Fission and Fusion

12 Key excerpts on "Fission and Fusion"

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  eBook - ePub

  Nuclear Engineering Fundamentals

  A Practical Perspective

  • Robert E. Masterson(Author)
  • 2017(Publication Date)
  • CRC Press

    (Publisher)

  billions of times more energy each day than fission does in the universe as a whole. Nuclear fusion is also the process that is responsible for creating the heat and light that are produced in stars such as our sun.

  Nuclear fission is based on the concept of inducing a heavy element (such as Uranium-233, Uranium-235, or Plutonium-239) to split apart into two or more parts . Practically speaking, this can be done by allowing one of these isotopes to absorb a slow-moving neutron and to transform themselves into an agitated state. The nucleus can only become stable again by releasing some of its excess energy and several photons and neutrons in the process. The difference between the mass of the nucleus before it splits apart and the mass of the nucleus after it splits apart (plus its by-products), when multiplied by the square of the speed of light c, is equal to the amount of kinetic energy E that is released. This kinetic energy is then converted into heat, which allows the blades of a steam turbine to spin, and for electrical energy to be produced. The key to all of this happening is to create what is known as a controlled nuclear chain reaction and to allow this chain reaction to occur for as long as possible without getting out of control. The length of time that this is possible is roughly proportional to the enrichment of the fuel. Commercial power reactors need to be partially refueled every 18 or 24 months, while military reactors can run for many years without the need for refueling. In this chapter, we would like to present the physical principles that allow the nuclear chain reaction to occur (see Figure 7.1

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  eBook - ePub

  Introduction to Nuclear Reactor Physics

  • Robert E. Masterson(Author)
  • 2017(Publication Date)
  • CRC Press

    (Publisher)

  billions of times more energy each day than fission does in the universe as a whole. Nuclear fusion is also the process that is responsible for creating the heat and light that are produced in stars such as our Sun.

  Nuclear fission is based on the concept of inducing a heavy element (such as Uranium-233, Uranium-235, or Plutonium-239) to split apart into two or more parts

  . Practically speaking, this can be done by allowing one of these isotopes to absorb a slow-moving neutron and to transform themselves into an agitated state. The nucleus can only become stable again by releasing some of its excess energy and several photons and neutrons in the process. The difference between the mass of the nucleus before it splits apart and the mass of the nucleus after it splits apart (plus its by-products), when multiplied by the square of the speed of light c, is equal to the amount of kinetic energy E that is released. This kinetic energy is then converted into heat, which allows the blades of a steam turbine to spin, and for electrical energy to be produced. The key to all of this happening is to create what is known as a

  controlled nuclear chain reaction

  and to allow this chain reaction to occur for as long as possible without getting out of control. The length of time that this is possible is roughly proportional to the enrichment of the fuel. Commercial power reactors need to be partially refueled every 18 or 24 months, while military reactors can run for many years without the need for refueling. In this chapter, we would like to present the physical principles that allow the nuclear chain reaction to occur (see Figure 7.1 ).

  FIGURE 7.1 Two universal symbols of the nuclear power industry in the world today. (a) A 3-meter tall sculpture of Einstein’s famous equation E = mc2

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  The Britannica Guide to the Atom

  • Britannica Educational Publishing, Erik Gregersen(Authors)
  • 2010(Publication Date)
  • Britannica Educational Publishing

    (Publisher)

  CHAPTER 6 N UCLEAR F ISSION T he subdivision of a heavy atomic nucleus, such as that of uranium or plutonium, into two fragments of roughly equal mass is called nuclear fission. The process is accompanied by the release of a large amount of energy. In nuclear fission the nucleus of an atom breaks up into two lighter nuclei. The process may take place spontaneously in some cases or may be induced by the excitation of the nucleus with a variety of particles (e.g., neutrons, protons, deuterons, or alpha particles) or with electromagnetic radiation in the form of gamma rays. In the fission process, a large quantity of energy is released, radioactive products are formed, and several neutrons are emitted. These neutrons can induce fission in a nearby nucleus of fissionable material and release more neutrons that can repeat the sequence, causing a chain reaction in which a large number of nuclei undergo fission and an enormous amount of energy is released. If controlled in a nuclear reactor, such a chain reaction can provide power for society’s benefit. If uncontrolled, as in the case of the so-called atomic bomb, it can lead to an explosion of awesome destructive force. The discovery of nuclear fission opened a new era—the “Atomic Age.” The potential of nuclear fission for good or evil and the risk/benefit ratio of its applications have not only provided the basis of many sociological, political, economic, and scientific advances but grave concerns as well. Even from a purely scientific perspective, the process of nuclear fission has given rise to many puzzles and complexities, and a complete theoretical explanation is still not at hand. HISTORY OF FISSION RESEARCH AND TECHNOLOGY The term fission was first used by the German physicists Lise Meitner and Otto Frisch in 1939 to describe the disintegration of a heavy nucleus into two lighter nuclei of approximately equal size

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  Energy in Perspective

  • Jerry B. Marion(Author)
  • 2013(Publication Date)
  • Academic Press

    (Publisher)

  Chapter 5

  NUCLEAR POWER

  Publisher Summary

  This chapter describes the nuclear Fission and Fusion processes and presents some details of nuclear reactor operations. The different nuclear forms of a particular element are called isotopes. Thus, there are three different isotopes of hydrogen—1 H, 2 H, and 3 H. All uranium nuclei contain 92 protons; the important isotopes of uranium contain 143 neutrons (235 U) and 146 neutrons (238 U). The absorption of neutrons by uranium produces a breakup or fission of the nucleus into two fragments, each with a mass roughly one-half the mass of the original uranium nucleus. It has been recognized that the fission process offers the possibility for the release of nuclear energy on a gigantic scale. When a heavy nucleus undergoes fission not only are two lighter nuclear fragments formed, but also two or three neutrons are released. If the system is designed such that, on average, exactly one neutron from each fission event triggers another event, then the fission energy can be released in a slow and controlled manner. This is the basic operating principle of the nuclear reactor.

  The survey of energy resources presented in the preceding chapter strongly suggests that we are facing a future in which nuclear power will play a major if not a dominant role. The reason is simple enough. Our supplies of fossil fuels are being depleted and we are forced to seek new sources of energy. At the present time, we do not know how to exploit solar energy or geothermal energy on a large scale nor do we know how to extract the petroleum locked in shale deposits in an economically feasible way. And we do not know how to obtain useful amounts of energy from nuclear fusion reactions.

  Probably all of these technological problems will eventually be solved, perhaps even within a relatively short time. But we cannot be certain of this. We would be courting disaster if we planned our future under the assumption that fusion reactors or solar power plants would be operational by the year 2000 or even by the year 2025. The one new source of energy that we know

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  Energy, Ecology, and the Environment

  • Richard F. Wilson(Author)
  • 2012(Publication Date)
  • Academic Press

    (Publisher)

  The reasons are too complex to go into here; all that matters, for our purposes, is that it is an experimental fact. [See Worksheet 5-2.] 147 Nuclear fission, often called splitting the atom, refers to dividing the nucleus into two or more parts. It is the process used in the atomic bomb and nuclear reactors. Let us assume that we can split the nucleus A = 238 into two other nuclei, say, A = 148 and A = 90. From the graph, we compare the binding energy per particle for each of these three nuclei. We start with a binding energy of 7.6 MeV/particle and end with a net of 8.5 MeV/particle. The energy liberated in this splitting is 238 (particles) x [8.5 - 7.6] (MeV/particle) = 215 MeV In summary, the heavy nucleus splits and gives off two lighter nuclei (fission fragments), each of which binds its nucleons more tightly than the uranium. The energy then becomes available, some directly, and some from decay products. A listing of the energy in the fission of U 2 35 is given in Table 5-1. 5 . Nuclear Fission and Fusion We shall look at two such nuclei, uranium (A = 236) and plutonium (A = 240). The shorthand notation for these nuclei are 92U 2 36 and gi+Pu 240 . We must first form these unstable nuclei, as because of their short lifetimes they are not found in nature. TECHNICAL NOTE 5 -3 Notation for Nuclear Reactions An atomic nucleus can be characterized by two numbers: Ζ is the atomic number, or the number of protons in the nucleus. The total charge of the nucleus is exactly Ζ multiplied by the proton charge. A is the mass number. This is defined as the number of protons in the nucleus plus the number of neutrons. The total mass of the atom is approximately A multiplied by the mass of a proton. It is actually a little less than this because of the binding of the nuclei. An atom that is electrically uncharged (neutral) will have exactly Ζ electrons to balance the charge of the protons.

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  eBook - ePub

  Fundamentals of Nuclear Physics

  • Ritesh Kohale, Sanjay J. Dhoble, Vibha Chopra(Authors)
  • 2009(Publication Date)
  • Bentham Science Publishers

    (Publisher)

  Nuclear Fission and Fusion Ritesh Kohale , Sanjay J. Dhoble , Vibha Chopra

  Abstract

  The present chapter deals with the analysis and relationship of significant features of theoretical nuclear physics. It is perhaps the most widely adopted chapter on the subject. The authors' line of understanding is subjected to “the theoretical perceptions, approaches, and deliberations formulated to infer the investigational matter and spread our aptitude to calculate and govern nuclear occurrences.” The present chapter elaborates on the features of conjectural nuclear physics. Its attention is classified agreeing to occurrences concerning nuclear fission, transition state (saddle point) and scission point, photo−fission, fissile materials and fertile materials, moderation and thermalization of the neutron, neutron transport in the matter, nuclear fusion and basic reaction for energy generation in the sun by fusion.

  Keywords: Fission, Fusion, Neutron Transport, Photo−fission.

  1. INTRODUCTION

  Energy from the nucleus draws attention to the two central approaches to generating energy from the nucleus: Fission and Fusion. In the present approach, the eminence of existing and upcoming reactors advanced security provisions and the eco-friendly effect of electrical energy generation from nuclear fission. The sections in the chapter proceeding with nuclear fusion address both inertial and magnetic confinement fusion.

  The significant aspect of fission is photo-fission was discovered in 1940 by a small team of engineers and scientists functioning the Westinghouse Atom Smasher at the company's Research Laboratories in Forest Hills, Pennsylvania [1 ]. They used a 5 MeV proton beam to bombard fluorine and produce high-energy photons, which were then exposed to samples of uranium and thorium [2 ]. In the low tens of MeV, Gamma radiation of modest energies can induce fission in conventionally fissile essentials such as the actinides thorium, uranium [3 ], plutonium, and neptunium [4

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  Halliday's Fundamentals of Physics, 1st Australian & New Zealand Edition

  • David Halliday, Jearl Walker, Patrick Keleher, Paul Lasky, John Long, Judith Dawes, Julius Orwa, Ajay Mahato, Peter Huf, Warren Stannard, Amanda Edgar, Liam Lyons, Dipesh Bhattarai(Authors)
  • 2020(Publication Date)
  • Wiley

    (Publisher)

  • Fission can be understood in terms of the collective model, in which a nucleus is likened to a charged liquid drop carrying a certain excitation energy. • A potential barrier must be tunnelled through if fssion is to occur. Fissionability depends on the relationship between the barrier height E b and the excitation energy E n transferred to the nucleus in the neutron capture. Why study physics? For decades, after World War II, Australia, New Zealand and Pacific nations protested against extensive atmospheric nuclear testing conducted by the United States, Britain and France in the Pacific Ocean. Wind and ocean currents spread the radioactive fallout to inhabited islands. Later, underground nuclear testing fractured the base of fragile atolls, leading to contamination of the marine environment. Today, adverse health and environmental impacts are the legacies of these nuclear testing programs. Pdf_Folio:1067 Let’s now turn to a central concern of physics and certain types of engineering: can we get useful energy from nuclear sources, as people have done for thousands of years from atomic sources by burning materials like wood and coal? As you already know, the answer is yes, but there are major differences between the two energy sources. When we get energy from wood and coal by burning them, we are tinkering with atoms of carbon and oxygen, rearranging their outer electrons into more stable combinations. When we get energy from uranium in a nuclear reactor, we are again burning a fuel, but now we are tinkering with the uranium nucleus, rearranging its nucleons into more stable combinations. Electrons are held in atoms by the electromagnetic Coulomb force, and it takes only a few electron-volts to pull one of them out. On the other hand, nucleons are held in nuclei by the strong force, and it takes a few million electron-volts to pull one of them out.

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  Nuclear Reactions in Heavy Elements

  A Data Handbook

  • V. M. Gorbachev, Y. S. Zamyatnin, A. A. Lbov(Authors)
  • 2013(Publication Date)
  • Pergamon

    (Publisher)

  PART II NUCLEAR FISSION CHAPTER 4 GENERAL CHARACTERISTICS OF THE FISSION PROCESS Fission of a nucleus means its disintegration into two (less frequently three or four) fragments accompanied by the liberation of a considerable amount of energy and the emission of secondary fission neutrons and -rays. Nuclei of heavy elements can fission either spontaneously (spontaneous fission) or due to bombardment of neutrons, charged particles and -rays (forced or induced fission). Most important in practice is fission caused by neutrons. Some isotopes (e.g. 2 3 3 U, 2 3 5 U, 2 3 9 Pu) can be fissioned by neutrons with arbitrary energies, others (e.g. 2 3 2 Th, 2 3 6 U, 238 U) only by neutrons having energies which exceed the fission threshold. The lifetime of a nucleus with regard to spontaneous fission is determined by the fission barrier penetration and will be dealt with in Chapter 5. In the case of forced fission, excitation of the nucleus is caused by a particle or photon, usually with the formation of a compound nucleus. Fission can then be considered as one of the possible competing processes of disintegration of the compound nucleus, the probability of which is described by the ratio of the fission width ry to the total width . The lifetime of the compound nucleus can be evaluated if the value of the total width is known; then r c =h/r where h is Planck's constant. For instance, to a value of ~ 1 eV corresponds r c ~ 10 15 sec. However, values of are known only for low excitation energies (since in this case discrete resonance levels of the compound nucleus are excited). At higher excitation energies the total width becomes comparable to the distance between levels and resonance effects disappear. A very effective experimental method for determining r c is the shadow method developed by A. F. Tulinov et al. [1-4]. In this method use is made of the effect of motion of the compound nucleus caused by the momentum of the incident particle.

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  eBook - PDF

  Principles of Physics: Extended, International Adaptation

  • David Halliday, Robert Resnick, Jearl Walker(Authors)
  • 2023(Publication Date)
  • Wiley

    (Publisher)

  4. Fission can be understood in terms of the collective model, in which a nucleus is likened to a charged liquid drop carrying a certain excitation energy. 5. A potential barrier must be tunneled through if fission is to occur. Fission- ability depends on the relationship between the barrier height E b and the excitation energy E n transferred to the nucleus in the neutron capture. LEARNING OBJECTIVES 1315 What Is Physics? Let’s now turn to a central concern of physics and certain types of engineering: Can we get useful energy from nuclear sources, as people have done for thousands of years from atomic sources by burning materials like wood and coal? As you already know, the answer is yes, but there are major differences between the two energy sources. When we get energy from wood and coal by burning them, we are tinkering with atoms of carbon and oxygen, rearranging their outer electrons into more stable combinations. When we get energy from uranium in a nuclear reactor, we are again burning a fuel, but now we are tinkering with the uranium nucleus, rearranging its nucleons into more stable combinations. Electrons are held in atoms by the electromagnetic Coulomb force, and it takes only a few electron-volts to pull one of them out. On the other hand, nucleons are held in nuclei by the strong force, and it takes a few million electron- volts to pull one of them out. This factor of a few million is reflected in the fact that we can extract a few million times more energy from a kilogram of uranium than we can from a kilogram of coal. In both atomic and nuclear burning, the release of energy is accompanied by a decrease in mass, according to the equation Q = –Δm c 2 . The central differ- ence between burning uranium and burning coal is that, in the former case, a much larger fraction of the available mass (again, by a factor of a few million) is consumed.

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  eBook - ePub

  Nuclear and Particle Physics

  An Introduction

  • Brian R. Martin, Graham Shaw(Authors)
  • 2019(Publication Date)
  • Wiley

    (Publisher)

  Although tokamak machines such as ITER and JET are likely be the first to achieve a self-sustaining reaction, a commercial reactor would have to satisfy additional financial and engineering constraints and other configurations are not ruled out. One of these is the spherical tokamak, the limiting case of the torus type. Experiments on this type of configuration started in the late 1980s and there is an on-going experimental programme at a small number of centres, an important one being Culham, the home of JET. Here a machine called MAST (Mega-Ampere Spherical Tokamak) is being used to carry out a range of studies to support the design work on ITER by studying plasma behaviour at the limit of conventional tokamak design. There are other groups in institutes around the world using small tokamaks to explore different approaches to producing a sustainable plasma.

  9.3 Nuclear weapons

  When nuclear reactions are used to produce power in a controlled way there is a clear distinction between Fission and Fusion processes. However, in the case of explosive power production, i.e. bombs, the distinction is not always so clear and some weapons use both Fission and Fusion in the same device. It is therefore appropriate to separate the discussion of nuclear weapons from the use of nuclear reactions for peaceful purposes.20

  9.3.1 Fission devices

  Despite the simple analysis in Section 9.1.1, fortunately it is not easy to make a nuclear bomb! A major problem is that the thermal energy released as the assembly becomes critical will produce an outward pressure that is sufficient to blow apart the fissile material before criticality is achieved, unless special steps are taken to prevent this. Even before the chain reaction occurs, there are problems to be overcome, which can be summarised as follows:

  1. keeping the fissile materials subcritical before detonation;
  2. bringing the material into a supercritical state while keeping it relatively free of neutrons;
  3. introducing neutrons to the critical mass at the optimum time;
  4. keeping the fissile material together until a substantial fraction of the mass has fissioned.

  Problems (a) and (b) are complicated by the fact that there will always be neutrons present from spontaneous fission of the fissile material. If we define the ‘insertion time’ as the time to reach a supercritical value of

  k = 2

  starting from the critical value

  k

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  Environmental Physics

  Sustainable Energy and Climate Change

  • Egbert Boeker, Rienk van Grondelle(Authors)
  • 2011(Publication Date)
  • Wiley

    (Publisher)

  6 Nuclear Power

  The energy to be gained by controlled nuclear reactions originates from the beginning of the solar system about 1010 years ago. At that time many atomic nuclei were formed of which only the stable ones and the very long lived are still present. The physics of nuclear power is understood from Figure 6.1 , which shows the binding energy per nucleon versus the mass number A for these nuclei. The binding energy is the energy required to separate all nucleons from each other. That is also the energy which is liberated if they all come together again. If one divides the binding energy by the mass number A one obtains the binding energy per nucleon shown in Figure 6.1 .

  Figure 6.1 Binding energy per nucleon versus the mass number A for stable nuclei. Fission of heavy nuclei or fusion of light ones will produce an increase in binding energy per nucleon and liberate nuclear energy.

  The curve in Figure 6.1 exhibits a maximum around A ≈ 60, in the vicinity of 56 Fe, which therefore is one of the most stable nuclei. One may check that the fission of a nucleus with A ≈ 235 into two parts of about A ≈ 118 would increase the binding energy by about 1 MeV per nucleon, which in total would be 235 [MeV]. In reality, the induced fission of 235 U liberates 207 [MeV] of energy. In nuclear power stations almost 200 [MeV] can be delivered as heat ([1], p. 12).

  In nuclear fusion two very light nuclei are forced to form a new nucleus. From Figure 6.1 it follows that in this case an even larger increase in binding energy per nucleon can be obtained.

  In order to appreciate the order of magnitude of the energy released one should remember that combustion of fossil fuels takes place by chemical reactions, that is by rearranging electrons in atomic or molecular orbits with energies in the order of [eV]. As the number of electrons is in the order of the number of nucleons, the use of nuclear power would liberate ≈1 [MeV]/electron, which gives a gain in energy by a factor 106

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  Release Of Thermonuclear Energy By Inertial Confinement, The: Ways Towards Ignition

  Ways Towards Ignition

  • Friedwardt Winterberg(Author)
  • 2010(Publication Date)
  • World Scientific

    (Publisher)

  Chapter 2 Nuclear Fission and Fusion Reactions 2.1 Nuclear Binding Energies In first approximation an atomic nucleus can be viewed as a spherical drop made up of nuclear matter. The radius of a nucleus is R = R 0 A 1 / 3 , R 0 = 1 . 4 × 10 − 13 cm (2.1) where A is the atomic number. (2.1) expresses the important result, that the nuclear volume is proportional to the number of neutrons and protons. For small values of A the binding energy E turns out to be proportional to A , and one has E/A ∼ = 6-8 MeV. As in a liquid drop, each nucleon, be it a proton or neutron, interacts with a limited number of adjacent nucleons. The forces between them saturate, with an additional nucleon, contributing about 6-8 MeV to the binding energy, independent of the number of the nucleons already present. And as in a liquid drop, there must be a negative surface energy contribution proportional to R 2 ∝ A 2 / 3 , because particles near the surface have unsaturated valences. For Z protons and N neutrons, with Z + N = A , the volume dependent part of the binding energy should only be a function of the concentrations Z/A resp. N/A : E volume A = f N A . (2.2) 9 10 CHAPTER 2. NUCLEAR Fission and Fusion REACTIONS Furthermore, if there is symmetry of the forces between the protons and neutrons, the function in (2.2) can only depend on the difference N − Z , and must be an even function of this difference: E volume A = f N − Z N + Z 2 = − a + b N − Z N + Z 2 + . . . (2.3) Finally, the electrostatic repulsion between the protons must be taken into account. This effect, small for light nuclei, becomes important for large nuclei. For a uniformly charged sphere of radius R this leads to a positive energy by the Coulomb repulsion: E el. = 3 e 2 5 R 0 Z 2 A 1 / 3 . (2.4) Because of the electrostatic repulsion between protons, the energy minimum at N = Z for light nuclei is shifted to N = 1 .

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