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Energy from splitting Uranium atoms
Nuclear power is generated using Uranium, which
is a metal mined in various parts of the world.
The first large-scale nuclear power station opened
at Calder Hall in Cumbria, England, in 1956.
Some military ships and submarines have nuclear power
plants for engines.
Nuclear power produces around 11% of the world's energy
needs, and produces huge amounts of energy from small amounts of
fuel, without the pollution that you'd get from burning fossil fuels.
How it works:
main bit to remember:
Nuclear power stations work in pretty much
the same way as fossil fuel-burning stations, except that a "chain
reaction" inside a nuclear reactor makes the heat instead.
The reactor uses Uranium rods as fuel, and the
heat is generated by nuclear fission: neutrons smash into
the nucleus of the uranium atoms, which split roughly in half and
release energy in the form of heat.
Carbon dioxide gas or water is pumped through
the reactor to take the heat away, this then heats water to make
Modern nuclear power stations use the same type of turbines and generators as conventional power stations.
Video clip: Nuclear
In Britain, nuclear power stations are often
built on the coast, and use sea water for cooling the steam ready to be
pumped round again. This means that they don't have the huge "cooling
towers" seen at other power stations.
The reactor is controlled with "control
rods", made of boron, which absorb neutrons. When the rods are lowered
into the reactor, they absorb more neutrons and the fission process slows
down. To generate more power, the rods are raised and more neutrons can
crash into uranium atoms.
Natural uranium is only
0.7% "uranium-235", which is the type of uranium that
undergoes fission in this type of reactor.
The rest is U-238, which just sits there getting in
Modern reactors use "enriched" uranium fuel,
which has a higher proportion of U-235.
The fuel arrives encased in metal tubes, which are
lowered into the reactor whilst it's running, using a special crane
sealed onto the top of the reactor.
With an AGR or Magnox station, carbon dioxide gas
is blown through the reactor to carry the heat away.
is chosen because it is a very good coolant, able to carry a great
deal of heat energy.
It also helps to reduce any fire risk in the
reactor (it's around 600 degrees Celsius in there) and it doesn't
turn into anything nasty (well, nothing long-lived and nasty) when
it's bombarded with neutrons.
You have to be very careful about the materials
you use to build reactors - some materials will turn into horrible
things in that environment.
If a piece of metal in the reactor pressure
vessel turns brittle and snaps, you're probably in trouble - once
the reactor has been built and started you can't go in there to
Uranium itself isn't particularly radioactive, so when the fuel
rods arrive at the power station they can be handled using thin
plastic gloves. A rod can last for several years before it needs
It's when the "spent" fuel rods are taken out of the reactor
that you need the full remote-control robot arms and Homer Simpson
Should I worry about nuclear power?
Nuclear power stations are not atomic bombs waiting
to go off, and are not prone to "meltdowns".
There is a lot of U-238 in there slowing things down - you need
a high concentration of U-235 to make a bomb.
If the reactor gets too hot, the control rods are lowered in and
it cools down.
If that doesn't work, there are sets of emergency control rods that
automatically drop in and shut the reactor down completely.
With reactors in the UK, the computers will shut the reactor down
automatically if things get out of hand (unless engineers intervene
within a set time). At Chernobyl, in Ukraine, they did not have such
a sophisticated system, indeed they over-rode the automatic systems
they did have. When they got it wrong, the reactor overheated, melted
and the excessive pressure blew out the containment system before
they could stop it. Then, with the coolant gone, there was a serious
fire. Many people lost their lives trying to sort out the mess. A
quick web search will tell you more about this, including companies
who operate tours of the site.
If something does go
wrong in a really big way, much of the world could be affected -
some radioactive dust (called "fallout") from the Chernobyl
accident landed in the UK. That's travelled a long way.
With AGR reactors (the most common type in Britain)
there are additional safety systems, such as flooding the reactor
with nitrogen and/or water to absorb all the neutrons - although
the water option means that reactor can never be restarted.
So should I worry? I think the answer is "so
long as things are being done properly, I don't need to worry too
much. The bit that does worry me is the small amount of high-level
nuclear waste from power stations. Although there's not much of
it, it's very, very dangerous and we have no way to deal with it
apart from bury it and wait for a few thousand years...
There are many different opinions about nuclear power,
and it strikes me that most of the people who protest about it don't have
any idea what they're talking about. But please make up your own
mind, find out as much as you can, and if someone tries to get
you to believe their opinion ask yourself "what's in it for them?"
Nuclear power costs about the same as coal, so
it's not expensive to make.
Does not produce smoke or carbon dioxide, so
it does not contribute to the greenhouse effect.
Produces huge amounts of energy from small amounts
Produces small amounts of waste.
Nuclear power is reliable.
Although not much waste is produced, it is very, very
It must be sealed up and buried for many thousands of years to allow
the radioactivity to die away.
For all that time it must be kept safe from earthquakes, flooding,
terrorists and everything else. This is difficult.
Nuclear power is reliable, but a lot of money has to
be spent on safety - if it does go wrong, a nuclear accident
can be a major disaster.
People are increasingly concerned about this - in the 1990's nuclear
power was the fastest-growing source of power in much of the world.
In 2005 it was the second slowest-growing.
Is it renewable?
Nuclear energy from Uranium is notrenewable.
Once we've dug up all the Earth's uranium and used it,
there isn't any more.
Actually, it's not
that simple - we can use "fast breeder" reactors to convert
uranium into other nuclear fuels whilst also getting the energy
from it. There are two types of breeder reactors - ones that make
weapons-grade plutonium and ones that are for energy production.