Both fission and fusion are nuclear reactions that produce energy, but the applications are not the same. Fission is the splitting of a heavy, unstable nucleus into two lighter nuclei, and fusion is the process where two light nuclei combine together releasing vast amounts of energy.

2. Fission and Fusion
Nuclear fission: Nuclear fission is a process in which a
heavy nucleus splits into two or more smaller nuclei and
release huge amount of energy.
In fission reaction, a slow-moving neutron is absorbed by a
nucleus of uranium-235. The resulting nucleus of uranium-
235 is unstable and splits into two daughter nuclei of
barium-144 and krypton-89, gamma radiation 3 more
neutrons. When these neutrons are absorbed by other
fissile nuclei then a chain reaction results.
Nuclear reacter: In a nuclear reacter, a neutron is captured by uranium-235 nucleus which splits
into two daughter nuclei Ba ,Kr and 3 more neutrons. these are absorbed by futher fissile nuclei,
leading to a uncontrolled chain reaction.
The process is controlled with the help of moderator and control rods for longer use of heat energy.
This heat energy is used to generate steam to turn turbines and drive generators.
Nuclear fusion: Nuclear fusion is a reaction in which a smaller nuclei join togeter to form a heavier
nuclei and releases a huge amount of energy.
In this reaction, a nucleus of deuterium collides with a nucleus of tritium to form the nucleus of
helium, a neutron and a large amount of energy.
+energy

3. Edexel International GCSE(9-1), Student book questions and answers.
1 a .Uranium-235 (U-235) is a fissile material. What does this mean.
It can split in smaller molecules when a lower energy neutron is fired at it.
b. If there is a large enough mass of U-235, it may cause a chain reaction.(This is called the critical
mass for the isotope)
(i) Describe how a chain reaction may take place when a U-235 nucleus splits apart.
The parents nucleas, U-235, produces two daughter nuclei and 3 electrons. If these neutrons are
absorbed by further fissile nuclei then a chain reaction results.
(ii)A chain reaction is unlikely to take place if there is only a small amount of U-235. Explain why
this is so.
If there is only a small amount, neutrons can escape the material without hitting any more
nuclei.
2. List two advantages and two disadvantages of nuclear fission as producing energy.
Advantages: Very low fuel cost, does not produce ‘greenhouse’gases.
Disadvantages: produces waste that remains extremely dangerous for thousands of years; very high
set-up and decommissioning costs.
3. In a nuclear fission reactor, fuel rods made up of a fissile material, like U-235, are lowered into
tubes in a large block of graphite. In between fuel rods are control rods made of boron which may
be raised out of reactor or lowered into it. The reactor container (vessel) is surrounded by steel
and a very thick layer of concrete.
a Explain the purpose of the graphite around the fuel rods.
Graphite is used as a moderetor to slow down the neutrons produced from fission.
b. Describe what effect the action of raising the control rods out of the reactor core has on the
behaviour of the reactor.
The control rods made of boron absorbs neutrons to take them out of action completely. The control
rods can be raised out of the reactor core allowing the chain reaction to speed up, or lowered
completely to shut down the chain reaction.
c .Explain how the workers in a nuclear power station are protected from the dangerous types of
radiation produced by this nuclear reactor.
The reactor vessel is made of steel and surrounded by a concrete layer about 5 metres in thickness.
This prevents radiation escaping, even neutrons
4. Describe the differences between nuclear fission and nuclear fusion.

4. Fission Fusion
Spliting of an atom into two or more smaller
atom
Joining together of two or more smaller atoms
to form a larger atom.
Fission happens with heavy elements. Fusion evolves lighter elements.
Energy from fission can be controlloed. It cannot be controlled
5. Explain why creating energy in a nuclear reactor by fusion is so much more difficult than
creating power by nuclear fission.
The problem is to create the very high temperature(100 milliono
c )to collide between the positive
electricaliy charged isotopes deuterium and tritium but still actually difficult. Fission is relatively
simple.