Radioactivity (6.36- 6.42)

Advantages

• Produces no carbon dioxide so it does not contribute to global warming
• Very small amount of nuclear fuel generates large amount of energy
• very low fuel costs
• power station has very long lifetime

Disadvantages

• Waste is radioactive and safe disposal is very difficult and expensive
• Local thermal pollution from waste water can affect marine life
• Large scale accident would be catastrophic→so public perception is negative
• cost of building and safely decommissioning nuclear power lant are very high

• nuclear reactions, including fission, fusion and radioactive decay, can be a source of energy

• Rather than emitiing small particles, nuclear fission involves a nucleus splitting into 2 daughter nuclei and 2 or more neutrons. This process releases energy.
• Although some isotopes fission themselves, more fission needs to be 'induced' by absorbing another particle, usually a neutron.
• The isotopes mosted used in nuclear reactors are Uranium-235 and Plutonium-239

Fission of U-235 produces 2 daughter nuclei, emits 2 or more neutrons and releases energy

• Fast neutrons scatter from the uranium nucleus, without causing it to split
• Slow neutrons are absorbed by ²³⁵U nucleus, becoming an unstable ²³⁶U nucleus which then splits indto two daughter nuclei and two or three neutrons.

Moderators and control rods

• Moderators slow down the neutrons to optimise fission
• Controls rods absorb the neutrons to control the rate of the chain reaction. They can be raised or lowered to change the rate, and lowered completely to stop it.

• The fission reaction releases energy in the form of kinetic energy of the products, which transfers to thermal energy
• Thermal energy heats water and high pressure steam drives tubines and generators

• Products of nuclear fission is radioactive
• radioactive waste can be radioactive for thousands of years
• it tends to be stored in containers and buried underground