Reactor Theory (Neutron Characteristics)DOE-HDBK-1019/1-93PROMPT AND DELAYED NEUTRONSRev. 0Page 29NP-02PROMPT AND DELAYED NEUTRONSNot all neutrons are released at the same time following fission. Most neutronsare released virtually instantaneously and are called prompt neutrons. A verysmall fraction of neutrons are released after the decay of fission products and arecalled delayed neutrons. Although delayed neutrons are a very small fraction ofthe total number of neutrons, they play an extremely important role in the controlof the reactor.EO 3.1STATE the origin of prompt neutrons and delayed neutrons.EO 3.2STATE the approximate fraction of neutrons that are born asdelayed neutrons from the fission of the following nuclear fuels:a.Uranium-235b.Plutonium-239EO 3.3EXPLAIN the mechanism for production of delayed neutrons.EO 3.4EXPLAIN prompt and delayed neutron generation times.EO 3.5Given prompt and delayed neutron generation times anddelayed neutron fraction, CALCULATE the average generationtime.EO 3.6EXPLAIN the effect of delayed neutrons on reactor control.NeutronClassificationThe great majority (over 99%) of the neutrons produced in fission are released within about 10-13seconds of the actual fission event. These are called prompt neutrons. A small portion of fissionneutrons are delayed neutrons, which are produced for some time after the fission process hastaken place. The delayed neutrons are emitted immediately following the first beta decay of afission fragment known as a delayed neutron precursor. An example of a delayed neutronprecursor is bromine-87, shown below.
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