INVESTIGATION OF GAMMA RADIATION SHIELDING AND LIQUID PERMEABILITY PROPERTIES OF KAOLIN, GRANITE AND THEIR COMPOSITES FOR RADIOACTIVE WASTE MANAGEMENT

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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/sComparing 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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