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Four Factor Formula
The four-factor formula, also known as Fermi's four factor formula is used in nuclear engineering to determine the multiplication of a nuclear chain reaction in an infinite medium. The symbols are defined as: *\nu, \nu_f and \nu_t are the average number of neutrons produced per fission in the medium (2.43 for uranium-235). *\sigma_f^F and \sigma_a^F are the microscopic fission and absorption cross sections for fuel, respectively. *\Sigma_a^F and \Sigma_a are the macroscopic absorption cross sections in fuel and in total, respectively. *N_i is the number density of atoms of a specific nuclide. *I_ is the resonance integral for absorption of a specific nuclide. **I_ = \int_^ dE' \frac \frac. *\overline is the average lethargy gain per scattering event. **Lethargy is defined as decrease in neutron energy. *u_f (fast utilization) is the probability that a fast neutron is absorbed in fuel. *P_ is the probability that a fast neutron absorption in fuel causes fission. *P_ is the probabil ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Nuclear Engineering
Nuclear engineering is the branch of engineering concerned with the application of breaking down atomic nuclei ( fission) or of combining atomic nuclei (fusion), or with the application of other sub-atomic processes based on the principles of nuclear physics. In the sub-field of nuclear fission, it particularly includes the design, interaction, and maintenance of systems and components like reactors, power plants, or weaponry. The field also includes the study of medical and other applications of radiation, particularly Ionizing radiation, nuclear safety, heat/thermodynamics transport, nuclear fuel, or other related technology (e.g., radioactive waste disposal) and the problems of nuclear proliferation. This field also includes chemical engineering and electrical engineering. Professional areas The United States currently generates about 20% of its electricity from nuclear power plants. Nuclear engineers in this field generally work, directly or indirectly, in the nuclea ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Nuclear Chain Reaction
In nuclear physics, a nuclear chain reaction occurs when one single nuclear reaction causes an average of one or more subsequent nuclear reactions, thus leading to the possibility of a self-propagating series of these reactions. The specific nuclear reaction may be the fission of heavy isotopes (e.g., uranium-235, 235U). A nuclear chain reaction releases several million times more energy per reaction than any chemical reaction. History Chemical chain reactions were first proposed by German chemist Max Bodenstein in 1913, and were reasonably well understood before nuclear chain reactions were proposed. It was understood that chemical chain reactions were responsible for exponentially increasing rates in reactions, such as produced in chemical explosions. The concept of a nuclear chain reaction was reportedly first hypothesized by Hungarian scientist Leó Szilárd on September 12, 1933. Szilárd that morning had been reading in a London paper of an experiment in which protons f ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Resonance Escape Probability
In nuclear physics, resonance escape probability p is the probability that a neutron will slow down from fission energy to thermal energies without being captured by a nuclear resonance. A resonance absorption of a neutron in a nucleus does not produce nuclear fission. The probability of resonance absorption is called the ''resonance factor'' \psi, and the sum of the two factors is p + \psi = 1. Generally, the higher the neutron energy, the lower the probability of absorption, but for some energies, called ''resonance energies'', the resonance factor is very high. These energies depend on the properties of heavy nuclei. Resonance escape probability is highly determined by the heterogeneous geometry of a reactor, because fast neutrons resulting from fission can leave the fuel and slow to thermal energies in a moderator, skipping over resonance energies before reentering the fuel. Resonance escape probability appears in the four factor formula and the six factor formula. To comput ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Uranium-235
Uranium-235 (235U or U-235) is an isotope of uranium making up about 0.72% of natural uranium. Unlike the predominant isotope uranium-238, it is fissile, i.e., it can sustain a nuclear chain reaction. It is the only fissile isotope that exists in nature as a primordial nuclide. Uranium-235 has a half-life of 703.8 million years. It was discovered in 1935 by Arthur Jeffrey Dempster. Its fission cross section for slow thermal neutrons is about 584.3±1 barns. For fast neutrons it is on the order of 1 barn. Most but not all neutron absorptions result in fission; a minority result in neutron capture forming uranium-236. Natural decay chain :\begin \ce \begin \ce \\ \ce \end \ce \\ \ce \begin \ce \\ \ce \end \ce \end Fission properties The fission of one atom of uranium-235 releases () inside the reactor. That corresponds to 19.54 TJ/ mol, or 83.14 TJ/kg. [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Nuclide
A nuclide (or nucleide, from nucleus, also known as nuclear species) is a class of atoms characterized by their number of protons, ''Z'', their number of neutrons, ''N'', and their nuclear energy state. The word ''nuclide'' was coined by Truman P. Kohman in 1947. Kohman defined ''nuclide'' as a "species of atom characterized by the constitution of its nucleus" containing a certain number of neutrons and protons. The term thus originally focused on the nucleus. Nuclides vs isotopes A nuclide is a species of an atom with a specific number of protons and neutrons in the nucleus, for example carbon-13 with 6 protons and 7 neutrons. The nuclide concept (referring to individual nuclear species) emphasizes nuclear properties over chemical properties, while the isotope concept (grouping all atoms of each element) emphasizes chemical over nuclear. The neutron number has large effects on nuclear properties, but its effect on chemical reactions is negligible for most elements. Even in the ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Nuclear Chain Reaction
In nuclear physics, a nuclear chain reaction occurs when one single nuclear reaction causes an average of one or more subsequent nuclear reactions, thus leading to the possibility of a self-propagating series of these reactions. The specific nuclear reaction may be the fission of heavy isotopes (e.g., uranium-235, 235U). A nuclear chain reaction releases several million times more energy per reaction than any chemical reaction. History Chemical chain reactions were first proposed by German chemist Max Bodenstein in 1913, and were reasonably well understood before nuclear chain reactions were proposed. It was understood that chemical chain reactions were responsible for exponentially increasing rates in reactions, such as produced in chemical explosions. The concept of a nuclear chain reaction was reportedly first hypothesized by Hungarian scientist Leó Szilárd on September 12, 1933. Szilárd that morning had been reading in a London paper of an experiment in which protons f ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Six Factor Formula
The six-factor formula is used in nuclear engineering to determine the multiplication of a nuclear chain reaction in a non-infinite medium. The symbols are defined as: *\nu, \nu_f and \nu_t are the average number of neutrons produced per fission in the medium (2.43 for uranium-235). *\sigma_f^F and \sigma_a^F are the microscopic fission and absorption cross sections for fuel, respectively. *\Sigma_a^F and \Sigma_a are the macroscopic absorption cross sections in fuel and in total, respectively. *N_i is the number density of atoms of a specific nuclide. *I_ is the resonance integral for absorption of a specific nuclide. **I_ = \int_^ dE' \frac \frac. *\overline is the average lethargy gain per scattering event. **Lethargy is defined as decrease in neutron energy. *u_f (fast utilization) is the probability that a fast neutron is absorbed in fuel. *P_ is the probability that a fast neutron absorption in fuel causes fission. *P_ is the probability that a thermal neutron absorption in ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Critical Mass
In nuclear engineering, a critical mass is the smallest amount of fissile material needed for a sustained nuclear chain reaction. The critical mass of a fissionable material depends upon its nuclear properties (specifically, its nuclear fission cross-section), density, shape, enrichment, purity, temperature, and surroundings. The concept is important in nuclear weapon design. Explanation of criticality When a nuclear chain reaction in a mass of fissile material is self-sustaining, the mass is said to be in a ''critical'' state in which there is no increase or decrease in power, temperature, or neutron population. A numerical measure of a critical mass is dependent on the effective neutron multiplication factor , the average number of neutrons released per fission event that go on to cause another fission event rather than being absorbed or leaving the material. When ''k'' = 1, the mass is critical, and the chain reaction is self-sustaining. A ''subcritical'' mass is a ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Nuclear Reactor
A nuclear reactor is a device used to initiate and control a fission nuclear chain reaction or nuclear fusion reactions. Nuclear reactors are used at nuclear power plants for electricity generation and in nuclear marine propulsion. Heat from nuclear fission is passed to a working fluid (water or gas), which in turn runs through steam turbines. These either drive a ship's propellers or turn electrical generators' shafts. Nuclear generated steam in principle can be used for industrial process heat or for district heating. Some reactors are used to produce isotopes for medical and industrial use, or for production of weapons-grade plutonium. , the International Atomic Energy Agency reports there are 422 nuclear power reactors and 223 nuclear research reactors in operation around the world. In the early era of nuclear reactors (1940s), a reactor was known as a nuclear pile or atomic pile (so-called because the graphite moderator blocks of the first reactor were placed into a tall pi ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Nuclear Technology
Nuclear technology is technology that involves the nuclear reactions of atomic nuclei. Among the notable nuclear technologies are nuclear reactors, nuclear medicine and nuclear weapons. It is also used, among other things, in smoke detectors and gun sights. History and scientific background Discovery The vast majority of common, natural phenomena on Earth only involve gravity and electromagnetism, and not nuclear reactions. This is because atomic nuclei are generally kept apart because they contain positive electrical charges and therefore repel each other. In 1896, Henri Becquerel was investigating phosphorescence in uranium salts when he discovered a new phenomenon which came to be called radioactivity. He, Pierre Curie and Marie Curie began investigating the phenomenon. In the process, they isolated the element radium, which is highly radioactive. They discovered that radioactive materials produce intense, penetrating rays of three distinct sorts, which they labeled al ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
