The diagram illustrates a chain reaction inside a nuclear reactor. For a controlled, sustained chain reaction in a nuclear reactor, on average how many neut...
Question 1 Report
The diagram illustrates a chain reaction inside a nuclear reactor.
For a controlled, sustained chain reaction in a nuclear reactor, on average how many neutrons from each fission event must go on to cause another fission?
Answer Details
When a uranium-235 nucleus undergoes fission, it releases two or three neutrons. In a controlled chain reaction (as needed in a nuclear power station), exactly one neutron from each fission event must, on average, go on to cause another fission.
If more than one neutron per fission causes further fission, the reaction rate increases exponentially - this is an uncontrolled chain reaction, which would lead to a dangerous meltdown or explosion. If fewer than one neutron per fission causes another fission, the reaction gradually dies out and power generation stops.
Control rods (made of materials like boron or cadmium that absorb neutrons) are inserted into or withdrawn from the reactor core to maintain this balance, ensuring exactly one neutron per fission sustains the reaction at a constant rate.
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