Unit 4 - Lesson 15: Nuclear Fusion & Nuclear Fission Flashcards
REVISION SHEET 1: NUCLEAR FUSION
REVISION SHEET 1: NUCLEAR FUSION
If two nuclei collide at high speed, what can they fuse to create?
A new nucleus, neutron and energy
If two nuclei collide at high speed, they fuse to create a new nucleus, neutron and energy. What is released and why?
Energy is released because the total mass of the original nuclei is larger than the mass of the new nucleus. The missing mass is released as energy.
Stars use nuclear fusion.
a) What is fused to make helium?
b) In the process of Hydrogen Nuclei being fused to make helium, what is released?
c) What does nuclear fusion in stars cause?
d) Energy is released during nuclear fusion. What does this released energy do?
e) How does the star remain stable after nuclear fusion?
f) What happens to the star when it runs out of hydrogen as fuel for fusion?
g) When a star collapses in on itself due to running out of hydrogen for nuclear fusion, it’s particles are very hot, and therefore there is high energy. Why does this result in the star expanding out?
a) Hydrogen nuclei.
b) Gamma energy is released.
c) Thermal Expansion.
d) The energy released is constantly trying to push outwards, making the star larger.
e) The star remains stable because of a balance between thermal expansion pushing out and gravity pulling in.
f) When a star runs out of hydrogen as fuel for fusion, the force due to gravity inwards is larger than the pressure pushing outwards of thermal expansion. Suddenly, the star collapses in on itself, becoming very small (in astronomical terms), dense and hot.
g) As the particles are very hot, there is high energy. This causes high pressure as the force of particles on the surface is greater. Suddenly it expands out.
If a star is smaller or the same size as our sun, what will it become?
A red giant.
If a star is larger than our sun, what will it become?
A red supergiant.
Give the formula expressing pressure defined as force per unit area.
P = F / A
(Pressure = Force / Area)
Is nuclear fusion a good power source? Why or why not?
What is the problem with trying to use nuclear fusion as a power source?
Yes. Nuclear fusion appears as an excellent source of energy to power our homes, industry and vehicles.
It produces lots of energy, with no radioactive waste.
The problem is nuclear fusion requires very hot temperatures (100,000,000 Degrees Celsius), very high pressures and a very strong magnetic field.
How do high temperatures and pressures help atoms fuse?
The nucleus of an atom is positively charged. It only has positive protons. Opposite charges attract and same charges repel (like a magnet). To get tow positively charged things to fuse, we need them flying at each other with a LOT of energy. High temperatures and pressures speed up the atoms to do this.
REVISION SHEET 2: NUCLEAR FISSION
REVISION SHEET 2: NUCLEAR FISSION
What happens to nuclei during nuclear fission?
Nuclei are split, releasing energy. This is different from nuclear fusion, where the nuclei are fused.
What does nuclear fission result in?
Two lighter elements, a neutron and gamma radiation.
Splitting an atom releases energy. What equation shows this eloquently?
e = mc^2
The greater the mass (m) of an atom, the more energy (e) it will release.
Fission can be spontaneous, but we can force it to occur in a nuclear reactor. How is this done?
Uranium^-235 OR U^-236 are normally the atom used.
The atom is bombarded with slow-moving neutrons.
When one is absorbed, it splits into two lighter nuclei and a neutron. Energy is also released.
The neutrons can then be absorbed by other nuclei causing further fissions.
What are daughter nuclei and why are they a major disadvantage to nuclear power?
Daughter nuclei are radioactive waste. This presents a major disadvantage to nuclear power.
What’s the problem with nuclear waste?
It’s radioactive, therefore it’s going to decay and release ionising radiation. High energy radiation like gamma rays can damage DNA and lead to cancer. To get rid of the waste, it needs to be stored in a sealed container for extremely long periods of time (depending on the half-life). The containers must be made of concrete and/or lead.
When nuclear fission occurs, a neutron is produced. What happens to the neutron?
The neutron produced can be absorbed by another U^-235 nucleus. This results in a chain reaction, where lots of energy is released.
When nuclear fission occurs, heat is produced. What is this heat used for?
The heat produced is used to heat water to steam which turns turbines and produces electricity.
In nuclear power plants, where is nuclear fission occurring?
The nuclear reactor.
What does the nuclear reactor do?
The reactor makes sure energy is produced, but also that the process is controlled and safe.
Draw a diagram of a nuclear reactor.
https://i.pinimg.com/736x/0e/3a/51/0e3a51fdf907396aaf18f0598da3d86f.jpg
How is it ensured that the reaction (nuclear fission) will happen? (Explain the process of forced nuclear fission in a nuclear reactor)
Rods of U^-235 OR U^-236 are placed in the reactor.
They are bombarded with neutrons. These must be slow moving, otherwise they won’t be absorbed.
As the neutrons are high energy when produced, they need to be slowed.
The moderator slows the neurons. It is usually made of graphite or water.
The energy produced from fission results in two lighter nuclei, a neutron and energy.
As kinetic energy rises in the reactor, heat rises (energy is transferred from the kinetic energy store to the thermal). This heat is forced over a heat exchanger (bendy pipe full of water) carried by CO^2.
This turns water to steam, which turns turbines attached to an electrical generator.
How is the nuclear fission reaction controlled in a nuclear reactor?
The chain reaction can get easily out of control.
As we don’t want a nuclear bomb, we must limit the rate of the chain reaction. Control rods do this by absorbing excess neutrons.
They are often made of boron or cadmium.
How is safety ensured when a nuclear fission reaction is occurring in a nuclear reactor?
The nuclear reactor is encased in a shield made of thick concrete and sometimes lead.
This prevents ionising radiation from escaping.
Are nuclear reactions (fission, fusion and radioactive decay) sources of energy?
Yes
COMPARING NUCLEAR FUSION AND FISSION:
a) Occurs naturally?
b) Process
c) Are radioactive particles (waste) produced?
d) Conditions required
Write the answers for fusion on the left and the answers for fission on the right.
a) Fusion = Yes. In Stars. | Fission = A hot topic. It has definitely occurred on Earth millions of years ago.
b) Fusion = Fusing of 2 or more lighter atoms to make a larger one. | Fission = Splitting of a large atom into 2 or more smaller ones.
c) Fusion = No | Fission = Yes. These need to be disposed of very carefully.
d) Fusion = High temperature and pressure | Fission = Slow moving neutrons.
