Nuclear fission and fusion

What is fission?

Very large nuclei splitting in two

What do nuclear power stations use as fuel

Uranium 235

Nuclear reactions, including fission, fusion and radioactive decay can be a source of what

Energy

Explain how uranium 235 can be split by collision w a neutron

Uranium 235 absorbs a neutron, results in it splitting into two smaller daughter nuclei and giving off 2 neutrons

Explain the chain reaction

When uranium splits, also releases two or three neutrons then absorbed by other uranium nuclei therefore gives out more neutrons when they split

What are the products of the fission of uranium 235

Two radioactive daughter nuclei and two or three neutrons

What do fuel rods do

Filled w/ uranium fuel, in central part of conductor

Moderator role

Slows down neutrons therefore inc chance of being absorbed by uranium nuclei therefore inc chance of fission

Moderator material

Graphite bc neutrons only collide w graphite atoms therefore not absorbed

Control rods role + material

Used to absorb neutrons therefore boron used bc it can absorb neutrons. Moves in and out of reactor core. Allows for fission reaction to be controlled

How do control rods work

Once in reactor core, absorbs lots of neutrons therefore slows the chain reaction. When pulled out, fewer neutrons absorbed therefore more neutrons free to cause fission and chain reaction gets faster

Role of shielding

Needed bc fission products are radioactive and emit ionising radiation which is v penetrating therefore could ionise cells and cause cancer

Where is shielding

Surrounds/is around reactor and made of a thick layer of lead or concrete

Difference between fission and fusion?

Fission - large nuclei splits to form 2 smaller daughter nuclei

Fusion - smaller nuclei combine to create a larger nucleus

Nuclear fusion is what

The creation of larger nuclei resulting in the loss of mass from smaller nuclei, accompanied by a release of energy

Fusion is the energy source for what

Stars

Why’s fusion the energy source for stars

Fusion only happens at high pressures and temps bc it takes a lot of energy to push the two positive nuclei (like charges repel) together

Why does fusion not happen at low temps and pressures

All nuclei positive therefore electrostatically repel each other and so must have a large amount of kinetic energy to overcome repulsion . High temp = high energy therefore fusion only occurs at high temp. High pressure = inc chance of successful collisions bc nuclei closer together

State an example of a nuclear reaction that can occur in the sun and in research facilities on earth

2 (top) 1 (bottom) H + 3 (top) 1 (bottom) → 4 (top) 2 (bottom) He + 1 (top) 0 (bottom) n