Murray Nuclear Energy

An Introduction to the Concepts, Systems, and Applications of Nuclear Processes
4. Auflage 2013
ISBN: 978-1-4832-8786-7
Verlag: Elsevier Science & Techn.
Format: EPUB
Kopierschutz: Adobe DRM (»Systemvoraussetzungen)

E-Book, Englisch, 462 Seiten

Reihe: Pergamon Unified Engineering Series

This expanded, revised, and updated fourth edition of Nuclear Energy maintains the tradition of providing clear and comprehensive coverage of all aspects of the subject, with emphasis on the explanation of trends and developments. As in earlier editions, the book is divided into three parts that achieve a natural flow of ideas: Basic Concepts, including the fundamentals of energy, particle interactions, fission, and fusion; Nuclear Systems, including accelerators, isotope separators, detectors, and nuclear reactors; and Nuclear Energy and Man, covering the many applications of radionuclides, radiation, and reactors, along with a discussion of wastes and weapons. A minimum of mathematical background is required, but there is ample opportunity to learn characteristic numbers through the illustrative calculations and the exercises. An updated Solution Manual is available to the instructor. A new feature to aid the student is a set of some 50 Computer Exercises, using a diskette of personal computer programs in BASIC and spreadsheet, supplied by the author at a nominal cost. The book is of principal value as an introduction to nuclear science and technology for early college students, but can be of benefit to science teachers and lecturers, nuclear utility trainees and engineers in other fields.

Autoren/Hrsg.

Murray, Raymond L.

Leseproben

1

Energy

Publisher Summary

Associated with each basic type of force is an energy, which may be transformed to another form for practical use. The addition of thermal energy to a substance causes an increase in temperature, the measure of particle motion. Electromagnetic radiation arising from electrical devices, atoms, or nuclei may be considered as composed of waves or of photons. Matter can be converted into energy and vice versa. There are a limited number of basic forces, namely, gravitational, electrostatic, electromagnetic, and nuclear. Associated with each of these is the ability to do work. Thus, energy in different forms may be stored, released, transformed, transferred, and used in both natural processes and manmade devices. This chapter discusses energy, which takes on various forms; it is classified according to the type of force that is acting. The water in the hydroelectric plant experiences the force of gravity and thus, gravitational energy is involved. It is transformed into mechanical energy of rotation in the turbine, which is then converted to electrical energy by the generator. At the terminals of the generator, there is an electrical potential difference, which provides the force to move charged particles through the network of the electrical supply system. The electrical energy may then be converted into mechanical energy as in motors, into light energy as in light bulbs, into thermal energy as in electrically heated homes, or into chemical energy as in a storage battery.

OUR MATERIAL world is composed of many substances distinguished by their chemical, mechanical, and electrical properties. They are found in nature in various physical states—the familiar solid, liquid, and gas, along with the ionic “plasma”. However, the apparent diversity of kinds and forms of material is reduced by the knowledge that there are only a little over 100 distinct chemical elements and that the chemical and physical features of substances depend merely on the strength of force bonds between atoms.

In turn, the distinctions between the elements of nature arise from the number and arrangement of basic particles—electrons, protons, and neutrons. At both the atomic and nuclear levels, the structure of elements is determined by internal forces and energy.

1.1 Forces and Energy

There is a limited number of basic forces—gravitational, electrostatic, electromagnetic, and nuclear. Associated with each of these is the ability to do work. Thus energy in different forms may be stored, released, transformed, transferred, and “used” in both natural processes and manmade devices. It is often convenient to view nature in terms of only two basic entities—particles and energy. Even this distinction can be removed, since we know that matter can be converted into energy and vice versa.

Let us review some principles of physics needed for the study of the release of nuclear energy and its conversion into thermal and electrical form. We recall that if a constant force is applied to an object to move it a distance , the amount of work done is the product . As a simple example, we pick up a book from the floor and place it on a table. Our muscles provide the means to lift against the force of gravity on the book. We have done work on the object, which now possesses stored energy (potential energy), because it could do work if allowed to fall back to the original level. Now a force acting on a mass provides an acceleration , given by Newton’s law . Starting from rest, the object gains a speed , and at any instant has energy of motion (kinetic energy) in amount . For objects falling under the force of gravity, we find that the potential energy is reduced as the kinetic energy increases, but the sum of the two types remains constant. This is an example of the principle of conservation of energy. Let us apply this principle to a practical situation and perform some illustrative calculations.

As we know, falling water provides one primary source for generating electrical energy. In a hydroelectric plant, river water is collected by a dam and allowed to fall through a considerable distance. The potential energy of water is thus converted into kinetic energy. The water is directed to strike the blades of a turbine, which turns an electric generator.

The potential energy of a mass located at the top of the dam is = , being the work done to place it there. The force is the weight , where is the acceleration of gravity. Thus = . For example, for 1 kg and 50 m height of dam, using = 9.8 m/sec2†, is (1)(9.8)(50) = 490 joules (J). Ignoring friction effects, this amount of energy in kinetic form would appear at the bottom. The speed of the water would be .

Energy takes on various forms, classified according to the type of force that is acting. The water in the hydroelectric plant experiences the force of gravity, and thus gravitational energy is involved. It is transformed into mechanical energy of rotation in the turbine, which then is converted to electrical energy by the generator. At the terminals of the generator, there is an electrical potential difference, which provides the force to move charged particles (electrons) through the network of the electrical supply system. The electrical energy may then be converted into mechanical energy as in motors, or into light energy as in lightbulbs, or into thermal energy as in electrically heated homes, or into chemical energy as in a storage battery.

The automobile also provides familiar examples of energy transformations. The burning of gasoline releases the chemical energy of the fuel in the form of heat, part of which is converted to energy of motion of mechanical parts, while the rest is transferred to the atmosphere and highway. Electricity is provided by the automobile’s generator for control and lighting. In each of these examples, energy is changed from one form to another, but is not destroyed. The conversion of heat to other forms of energy is governed by two laws, the first and second laws of thermodynamics. The first states that energy is conserved; the second specifies inherent limits on the efficiency of the energy conversion.

Energy can be classified according to the primary source. We have already noted two sources of energy: falling water and the burning of the chemical fuel gasoline, which is derived from petroleum, one of the main fossil fuels. To these we can add solar energy, the energy from winds, tides, or the sea motion, and heat from within the earth. Finally, we have energy from nuclear reactions, i.e., the “burning” of nuclear fuel.

1.2 Thermal Energy

Of special importance to us is thermal energy, as the form most readily available from the sun, from burning of ordinary fuels, and from the fission process. First we recall that a simple definition of the temperature of a substance is the number read from a measuring device such as a thermometer in intimate contact with the material. If energy is supplied, the temperature rises; e.g., energy from the sun warms the air during the day. Each material responds to the supply of energy according to its internal molecular or atomic structure, characterized on a macroscopic scale by the specific heat . If an amount of thermal energy added to one gram of the material is , the temperature rise, ?, is . The value of the specific heat for water is = 4.18 J/g-°C and thus it requires 4.18 joules of energy to raise the temperature of one gram of water by one degree Celsius (1°C).

From our modern knowledge of the atomic nature of matter, we readily appreciate the idea that energy supplied to a material increases the motion of the individual particles of the substance. Temperature can thus be related to the average kinetic energy of the atoms. For example, in a gas such as air, the average energy of translational motion of the molecules is directly proportional to the temperature , through the relation , where is Boltzmann’s constant, 1.38 × 10-23 J/K. (Note that the Kelvin scale has the same spacing of degrees as does the Celsius scale, but its zero is at -273°C.)

To gain an appreciation of molecules in motion, let us find the typical speed of oxygen molecules at room temperature 20°C, or 293K. The molecular weight is 32, and since one unit of atomic weight corresponds to 1.66 × 10-27 kg, the mass of the oxygen (O2) molecule is 5.3 × 10-26 kg. Now

and thus the speed is

Closely related to energy is the physical entity , which is the rate at which work is done. To illustrate, suppose that the flow of water in the hydroelectric plant if Section 1.1 were 2 × 106 kg/sec. The corresponding energy per second is (2 × 106) (490) = 9.8 × 108 J/sec. For convenience, the unit joule per second is called the watt (W). Our plant thus involves 9.8 × 108 W. We can conveniently express this in kilowatts (1 kW = 103 W) or megawatts (1 M W = 106 W). Such multiples of units are used because of the enormous range of magnitudes of quantities in...