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Subcritical
In the operation of a nuclear reactor, criticality or critical state is the state in which a nuclear chain reaction is self-sustaining but not growing. Subcriticality or subcritical state is the state in which a nuclear chain reaction is not self-sustaining. Supercriticality or supercritical state is the state in which a nuclear chain reaction is self-sustaining and growing. Sometimes, less preferably, criticality takes a wider definition, and refers to the any state in which a nuclear chain reaction is self-sustaining, no matter growing or not (encompassing criticality in strict definition and supercriticality). In terms of reactivity, reactivity is 0 in criticality, less than 0 in subcriticality, greater than 0 in supercriticality. In terms of effective neutron multiplication factor (), is 1 in criticality, less than 1 in subcriticality, greater than 1 in supercriticality. Applications Criticality is the normal operating condition of a nuclear reactor, in which nuclear fuel ... [...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 or "positive feedback loop" 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 ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Nuclear Reactor
A nuclear reactor is a device used to initiate and control a Nuclear fission, fission nuclear chain reaction. They are used for Nuclear power, commercial electricity, nuclear marine propulsion, marine propulsion, Weapons-grade plutonium, weapons production and Research reactor, research. Fissile material, Fissile nuclei (primarily uranium-235 or plutonium-239) absorb single neutron, neutrons and split, releasing energy and multiple neutrons, which can induce further fission. Reactors stabilize this, regulating Neutron absorber, neutron absorbers and neutron moderator, moderators in the core. Fuel efficiency is exceptionally high; Enriched uranium#Low-enriched uranium (LEU), low-enriched uranium is 120,000 times more energy dense than coal. Heat from nuclear fission is passed to a working fluid Nuclear reactor#By coolant, coolant. In commercial reactors, this drives Turbine, turbines and electrical generator shafts. Some reactors are used for district heating, and isotopes, isoto ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Dollar (reactivity)
A dollar is a unit of reactivity for a nuclear reactor, calibrated to the interval between the conditions of criticality and prompt criticality. Prompt criticality will result in an extremely rapid power rise, with the resultant destruction of the reactor, unless it is specifically designed to tolerate the condition. A cent is of a dollar. In nuclear reactor physics discussions, the symbols are often appended to the end of the numerical value of reactivity, such as 3.48$ or 21 ¢. Reactivity (denoted ρ or ΔK/K) is related to the effective neutron multiplication factor (''keff''), the average number of all neutrons from one fission that cause another fission. ρ = But in nuclear physics, it useful to talk about the reactivity contributed by just the prompt neutrons. This is the reactivity in dollars or cents. Reactivity in its most general sense would not be measured in dollars or cents. This is because keff measures the total value of reactivity, a summation of the react ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Prompt Criticality
In nuclear engineering, prompt criticality is the criticality (the state in which a nuclear chain reaction is self-sustaining) that is achieved with prompt neutrons alone (without the efforts of delayed neutrons). As a result, prompt supercriticality causes a much more rapid growth in the rate of energy release than other forms of criticality. Nuclear weapons are based on prompt criticality, while nuclear reactors rely on delayed neutrons or external neutrons to achieve criticality. Criticality An assembly is critical if each fission event causes, on average, exactly one additional such event in a continual chain. Such a chain is a self-sustaining fission chain reaction. When a uranium-235 (U-235) atom undergoes nuclear fission, it typically releases between one and seven neutrons (with an average of 2.4). In this situation, an assembly is critical if every released neutron has a 1/2.4 = 0.42 = 42 % probability of causing another fission event as opposed to either bei ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Prompt Critical
In nuclear engineering, prompt criticality is the criticality (the state in which a nuclear chain reaction is self-sustaining) that is achieved with prompt neutrons alone (without the efforts of delayed neutrons). As a result, prompt supercriticality causes a much more rapid growth in the rate of energy release than other forms of criticality. Nuclear weapons are based on prompt criticality, while nuclear reactors rely on delayed neutrons or external neutrons to achieve criticality. Criticality An assembly is critical if each fission event causes, on average, exactly one additional such event in a continual chain. Such a chain is a self-sustaining fission chain reaction. When a uranium-235 (U-235) atom undergoes nuclear fission, it typically releases between one and seven neutrons (with an average of 2.4). In this situation, an assembly is critical if every released neutron has a 1/2.4 = 0.42 = 42 % probability of causing another fission event as opposed to either being a ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Chernobyl Disaster
On 26 April 1986, the no. 4 reactor of the Chernobyl Nuclear Power Plant, located near Pripyat, Ukrainian Soviet Socialist Republic, Ukrainian SSR, Soviet Union (now Ukraine), exploded. With dozens of direct casualties, it is one of only two nuclear energy accidents rated at the maximum severity on the International Nuclear Event Scale, the other being the 2011 Fukushima nuclear accident. The response involved more than Chernobyl liquidators, 500,000 personnel and cost an estimated 18billion Soviet ruble, rubles (about $84.5billion USD in 2025). It remains the worst nuclear disaster and the List of disasters by cost, most expensive disaster in history, with an estimated cost of US$700 billion. The disaster occurred while running a test to simulate cooling the reactor during an accident in blackout conditions. The operators carried out the test despite an accidental drop in reactor power, and due to a design issue, attempting to shut down the reactor in those conditio ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Nuclear Physics
Nuclear physics is the field of physics that studies atomic nuclei and their constituents and interactions, in addition to the study of other forms of nuclear matter. Nuclear physics should not be confused with atomic physics, which studies the atom as a whole, including its electrons. Discoveries in nuclear physics have led to applications in many fields such as nuclear power, nuclear weapons, nuclear medicine and magnetic resonance imaging, industrial and agricultural isotopes, ion implantation in materials engineering, and radiocarbon dating in geology and archaeology. Such applications are studied in the field of nuclear engineering. Particle physics evolved out of nuclear physics and the two fields are typically taught in close association. Nuclear astrophysics, the application of nuclear physics to astrophysics, is crucial in explaining the inner workings of stars and the origin of the chemical elements. History The history of nuclear physics as a discipline ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Nuclear Chemistry
Nuclear chemistry is the sub-field of chemistry dealing with radioactivity, nuclear processes, and transformations in the nuclei of atoms, such as nuclear transmutation and nuclear properties. It is the chemistry of radioactive elements such as the actinides, radium and radon together with the chemistry associated with equipment (such as nuclear reactors) which are designed to perform nuclear processes. This includes the corrosion of surfaces and the behavior under conditions of both normal and abnormal operation (such as during an accident). An important area is the behavior of objects and materials after being placed into a nuclear waste storage or disposal site. It includes the study of the chemical effects resulting from the absorption of radiation within living animals, plants, and other materials. The radiation chemistry controls much of radiation biology as radiation has an effect on living things at the molecular scale. To explain it another way, the radiation alters th ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Critical Mass
In nuclear engineering, critical mass is the minimum mass of the fissile material needed for a sustained nuclear chain reaction in a particular setup. 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. It is an important parameter of a nuclear reactor core or nuclear weapon. The concept is important in nuclear weapon design. Critical size is the minimum size of the fissile material needed for a sustained nuclear chain reaction in a particular setup. If the size of the reactor core is less than a certain minimum, too many fission neutrons escape through its surface and the chain reaction is not sustained. Criticality When a nuclear chain reaction in a mass of fissile material is self-sustaining but not growing, the mass is said to be in a critical state, in which there is no increase or decrease in power, temperature, or ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Criticality Accident
A criticality accident is an accidental uncontrolled nuclear fission chain reaction. It is sometimes referred to as a critical excursion, critical power excursion, divergent chain reaction, or simply critical. Any such event involves the unintended accumulation or arrangement of a critical mass of fissile material, for example enriched uranium or plutonium. Criticality accidents can release potentially fatal radiation doses if they occur in an unprotected environment. Under normal circumstances, a critical or supercritical fission reaction (one that is self-sustaining in power or increasing in power) should only occur inside a safely shielded location, such as a reactor core or a suitable test environment. A criticality accident occurs if the same reaction is achieved unintentionally, for example in an unsafe environment or during reactor maintenance. Though dangerous and frequently lethal to humans within the immediate area, the critical mass formed would not be capable of ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
TRIGA
TRIGA (Training, Research, Isotopes, General Atomics) is a class of nuclear research reactor designed and manufactured by General Atomics. The design team for TRIGA, which included Edward Teller, was led by the physicist Freeman Dyson. Design TRIGA is a swimming pool reactor that can be installed without a containment building, and is designed for research and testing use by scientific institutions and universities for purposes such as undergraduate and graduate education, private commercial research, non-destructive testing and isotope production. The TRIGA reactor uses uranium zirconium hydride (UZrH) fuel, which has a large, prompt negative fuel temperature coefficient of reactivity, meaning that as the temperature of the core increases, the reactivity rapidly decreases. Because of this unique feature, it has been safely pulsed at a power of up to 22,000 megawatts. The hydrogen in the fuel is bound in the uranium zirconium hydride crystal structure with a vibrational energ ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
