Nuclear

Topic 8: Energy, power and climate change (18 hours)


 * 8.4 Non-fossil fuel power production**

l Nuclear transmutation : changes in nuclei whenever a parent nuclide gains, loses or changes one of its nucleons (proton or neutron), which forms daughter nuclides and elementary particles Ø E.g. Nuclear fission reaction caused by neutron activation : the parent nuclide is bombarded with low-energy (= 1 eV) neutrons l Critical mass : the smallest possible amount of fissionable material that will sustain a chain reaction l Any nuclear reaction obey Conservation Laws : Ø Momentum is conserved Ø Total charge is conserved Ø Number of nucleons remain constant Ø Mass-energy is conserved
 * 8.4.1 Describe how neutrons produced in a fission reaction may be used to initiate further fission reactions (chain reaction)**


 * 8.4.2 Distinguish between controlled nuclear fission (power production) and uncontrolled nuclear fission (nuclear weapons)**

l In a nuclear reactor, large amount of energy (produced by the chain reaction) causes the fuel to melt and set fire to the reactor – meltdown, which is controlled. However, too many neutrons can lead to a runaway reaction, which will cause an explosion (e.g. atomic bomb – nuclear weapons) and have destructive capability

l Uranium-235 isotope (radioactive) is required for fission, which only occupied a small amount in the uranium ore (the rest is Uranium-238). By enriching the uranium, it raises the concentration of Uranium-235 up to 3.5% and make nuclear fission more likely to happen
 * 8.4.3 Describe what is meant by fuel enrichment**

l Essential features of a thermal reactor: Ø Moderator : slow down the fast neutrons for maintaining a self-sustained reaction without absorbing them when collide with the moderator material Ø Control rods : moveable roads that absorb neutrons in order to control the chain reaction
 * 8.4.4 Describe the main energy transformations that take place in a nuclear power station**
 * 8.4.5 Describe the role of the moderator and the control rods in the production of controlled fission in a thermal fission reactor**

l Heat exchanger allows the nuclear reactions to occur in a place that is sealed, and the thermal energy generated from the fission reaction is used to produce steam, which turns the turbines
 * 8.4.6 Describe the role of the heat exchanger in a fission reactor**
 * 8.4.7 Describe how neutron capture by a nucleus of uranium-238 (238U) results in the production of a nucleus of plutonium-239 (239Pu)**

l Fast breeder reactor is designed to utilizes plutonium-239 (239Pu)
 * 8.4.8 Describe the importance of plutonium-239 (239Pu) as a nuclear fuel**

l Possibility of thermal meltdown due to uncontrolled nuclear fission, which means radioactive materials would be spread around the surrounding areas to cause catastrophe l Nuclear wastes which are still radioactive for decades or centuries are produced, and current solution is to bury them l Ore of uranium is radioactive as well, which means extra precaution is required, and mining operation itself is risky l By-products of the civilian use (民用 ) of nuclear power can be used to produce nuclear weapons l Advantages Ø Extremely high “energy density” – very small mass of uranium but huge amount of energy Ø Much more uranium resources compared with oil l Disadvantages Ø Radioactive nuclear wastes are produced Ø Very risky (things can go wrong) Ø Nonrenewable
 * 8.4.9 Discuss safety issues and risks associated with the production of nuclear power**

l Nuclear fusion use hydrogen as fuel, which produces much less radioactive wastes than nuclear fission l The reaction is the same as the process happening in the sun, which requires high temperature to ionize atomic hydrogen into a plasma state (where electrons and protons mover independently without bounding in the atoms) l Therefore, the current challenges are how to maintain and confine the plasma at such a high temperature and the density for fusion to take place
 * 8.4.10 Outline the problems associated with producing nuclear power using nuclear fusion**


 * 8.4.11 Solve problems on the production of nuclear power**