Know and understand that during the process of nuclear fission atomic nuclei split.
Know and understand that this process releases
energy, which can be used to heat water and turn it into steam.
a) Appreciate there are two fissionable
substances in common use in nuclear reactors:
b) Know and understand that nuclear fission is the
splitting of an atomic nucleus.
c) Know that for fission to occur the
uranium-235 or plutonium-239 nucleus must first absorb a neutron.
d) Know that the nucleus undergoing
fission splits into two smaller nuclei and two or three neutrons and energy
e) Know and understand that the neutrons may go on
to start a chain reaction to continue the fission process.
f) Know and understand that the steam drives a turbine, which is connected to
a generator and generates electricity.
g) Compare the uses of nuclear fusion and nuclear fission,
but limited to the generation of electricity .
and comparison of methods of generating electricity
nuclear power energy resources
When large atomic nuclei
are hit with slow moving neutrons they can become highly unstable if the neutron is absorbed
by the nucleus.
The larger unstable nucleus breaks into two
smaller 'daughter' nuclei and also release more neutrons, as well as the
production of beta and alpha
particles and gamma radiation.
The neutrons must be slow moving to be
absorbed by a uranium or plutonium atom.
The heavier resulting nucleus is
unstable and spontaneously breaks apart - nuclear fission, with the formation
of several smaller atoms, neutrons and lots of nuclear energy
released, which mainly ends up as heat energy.
The two smaller atoms formed are themselves
may be unstable too and
The fission products are often
isotopes if elements with the wrong neutron/proton ratio for nuclear
Therefore highly radioactive waste'
products are formed e.g. in a nuclear reactor.
The nuclear fission equations below are a gross simplification of
Lots of fission products are possible
e.g. uranium ==> lanthanum + bromine
Note the production of more
neutrons that you started with (2-3 per uranium atom fission) and
these go on to split more of the uranium atoms causing a chain reaction.
After the uranium nucleus absorbs the
neutron it has now split into two smaller nuclei (often radioactive
themselves), sometimes called 'daughter nuclei'.
The overall process is called nuclear fission and because it is
accompanied by an enormous release of energy, it forms the basis of nuclear
The radioisotope uranium-235
is particularly useful for energy generation by nuclear fission.
Much of the energy released is
initially the kinetic energy of the fission fragments, but collisions,
radioactive decay etc. result in most of it changing to heat
and some as electromagnetic radiation.
The nuclear fission process of
energy release is carried out under controlled conditions in a nuclear
The nuclear reaction must be
well sealed with thick walls of concrete and steel.
Heat exchange pipes of water or
carbon dioxide convey the heat from the reactor to the boilers which
generate the steam to drive the steam turbines and generators.
The heat energy from nuclear fission
processes in the nuclear reactor, via a heat exchange system, can be used
to boil water to make steam to drive a turbine and electrical generator in a
nuclear power station.
The energy release is much
greater than for exothermic chemical reactions eg 1g uranium nuclear fuel
releases the same amount of energy as 1 tonne of coal (= 1000kg
= 1000000g), a million x energy density factor!
One consequence of fission is that more neutrons are formed, these in
turn 'split' other atoms making even more neutrons (2-3 neutron per fission),
which, will then facilitate even more energy releasing nuclear fission
This is called a chain
reaction and leads to acceleration in the atom 'splitting' and hence an even
greater energy release which must be controlled.
If fission is uncontrolled a
nuclear explosion results.
The energy release in nuclear
reactions is much greater then the energy release in chemical reactions.
bomb based on uranium-235 was dropped on the Japanese city of Hiroshima in 1945,
Nagasaki was hit by a plutonium based fission bomb later in the same year.
Both of these 'fission bomb' nuclear
weapons relied on preventing fission happening until the bomb mechanism
explodes a neutron source and uranium/plutonium metal into each other, then
fission happens in a totally uncontrolled way within a deadly split second.
BUT, we need controlled fission:
Surrounding the uranium fuels rods with a
moderator material e.g. graphite or 'heavy water' to absorb some
of the neutrons, but that is not usually enough for full control.
Thankfully in nuclear reactors,
control rods of an excellent
'moderator' like boron can lowered into
the reactor core to absorb neutrons
and slow down fission to keep the chain reaction and energy release under control.
Ideally, you just want one of the two or
three neutrons produced to go and initiate a fission reaction.
If heat production become to low, the
boron moderator can be raised out of the reactor to allow more fission to
again, the balancing of nuclear equations for, in this case, fission reactions
(somewhat simplified!) ...
When the spent uranium nuclear
fuel is removed from a nuclear reactor, it is sent for reprocessing.
This is an extremely complicated
and costly process.
However, one idea was to extract
plutonium metal, which is formed as a natural 'nuclear consequence' of the
nuclear reactions in a uranium nuclear reactor.
Plutonium, like uranium, is a
readily fissile material i.e. it readily undergoes fission under neutron
bombardment to release considerable quantities nuclear energy.
Nuclear power is controversial and
many issues are involved.
The public perception of nuclear power
often very negative and not worth the risk i.e. it is seen as very dangerous
from radioactive leaks, overheating or explosions of reactors, unsafe
storage of harmful radioactive waste, and to be fair, these fears are not
without foundation, all have happened, and, rightly, these concerns must be
addressed by scientists, design engineers and politicians etc.
Arguments for nuclear power:
It contributes little to the greenhouse
effect and global warming since there is no emission of carbon dioxide from
fossil fuels, so climate change isn't an issue for nuclear power.
Nuclear power stations can produce a high
base load of electricity from relatively little fuel.
Unlike nuclear power, burning fossil
fuels produces pollution effects from harmful gases e.g. nitrogen oxides are
bad for the lungs, sulfur oxides produce acid rain causing environmental
damage e.g. acidified lakes, building corrosion.
Fossil fuels are a finite resource and
can't last for ever and there is probably enough uranium ores to last for
many years even though these are also finite resources. A little uranium can
go a long way!
Generally speaking it is a reasonably
safe and reliable way of generating electricity and don't forget the workers
lives lost in the extraction of oil & gas and coal mining to feed fossil
fuel power stations.
Arguments against nuclear power:
of radioactive material into the environment.
difficulty of safely disposing of highly radioactive nuclear waste for a
long period of time.
The huge capital cost of building a
nuclear power station and the equally huge cost of decommissioning spent
reactors. The latter is not well understood by the public taxpayer since the
energy companies in the UK don't appear to want have anything to do with
The length of time for construction,
maybe 10-20 years and decommissioning takes decades too!
Some of these points are further
elaborated on below:
It is no simple decision to build a
nuclear power station.
Theoretically it provides a reliable
large scale source of electricity - unlike e.g. wind power or solar power
which can be unreliable and cannot provide the same concentration of power.
No carbon dioxide is produced, so it
doesn't contribute to global warming and climate change in the way that
fossil fuel power stations do.
It benefits a large number of people and
provides lots of jobs in construction and when its finished and operating.
BUT, running a nuclear power station is
not without risks e.g. increase in background radiation expose to local
inhabitants, risk of accident, (see below).
So, to make any major infrastructure
planning decision to build a nuclear power station you have to weigh up the
benefits, drawbacks like ....
cost and operating problems because of
the complex technology and high safety standards,
risks e.g. increased radiation exposure,
Problems with nuclear power
(despite not contributing to global warming).
Nuclear power contributes very little to
global warming since carbon dioxide is not form in the process, as is the
case with burning fuels. This is one of the principal arguments for
developing nuclear power projects.
Also, the nuclear fuel like uranium are
not that costly, at least compared to the huge capital cost of building and
running a nuclear power station.
Not only is building/running nuclear
power plants very costly, BUT the cost of decommissioning them is also very
Nuclear power plants cost billions of £/$
to build and cost £/$ billions to decommission!
Energy companies in the UK are doing
their best to avoid paying decommissioning and it looks like the UK taxpayer
will pay the huge bill!
Also, nuclear fuels based on
uranium, plutonium and thorium, are nonrenewable because there is
only a limited amount of suitable ores around the world.
Decommissioning a nuclear plant involves
taking everything apart and disposing of all the waste materials like
concrete, nuclear reactor components (most radioactive) etc. and may take
many years (decades!) to fully dismantle and safely deal with all the waste.
The nuclear waste problem
Unfortunately, even before decommissioning,
when the nuclear power plant is operating, considerable
amounts of highly radioactive waste are formed which must be disposed of safely
(NOT easy, you can't just dump it like any old refuse!). The waste must be added
to in the long-run from future decommissioned nuclear reactors and
Reprocessing nuclear waste is technically
complex, potentially dangerous and very costly, especially when dealing
highly radioactive material in which there may be radioisotopes with
half-lives of thousands of years - a long safe storage time required.
Much of this waste from the working
nuclear reactors or decommissioned nuclear power plants is dangerously
radioactive for many months or years.
Some radioactive atoms take thousands of
years to fully decay to stable isotopes which are safe and no longer
This raises considerable technical issues
for even temporary as well as long term safe storage and leaks seem to be
Any leakage from this dangerous waste is potentially harmful to the
environment and its inhabitants and must be stored in a secure location well
away from people.
Currently, much of the dangerous
radioactive waste is dealt by a process of vitrification. The waste is
mixed with ceramic producing materials and melted to form a sort of
glass. The liquid glass is poured into steel cylinders, cooled and
securely sealed. The containers are then stored in a suitable waste dump
which doesn't have to be underground. The idea is that its quite
difficult for the radioactive materials to diffuse out of the glass.
The radioactive waste can also be
stored in thick sided metal containers and bury them deep underground
with tons of protective concrete so no dangerous radiation ever reaches
Potential for a major catastrophe: As was
seen at Chernobyl in the Ukraine (from operational mistakes, April
1986) and Fukushima in Japan (from
earthquake, March 2011), dangerous explosions occurred releasing
considerable amounts of dangerous radioactive materials into the
half-life of radioisotopes and
structure, radioactivity and
nuclear physics revision notes index
Atomic structure, history, definitions,
examples and explanations including isotopes gcse chemistry
structure and fundamental particle knowledge needed to understand radioactivity gcse physics
is Radioactivity? Why does it happen? Three types of atomic-nuclear-ionising radiation
gcse physics notes
3. Detection of
radioactivity, its measurement
and radiation dose units, ionising
- radioactive materials, background radiation gcse physics revision
4. Alpha, beta & gamma radiation - properties of 3 types of radioactive
nuclear emission & symbols ,dangers of radioactive emissions - health and safety issues and ionising radiation
gcse physics revision
Uses of radioactive isotopes emitting alpha, beta (+/–) or gamma radiation in
industry and medicine gcse notes
6. The half-life of a radioisotope - how
long does material remain radioactive? implications!, uses of decay data and half-life values
archaeological radiocarbon dating, dating ancient rocks
gcse physics revision
actually happens to the nucleus in alpha and beta radioactive decay and why? nuclear
production of radioisotopes - artificial sources of radioactive-isotopes,
cyclotron gcse physics revision notes
fusion reactions and the formation of 'heavy elements' by bombardment techniques
gcse physics notes
9. Nuclear Fission Reactions, nuclear power
as an energy resource gcse physics revision
multiple choice QUIZZES
word-fills on radioactivity
puzzle on radioactivity
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