Nuclear Power Flashcards
What is nuclear fission?
It’s the splitting of a large nucleus to produce two smaller ones. Two or three neutrons are also released in the process. The energy form the neutrons power a nuclear reactor.
How does nuclear fission help power a power station?
In a nuclear reactor, a slow moving neutron is absorbed into a nucleus (usually uranium 235). This causes the nucleus to become uranium 236 which is unstable.
The entire nucleus splits into two large fragments called ‘daughter nuclei’. In addition to the ‘daughter’ products, two or three neutrons also explode out of the fission reaction and these can collide with other uranium nuclei to cause further fission reactions. This is known as a chain reaction.
The fast moving neutrons carry most of the energy from the reaction with them (99%) but before the neutrons can collide with fresh uranium nuclei, they need to be slowed down.
Their energy is passed on to other components in the nuclear reactor, which is used to heat water to drive the turbines that turn the generators.
What is nuclear fuel?
The uranium or plutonium isotope that will split when triggered by an incoming neutron. The fuel is held in rods so the neutrons released will fly out and cause nuclear fission in other rods.
What does the moderator do?
The graphite core slows down the neutrons in a nuclear fission reactor.
What is the purpose of the control rods?
These are raised are lowered to stop neutrons from travelling between fuel rods and therefore can change the speed of the chain reaction.
What is the coolant used for?
It is heated up by the energy from fission reactions and is usd to boil water to drive turbines in a power station.
What does the concrete shield do?
The daughter products of the fission reaction are radioactive and can be a hazard so need to be contained.
What are some advantages of a nuclear power station?
Produces no polluting gases Does not contribute to global warming Very low fuel costs Low fuel quantity reduces effect on environment Very long lifetime
What are some disadvantages of nuclear reactors?
Waste is radioactive and safe disposal is very difficult and expensive.
Large scale accidents can be catastrophic
Public perception is negative
Costs of building are very high
Cannot react quickly to changes in electricity demand
What is nuclear fusion?
The joining together of two smaller atomic nuclei to produce a larger nucleus. Radiation is released when this happens. Nuclear fusion happens in stars like our Sun, and in hydrogen bombs.
What is the problem with nuclear fusion?
Both nuclei are positively charged so repel each other. In order for this to happen it needs to be done under intense pressure and very high temperatures in order to force the nuclei together and overcome the electrostatic repulsion.
What are fusion reactions not viable yet?
The very high temperature and pressure makes it very difficult to build a practical and economic fusion power station. For fusion to occur at the lower pressures in a reactor on Earth, the temperature would need to be between 100 and 200 million degrees.
