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Nuclear Fission

An A2 physics look at the process of nuclear fission
by

Chris Eddy

on 8 July 2010

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Transcript of Nuclear Fission

Nuclear Fission The Process Neutrons are fired at atoms.
The atom becomes unstable, and splits into several parts: Two daughter nucleii Several free neutrons Lots of energy! Nuclear Fission reactors
are there to capture the
energy and make it into a
useable form. The Reactor Core Fuel Rods Coolant Moderator Control Rods Shield UO2 pellets (usually)
arranged in rods,
arranged in grids. UO2 rods - these are
where the fission actually takes place. Transfers the thermal energy. Slows down the neutrons to allow chain reactions Adjustable - control
the rate of reaction by absorbing neutrons Safety feature -
usually concrete If the emitted neutrons
travel too fast then they
don't collide often enough
to sustain a chain reaction. Often mixed in
with the coolant. Can be water, heavy water, graphite or
other. Cadmium or Boron -
good neutron absorbers. Average neutron
emission energy is
2MeV Become 'thermal neutrons' Can be slowed to
'intermediate speeds':
No moderator needed. The Reactor High Pressure: Water is heated
to around 325C. But cannot be
allowed to boil Therefore kept
at high pressures
(150atm) Safety feature:
Coolant also moderates
So if it boils, fewer
collisions, so neutrons
not slowed down and reaction
stops. Energy Outputs 13-14% of the world energy Also, around
150 naval vessels Even some
space craft A good sized, modern plant can generate around 1500MW. Generally speaking,
allow 1000MW for every million homes Could be sustainable,
apart from safety concerns. Eg. Terrorism or problems with fuel disposal Eg. Derby Because E=mc Because E=mc 2 The waste product is
radioactive uranium -
coolant and moderator
also become radioactive. Weapons No control features Reaction happens
very quickly Do use a moderator
Full transcript