kev photon energy on unbaked kaolin composites 97
4.26: Simple linear regression
analysis correlating mac experimental to theoretical (WinXCOM) results for
661.6kev photon energy on unbaked kaolin composites 97
4.27: Simple linear regression
analysis correlating mac experimental to theoretical (WinXCOM) results for
661.7kev photon energy on baked granite composites 98
4.28: Simple linear regression analysis
correlating mac experimental to theoretical
(WinXCOM) results for 1332.3kev photon energy on baked granite composites 98
4.29: Simple linear regression analysis correlating
mac experimental to theoretical (WinXCOM) results for 1332.3kev photon energy
on baked granite composites 99
4.30: Simple linear regression analysis correlating mac
experimental to theoretical (WinXCOM) results for 666.7kev photon energy on
baked kaolin composites 99
4.31: Simple linear regression analysis correlating mac
experimental to theoretical (WinXCOM)results for 1173.2kev photon energy on
baked kaolin composites 100
4.32: Simple linear regression analysis correlating mac
experimental to theoretical (WinXCOM)
results for 1332.3kev photon energy on baked kaolin composites. 100
LIST OF PLATES
PLATE
1: Co-60 Gamma-ray spectra data for unbaked GK00 sample 131
PLATE
2: Cs-137 Gamma-ray spectra data for unbaked GK00 sample 131
PLATE
3: Co-60 Gamma-ray spectra data for unbaked GK10 sample 132
PLATE
4: Cs-137 Gamma-ray spectra data for unbaked GK10 Sample 132
PLATE
5: Co-60 Gamma-ray spectra data for unbaked GK20 sample 133
PLATE
6: Cs-137 Gamma-ray spectra data for unbaked GK20 sample 133
PLATE
7: Co-60 Gamma-ray spectra data for unbaked GK30 sample 134
PLATE
8: Cs-137 Gamma-ray spectra data for unbaked GK30 sample 134
PLATE
9: Co-60 Gamma-ray spectra data for unbaked GK30 sample 135
PLATE
10: Cs-137 Gamma-ray spectra data for unbaked GK40 sample 135
PLATE
11: Co-60 gamma-ray spectra data for unbaked GK50 sample 136
PLATE 12: Cs-137 Gamma-ray spectra data
for unbaked GK50 sample 136
PLATE
13: Co-60 Gamma-ray spectra data for unbaked KG00 sample 137
PLATE 14: Cs-137 Gamma-ray spectra data for
unbaked KG00 sample 137
PLATE 15: Co-60 Gamma-ray spectra data for
unbaked KG10 sample 138
PLATE 16: Cs-137 Gamma-ray spectra data for
unbaked KG10 sample 138
PLATE
17: Co-60 Gamma-ray spectra data for unbaked KG20 sample 139
PLATE
18: Cs-137 Gamma-ray spectra data for unbaked KG20 sample 139
PLATE
19: Co-60 Gamma-ray spectra data for unbaked KG30 sample 140
PLATE
20: Cs-137 Gamma-ray spectra data for unbaked KG30 sample 140
PLATE
21: Co-60 Gamma-ray spectra data for unbaked KG40 sample 141
PLATE
22: Cs-137 Gamma-ray spectra data for unbaked KG40 sample 141
PLATE
23: Co-60 Gamma-ray spectra data for unbaked KG50 sample 142
PLATE
24: Cs-137 Gamma-ray spectra data for unbaked KG50 sample 142
PLATE
25: Co-60 Gamma-ray spectra data for baked GK00 sample 143
PLATE 26: Cs-137 Gamma-ray spectra data
for baked GK00 sample 143
PLATE
27: Co-60 Gamma-ray spectra data for baked GK10 sample 144
PLATE 28: Cs-137 Gamma-ray spectra data
for baked GK10 sample 144
PLATE
29: Co-60 Gamma-ray spectra data for baked GK20 sample 145
PLATE
30: Cs-137 Gamma-ray spectra data for baked GK20 sample 145
PLATE
31: Co-60 Gamma-ray spectra data for baked GK30 sample 146
PLATE
32: Cs-137 Gamma-ray spectra data for baked GK30 sample 146
PLATE
33: Co-60 Gamma-ray spectra data for baked GK40 sample 147
PLATE
34: Cs-137 Gamma-ray spectra data for baked GK40 sample 147
PLATE
35: Co-60 Gamma-ray spectra data for baked GK50 sample 148
PLATE 36: Cs-137 Gamma-ray spectra data for baked GK50 sample 148
PLATE
37: Co-60 Gamma-ray spectra data for baked KG00 sample 149
PLATE
38: Cs-137 Gamma-ray spectra data for baked KG00 sample 149
PLATE 39: Co-60 Gamma-ray spectra data for baked KG10 sample 150
PLATE
40: Cs-137 Gamma-ray spectra data for baked KG10 sample 150
PLATE 41: Co-60
Gamma-ray spectra data for baked KG20 sample 151
PLATE 42: Cs-137
Gamma-ray spectra data for baked KG20 sample 151
PLATE 43: Co-60
Gamma-ray spectra data for baked KG30 sample 152
PLATE 44: Cs-137 Gamma-ray spectra data for
baked KG30 sample 152
PLATE 45: Co-60 Gamma-ray spectra
data for baked KG40 sample 153
PLATE 46: Cs-137 Gamma-ray spectra
data for baked KG40 sample 153
PLATE 47: Co-60 Gamma-ray spectra
data for baked KG50 sample 154
PLATE 48: Cs-137 Gamma-ray spectra
data for baked KG50 sample 154
CHAPTER 1
INTRODUCTION
1.1
BACKGROUND TO THE RESEARCH
The
rising application of radioactive materials in agriculture, research, medicine,
manufacturing industries and power generation has generated global concern for
radiation protection and radioactive / nuclear waste management. After the Chernobyl and Fukushima events, the
safe storage and disposal of radioactive waste materials / substances have
become a burning issue for some researchers in physics and engineering. The
hazardous impact of radioactive materials on humans, animals and environment
cannot be over emphasized. The impact includes increase in cancer,
miscarriages, stillbirth, physical and mental disorders in new born babies
(UNSCEAR, 2017). Among other kinds of ionizing radiations like X-rays, alpha
rays, beta rays; gamma radiation has proven to be the most difficult radiation
to manage (Yilmaz et
al, 2011). This is as a result of the higher penetration power of
gamma radiation and due to the fact that it has no charge or mass. Liquid
radioactive waste which is a major source of gamma radiations has the ability
to penetrate the ground and contaminate underground water bodies if it is not
well managed. Effective gamma shielding and radioactive waste management, could
be achieved by the use of solid-state engineered barriers with relatively high
density, high radiation shielding ability (high linear attenuation coefficients)
and low liquid permeability coefficient (Isfahani et al, 2018a). Many
methods have been applied in radioactive waste management and disposal. These
include thermal evaporation, chemical precipitation, ion exchange,
sedimentation, biological methods and physical methods (Ipek et al,
2002). The process examined in this study is a
physical method of shielding, isolation and immobilization of radioactive waste
which is recommended for developing countries with low technological expertise
in radioactive waste management.
Recently,
some of the foremost radiation shielding materials like lead (Pb) and red mud
have become less attractive because of their inherent disadvantages such as
toxicity (lead poisoning) in the case of lead, corrosion and high liquid permeability
in the case of red mud (Obaid et al, 2018). ACCEPTED MANUSCRIPT
Some of the alternative materials which include kaolin, granite,
concrete, clay- steel slag, clay- fly ash, bentonite – red mud composites, etc.,
are currently under consideration. Several researches have shown kaolin and
granite as a naturally, inexpensive material with high thermo-chemical
stability, eco-friendly, corrosion resistance, and
readily available with excellent performance in radiation shielding (Kacal
et al, 2018; Galán and Aparicio, 2014). Further studies have also shown kaolin and
granite as materials with excellent thermophysical and mechanical properties
with high stability with respect to mechanical stress (Wang et al, 2014;
Štubňa et al, 2012).
Kaolin which is a special form of clay popularly known as white
clays has been receiving great attention due to its inherent low moisture
permeability factor when it is baked with very high temperature (Štubňa
et al, 2012). Granite which is a higher density solid
material has also shown good prospect in radiation shielding (Najam et al, 2016).
Regardless
of many benefits that come from the application of radiations, they are hazardous
to human cells, for example, any radiation more than
the standard limit of 1msv/yr in human body gives rise to various problems like;
negative genetic effects, different types of cancerous growth and consequently
death of body cells (Gillies et al, 2017). Therefore, the basic function of a radiation shielding
material or absorber is to shield radiations emanating from radioactive
substances to an acceptable level at the zone behind the shielding material, considering
the impact from exposure to such ionizing radiations (Knoll, 2000).
Gamma
radiation attenuation is therefore effectively achieved by using substance with
higher atomic mass and high density (Alallak,
2012). The interaction of gamma-ray(γ) is a function of the photon energy.
The linear attenuation coefficient (LAC) measured in (cm-1)
is an important parameter associated with the diffusion and penetration of
gamma radiation with respect to a given medium (Sayyeda et
al, 2018). The linear attenuation coefficient (μ), is
the quantity of gamma radiation scattered or absorbed per unit thickness of an
absorber. The total linear attenuation coefficient (μ)
is a function of total contributions of all physical processes like photoelectric
effect, Compton scattering, and pair production involved in the interaction of
specific energy photon with matter. The mass attenuation coefficient (MAC)
which is density normalized LAC, is a more fundamental attenuation parameter (Kacal et al,
2018). The determination of accurate
values of these interaction parameters (LAC, MAC, etc.) for any shielding
material is necessary before the application and deployment of these materials.
In
order to investigate gamma radiation attenuation properties of any material,
the following basic parameters; linear attenuation coefficient (LAC), the mass
attenuation coefficient (MAC), half value layer (HVL), tenth value layer (TVL),
mean free path (MFP) and the radiation protection efficiency (RPE) must be
determined. These properties are very important in specifying shielding
characteristics of any material especially in composite material such as
kaolin- granite (Chanthima
and Kaewkhao, 2013).
1.2 THEORETICAL
BACKGROUND
To
investigate radiation attenuation properties of any material, basic knowledge
of the theory of radiation shielding is very important. Radioactive materials
produce different radiations such as Alpha-ray,
Beta-ray, X-ray, and Gamma-ray. Alpha, Beta
and X- rays exhibit higher energy levels, but loses
their energies in a medium after passing through a shorter distance. Therefore,
their radiation hazards are of less concern.
Gamma radiation is described as massless with no electrical charge. However, it has the ability to penetrate into various
materials more than Beta ray, X-ray and Alpha ray (Martin,
2006). When gamma radiation interacts
with a sample, in the process of passing through the sample of thickness x (cm)
based on narrow collimated beam geometry, the radiations are transmitted in accordance
with Beer - Lambert’s law:
For
broad beam geometry arrangement, build up factor
(B*) is introduced to normalize the scattering effect of the beam.
The
build-up factor is the ratio of total quantity of a specified
radiation at any point to the total contribution to that quantity of radiation reaching the said point without interaction
or collision (Singh et al, 2010). American
Nuclear Society reported compilation for build-up factors by various codes.
Under
broad beam geometry arrangement, Beer - Lambert’s law
is modified to;
In
this study, the build-up value was ignored because of the adoption of narrow
beam geometry and shorter distance arrangement between the detector and the
source. However, build up factor is considered very important in larger source with
longer distance arrangement.
is an exponential decay equation describing the change in intensity of
radiation as it transmits through an absorbing medium / material of thickness (x)
Considering the density of the absorber, the
Beer – Lambert’s equation becomes
where ρ represent density, μ/ρ represent mass attenuation coefficient
(MAC), while ρx is the mass per unit area of the material. Equation 1.3 can be shown
as:
If the radiation absorber is made up of two or more elements, the MAC
is obtained using Equation 1.5.
where, (μ/ρ)i gives the mass attenuation coefficient and wi
represent the weight fraction of the ith element in the material. Equation 1.5
is known as mixture rule (Olukotun et al., 2018).
The
Radiation Protection Efficiency (RPE) gives the effectiveness of any material
to attenuate radiations. The RPE values obtained for the media under
investigation in this study were evaluated with Equation 1.6 (Singh et al, 2018; Mann
et al, 2016a).
The Half-Value Layer (HVL) and the Tenth Value Layer (TVL) are the thickness of an absorber that will minimize
the intensity of radiation by a factor of two and ten respectively. The HVL and
TVL values which are functions of the linear attenuation coefficient are given
by the following equations:
and
Another parameter which depends on the linear attenuation coefficient
is the Mean Free Path
(MFP). This gives the thickness of an absorber that can attenuate the original
intensity of a radiation to 36.8 %, and it can be determined by Equation 1.9.
where, μ is the linear attenuation coefficient for a monoenergetic
photons/ radiations.
The
Relative Deviations (RD) between theoretical (WinXCOM) and experimental results
for MAC were deduced using of the following relations (Agar
et al,2018).
where 
denote the experimental and
theoretical mass attenuation coefficients respectively.
For
liquid permeability also referred to
as hydraulic conductivity of a sample gives a measure of the ease
at which the sample will allow the passage of radioactive fluids through it. In
order to determine the liquid permeability coefficient of the samples, Darcy
formula was applied.
Darcy’s
equation is given as
Therefore;
where:
Q
= volume of fluid collected (cm3)
t = time
of fluid flow (sec)
Δh = change in water pressure height (atm)
α
= the fluid dynamic viscosity in (poise or
Pa.s) for distill water is 1
L
= the vertical Thickness of the sample (cm)
K = the permeability
of the sample (darcy)
A
= the area of the sample (cm2)
1.3 STATEMENT
OF THE PROBLEM
Radioactive
materials are hazardous to the environment, human and animal health. The
increasing application of radioactive materials in manufacturing industries, research,
agriculture, medicine and power generation, generate radiations and radioactive
wastes. These definitely constitute
environmental hazard if a reliable radiation protection and effective
radioactive waste disposal mechanism is not put in place. Recently, several
authors have investigated the radiation shielding capability of different
materials like; kaolin, granite (Olukotun et al.,2018;
Mann et al., 2016; Kacal et
al., 2018; Najam et al., 2016) without
consideration to the liquid permeability coefficients and thermochemical
stability of these materials and their composites which are major properties for consideration in choosing high
performance materials for radiation attenuation and radioactive waste
management. The lack of liquid permeability evaluation of
any radiation shielding material may result to radioactive waste leakage which
has the potential to contaminate the environment and underground water bodies
(Kozlowski and Ludynia, 2019; Le et al., 2015; Rowe et al, 1995; Osinubi and Eberemu,
2013).
Some
traditional materials mostly used for radiation attenuation like lead (Pb) and
red mud have become less attractive because of their inherent disadvantages such
as toxicity for lead; corrosion and high liquid permeability in the case of
bauxite residue (red mud) (Obaid et al,
2018).C However, alternative
materials which include concrete, clay- steel slag, clay- fly ash, barite,
bentonite – red mud composites etc are currently under investigation for
possible deployment in radiation shielding and radioactive waste management (Isfahani et al,2018a,
2018b. Olukotun et al, 2018; Mann
et al, 2016; Kacal et al, 2018;
Najam et
al, 2016; Akkurt et al 2010),. But there still exist some limitations in the
ability of these materials to shield and immobilize radioactive liquid
materials.
1.4 AIM AND OBJECTIVES
The
major aim of this research is to investigate radiation shielding properties,
thermochemical stability and liquid permeabilities coefficients of baked and
unbaked kaolin, granite and their composites for possible deployment as a
storage barrier facility for radioactive waste management and immobilization.
The
objectives are
1. To
provide a valid alternative material for radioactive waste management, that is
efficient, portable, cost effective, eco-friendly and readily available for
radiation shielding.
2. To
determine the liquid permeability coefficients of kaolin, granite and their
various percentage composites for used in liquid radioactive waste immobilization.
3. To
determine the thermochemical stability kaolin, granite and their various
percentage composites by comparing their shielding properties for baked and
unbaked samples.
4. To
critically examine the radiation shielding and liquid permeability properties
of kaolin, granite and their various percentage composites as well as compare
the results obtained with results for other emerging alternatives obtained from
literatures.
5. To
characterize kaolin and granite samples obtained from the said locations which
have not been characterized before now.
6. Finally,
to advance the call for the deployment of kaolin and granite composites as solid- state engineered barrier facility for
the management of radioactive waste.
This
will be achieved by finding the radiation shielding performance of baked and
unbaked granite treated with different
percentage of micro-scale kaolin powder,
to determine the optimum percentage of micro-scale granite particles in a
kaolin and the optimum percentage of micro-scale kaolin particles in granite
sample to give highest gamma radiation
shield with lowest liquid permeability
coefficient for radioactive waste management / immobilization and efficient
radiation shielding in Radio-Diagnostic centers.
1.5 JUSTIFICATION
Many researchers have conducted research on different materials to
determine the radiation shielding ability of these materials without
considering their liquid permeability coefficient, which is an important factor
in the fluid transport characterization of any material (Reddy
et al., 2021; Ryan, 1998). Most of these
materials have shown excellent performance in radiation shielding but poor performance
in liquid permeability coefficient, this is a very big challenge in radioactive
waste management bearing in mind that some of these radioactive wastes are in
liquid form. Therefore, the need to investigate other materials which are
natural, inexpensive, eco-friendly, and readily available with promising performance
in radiation shielding and very low liquid
permeability coefficient is very important
for effective radioactive waste immobilization and management. The novelty of
this research is based on the consideration of gamma radiation shielding, liquid
permeability coefficient and thermo- chemical stability of granite, kaolin and their
composites which have never been investigated before now. Formally, Lead was
commonly used as gamma radiation shield and in radioactive waste management but
due to high cost, high liquid permeability and poisonous nature of lead, attention
is now shifting to other material especially composites materials that are
readily available with relatively high density. The lack of liquid permeability evaluation of any radiation
shielding material may result in radioactive leakage which may contaminate the
environment and underground water bodies.
1.6 SCOPE OF THE STUDY
This study covered the experimental
and theoretical investigation of the radiation attenuation ability of baked and
unbaked granite treated with different percentage of micro-scale kaolin powder to
ascertain their degree of efficiency in
overcoming most of the limitations observed in previous researchers in terms of
liquid radioactive waste immobilization, thermochemical stability and shielding
capability. Thus, the present study is designed to investigate the radiation
shielding and liquid permeability properties of granite, kaolin and their composites
at different percentage mixtures. The expected results will be critically
examined and compared with results of other emerging alternatives for
consideration and possible deployment in liquid radioactive waste management.
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