Nuclear decay and nuclear energy

What is nuclear fission?

A decay process where a unstable heavy nucleus splits into two lighter nuclei

How does nuclear fission occur?

Slow moving neutrons are absorbed by heavy U-235 nuclei during collisions releasing further fast moving neutrons leading to a sustainable chain reaction

What is the function of the control rods?

• They are arranged to absorb neutrons so that for every two or three neutrons that are released from a fission reaction, only one goes on to produce further fission

• Can be made of boron and cadmium

• If a fault occurs control rods should drop into the reactor

What is the function of the moderator?

Slows down fast moving neutrons to enable absorption by U-235 nuclei to occur. Some use water and some use graphite rods as a moderator but water can be used as the coolant to transfer heat energy but if the coolant is lost the neutrons wont slow down so the nuclear chain stops and causes the reactor to overheat.

What is used as a material for the reactor vessel?

Steel surrounded by concrete

What is wrong with the fission products?

• long half lives

• must be stored safely in cooling ponds which provides shielding from the radiation

What is nuclear fusion?

Two light nuclei such as heavy hydrogen collide and fuse producing helium and releasing energy

What are the advantages of nuclear fission?

• Does not produce greenhouse gases

• Large amounts of power produced

• Uses small amounts of fuel

What are the disadvantages of nuclear fission?

• Radioactive material produced with long half life

• Risk of nuclear meltdown

• High cost of decommissioning the power station and storing of waste material

What are the advantages of nuclear fusion?

• Abundant source in seawater

• Does not produce greenhouse gases

• No long lived radioactive materials are produced

What are the disadvantages of nuclear fusion?

• High temperature and pressure required to overcome the mutual repulsion of nuclei making it difficult to contain

• Shielding of neutrons using concrete

• High energy input required