Physics
Nuclear Reactors
Nuclear reactors are devices that initiate and control nuclear reactions to generate electricity or produce materials for medical and industrial use. They use controlled nuclear fission to release energy, which is then converted into heat and used to produce steam to drive turbines. The main types of nuclear reactors include pressurized water reactors, boiling water reactors, and advanced gas-cooled reactors.
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10 Key excerpts on "Nuclear Reactors"
No longer available |Learn more- (Author)
- 2014(Publication Date)
- College Publishing House(Publisher)
(There are several early counter-examples, such as the Hanford N reactor, now decommissioned). Power reactors generally convert the kinetic energy of fission products into heat, which is used to heat a working fluid and drive a heat engine that generates mechanical or electrical power. The working fluid is usually water with a steam turbine, but some designs use other materials such as gaseous helium. Research reactors produce neutrons that are used in various ways, with the heat of fission being treated as an unavoidable waste product. Breeder reactors are a specialized form of research reactor, with the caveat that the sample being irradiated is usually the fuel itself, a mixture of 238 U and 235 U. ________________________ WORLD TECHNOLOGIES ________________________ Nuclear Power The Ikata Nuclear Power Plant, a pressurized water reactor that cools by secondary coolant exchange with the ocean. ________________________ WORLD TECHNOLOGIES ________________________ The Susquehanna Steam Electric Station, a boiling water reactor. The reactors are located inside the rectangular containment buildings towards the front of the cooling towers. ________________________ WORLD TECHNOLOGIES ________________________ Three nuclear powered ships, (top to bottom) nuclear cruisers USS Bainbridge and USS Long Beach with USS Enterprise the first nuclear powered aircraft carrier in 1964. Crew members are spelling out Einstein's mass-energy equivalence formula E = mc 2 on the flight deck. Nuclear power is produced by controlled (i.e., non-explosive) nuclear reactions. Commercial and utility plants currently use nuclear fission reactions to heat water to produce steam, which is then used to generate electricity. In 2009, 13–14% of the world's electricity came from nuclear power. Also, more than 150 naval vessels using nuclear propulsion have been built.
eBook - ePub- Ritesh Kohale, Sanjay J. Dhoble, Vibha Chopra(Authors)
- 2009(Publication Date)
- Bentham Science Publishers(Publisher)
i.e., nuclear fission, to generate power. The energy eliminated away in Nuclear Reactors may be used for the constructive cause and the production of electricity. In 1939, during their experiments on fission reactions, scientists Hahn and Strassman came across the rare-earth elements in uranium after irradiating it with neutrons. O. Frisch and L. Meitner afterward acknowledged this advent as being due to neutron-induced fission of uranium. This finding was scrutinized, monitored and modified with a few more suggestions. Considering that, on December 2, 1942, Enrico Fermi aimed a chain reaction in a device that consisted of a periodic chimney of herbal uranium separated by graphite moderators. Therefore, Fermi confirmed experimentally the idea of the unique length of the chimney to confirm a sequence reaction. This was performed with a very insignificant collective power of the device, ~ 1W. Contemporary electricity reactors accomplish powers of ~ 3 GW. The rise in electricity in fission reactions was in distinction with managed fusion structures.Steam generated in Nuclear Reactors finds application in commercial heating or industrial purposes. A few reactors find their application in the production of isotopes for industrial and scientific usage or weapons-grade plutonium. As perthe early 2019 records of IAEA [1 ], there are 226 nuclear studies reactors and 454 nuclear power reactors being used worldwide [2 , 3 ].1.1. Principle of Operation
The fundamental Nuclear Reactors exchange the energy generated by controlled nuclear fission into thermal energy for further conversion to electrical or mechanical systems similar to thermal power stations that produce electricity from burning fossil fuels.1.2. Fission
Nuclear fission proceeds when a huge fissile nucleus with uranium (235U) or plutonium (239Pu) captivates a neutron. A bulky nucleus splits into two or extra lighter nuclei during a fission reaction emitting gamma radiation, kinetic energy and free neutrons. The ratio of these neutrons may get consumed by other fissile atoms, which results in the acceleration of additional fission reactions, due to which additional neutrons are released, termed as a nuclear chain reaction. The nucleus of a uranium (235 U) atom absorbs a neutron and liberates free neutrons and fast-transferring lighter elements called fission products. However, reactors and nuclear weapons both proceed through a nuclear chain reaction; the rate of reactions in a reactor is more than in a bomb. An illustration of an induced nuclear fission occurrence is shown in Fig. (Fig. (6.1)) An illustration of an induced nuclear fission event. Courtesy: “Wikimedia Commons.” Originally created by Fast fission in Illustrator. Source: https://commons.wikimedia.org/w/index.php?curid=486924 .).6.1To regulate such a nuclear chain reaction, control rods encompassing neutron moderators and neutron contagions can modify the percentage of neutrons that will cause additional fission [4 ]. If monitoring or instrumentation suffers from unsafe conditions, Nuclear Reactors normally have spontaneous and physical systems to close the fission reaction [5
No longer available |Learn more- (Author)
- 2014(Publication Date)
- Academic Studio(Publisher)
(There are several early counter-examples, such as the Hanford N reactor, now decommissioned). Power reactors generally convert the kinetic energy of fission products into heat, which is used to heat a working fluid and drive a heat engine that generates mechanical or electrical power. The working fluid is usually water with a steam turbine, but some designs use other materials such as gaseous helium. Research reactors produce neutrons that are used in various ways, with the heat of fission being treated as an unavoidable waste product. Breeder reactors are a specialized form of research reactor, with the caveat that the sample being irradiated is usually the fuel itself, a mixture of 238 U and 235 U. ________________________ WORLD TECHNOLOGIES ________________________ Nuclear Power The Ikata Nuclear Power Plant, a pressurized water reactor that cools by secondary coo-lant exchange with the ocean. ________________________ WORLD TECHNOLOGIES ________________________ The Susquehanna Steam Electric Station, a boiling water reactor. The reactors are located inside the rectangular containment buildings towards the front of the cooling towers. ________________________ WORLD TECHNOLOGIES ________________________ Three nuclear powered ships, (top to bottom) nuclear cruisers USS Bainbridge and USS Long Beach with USS Enterprise the first nuclear powered aircraft carrier in 1964. Crew members are spelling out Einstein's mass-energy equivalence formula E = mc 2 on the flight deck. Nuclear power is produced by controlled (i.e., non-explosive) nuclear reactions. Com-mercial and utility plants currently use nuclear fission reactions to heat water to produce steam, which is then used to generate electricity. In 2009, 13–14% of the world's electricity came from nuclear power. Also, more than 150 naval vessels using nuclear propulsion have been built.
No longer available |Learn more- (Author)
- 2014(Publication Date)
- Academic Studio(Publisher)
____________________ WORLD TECHNOLOGIES ____________________ Chapter- 2 Nuclear Reactor Technology Core of CROCUS, a small nuclear reactor used for research at the EPFL in Switzerland. A nuclear reactor is a device to initiate and control a sustained nuclear chain reaction. The most common use of Nuclear Reactors is for the generation of electrical power and for the power in some ships. This is usually accomplished by methods that involve using heat from the nuclear reaction to power steam turbines. There are also other less common uses as discussed below. ____________________ WORLD TECHNOLOGIES ____________________ How it works An induced nuclear fission event. A neutron is absorbed by the nucleus of a uranium-235 atom, which in turn splits into fast-moving lighter elements (fission products) and free neutrons. Though both reactors and nuclear weapons rely on nuclear chain reactions, the rate of reactions in a reactor is much slower than in a bomb. Just as conventional power stations generate electricity by harnessing the thermal energy released from burning fossil fuels, Nuclear Reactors convert the thermal energy released from nuclear fission. Fission When a large fissile atomic nucleus such as uranium-235 or plutonium-239 absorbs a neutron, it may undergo nuclear fission. The heavy nucleus splits into two or more lighter nuclei, releasing kinetic energy, gamma radiation and free neutrons; collectively known as fission products. A portion of these neutrons may later be absorbed by other fissile atoms and trigger further fission events, which release more neutrons, and so on. This is known as a nuclear chain reaction. ____________________ WORLD TECHNOLOGIES ____________________ The reaction can be controlled by using neutron poisons, which absorb excess neutrons, and neutron moderators which reduces the velocity of fast neutrons, thereby turning them into thermal neutrons, which are more likely to be absorbed by other nuclei.
eBook - PDFElectrons, Neutrons and Protons in Engineering
A Study of Engineering Materials and Processes Whose Characteristics May Be Explained by Considering the Behavior of Small Particles When Grouped Into Systems Such as Nuclei, Atoms, Gases, and Crystals
- J. R. Eaton(Author)
- 2013(Publication Date)
- Pergamon(Publisher)
CHAPTER 22 Nuclear Reactors THE possibility of the production of useful energy from the fission of uranium and other materials was made evident from the discussion of the previous chap-ter. To utilize this energy it is necessary to construct a machine in which the fission process may occur at a rate that is under control by suitable means, while the heat released is extracted from the fissioning material and passed on to other equipment for which it is needed. Although the principal commercial interest in the fission process is in the heat released, many scientific and indus-trial uses have been found for the radiation released at the time of fission and by the fission products. As these rays are very harmful to living tissue and are damaging to some inert materials, adequate shielding must be provided. Al-though the ultimate use of reactors will be, primarily, the production of power, most of those built up to the present time have been for research studies pertaining to the problems of controlled fission. As the problems of fission are better understood, reactors for power production purposes are increasing in number and size. Since industrial growth is very much influenced by the availability of power, it is apparent that the development of Nuclear Reactors may profoundly in-fluence economic life throughout the world. Reactor development will be of particular significance in those regions which have limited supplies of fossil fuels and water power, and which consequently are dependent on the long-distance transportation of fuel from other parts of the world. 22.1. A CRITICAL ASSEMBLY The fission process described in considerable detail in the previous chapter is in itself quite simple, and is reviewed in Fig. 22.1. In (a), a neutron approaches the nucleus of a uranium-235 atom. In (b) the neutron has joined the nucleus resulting in a U-236 nucleus in the excited state. This nucleus is unstable and, in many instances, breaks into several pieces as shown in (c).
eBook - PDF- G R Jones(Author)
- 2013(Publication Date)
- Newnes(Publisher)
When a self-sustaining chain reaction has been achieved the reactor is said to be 'critical'. Departure from criticality is measured by the reactivity of a reactor. Positive or negative reactivities correspond to divergent (more intense) and convergent (dying away) chain reactions, respectively. Most of the energy released in the fission process appears initially as kinetic energy of the fission fragments, and this is rapidly converted, by collision, into thermal energy: some of this energy is deposited in the moderator rather than in the fuel. Some 8% of the energy, however, is associated with the radioactive decay of the fission fragments and does not appear immediately, but with a delay determined by the half-lives of the associated radioactive processes, which range from a fraction of a second to thousands of years. This means that when a nuclear power reactor is 'shut down' (i.e. the fission chain reaction is stopped), the reactor will continue to gener-ate significant amounts of thermal energy from the radioactive decay of the fission fragments. This residual energy, which for a 1000 megawatt-electric (MW(e)) reactor would be of the order of 240 megawatt-thermal (MW(th)) immediately after shut-down, is known as decay heat. If the shut-down followed a prolonged period at full power, the decay heat would still be 40 MW after 1 day. In the design of reactor plant, provision has to be made for the safe removal of this decay heat under both normal and accident conditions. 19.2.4 Nuclear fuel Nuclear fuel provides a highly compact source of energy; the complete fission of 1 g of 235 U would release approximately 1 MW.day of thermal energy, so that a typical 1000 MW(e) commercial nuclear reactor operating at one-third thermal efficiency would consume only 3 kg of 235 U per day.
eBook - PDF- H Nifenecker, O Meplan, S David(Authors)
- 2003(Publication Date)
- CRC Press(Publisher)
Chapter 3 Elementary reactor theory Before describing the physics specific to hybrid reactors, it is appropriate to review the basics of nuclear reactor theory. We first recall some elements of neutron physics which apply to both critical and subcritical systems. 3.1 Interaction of neutrons with nuclei 3.1.1 Elementary processes In a nuclear reactor neutrons are produced, slowed down and captured. Furthermore, energy is produced by the fission process and, to a lesser extent, by radioactive decay. The most important nuclear characteristics of a nucleus present in a reactor are therefore: . The fission cross section ' F . . The capture or (n, Þ cross section ' c . . The number of neutrons emitted following the capture of a neutron by a fissile nucleus. This quantity is crucial to the possibility of establishing a chain reaction. It can be split into two factors: the probability that an absorption leads to fission, ' F = ð ' F þ ' c Þ ¼ 1 = ð 1 þ Þ where ¼ ' c =' F ; and the mean number of neutrons # emitted per fission. Thus, ¼ #= ð 1 þ Þ . . The scattering cross sections, either elastic ' s or inelastic ' in , which control the propagation of neutrons in the medium. . The atomic mass of the nucleus A which controls the amount of slowing down of the neutron following an elastic scattering. After scattering at an angle in the centre of mass, the final laboratory energy of a neutron, whose initial energy is E 0 , is given by E f ¼ E 0 2 1 þ A ÿ 1 A þ 1 2 þ 1 ÿ A ÿ 1 A þ 1 2 cos ð Þ : ð 3 : 1 Þ The absorption cross-section ' a ¼ ' c þ ' F . 39 If the scattering in the centre of mass is isotropic it follows that all final energies between E 0 and E 0 f½ð A ÿ 1 Þ = ð A þ 1 Þ 2 g are equiprobable.
eBook - PDFRadiochemistry and Nuclear Chemistry
2nd Edition of Nuclear Chemistry, Theory and Applications
- Gregory Choppin, Jan-Olov Liljenzin, Jan Rydberg, JAN RYDBERG(Authors)
- 2016(Publication Date)
- Butterworth-Heinemann(Publisher)
Since a few samples enriched in 235U also have been found, it is believed that in some places in Oklo breeding conditions may temporarily have existed, cf. § 22 . 12 . It has been calculated that many uranium rich ore deposits 2 — 3 X 10 9 y ago must have been supercritical in the presence of moderating water. Therefore natural nuclear chain reactions may have had an important local influence on the early environment of earth. 19.11. Reactor concepts Nuclear Reactors are designed for production of heat, mechanical and electric power, radioactive nuclides, weapons material, research in nuclear physics and chemistry, etc. The design depends on the purposes, e.g. in the case of electric power production the design is chosen to provide the cheapest electricity taking long term reliability in consideration. This may be modified by the availability and economy of national resources such as raw material, manpower and skill, safety reasons, etc. Also the risk for proliferation of reactor materials for weapons use may influence the choice of reactor type. Many dozens of varying reactor concepts have been formulated, so we must limit the discussion in this chapter to a summary of the main variables, the most common research and power reactors and a novel fast reactor concept. We have already mentioned three basic principles for reactor design: the neutron energy (thermal or fast reactors), the core configuration (homogeneous or heterogeneous aggregation of fuel and coolant), and the fuel utilization (burner, converter or breeder). In the homogeneous reactor the core can be molten metal, molten salt, an aqueous or an organic solution. In heterogeneous reactors the fuel is mostly rods filled with metal oxide. The fuel material can be almost any combination of fissile and fertile atoms in a mixture or separated as in the core (fissile) and blanket (fertile) concept (Ch. 20). The choice of moderator is great: H 2 0 , D 2 0 , Be, graphite, or organic liquid.
eBook - PDF- Richard Dunlap(Author)
- 2018(Publication Date)
- Cengage Learning EMEA(Publisher)
Once their energy has been reduced to a very low value, they are allowed to be incident on a collection of uranium nuclei, where they are almost certain to induce fission in a 235 U nucleus. This procedure ensures that the neutron will interact with a 235 U nucleus and induce fission rather than being lost by undergoing a reaction (as in reaction 2) with either 235 U or 238 U. This approach can be implemented by making the pieces of uranium (the fuel elements) in the reactor fairly small (i.e., much less than the critical mass). This means that when a neutron is emitted from a fission event, it quickly exits the fuel element process 3) and travels through a substance (not containing uranium) known as a moderator that reduces the energy of the neutron. The moderator low-ers the energy of the neutron until the level is comparable to the thermal energy of the atoms in the moderator, around 0.03 eV. The neutrons are then referred to as thermal neutrons , and the reactor that operates on this principle is referred to as a thermal reactor , or thermal neutron reactor. When the neutrons enter another fuel element, they quickly induce fission in 235 U nuclei. The flow of neutrons between fuel elements is controlled by control rods made of a material (often cadmium or boron) that easily absorbs neutrons (without undergoing any undesirable nuclear reactions). The general design of a nuclear reactor core is shown in Figure 6.5. Figure 6.5: Design of a thermal nuclear reactor core showing the fuel elements, the control rods, and the moderator. Based on from R.A. Dunlap, An Introduction to the Physics of Nuclei and Particles, Brooks-Cole, Belmont (2004) Control rod drive mechanism Reactor vessel Fuel assembly Moderator Control rod Copyright 2019 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s).
eBook - ePub- Gregory Choppin, Jan Rydberg, Jan-Olov Liljenzin, JAN RYDBERG(Authors)
- 2001(Publication Date)
- Butterworth-Heinemann(Publisher)
Chapter 22 .The broad functions of the safety systems are common to most reactors. In the event of an abnormal condition they should shut down the reactor, ensure a sufficient supply of coolant for the fuel, and contain any fission products which might escape from the fuel elements. Such safety features can be active (requiring some action from a control system, involving mechanical devices, and relying on an external power source in order to operate) or passive (built-in physical fail-safe features whose operation is not dependent on any control system, mechanical device or external power source).Active safety systems are normally used and must be designed with a high degree of redundance (duplication) and diversity (difference in principle), so that if one safety systems fails another shall function. Several redundant active safety systems are required which are logically and physically separated from one another, and from the reactor process systems, as much as possible. They are also often based on different principles in order to reduce the probability of common-mode failures. This confers considerable immunity against events such as external explosions or internal fires. Each safety system alone should be capable of protecting the reactor core and building from further damage.Passive safety systems are less common than active ones. However, introduction of passive (inherent) safety functions into new reactor designs is much discussed within the nuclear industry. Several ideas have been developed into new design proposals. As an example, the SECURE district heating reactor, developed by ABB-Atom1 , uses a hydrostatically metastable operating condition which causes shut-down of the reactor as soon as the normal coolant flow becomes too low for safe operation or if the core generates too much heat. Figure 19.14 illustrates the operating principle. During normal operation (a in Fig. 19.14 ) temperature and pressure differences keeps the system in a hydrostatically metastable state with the hot primary coolant separated from the borated shut-down solution. Power is regulated by changing the concentration of boron in the primary coolant. If either temperature in the core increases or flow through the core decreases, the gas bubble above the core will escape and the reactor shuts itself down as cold borated water enters the primary system (b in Fig. 19.14
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