Nuclear Fission And Fusion Flashcards
(23 cards)
What fuel is usually split in the process of nuclear fission?
Usually uranium 235 though sometimes plutonium 239 or both
What is nuclear fission?
The splitting up of big atomic nuclei
How do nuclear power stations work?
In a nuclear reactor, a controlled chain reaction takes place in which atomic nuclei split up and release energy in the form of heat. This heat is used to heat water to make steam which drives the steam turbine which is connected to an electricity generator.
Advantages of nuclear fission:
Nuclear fuel is cheap
Can continuously provide electricity
Provides lots of energy
Disadvantages of nuclear fission:
Power plant is expensive
Decommissioning and dismantling is expensive
Waste disposal is difficult
Risk of radiation leaks
What is nuclear fusion?
The joining of small atomic nuclei
What releases more energy, fission or fusion?
Fusion
Advantages of nuclear fusion
Environmentally friendly
Doesn’t leave loads of radioactive waste
Plenty of hydrogen to use for fuel
Disadvantages of nuclear fusion
Fusion can only occur at very high temperatures-about 10,000,000 degrees
You can’t hold the hydrogen at the high temperatures and pressures required for fusion in an ordinary container, you need a very strong magnetic field.
How do protostars form?
From clouds of dust and gas, the force of gravity makes the dust and gas spiral in together and form a protostar.
When making a protostar, what causes the dust and gas to spiral in together?
Gravity
Why does the temperature of a protostar rise?
The gravitational energy is converted into heat
What happens when the temperature of a protostar gets high enough?
Hydrogen nuclei undergo nuclear fusion to form helium nuclei and give out masses of heat and light.
What is the long stable period that is found in a main sequence star?
Where the heat created by nuclear fusion provides an outward pressure to balance the force of gravity pulling everything inwards.
Why can a star maintain its energy output for millions of years?
Due to the masses of hydrogen it consumes.
What happens when the hydrogen begins to run out?
Heavier elements such as iron are made by nuclear fusion of helium. The star then swells into a red giant if it’s a small star or a red super giant if it’s a big star.
Why do red giants and super red giants turn red?
Because the surface cools.
What happens to a small to medium sized star like the sun after the red giant stage?
It becomes unstable and ejects its outer layer of dust and gas as a planetary nebula.
What does a planetary nebula leave behind?
A hot dense solid core- a white dwarf, which just cools down to a black dwarf that eventually disappears.
What happens to big stars after the red super giant stage?
They start to glow brightly again as they undergo more fusion. They expand and contract several times, forming elements as heavy as iron in various nuclear reactions. Eventually they explode in a supernova forming elements heavier than iron and ejecting them into the universe to form new planets and stars.
What happens after the exploding supernova?
The exploding supernova throws the outer layers of dust and gas into space, leaving a very dense core called a neutron star. If the star is big enough this will become a black hole.
Name the stages in a life cycle of a star:
Dust and gas.
Protostar.
Main sequence star
Red super giant. Red giant.
Supernova. (Planetary nebula)
Neutron star. White dwarf.
Black hole.
Why is fusion not used to generate electricity at present?
Fusion only works at such high temperatures that it uses more energy than it could produce.
