Nuclear Fusion and Nuclear Fission

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Physics Notes
Nuclear Fission
Nuclear power reactors use a reaction called nuclear fission.
The fission is a source of energy for the generation of power.
Two isotopes in common use as nuclear fuels are uranium-235 and plutonium-239.
Fission is another word for splitting.
Uranium and Plutonium have relatively large nucleithat are easy to split, especially when
hit by neutrons .
When a uranium-235 or plutonium-239 nucleus is hit by a neutron, the following happens:
1. The nucleus splits into two smaller nuclei ­ daughter nuclei, which are radioactive
2. Two or three more neutrons are released
3. Some energy is released
The additional neutrons released may also hit other uranium or plutonium nuclei and
cause them to split. Even more neutrons are then released, which in turn can split more
nuclei. This is called a chain reaction .
Nuclear Power Reactors
The nuclear reactor is designed to allow a
controlled chain reaction to take place. Each
time a uranium nucleus splits up it releases
energy and three neutrons . If all the neutrons
are allowed to be absorbed by other uranium
nuclei the chain reaction will spiral out of control
causing an explosion . To control the energy
released in the reactor moveable control rods
are placed between the fuel rods . These control
rods are made of boron which absorbs some of
the neutrons so fewer neutrons are available to
split uranium nuclei. The control rods are raised
to increase and lowered to decrease the
number of free neutrons .

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Nuclear fusion
Nuclear fusion involves two atomic nuclei joining to make a large nucleus .Energy is
released when this happens.
Nuclear fusion involves a deuterium and a tritium nucleus colliding and being forced
together. Both nuclei are positively charged and therefore will repel each other . This is
known as electrostatic repulsion . The nuclei have to get very close in order to collide,
which is approximately a million millionth of a millimetre.…read more


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