![]() ![]() There is always a competition for the fission neutrons in the multiplication environment. It is necessary to decrease the non-fission neutron absorption in the system (e.g., to withdraw control rods) to sustain the chain reaction. On the other hand, if one neutron causes less than one further fission, the number of neutrons in the multiplication system will decrease in time, and the reactor power (reaction rate) will also decrease in time. The nuclear chain reaction occurs when one single nuclear reaction causes an average of one or more subsequent nuclear reactions. Moreover, this multiplication environment ( the nuclear reactor) behaves like an exponential system, which means the power increase is not linear, but it is exponential. To stabilize such a multiplication environment, it is necessary to increase the non-fission neutron absorption in the system (e.g., to insert control rods). In that case, the number of neutrons in the multiplication system will increase in time, and the reactor power ( reaction rate) will also increase in time. Suppose one neutron causes two further fissions. The chain reaction can take place only in the proper multiplication environment and only under proper conditions. This sequence of fission events is known as the fission chain reaction, and it is important in nuclear reactor physics. The fission process may produce 2, 3, or more free neutrons that are capable of inducing further fissions and so on. A nuclear fission chain reaction is a self-propagating sequence of fission reactions in which neutrons released in fission produce additional fission in at least one other nucleus.
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