Nuclear fission basics

The step from nuclear fission to a nuclear chain reaction and the atomic bomb was, in principle, quite straightfoiward. In practice, however, it consumed more time and money than was ever foreseen. Although it was her basic insight that eventually led to the fission bomb dropped on Hiroshima, Meitner refused to work on the bomb and, for humanitarian reasons, hoped that it would not work. 

Nuclear fission reactors ( nuclear power reactors ) are devices that use controlled neutron-induced fission to generate energy. While a complete description of the design of these devices is beyond the scope of this book, there are certain basic principles related to nuclear reactors that are worth studying and that can be described and understood with a moderate effort. 

The discovery in 1938-1939 of nuclear fission of uranium, which led ultimately to the discovery of nuclear power, heralded a new, extraordinarily fruitful stage in Ya.B. s scientific activity. His interests were concentrated on the study of the mechanism of fission of heavy nuclei and, what proved particularly important, on the development of a theory of the chain fission reaction of uranium. During 1939-1943 Ya.B. wrote several papers which laid the foundation for this subject and were of fundamental value. We note that four of these papers, written in collaboration with Yu. B. Khariton, were done practically in two years before the war. The papers of this series form the foundation of modern physics of reactors and nuclear power they are widely known and do not require special commentary—a short review of the basic physical results is eloquent enough. 

In addition to the huge amount of energy released by nuclear fission reactions, another important result of such reactions is that more neutrons are produced than the number of neutrons used to bombard. The produced neutrons may also strike other 235(J isotopes and causes new fissions. The new nuclear fission reactions also produce neutrons with huge amounts of energy, and so on. This continuous process is said to be the atomic bomb, and is the basic principle of nuclear reactors. 

During World War II an intense research effort (the Manhattan Project) was carried out by the United States to build a bomb based on the principles of nuclear fission. This program produced the fission bombs that were used with devastating effects on the cities of Hiroshima and Nagasaki in 1945. Basically, a fission bomb operates by suddenly combining two subcritical masses of fissionable material to form a supercritical mass, thereby producing an explosion of incredible intensity. 

Fermi, Enrico (1901-1954). First to achieve a controlled nuclear fission reaction (1939) basic research on subatomic particles. Nobel Prize 1938. Lawrence, Ernest O. (1901-1958). Invented the cyclotron in which first synthetic elements were created. Nobel Prize 1939. 

The 4th Euratom FP consisted basically of two specific programmes, one on controlled thermonuclear fusion, the other on nuclear fission safety. The EURO 170.5 million for the indirect actions under the nuclear fission safety programme was spent mainly to finance research projects, but also on various accompanying measures and training schemes. Under... 

Understanding radioactivity and radioactive decay Figuring out haif-iives The basics of nuclear fission Taking a look at nuclear fusion Tracing the effects of radiation... 

This section gives a short summary of some results discussed in more detail in various parts of O Chap. 2 ( Basic Properties of the Atomic Nucleus ) and O Chap. 4 ( Nuclear Fission ) concerning the dependence of the decay constant on various physical parameters for the most... 

Spontaneous fission (SF) is observed only in elements with Z> 90 where Coulomb forces make the nucleus unstable toward this mode of decay, although energetically SF is an exothermic process for nuclei with A > 100. Numerous reviews of SF properties, half-lives, and properties of fission fragments, have been summarized by several authors (von Gunten 1969 Hoffinan and Hoffinan 1974 Hoffinan and Somerville 1989 Hulet 1990b, Wagemans 1991 Hoffinan and Lane 1995 Hoffinan et al. 1996) and basic properties of nuclear fission are described in Chap. 4 of Vol. 1. However, some current topics concerning SF are presented in this Subsection. 

From these two main groups of the Periodic System of Elements, only the elements bromine, iodine, rubidium and cesium are produced by nuclear fission to an extent worth mentioning. Iodine and cesium are of particular interest during plant normal operation as well as in accident situations, because of their comparatively high fission yields, their enhanced mobility in the fuel at higher temperatures and the radiotoxicity of some of their isotopes. Both elements are often summarized under the term volatile fission products their similar properties justify their treatment in the same context, despite pronounced differences in their basic chemical behavior. 

Duderstadt, J. J. and L. J. Hamilton. 1976. Nuclear Reactor Analysis. New Yoik John Wiley Sons. Designed for the nuclear engineering student, this book provides the basic scientific principles of nuclear fission chain reactions and applications in nuclear reactor design. References and problems are included at the end of each chapter along with appendices, which include selected nuclear data, selected mathanatical formulas, and nuclear power reactor data. 

Over the more than 40 years since the first nuclear fission reactor was constructed numerous designs of reactor have been evolved by variation of the basic parameters such as fuel type, moderator, and coolant. One possible classification is by intended use, e.g., research, plutonium production, electricity generation, or propulsion units for submarines or surface ships. In this chapter we will concentrate on power reactors, both on account of their practical importance and because of the complexity in engineering design introduced by the need to convert the energy released by nuclear fission into a mechanical or electrical output. Many of the characteristics of the various reactor types have been touched on in earlier chapters, but the objective in the present chapter is to provide a systematic summary of the main classifications of reactor prior to the more detailed descriptions to be given in the following chapters. 

The first two chapters serve as an introduction to the basic physics of the atom and the nucleus and to nuclear fission and the nuclear chain reaction. Chapter 3 deals with the fundamentals of nuclear reactor theory, covering neutron slowing down and the spatial dependence of the neutron flux in the reactor, based on the solution of the diffusion equations. The chapter includes a major section on reactor kinetics and control, including temperature and void coefficients and xenon poisoning effects in power reactors. Chapter 4 describes various aspects of fuel management and fuel cycles, while Chapter 5 considers materials problems for fuel and other constituents of the reactor. The processes of heat generation and removal are covered in Chapter 6. 

The chronology of the development of nuclear reactors can be divided into several principal periods pre-1939, before fission was discovered (12) 1939—1945, the time of World War II (13—15) 1945—1963, the era of research, development, and demonstration (16—18) 1963—mid-1990s, during which reactors have been deployed in large numbers throughout the world (10,18) and extending into the twenty-first century, a time when advanced power reactors are expected to be built (19—23). Design of nuclear reactors has been based on a combination of theory, measurement of basic and derived parameters, and experiments with complete systems (24—27). 

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