4.4 Nuclear Fission and Fusion Flashcards
what is nuclear fission?
the splitting of large, unstable nuclei to form smaller more stable nuclei (+the emission of spare neutrons).
what usually needs to happen to induce fission?
- the unstable nuclei must absorb a neutron
- spontaneous fission (where no neutron absorption occurs) is rare
give an example of a fissionable isotope.
uranium - 235
what is the consequence of an uncontrolled chain reaction?
- the rate of fission events becomes to high and results in the production of too much energy
- this can lead to a nuclear explosion
alongside two smaller nuclei, what else is emiited in a fission reaction?
- two or three neutrons
- gamma rays
- energy
what form of energy do all fission prodcucts have?
kinetic energy.
what are the three main components of the core a nuclear reactor?
- fuel rods
- control rods
- moderator
what takes place during a chain reaction in a nuclear reactor?
- an unstable nucleus absorbs a neutron
- the nucleus undergoes fission and releases 2 or 3 further neutrons
- these induce more fission, which results in a chain reaction
what is the role of the moderator in a nuclear reactor?
to slow down the neutrons so they are travelling at speeds which allow them to be absorbed by fissile nuclei and cause fission.
how is the chain reaction in a fission reactor kept under control?
- control rods are positioned in between the fuel rods
- the rate of fission is controlled by moving these rods up and down
- the lower the rods are inserted, the slower the rate of fission
what term is used to describe nuclei in which fission can be induced through the absorption of slow neutrons?
fissile nuclei
what is nuclear fusion?
the joining of two light nuclei to produce a heavier nuclei and release energy.
name two isotopes of hydrogen which are commonly used in nuclear fusion.
deuterium and tritium
which releases more energy, nuclear fission or nuclear fusion?
nuclear fusion.
explain the difficulty of generating energy through nuclear fusion.
fusion requires very high temperatures which in itself requires large quantities of energy and also requires casing which can withstand them.