What is nuclear fission?
Nuclear fission is the splitting of a nucleus into two approximately equal fragments with the release of two or three neutrons along with radioactive waste
Energy released from nuclear fission:
Energy in the form of radiation plus kinetic energy of the fission neutrons and the fragment nuclei
Uranium-235 or Plutonium-239 A neutron hits the nucleus of one of these isotopes and the nucleus splits A chain reaction then occurs in a nuclear reactor as each fission event causes further fission events
Nuclear Reactor Diagram:
Nuclear Reactor Components:
A nuclear reactor consists of uranium fuel rods spaced evenly in the reactor.
The reactor core contains the fuel rods, control rods and water at high pressure
Fission neutrons are slowed down by collisions with water molecules
This is important as fast neutrons do not cause further fission of U-235
The water is a moderator as it slows down the fission neutrons
Control rods- absorb surplus neutrons. Depth of rods is adjusted to maintain a steady chain reaction
Water acts as a coolant. Its molecules gain KE from neutrons and fuel rods. Then the water gets pumped through the core to and from a heat exchanger.
Water transfers energy for heating to the heat exchanger from the core
Nuclear Fission Reaction:
What is nuclear fusion?
Nuclear fusion is the process of forcing two nuclei close enough together so they form a single larger nucleus
Nuclear fusion and Energy release:
Nuclear fusion releases energy only if the relative mass of the nucleus formed is no more than about 55 (about the same as an iron nucleus). Energy must be supplied to create bigger nuclei
How is nuclear fusion brought about?
Nuclear fusion is brought about by making two light nuclei collide at very high speed
The sun and nuclear fusion:
- Two protons (i.e. hydrogen nuclei) fuse, they form a 'heavy hydrogen' nucleus 2H1. Other particles are created and emitted at the same time
- Two more protons collide separately with two 2H1 nuclei and turn them into heavier nuclei
- The two heavier nuclei collide to form the helium nucleus 4He2
- The energy released at each stage is carried away as kinetic energy of the product nucleus and the other particles emitted
Fusion reactor conditions:
- The reactor needs to be at a very high temperature
- This is because the two nuclei approaching each other will repel each other due to their positive charges. If they are moving fast enough, they can overcome the force of repulsion and fuse together
What happens to the plasma in a fusion reactor?
- The plasma is heated by passing a very large electric current through it
- The plasma is contained by a magnetic field so it doesn't touch the walls.
- If it does, it would go cold and fusion would stop
The promising future of nuclear fusion:
- Fuel for fusion reactors is readily available as heavy hydrogen is naturally present in sea water
- The reaction product, helium is a non-radioactive inert gas so it is harmless
- The energy released could be used to generate electricity
- But still in the development stages
What is radon gas?
Radon gas is an alpha emitting isotope that seeps into houses in certain areas through the ground
What are methods to reduce the exposure to radon gas?
Pipes under buildings can be installed and fitted to a suction pump to draw the gas out of the ground before it seeps into the building
Could Chernobyl happen again?
- Most nuclear reactors are of a different design
- The Chernobyl accident did not have a high-speed shutdown system like most reactors have
- The operators at Chernobyl ignored safety instructions
- There are thousands of nuclear reactors in the world. They have been working safely for many years
The effect on living cells of radiation from radioactive substances depends on:
- The type and amount of radiation received (dose)
- Whether the source of radiation is inside or outside the body
- How long the living cells are exposed to the radiation
Complete the sentence
The larger the dose of radiation someone gets...
the greater the risk of cancers developing. High doses kill living cells
Complete the sentence:
The smaller the dose...
the lower the risk- but it is never zero
How can workers reduce their exposure to radiation?
- They can stay far away from the source of radiation. Eg: using special tools with long handles
- They can spend as little time as possible in 'at-risk' areas
- They can shield themselves from the radiation by staying behind thick concrete barriers and/or using thick lead plates
What is done to nuclear waste after its use?
The nuclear waste is stored in safe and secure conditions for many years after unused uranium and plutonium (to be used in the future) are removed from it