Fission and Fusion

Fission is the splitting of a heavy atom into

Two or more lighter nuclei

Fusion is combining two small nuclei to make a heavier nucleus

Fission and Fusion break the Law of Conservation of Mass!!!

The law says mass (matter) can not be created or destroyed.

However, in these nuclear reactions, a bit of mass IS destroyed, and converted into….

LOTS OF ENERGY!

How much energy?

Einstein says…..

Einstein’s equation

Energy = mass x (speed of light)

2

Very small X very very bigVery big =

• In fusion and fission, small amounts of mass are converted into huge amounts of energy

• Compared to a gram of natural gas (methane), a gram of material converted to energy in a nuclear reaction gives off one BILLION times more energy

Fission Reactions

Neutron + U-235

A neutron is fired at U-235 and is captured, forming unstable U-236, which then splits up

Fission Reactions

n + U Ba + Kr + 3 n + energy1

023592

14256

9136 0

A neutron bombards a U-235 and it splits into Ba-142, Kr-91 three neutrons and ENERGY

The three neutrons can then go on to start other fission reactions

1

This can be the start of a chain reaction

Nuclear power plants use fission to create energy to make electricity

Three Mile Island

Nuclear Reactors

FUEL

• Must be FISSIONABLE• Controlled chain

reactions• U-233• U-235• Pu-239• Radioactive Waste can

be solid, liquid or gas

CONTROL• Control Rods

(MODERATORS) absorb neutrons

• Control rods made of Cadmium (Cd), Graphite (C), Boron (B)

• COOLANT = Liquid Sodium Na (l) or Heavy Water

• Steel and High Density concrete shield personnel

Nuclear Reactor

Nuclear accidents can happen when the chain reaction goes out of control

Thanks to FUSION, we have sunlight!

Hydrogen fuses withHydrogen to makeHelium + energyin stars, like our own sun

Fusion

Fusion is not as dangerous as fission

Unfortunately ……

it can not yet be used in power plants because too much energy is needed to overcome the repulsion of the two positively charged nuclei to be cost effective