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TSL snowshoes now in stock!! The chain reaction lets you reward workers as the company prospers, instead of seeking to prosper on the backs of workers. Flipping the means and the ends does not work. Reducing costs as the result of process improvement is effective management.
Your email address will not be published. Save my name, email, and website Chain Reaction this browser for the next time I comment. Skip to content. The sum of the rest masses of the fission fragments and ejected neutrons is less than the sum of the rest masses of the original atom and incident neutron of course the fission fragments are not at rest. Due to the extremely large value of the speed of lightca small decrease in mass is associated with a tremendous release of active energy for example, the kinetic energy of the fission fragments.
This energy in the form of radiation and heat carries the missing mass, when it leaves the reaction system total mass, like total energy, is always conserved. While typical chemical reactions release energies on the order of a few eVs e. Two typical fission reactions are shown below with average values of energy released and number of neutrons ejected:. Note that these equations are for fissions caused by slow-moving thermal neutrons.
The average energy released and number of neutrons ejected is a function of the incident neutron speed. The prompt neutron lifetimelis the average time between the emission of neutrons and either their absorption in the system or their escape from the system. The term lifetime is used because the emission of a neutron is often considered its "birth," and the subsequent absorption is considered its "death".
The average also referred to as the adjoint unweighted prompt neutron lifetime takes into account all prompt neutrons regardless of their importance in the reactor core; the effective prompt neutron lifetime referred to as the adjoint weighted over space, energy, and angle refers to a neutron with average importance.
The two times are related by the following formula:. The six factor formula effective neutron multiplication factor, kis the average number of neutrons from one fission that cause another fission. The remaining neutrons either are absorbed in non-fission reactions or leave the system without being absorbed.
The value of k determines how a nuclear chain reaction proceeds:. InHour from inverse of an hoursometimes abbreviated ih or inhr is a unit of reactivity of a nuclear reactor. In a nuclear reactor, k will actually oscillate from slightly less than 1 to slightly more than 1, due primarily to thermal effects Chain Reaction more power is produced, the fuel rods warm and thus expand, lowering their capture ratio, and thus driving k lower.
This leaves the average value of k at exactly 1. Delayed neutrons play an important role in the timing of these oscillations.
In an infinite medium, the multiplication factor may be described by the four factor formula ; in a non-infinite medium, the multiplication factor may be described by the six factor formula. Not all neutrons are emitted as a direct product of fission; some are instead due to the radioactive decay of some of the fission fragments. The neutrons that occur directly from fission are called "prompt neutrons," and the ones that are a result of radioactive decay of fission fragments are called "delayed neutrons".
The delayed neutrons allow a nuclear reactor to respond several orders of magnitude more slowly than just prompt neutrons would alone. It is in this region that all nuclear power reactors operate. The change in k needed to go from critical to prompt critical is defined as a dollar. For a given mass of fissile material the value of k can be increased by increasing the density.
Since the probability per distance travelled for a neutron to collide with a nucleus is proportional to the material density, increasing the density of a fissile material can increase k. This concept is utilized in the implosion method for nuclear weapons. In these devices, the nuclear chain reaction begins after increasing the density of the fissile material with a conventional explosive.
In the gun-type fission weapontwo subcritical pieces of fuel are rapidly brought together. The value of k for a combination of two masses is always greater than that of its components. The magnitude of the difference depends on distance, as well as the physical orientation. The value of k can also be increased by using a neutron reflector surrounding the fissile material. Once the mass of fuel is prompt supercritical, the power increases exponentially. However, the exponential power increase cannot continue for long since k decreases when the amount of fission material that is left decreases i.
Also, the geometry and density are Chain Reaction to change during detonation since the remaining fission material is torn apart from the explosion. Detonation of a nuclear weapon involves bringing fissile material into its optimal supercritical state very rapidly. During part of this process, the assembly is supercritical, but not yet in an optimal state for a chain reaction.
Free neutrons, in particular from spontaneous fissionscan cause the device to undergo a preliminary chain reaction that destroys the fissile material before it is ready to produce a large explosion, which is known as predetonation.
To keep the probability of predetonation low, the duration of the non-optimal assembly period is minimized and fissile and other materials are used that have low spontaneous fission rates. In fact, the combination of materials has to be such that it is unlikely that there is even a single spontaneous fission during the period of supercritical assembly. In particular, the gun method cannot be used with plutonium see nuclear weapon design.
Chain reactions naturally give rise to reaction rates that grow or shrink exponentiallywhereas a nuclear power reactor needs to be able to hold the reaction rate reasonably constant. To maintain this Chain Reaction, the chain reaction criticality must have a slow enough time scale to permit intervention by additional effects e. Consequently, all nuclear power reactors even fast-neutron reactors rely on delayed neutrons for their criticality.
An operating nuclear power reactor fluctuates between being slightly subcritical and slightly delayed-supercritical, but must always remain below prompt-critical. It is impossible for a nuclear power plant to undergo a nuclear chain reaction that results in an explosion of power comparable with a nuclear weapon, but even low-powered explosions due to uncontrolled chain reactions that would be considered "fizzles" in a bomb may still cause considerable damage and meltdown in a reactor.
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