Figure 2 shows a simplification of the fission chain reaction. If every fission event leads to exactly one more fission event, the nuclear chain reaction is said to be critical. Contrary to what one may expect, difficulties arise in getting enough neutrons to go on and make a sustained nuclear reaction, rather than having too many nuclear reactions. Careful engineering must go into having those neutrons go on to create more fission events. When 235U undergoes fission, it gives off, on average, ~2.5 neutrons per fission event. The most convenient nuclear species to use for nuclear chain reactions is a fissile isotope of uranium, 235U. In order to sustain a nuclear chain reaction, every fission event must lead to exactly one more fission event. When they do occur, there is substantially more energy available, leading to nuclear having a much higher energy density for its fuel. Nuclear chain reactions require an abundance of careful planning. Nuclear chain reactions require careful engineering and as far as we know, a natural nuclear chain reaction has only occurred once. For example, fire is a chemical chain reaction. This means that chemical chain reactions occur much more easily than nuclear reactions. Nuclear reactions release roughly one million times as much energy as chemical reactions. While these similarities exist, there are some important differences as well. Released energy is often output as thermal energy, becoming heat that can be harnessed by heat engines to do useful work like make electricity.Energy is often released as the reactions occur.That the chain reactions are controlled (starting, speeding up, slowing down and stopping) by adding or removing chemical or nuclear species in that chain. A common fission reaction produces barium- (141) and krypton- (92).The chain reaction stops when the species are removed or are used up. That the reactions are sustained when chemical or nuclear species available to react.In the reaction we just saw, the total mass on the right side of the. Many chemical reactions are also chain reactions, with many similarities to nuclear chain reactions. The energy released by each fission can be found by calculating the masses of the atoms on each side of the equation. Nuclear reactions involve different flavours of nuclei (called nuclear species) interacting. Nuclear chain reactions are essential to the operation of nuclear power plants.Ĭhemical reactions involve different chemical species recombining. It is these excess neutrons that can go on to cause more fission events to occur, hence the name chain reaction. These chain reactions are almost always a series of fission events, which give off excess neutrons. Unlike in the figure, on average one new fission event happens as a result of these released neutrons.Ī nuclear chain reaction occurs when the output of one nuclear reaction causes more nuclear reactions to occur. A neutron strikes a 235U nucleus and causes a fission event.
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