Nuclear Fission and it's 2 Major Uses
Nuclear Fission and it's 2 Major Uses
Nuclear fission can be used in two major ways, as fuel
for nuclear power plants and as an extremely explosive
ingredient of a nuclear bomb. Nuclear fission is the cleavage
of one nucleus into two, resulting in a substantial amount
of energy. Enrico Fermi experimented with increasing the size
of a nucleus to form larger elements, it is believed that he
achieved a fission reaction but was not aware of it as he
couldn’t identify the fission products, this took place in 1934.
Only 5 years later in 1939 Otto Hahn and Fritz Strassmann
seperated the fission products and discovered that a uranium
nucleus had been split into two pieces. For this discovery of
fission, in 1944 Otto Hahn received the Nobel prize for
Chemistry. The only naturally occurring element that can undergo
nuclear fission is uranium-235. It was found that when
uranium-235 gains a neutron it becomes a heavy isotope which
divides into two smaller elements, this division is the process
of nuclear fission. The two smaller elements created in this
reaction are not always the same, there are many different
combinations that can be produced. During this fission process
approximately three neutrons are released along with two fission
fragments. These three neutrons that were released are now free
to be gained by another uranium-235 atom which would fission,
creating a cycle that will continue until interrupted or all
of the fissionable material has been utilized. This cycle is
known as a nuclear chain reaction.
When this process of breaking the nuclear strong force
takes place, each kilogram of uranium-236 gives off
90,000,000,000,000,000 J of energy. This amount of energy is
enough to supply all of Canada for three days. The net gain of
energy is quite beneficial for the uses of electrical power and
for nuclear weapons. In both cases the amount of energy released
greatly exceeds the amount needed to release it. This nuclear
fuel is made of uranium in the form of pellets, one of these
small pellets (roughly the size of a pencil top eraser) has
roughly the same amount of energy as one ton of coal. The
uranium that is used has previously been enriched which
means that there are more uranium-235 isotopes in it than there
would be in natural uranium, this increases the amount of
fissionable uranium from 0.7% to 4% which although not a great
change is significantly better for fission purposes.
Power plants that generate energy from nuclear energy
are similar to other power plants except hydro-electric. It uses
the energy gained from nuclear fission to produce steam to
drive a turbine. In a nuclear reactor the uranium is located
in the core. Heat is generated from the fissioning of uranium.
This heat is transferred to water that is circulated in the
primary loop. The primary loop is kept at high pressure to keep
the water from boiling even though its temperature can reach
over 212 degrees on the Fahrenheit scale. The reactor core
consists of uranium pellets which stacked end to end inside
12-foot long metal tubes. The metal which is zirconium alloy,
is used because of its ability to resist the effects of heat,
radiation and corrosion. These tubes are arranged in assemblies
with about 179 rods in each. The assemblies are arranged with
spaces that allow room for the control rods. Control rods are
substances which can absorb neutrons such as Boron, Cadmium or
Carbon. These control rods are inserted and removed from the
reactor. The more they are inserted, the more neutrons they absorb
and the slower the reaction gets and inversely, if you remove the
control rods then the speed of the reaction will increase. Water
flows up between the assemblies and control rods and removes the
heat from the fission reaction that takes place within.
This heated water is circulated through a steam generator
which in turn heats the water in the generator to steam
which drives the steam turbine. This turbine creates electricity
in the same way that a hydro-electric plant would.
In the diagram:
Nuclear bombs run on the same kind of fission as nuclear
power plants. Nuclear bombs have many different kinds of
destruction, blast, vacuum pressure, shock, heat and radiation.
There are two kinds of nuclear bombs, Atomic which is a fission
bomb and Hydrogen which is a fusion bomb (we however are only
interested in the fission bomb). As was expressed earlier, the
only difference is that a bomb is an uncontrolled reaction. The
way that a bomb works is to complete a powerful reaction before
the encasing of the bomb has time to burst. In a nuclear
fission bomb it takes approximately 0.00000008 seconds for most
of the fuel to be converted into fission fragments, this is also
about the time that the bomb splits apart.
This uncontrolled reaction can only take place if there
is sufficient mass of fissionable material, this is known as
critical mass. Critical mass is achieved when there are
enough uranium-235 isotopes that the number of neutrons
being absorbed is greater than the number that is escaping
from the mass. If there is insufficient mass to for a
self-sustaining chain reaction then the amount of mass is
known as sub-critical, on the other hand, if there is more
than enough for a self-sustaining reaction then the mass is
known to be supercritical. Nuclear fission bombs can be made
in two different methods, the gun method and the implosion method.
The gun method requires two pieces of sub-critical mass
to be places at opposite ends of a device similar to a
gun barrel. One of these masses has a conventional explosive
packed behind it, the barrel is sealed at both ends and the
detonation of this bomb propels one of the masses into the
other at a very high speed. When these two masses collide, a
new mass is formed that is supercritical. Now supercritical
mass has been achieved a self-sustaining reaction takes place
and ultimately a nuclear explosion. This is the method used
to create the nuclear bomb that was used on Hiroshima in August
of 1945.
The implosion method uses one ball-shaped sub-critical
mass. This mass is placed in the middle of conventional
explosives. When the bomb is detonated the conventional
explosives all go off at the same time, this compresses the
sub-critical mass into a smaller volume leaving it supercritical.
Then, just as in the gun method a self-sustaining reaction takes
place and the nuclear explosion quickly follows. This method
was used in the bomb that was dropped on Nagasaki in August of
1945.
Many people are skeptical about nuclear fission. Some
of their concerns are the possibility of another Chernobyl
disaster, the disposal of nuclear waste, the cost of energy,
and the danger of radiation from operating nuclear reactors.
Many of these concerns are unfounded and based on myths.
Some people don’t know the difference between a nuclear
power plant and a nuclear bomb, therefore thinking that
a power plant can blow up like a bomb. This concern is
totally impossible. A controlled chain reaction is the
basis for nuclear power where an uncontrolled chain
reaction is the basis for a nuclear weapon. A nuclear
bomb is so compact the neutrons have a very short distance
to travel. A power plant is too big for the same type
of process. In nuclear power plants control rods directs
the rate of the reaction. The water in a nuclear power plant
also acts as a moderator in that if the water begins to boil
it will stop the reaction.The disposal of nuclear waste is a
major concern for most people. Due to the fact that most
people are uninformed on the topic of nuclear fission they
believe that nuclear waste lasts millions of years. The
truth of the matter is that the nuclear waste is
put into a large tank containing water. While placed
in the water the waste becomes less and less radioactive.
The more highly radioactive isotopes decay and produce
less heat. The longer the spent fuel is stored the easier
it will be to control. After ten years the fission products
are one thousand times less radioactive. After five hundred
years the fission products will be less radioactive than the
uranium they were initially taken from. Many tanks
are getting too full, generating the decision to remove the
control rods or to build more tanks. A large reactor produces
about a cubic meter of fission products per year. The chance
of another catastrophe such as Chernobyl causes fear for
everyone. In this disaster the Chernobyl plant reached one
hundred fifty times its normal power level before the water
turned into high-pressure steam and blew the plant apart,
therefore drowning the reaction within a few seconds.
In Western civilization, fault trees for possible failures
have been generated and studied. However, there could be
something not taken into account. Of the large quantity of
nuclear reactors present in the world, Chernobyl is the
only incident to have caused harm to the public.Ultimately
nuclear power plants are much like other power plants. They
use high-pressured steam to turn a turbine to spin the shaft
of a generator, therefore creating electricity. Nuclear power
is better than other power plants because they are
cleaner, cheaper, and more efficient than coal, oil, and
natural.