E.4 Fission Flashcards
Nuclear power stations
Energy released from nuclear fission turns water into steam which turns turbine connected to generators to produce electrical energy
Most common fuel source in nuclear power stations
Uranium 235
How does fission of a uranium 235 nucleus occur?
Collision with a neutron causes the nucleus to split into two smaller nuceli and three neutrons
Neutron sources for fission
Americium 241 and beryllium 9
Critical mass
If the mass of uranium 235 is large enough, neutrons produced in fission can collide with more nuclei, causing a chain reaction
What does enriching uranium do?
Increases the proportion of U-235 to around 5% so it can be used in a nuclear reaction
Naturally occurring uranium composition
99.3% U-238 and 0.7% U-235
U-238 will absorb neutrons but only undergoes fission when…
Neutrons have very high energy levels
What are the three key parts of a nuclear reactor?
Moderator, control rods and heat exchanger
Moderator
Makes fission happen- high energy neutrons must be slowed down for collision with nuclei to occur. Collisions with the moderators neutrons reduce Ek of neutrons from MeVs to Evs
Control rods
Controls rate of fission - absorb neutrons by lowering in/out of the reactor core so fission be controlled
Heat exchanger
Water is heated by the fission and the thermal energy is transferred to cold water to convert it to steam
Low level waste disposal
Handling of uranium leaves traces of radioactive materials that have to carefully disposed of (100-500 years). Old nuclear reactors must be encased in concrete or left for many years before demolition
High level waste disposal
Fuel rods contain radiation from fission. Half lives of thousands of years - they can be stored underwater for several years to cool down and then encased in steel and buried.
