Nuclear Fission And Fusion Flashcards
Describe the process of nuclear fission
A slow moving neutron must be absorbed into a uranium or plutonium nucleus. The addition of the neutron makes the nucleus unstable, causing it to split
Each time the uranium or plutonium nucleus split, 2 or 3 neutrons are released, where one might hit another nucleus, causing it to split. This keeps the chain reaction going
Which elements do most reactors use?
U-235
Why do nuclear reactors contain water?
The fission neutrons are slowed down by collision with the atoms in the water molecules.So there is no further fission of U-235. The water acts as a moderate, because it slows down fission neutrons.
Water also acts as a COOLANT
Its molecules gain kinetic energy from the neutrons and the fuel rods. The water is pumped through the core. Then it goes through sealed pipes to and from a heat exchange outside the core. The water transfers energy for heating to the heat exchanger from the
Why do nuclear reactors have control rods in the core?
They absorb surplus neutrons. This keeps the chain reaction under control so the reactor doesn’t overheat.
How do nuclear power stations use nuclear fission?
In a nuclear reactor, energy is released from nuclear fission, forming heat. The heat is then used to heat water and make steam, which is used to drive a steam turbine, connected to an electricity generator
Why is the reactor core made of thick steel?
To withstand the very high temperature and pressure in the core.
Why is the core enclosed by thick concrete walls?
These absorb radiation that escapes through the walls of the steel vessel
What is nuclear fission?
Nuclear fission is the splitting up of a nucleus into two approximately equal fragments and the release of two or three neutrons.
What is nuclear fusion?
The process of forcing two light nuclei close enough together so they form a single larger nucleus. This process releases energy.
Normally 2 nuclei approaching each other will repel each other due to a positive charge, but if nuclei are moving fast enough they can overcome the force of repulsion
A common e.g is using two different hydrogen nuclei to form helium
What is the good thing about fusion?
Fusion releases a lot of energy( more than fission for a given mass)
Where does fusion occur naturally?
All energy released in STARS comes from fusion at extremely high temperatures and pressures.
What does the sun consist of?
Consists of plasma of bare nuclei with no electrons
What happens in a fusion reactor?
The plasma is heated by passing a very large current through it.
The plasma is contained by a magnetic field, so it doesn’t touch reactor walls. If it did. It would go cold and fusion would stop
What are the advantages and disadvantages of possibly using fusion of hydrogen as a fuel?
It is readily available as heavy hydrogen , which is naturally presented in sea water. So it’s easy to extract
Fission uses uranium which is only found in some parts of the world.
The only product helium is a non radioactive, inert gas, so it is harmless.
But nuclear fission produces radio active waste.
Fusion however happens at really high temperature and pressures so it is extremely expensive. Furthermore no material can physically withstand that kind of pressure, so fusion reactors are really hard to build and safely control.
It’s also hard to safely control the high temperatures and pressures
