Nuclear Energy Flashcards
Relate the energy of an object to its mass
E = mc²
When a particle and its corresponding antiparticle collide, what happens, what is produces and what are the products’ energies?
They annihilate
2 gamma photons are produced
Each gamma photon has energy mc²
For a spontaneous reaction where no energy is supplied, give the equation for the energy released
Q = Δmc²
where Δm is the total mass before and after the reaction
For α decay, how is the energy released distributed between the the products and how is the energy related to the products’ masses?
- The nucleus recoils so the energy released is shared between the α particle and the nucleus
- Due to the conservation of momentum, the energy released is shared between the to particles in inverse proportion to their masses
For β decay, how is the energy released distributed between the the products and how is the energy related to the products’ kinetic energies?
-The energy released is shared in variable proportions between the β particle, the nucleus and the neutrino or antineutrino.
-When the β particle has maximum KE, the neutrino or antineutrino has negligible kinetic energy in comparison.
The maximum KE of the β is very slightly less than the energy released in the decay because of the recoil of the nucleus
For electron capture, which product carries the energy released in the decay?
The neutrino carries away the energy released
The atom also emits an X-ray photon when the inner-shell vacancy (due to the electron capture) is filled
Give the average strength of the strong nuclear force over a distance of about 1x10⁻¹⁵m (1fm)
200N
Define the binding energy of a nucleus
The binding energy of the nucleus is the work that must be done to separate a nucleus into its constituent neutrons and a protons
Define the mass defect of a nucleus
The mass defect Δm, of a nucleus is the difference between the mass of the separated nucleons and the mass of the nucleus
Describe what causes the mass defect of a nucleus
When a nucleus is formed from its constituent nucleons, energy is released because the strong nuclear force does work pulling the nucleons together (binding energy)
Give the equation for the mass defect for the nucleus of an isotope X with mass number A and Z number of protons
Mass defect Δm =Zmᴾ + (A-Z)mᴺ - mᴺᵘᶜ
where mᴾ and mᴺ represent the masses of the proton and the neutron respectively
Give the equation for the binding energy of a nucleus
Binding energy = Δmc²
Give 1Mev in Joules
1.6x10⁻¹³ J
Explain the cause of quantum tunnelling for an α particle.
The binding energy of an α-particle is very large (7 MeV per nucleon). The α-particle gains sufficient kinetic energy to give it a small probability of ‘quantum tunnelling’ from the nucleus
In a diagram for the energy of a nucleus, give the forces that are responsible for:
i) The ‘coulomb barrier’
ii) The ‘well’ of stability
i) The electrostatic force on the α-particle
ii) The strong nuclear force
Define the binding energy per nucleon of a nucleus
The binding energy per nucleon of a nucleus is the average work done per nucleon to remove all the nucleons from a nucleus and is thus a measure of the stability of a nucleus.
Describe how the binding energy per nucleon changes as mass number, A, increases
- When A 50, an increase in mass number causes a gradual decrease in binding energy from between 8.5MeV when A=50, to about 6MeV when A=250
Give the name of the process that causes the mass number of a nucleus to increase and when is it most stable?
Fusion
Give the name of the process that causes the mass number of a nucleus to decrease and when is it most stable?
Fission
Define induced fission
When a fissionalable nucleus (e.g. U²³⁵ or Pu²³⁹) is bombarded with neutrons and the nucleus splits into two approximately equal fragments
Explain why a chain reaction is possible in a fission reaction
Because fission neutrons are released in a fission event, which are each capable of causing a further fission event as a result of a collision with another fissionable nucleus
What is the average energy released by each fission event
200 MeV
Why is energy released when a fission event occurs?
Energy is released because the fragments repel each other (due to being +ve charged) with sufficient force to overcome the strong force.
The fragment nuclei and the fission neutrons therefore gain kinetic energy.
The binding energy increases due to the decrease in size of the nucleus and thus the energy released is equal to the change in binding energy
Explain the change in binding energy for a fission event
The binding energy changes from about 7.5 - 8.5 MeV because because the size of the nucleus decreases (the mass number A, decreases so the binding energy per nucleon increases).
Define fusion
A nuclear reaction in which atomic nuclei of low atomic number fuse to form a heavier nucleus with the release of energy.
Explain why energy is released during fusion
Because the binding energy per nucleon of the product nucleus is greater than of the initial nuclei
Give the condition required for nuclear fusion to take place and explain why
The nuclei must collide at high speed so that they overcome the electrostatic repulsion between the two nuclei so they become close enough that they interact through the strong nuclear force
Give the fusion reaction between 2 protons
p¹₁ + p¹₁ → H²₁ + β⁰₋₁ + ν̄ₑ
Give the name for H²₁
Deuterium
Give the fusion reaction between Deuterium and a proton
H²₁ + p¹₁ → He³₂ + β⁰₋₁ + ν̄ₑ
Give the fusion reaction between 2 helium nuclei
He³₂ + He³₂ → He⁴₂ + 2p¹₁
Give the equation for the energy released during a fusion reaction
Q = Δmc²
where Δm is the difference between the total mass before and after the event
What is produced as a result of fusion inside the sun
Solar energy
At high temperatures of about 10⁸K, what happens to atoms and what is the name of this state
The atoms are stripped of their electrons
This state is referred to as ‘plasma’
How does a nuclear reactor work?
Enriched Uranium rods containing 2-3% U-235 heats up water which heats a steel pipe of water in steam which turns a turbine. The reactor is controlled by control rods which absorbs neutrons from the fission reactions of the Uranium so to keep the number of neutrons in the reactor constant.
What does PWR stand for?
Pressurised water reactor
What is the use of a moderator in a fission reactor and what is the moderator in a PWR?
The moderator surrounds the fuel rods so that the fission neutrons emitted are slowed down, since without it, they are going too fast to cause further fission
Water is the moderator and coolant in the PWR
Define and explain critical mass
The minimum amount of fissile material needed to maintain a nuclear chain reaction
This is because some fission neutrons escape from the fissile material without causing fission and some are absorbed by other nuclei without fission
Define fissile material
The material capable of sustaining a nuclear fission chain reaction.
Fissile material can sustain a chain reaction with neutrons of any energy
What does AGR stand for?
Advanced Gas-cooler Reactor
Give 4 common safety features for nuclear reactors
1) The reactor core is a thick steel vessel designed to withstand high pressure and temperature in the core
It also absorbs all β-radiation as well as some γ-radiation and some neutrons
2) The core is in a building with very thick concrete walls which absorb the neutrons and γ-radiation that escape from the reactor vessel
3) Every reactor has an emergency shut-down system designed to insert the control rods fully into the core to stop fission completely
4) The sealed fuel rods are inserted and removed from the reactor by means of remote handling devices
What is radioactive waste categorised into?
- High-level radioactive waste
- Intermediate-level radioactive waste
- Low-level radioactive waste
Give an example of high-level radioactive waste and how they are disposed of/stored
- Spent fuel rods from a nuclear power station
- The fuel rods are removed by remote control and stored underwater in cooling ponds for up to a year due to the heat released. They can then be stored in sealed steel containers for centuries or the waste can be vitrified by mixing it with molten glass and storing is as glass blocks in underground caverns
Described how intermediate-level radioactive waste is stored
They are sealed in drums that are encased in concrete and stored in specially constructed buildings with walls of reinforced concrete
Describe how low-level radioactive waste is disposed
They are sealed in metal drums and buried in large trenches
