8.2 Nuclear Power Flashcards
How much energy is produced from nuclear fuels?
11% worldwide.
What is a nuclear reactor?
A machine which nuclear reactions take place producing energy. The fuel of the reactor is typically uranium 235.
What is a chain reaction?
The fast neutrons produced in the fission of U235 are then slowed down when they collide with other U235 nuclei in the reactor producing more fission, energy and neutrons. The reaction is thus self sustaining.
What is the critical mass?
The minimum mass of U 235 for a chain reaction to sustain itself, with a lower mass many neutrons escape without causing further reactions.
What is uranium enrichment?
The uranium commonly mined us U238 which contains small traces of U235 enrichment is the process of increasing the contraption of the useful U235 in uranium samples. For nuclear power plants the concentration is increased to 5%.
What are fuel rods?
Rods containing the nuclear fuel in pellet or powder firms. In the case of uranium the fuel rods contain a mixture of fissionable U235 and non fissionable U238.
What are control rods?
These rods can be inserted to absorb excess neutrons in order to control the rate of the fission reaction.
What is a moderator?
The neutrons produced in the fission reaction must be slowed down if they are to be used to cause further fissions. This is achieved through collisions of the neutrons with atoms of the moderator, the material surrounding the fuel rods.
What is a heat exchanger?
The kinetic energy of the reaction products is converted to thermal energy in the moderator. A coolant passing through the moderator can extract this thermal energy and use it to turn to steam at high temperature and pressure. This can be used to turn the turbines of a power station producing electricity.
What are advantages of energy production by nuclear fission?
High power output (high energy density)
Large available reserves of nuclear fuel]
No greenhouse gas emissions
What are disadvantages of energy production by nuclear fission?
The fast neutron produced in a fission reaction may be used to bombard uranium 238 and produce plutonium 239. Thus non fissionable U238 is being converted to fissionable plutonium 239 which can be used in the production of nuclear weapons or as a nuclear fuel in flat breeder reactors.
The spent fuel and the reaction products are highly radioactive with long half lives. Safe disposal of this material is a serious issue in commercial energy production.
Even if the reactor is shut down production of thermal energy continues due to beta decay of the product nuclei.
A fission rector can become a major public health hazard if control or back up system fail and an uncontrolled chain reaction leads to rector meltdowns.
Uranium decays into radon gas a which is carcinogenic. Inhalation of this gas ad of radioactive dust particles is a major hazard in uranium mining.
