Micro and Nanostructured Composite Materials for Neutron Shielding Applications

Sajith Thottathil Abdulrahman, Sabu Thomas, Zakiah Ahmad

• Publisher: Woodhead Publishing
• Year: 2020
• Print ISBN: 9780128194591
• eBook ISBN: 9780128194621
• Topic: Technology & Engineering
• Subtopic: Materials Science
• Index: Technology & Engineering

Micro- and Nanostructured Composite Materials for Neutron Shielding Applications presents recent developments and future possibilities for neutron shielding materials. Emphasis is placed on the correlation between the morphology, shielding mechanisms, and other desired properties, including their mechanical and thermal properties. The effect of neutron absorbing fillers, including their size on final properties is also examined, as are recent advancements in preparation, characterization and simulation techniques. Written by specialists in their respective fields, this comprehensive resource will help professionals and students understand the fundamentals of neutron shielding, as well as the properties of micro- and nanopolymer-based composites, concrete materials, alloy materials and metal-ceramic composites. - Provides an up-to-date understanding of the fundamentals of shielding mechanisms, morphology and material property correlations - Covers a broad range of micro and nano composite materials for neutron shielding - Discusses recent advances surrounding the synthesis and processing of nanostructures and nanocomposite materials

Chapter 1

Introduction to neutron-shielding materials

Sajith Thottathil Abdulrahman^a; Zakiah Ahmad^a; Sabu Thomas^b; Azerai Ali Rahman^{a a} Faculty of Civil Engineering, Universiti Teknologi Mara, Shah Alam, Selangor, Malaysia
^b International and Inter University Centre for Nanoscience and Nanotechnology, Mahatma Gandhi University, Kottayam, Kerala, India

Abstract

Neutron radiation exposure can cause serious illnesses in humans such as cancer, cardiovascular disease, hemopoietic syndrome, etc. Due to advances in neutron-based technology over the last decade, the need for advanced shielding materials continues to increase. The selection of materials that attenuate neutrons depends solely on the energy of the incident neutrons. In heavy structures such as nuclear power plants and health industries, concrete materials are used as shields, whereas metal-based neutron is preferred in applications requiring high-temperature stability and durability. Concentration of material having low atomic numbers plays a significant role in slowing the neutrons down. Another necessary factor for neutron-shielding material is fillers with greater macroscopic cross section for neutron absorption. Subsequently, polymer composites of neutron shielding show excellent characteristics such as lightweight, hydrogen richness, ease of distribution of neutron-absorbing fillers, making them suitable for applications in areas such as aerospace, portable neutron sources, etc. A review of various neutron-shielding materials based on their applications is conducted in this chapter.

Keywords

Neutron shielding; Concrete neutron shield; Metal neutron shield; Polymer neutron shield; Flexible neutron shield; borated materials

1.1 Introduction

Developments in neutron science and technology have led to the emission of unwanted neutron particle, which often occur in nuclear power plants, medical sector, and aerospace industry [1, 2]. A wide range of applications that emit neutron radiation show the need for protection in accordance with appropriate safety standards. Advances in the use of neutron sources such as neutron activation analysis (NAA), neutron radiography, active neutron interrogation technique, and neutron capture therapy over the past two decades show its importance. During operating conditions in such applications, unwanted neutron particle radiation escapes and interacts with the atoms of the surrounding materials which make the environment radioactive. Consequently, shielding materials with structural and functional integrity are important for the safer use of these applications. Table 1.1 lists the application of neutron-shielding materials in various sectors according to the incident energy of the undesired neutron radiations.

Table 1.1

Neutron-shielding material application in various sectors.

Sl. no.	Categories	Energy of neutrons	Shielding material	Reference
1.	Nuclear power plants	> 2 MeV	Concrete wall	[3–5]
			Water (moderator)
			Polymer composites
			Metal cask (spent fuel)
2.	Medical hospitals	10–25 MeV	Concrete wall	[6–9]
			Metal composites
			Polymer composites
3.	Aerospace	> 1 MeV	Polymer composites	[10–12]
4.	Neutron radiography	~ 4 MeV	Polymer composites	[13–17]
	Neutron activation analysis
	Active neutron interrogations

Nuclear power plants are an alternate source of energy to traditional fossil fuels with negligible carbon emissions, thus being relatively clean and efficient. Neutron emitted in reactors during the nuclear fission process must be shielded with suitable shielding materials. Specifically, high-energy neutrons exceeding 2 MeV energy during operation must be shielded to protect workers and the environment [3, 4]. Concrete has been generally used to attenuate the very fast neutrons with sufficient additives, including hydrogen-rich neutron moderators (water and polymer) and slow neutron absorbers. Additional shielding materials (flexible polymer-based) were applied to the curved and irregular plumbing surface ducts, etc., to prevent the neutrons from escaping through them [18]. Furthermore, radiations from the radioactive waste material (spent fuel) from reactors also require proper disposal. The storage casks, based on metal materials with long-term durability, are usually used to dispose of spent nuclear fuel, which is another environmental issue that needs to be addressed.

Understanding the radiobiological effectiveness of by-product neutron doses occurring during radiation therapy treatment has been very important due to public health consequences [6]. Photo neutrons of 25–10 MeV generated during the acceleration of the electron in radiation therapy will result in in-room contamination, which is a threat to the patient [7,8]. Most neutrons are generated on collimation systems, applicators, and scattering foils in the accelerator. Metal-based and polymer-based shielding materials are provided to protect the patient from exposure to these neutron radiations and, in particular, flexible materials are needed to protect ventilation ducts, air conditioning, etc. [9]. In addition, boron neutron capture therapy is an emerging cancer therapy in circumstances where traditional radiation therapies become ineffective.

Galactic cosmic rays and solar energetic particles in outer space contains neutrons and protons of high energy (> 1 MeV to 1 GeV) [11, 12]. Proper shielding has always been needed to protect electronics and humans from these radiation exposures. High secondary radiation is produced during interaction between radiation and heavy atoms in metals and concrete, so polymer-based composites were commonly preferred, which also helps to reduce the weight of the spacecraft, making it cost effective.

Neutron radiography has been used as a nondestructive test of objects in security applications, engineering studies, geology, biological medicine, and industry to determine structural defects. The unique chargeless characteristics of neutrons make them suitable for nondestructive testing of bulk compounds. They can provide excellent contrast for light atoms even in the presence of heavy atoms and can also easily distinguish between isotopes of the same element due to the significant variation in scattering and absorption cross sections during neutron interaction [13]. NAA technique is widely used in elemental composition studies related to environmental and industrial applications. It helps to analyze trace elements in vegetables [14] and to understand the spatial distribution of elements and isotopes in samples [15]. Prompt gamma NAA technique has emerged as an effective technique for monitoring heavy metals in groundwater contamination, which is a matter of serious concern to agriculture and modern industry [16]. Active neutron interrogation techniques are also used to detect bombs, land mine, and reliably identify elements in prehistoric utensils [17]. The neutron source used for the above techniques is Am/Be, Pu/Be, etc., which emits 4–5 MeV neutrons requiring adequate protection. Polymer composites such as polyethylene, paraffin, etc., are used to cover this neutron source in order to generate an isostatic neutron beam for the application. In turn, the portable neutron source should be lightweight and easy to transport from place to place.

In all of the above applications, proper protective measures should be taken considering unwanted neutron radiation generated during operating conditions. Neutron radiation is a type of ionizing radiation consisting of uncharged particles that pass-through electron clouds and interact directly with the nucleus of the atom. Apart from neutron sources and reactors, many high-energy radiations like X-rays, proton rays, γ-rays, etc., used in different applications often emit unwanted neutrons [6]. Compared with other radiations, these neutrons may cause severe damage to the nucleus of human tissues resulting in diseases such as cancer, cardiovascular disease, hemopoietic syndrome, etc. [19,20]. All nuclear-related activities are implemented with radiation safety concept “ALARA” or “as low as reasonably a...

Table of contents

• Cover image
• Title page
• Table of Contents
• Copyright
• Contributors
• Editors biography
• Chapter 1: Introduction to neutron-shielding materials
• Chapter 2: Review on neutron-absorbing fillers
• Chapter 3: Thermoplastic micro- and nanocomposites for neutron shielding
• Chapter 4: Thermosetting micro- and nanocomposites for neutron radiation shielding
• Chapter 5: Elastomeric micro- and nanocomposites for neutron shielding
• Chapter 6: Metal and alloy composites for neutron shielding
• Chapter 7: Shielding concrete with neutron attenuating and absorbing components
• Chapter 8: Neutron shielding concrete in medical applications
• Chapter 9: Advancements in shielding materials for spent fuel storage
• Chapter 10: Neutron radiation shielding composites for deep space exploration: An introduction
• Chapter 11: Functional characterization of neutron-shielding materials
• Chapter 12: Advanced multilayer composite structures for fast neutron detection and shielding protection applications
• Chapter 13: Neutron spectroscopy techniques
• Chapter 14: Advancements in computational methods for neutron shielding
• Chapter 15: Effect of spent nuclear fuel neutron aging on dry cask shielding material
• Index