Nuclear Fusion Flashcards
What are the benefits of nuclear fusion compared to fission?
Production of shorter-lived radionuclides
Fuel is practically unlimited
No risk of a runaway criticality
Why is the triple product (ntT) a useful comparative parameter?
The triple product is a measure of merit in the nuclear industry. The value of the triple product should be as high as possible
What are the key conditions for fusion?
High plasma density
High plasma temperature
Long plasma confinement time
What is the difference between the breakeven and ignition conditions in a nuclear fusion reactor?
At breakeven, the energy produced from fusion reactions in the reactor balance the power absorbed in the plasma. At ignition, the self heating of the plasma due to fusion reactions is equal to the energy losses in the plasma. Hence, at ignition, external heating is not required.
Compare deuterium and tritium as nuclear fusion fuels
Deuterium is readily available and is largely inexhaustible. Deuterium is also stable and harmless. It is already being routinely produced
Tritium is not naturally occurring and is radioactive with a 12yr half life. It can be bred from the neutron absorption of lithium 6, producing H3 and He4
Why is D-D fusion not favoured
While it has a high cross-section, D-D fusions produce less energy than D-T fusions (3 MeV vs 18 MeV)
Why is D-He3 fusion not favoured?
Has a good cross section, the highest Q value of considered fusion reactions and doesn’t produce neutrons, but requires a higher temperature to achieve fusion, and 3He cannot be found on earth.
Why is p-B11 fusion not favoured?
Produces no neutrons, B11 is readily mineable but requires high temperatures and produces a lower Q value (9 MeV)
How is confinement and heating achieved in a Magnetic Confined Fusion reactor?
The plasma is confined by toroidal and poloidal magnetic field coils.
Plasma is heated through resistive heating, radio waves and neutral particle beams
How does Inertial Confinement Fusion work?
Surface of fuel pellet is rapidly heated using lasers, creating a plasma. Surface is violently ejected, causing fuel to compress, causing the fuel to heat and resulting in ignition
What are the disadvantages and challenges that ICF faces?
Process is discontinuous
Challenges include: stable energy delivery to the target, controlling the symmetry of imploding fuel, preventing the premature heating of the fuel, preventing the mixing of hot and cold fuel
What is the function of the divertor?
The divertor removes heat and ash from the reactor. It is made of tungsten to withstand the high operating temperatures
What are the plasma challenges of fusion?
How the B field affects the plasma
The plasma exhaust
How current is driven in the plasma.
What are the fuel system challenges of fusion?
Optimising the blanket design for tritium breeding
Minimising the tritium inventory to meet regulations
Minimising waste
What are the six key challenges that tokamak-fusion will need to overcome in order to produce electrical power for a competitive market?
Planned availability- High capital cost, requirement of continuous power is demanding for Tokamak’s pulsed output
Reliability- Unscheduled lack of availability must be avoided, shutdown in peak period might mean that the tokamak could not be restarted due to high energy requirement.
Structural integrity- tokamak will be subjected to 1000s of pulses, structure will be subjected to high temperatures and high neutron fluxes
Helium supply- must be a long term source of helium for cooling magnets, commercial helium is produced through natural gas industry
High-temperature plasma facing materials- some materials must directly face plasma, this means that they’ll get very hot. Divertor tiles need to be replaced robotically
Problematic materials- radio activation of tokamak,
