1.1 The Nuclear World and the Nuclear Power Industry
In this chapter, we would like to discuss the atomic world upon which the nuclear power industry is based. Compared to the physical world that we live in every day, the nuclear world is far stranger and it can even be considered to be bizarre. In addition, many of its underlying physical processes are governed by statistical probability distributions rather than deterministic Newtonian laws. In many cases, the outcome of a particular reaction follows a statistical probability distribution that can be derived from the Schrödinger wave equation. In the following sections, we would like to present a brief glimpse into what this nuclear world looks like and how the underlying “plumbing” works. If you have never taken a course in nuclear physics before, you will find what we have to say to be strange and even counterintuitive. Nevertheless, the entire nuclear power industry is based on the rules of this subatomic world, and so we would like to describe the inner workings of this world for you now. In future chapters, we will then apply some of these rules to illustrate how they can affect the behavior of a nuclear power plant. In general, nuclear engineering requires a much deeper understanding of the underlying physical processes than other energy sources do.
1.2 Atom and Its Structure
As everyone knows, an atom consists of primarily of empty space. In fact, over 99.999% of the volume of an atom contains nothing at all. This means that the atom is essentially hollow, with the exception of the atomic nucleus, which we will subsequently discuss. Nuclear particles inside of the atom exist within a 3D space that has come to be known as the vacuum. In classical mechanics, the vacuum is “empty” but in quantum mechanics, it is not. Within the vacuum, the laws governing the behavior of the nuclear world are written at an incredibly small distance scale called the Planck scale, which was named for the German physicist Max Planck. The Planck scale corresponds to a distance of about 1.6 × 10−37 cm and an energy of about 1.2 × 1019 GeV. At these distance and energy scales, space itself begins to twist and turn and quantum mechanics and quantum gravity merge. Their rate of convergence is determined by Planck’s constant h, which has a value of h = 6.626 × 10−34 kg m2/s in the SI unit system. This fundamental constant of nature is named in honor of Max Planck, whose picture is shown in Figure 1.1b. Planck’s constant is a key component of the Heisenberg uncertainty principle, which will be discussed later in this chapter.
Scientists believe that space at the Planck scale can be described by a seething sea of virtual black holes or multidimensional manifolds (called Calabi–Yau manifolds) that determine the statistical probability distributions that the particles in nuclear reactors obey. Many Nobel Prize winners even believe that our 3D universe is sitting on a “brane” which is contained within a higher dimensional universe in which the force of gravity is stronger than it is in ours. The theory of strings, which is the most complete theory of physical reality ever developed, is based in part on these and other innovative ideas. In the next few chapters, we would like to illustrate how these concepts can be used to design and build a nuclear power plant. Normally, classical nuclear engineering is not approached in this way.
To begin our discussion, consider for the moment a typical atom and the “empty” space it contains. We will start with a very simple view of the atom and then expand upon it. To give you an idea of how much space exists in an atom, suppose that we do a thought experiment where we are able to expand the atom to the size of a modern football stadium and the parking lot around it (which is typically about 500 yards or half of a kilometer in diameter). In this case, the nucleus of the atom would be about the size of a “pea” located at the 50 yard line and about 99.999% of the mass of an atom would be found inside of this “pea.” This implies that the average atom has a diameter of about 1 × 10−8 cm, and this diameter is defined as the distance from one side of the electron cloud to the other. The nucleus inside of the electron cloud has an average diameter of about 1 × 10−12 cm, which is about 10,000 times smaller. The volume of the nucleus is therefore times less than that of the atom as a whole. Hydrogen, which is the smallest atom, has an electron cloud with a diameter of about 0.25 × 10−8 cm, while larger atoms like cesium (Cs) have an electron cloud with a diameter of about 1.6 × 10−8 cm. Hence, the electron clouds can vary in diameter by a factor of about 8, and their total volume can vary by a factor of about 500(V ∝ D). The diameters of the electron clouds for most atoms tend to fall somewhere between these two extremes (see Figure 1.2). However, because of the orbital configurations of the electrons, heavier atoms do not always have larger electron clouds than lighter atoms do. In particular, notice that the uranium atom, which is the heaviest naturally occurring element, has a smaller electron cloud than the cesium atom does. Exercise 1.1 shows how the diameters of these two electron clouds compare. In reality, the electron “cloud” surrounding the nucleus is not a well-defined structure, and the surface of the nucleus of the atom is also not a well-defined surface. In fact, it tends to oscillate like a drop of incompressible fluid. This undulation can be described by the liquid drop model of nuclear structure, which is discussed in great detail in Chapter 9. The various orbital configurations of the electrons are also described there.