Nuclear Fission

What is nuclear fission and how is it useful?

Starter:Electricity generation – how is this normally achieved?

Outcomes

• compare energy released in nuclear fission and in a chemical reaction; (H: E = mc2)

• H: explain nuclear fission and a chain reaction

• H: explain how fission is controlled in a nuclear power station

Chain reactions • There are 2 types of chain reaction.

1) The reaction starts and the rate continues at the same pace.

2) The chain reaction starts and the rate continues to increase.

Observe these domino effects.

Unlike radiation emitting small particles, nuclear FISSION involves a nucleus SPLITTING into two LARGE FRAGMENTS.

The isotopes most used in nuclear reactors are Uranium-235 and Plutonium-239

Nuclear Fission

• A nucleus undergoes fission when it is hit by a neutron. This releases ……

2 or 3 neutrons (fission Neutrons) at high speed.Energy in the form of radiation (useful for nuclear

reactors)

Fission neutrons can go on to cause further fission leading to a chain reaction.

Energy released in nuclear fission

• Using the equation E=mc2 we can work out the amount of energy produced in a nuclear reaction.

• E= energy• M = mass• C = speed of light

• The small mass that is released during fission produces a huge amount of energy. In fact 100’000’000 times the amount in a normal chemical reaction.

Using fission in a nuclear reactor

What is needed to make use of the energy from nuclear fission?Uranium-235. Natural uranium from mines is mainly U-238 and so must be ENRICHED to raise the % of U-235

1. FUEL RODS –U-235

2.CONTROL RODS– ABSORB surplus NEUTRONS.

3. Water acts as a coolant. Its molecules gain KE from the neutrons.

4. Reactor core is made of thick steel to withstand high pressure and temp.

The core is enclosed by thick concrete to absorb radiation.

REACTOR CORE

THICK CONCRETE BIOSHIELDING NEEDED

The PRIMARY COOLANT (which carries heat from the core) can be GAS or LIQUID. It becomes RADIOACTIVE

WATER is usually used as the SECONDARY COOLANT. The steam generated turns turbines. It is not radioactive.

Inside a Nuclear Reactor

This UNFILLED CORE is made from GRAPHITE

FUEL RODS (U) CONTROL RODS (B)

An operating reactor with a water moderator

In 1945, the first Nuclear bomb was tested in a desert. It lit up the night sky and turned all the sand around it for 700m, into glass. 2 weeks later, the USA dropped 2 nuclear bombs on Japan.